New experiments physico-mechanical, touching the air

TO THE LORD of DUNGARVAN, My Honored and Dear NEPHEW.

My Dear Lord,

REceiving in your last from Paris, a desire that I would adde some more Experiments to those I formerly sent You over: I could not be so much your Ser∣vant as I am, without looking upon that Desire as a Com∣mand; and consequently, without thinking my self obliged to consider by what sort of Experiments it might the most acceptably be obey'd. And at the same time, perceiving by Letters from some other Ingenious Persons at Paris, that se∣veral of the Virtuosi there, were very intent upon the exa∣mination of the Interest of the Air, in hindring the descent of the Quick-silver, in the famous Experiment touching a Vacuum: I thought I could not comply with your Desires in a more fit and seasonable manner, than by prosecuting and endeavouring to promote that noble Experiment of Tor∣ricellius: and by presenting Your Lordship an account of my attempts to illustrate a Subject, about which (its being so much discours'd of where you are, together with your inbred Curiosity, and love of Experimental Learning) made me suppose you sufficiently inquisitive.

And though I pretend not to acquaint you, on this occasi∣on, with any store of new Discoveries, yet possibly I shall be so happy, as to assist you to know some things which you did formerly but suppose; and shall present you, if not with new Theories, at least with new Proofs of such as are not yet be∣come unquestionable. And if what I shall deliver, hath the good fortune to encourage and assist you to prosecute the Hints it will afford, I shall account my self, in paying of a duty to you, to have done a piece of Service to the Commonwealth

of Learning. Since it may highly conduce to the advance∣ment of that Experimental Philosophy, the effectual pursuit of which, requires as well a Purse as a Brain, to endear it to hopefull Persons of your Quality: who may accomplish ma∣ny things, which others can but wish, or at most, but design, by being able to imploy the Presents of Fortune in the search of the Mysteries of Nature.

And I am not faintly induc'd to make choice of this Sub∣ject, rather than any of the expected Chymical ones, to en∣tertain Your Lordship upon, by these two Considerations: The one, That the Air being so necessary to humane Life, that not only the generality of Men, but most other Creatures that breathe, cannot live many minutes without it; any consider∣able discovery of its Nature, seems likely to prove of moment to Mankind. And the other is, That the ambient Air, be∣ing that whereto both our own Bodies, and most of the others we deal with here below, are almost perpetually con∣tiguous; not only its alterations have a notable and manifest share in those obvious Effects, that Men have already been invited to ascribe thereunto (such as are the various Distem∣pers incident to humane Bodies especially if crazy in the Spring, the Autumn, and also on most of the great and sudden changes of Weather) but likewise, the further discovery of the Nature of the Air, will probably discover to us, that it concurs more or less to the exhibiting of many Phaenomena, in which it hath hitherto scarce been suspected to have any In∣terest. So that a true account of any Experiment that is New concerning a thing, wherewith we have such constant and necessary intercourse, may not only prove of some ad∣vantage to humane Life, but gratifie Philosophers, by pro∣moting their Speculations on a Subject which hath so much opportunity to solicite their Curiosity.

And I should immediately proceed to the mention of my Experiments, but that I like too well that worthy saying of In Praefat. lib. 1. the Naturalist Pliny, Benignum est & plenum inge∣nui

pudoris, fateri per quos profeceris, not to conform to it, by acquainting your Lordship, in the first place, with the Hint I had of the Engine I am to entertain you with. You may be pleas'd to remember, that a while before our separa∣tion in England, I told you of a Book that I had heard of, but not perus'd, publish'd by the industrious Jesuit Schottus, wherein 'twas said, He related how that ingenious Gentle∣man, Otto Gericke, Consul of Magdeburg, had lately prac∣tis'd in Germany a way of emptying Glass Vessels, by suck∣ing out the Air at the mouth of the Vessel, plung'd under Water: And you may also perhaps remember, that I ex∣press'd my self much delighted with this Experiment, since thereby the great force of the external Air (either rushing in at the open'd Orifice of the empty'd Vessel, or violently for∣cing up the Water into it) was rendred more obvious and conspicuous than in any Experiment that I had formerly seen. And though it may appear by some of those Writings I some∣times shew'd your Lordship, that I had been solicitous to try things upon the same ground; yet in regard this Gentle∣man was before-hand with me in producing such considera∣ble Effects, by means of the exsuction of Air, I think my¦self oblig'd to acknowledge the assistance and encouragement, the Report of his Performances hath afforded me.

But, as few inventions happen to be at first so compleat, as not to be either blemished with some deficiencies needful to be remedi'd, or otherwise capable of improvement: so when the Engine we have been speaking of, comes to be more attentive∣ly consider'd, there will appear two very considerable things to be desir'd in it. For first, the Wind Pump (as some body not improperly calls it) is so contriv'd, that to evacuate the Vessel, there is requir'd the continual labour of two strong Men for di∣vers hours. And next (which is an imperfection of much grea∣ter moment) the Receiver, or Glass to be empty'd, consisting of one entire and uninterrupted Globe and Neck of Glass; the whole Engine is so made, that things cannot be convey'd into it,

whereon to try Experiments: So that there seems but little (if any thing) more to be expected from it, than those very few Phaenomena that have been already observ'd by the Author, and recorded by Schottus. Wherefore to remedy these Inconveni∣ences, I put both Mr.G. and R. Hook (who hath also the Ho∣nour to be known to your Lordship, and was with me when I had these things under consideration) to contrive some Air Pump, that might not, like the other, need to be kept under Water (which on divers occasions is convenient) and might be more easily manag'd: And after an unsuccessful tryal or two of ways propos'd by others, the last nam'd Person fitted me with a Pump, anon to be describ'd. And thus the first Imperfection of the German Engine, was in good measure, though not perfectly remedy'd: And to supply the second de∣fect, it was considered that it would not perhaps prove im∣possible to leave in the Glass to be empty'd, a hole large enough to put in a Man's Arm cloath'd; and consequently other Bo∣dies, not bigger than it, or longer than the inside of the Vessel. And this Design seem'd the more hopeful, because I remembred, that having several years before often made the Experiment De Vacuo with my own hands; I had, to examine some Conjectures that occurr'd to me about it, caused Glasses to be made with a hole at that end, which uses to be seal'd up, and had nevertheless been able, as occasion requir'd, to make use of such Tubes, as if no such holes had been left in them, by devising stopples for them, made of the common Plaister call'd Diachylon: which I rightly enough guess'd, would, by reason of the exquisite commixtion of its small parts, and closeness of it's texture, deny all access to the exter∣nal Air. Wherefore, supposing that by the help of such Plai∣sters carefully laid upon the commissures of the stopple and hole to be made in the Receiver, the external Air might be hin∣dred from insinuating it self between them, into the Vessel, we caus'd several such Glasses, as you will find describ'd a little lower, to be blown at the Glass-house; and though we could

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not get the Work-men to blow any of them so large, or of so convenient a shape as we would fain have had; yet finding one to be tolerably fit, and less unfit than any of the rest, we were content to make use of it in that Engine: Of which, I suppose, you by this time expect the Description, in order to the recital of the Phaenomena exhibited by it.

To give your Lordship then, in the first place, some account of the Engine it self: It consists of two principal parts; a glass Vessel, and a Pump to draw the Air out of it.

The former of these (which we, with the Glass-men, shall often call a Receiver, for its affinity to the large Vessels of that name, used by Chymists) consists of a Glass with a wide hole at the top, of a cover to that hole, and of a Stop-cock fastned to the end of the Neck, at the bottom.

The shape of the Glass, you will find express'd in the first Figure of the annexed Scheme. And for the size of it, it con∣tain'd about 30 Wine Quarts, each of them containing near two Pound (of 16 Ounces to the Pound) of Water: We should have been better pleas'd with a more capacious Vessel, but the Glass-men professed themselves unable to blow a larger, of such a thickness and shape as was requisite to our purpose.

At the very top of the Vessel, (A) you may observe a round hole, whose Diametre (BC) is of about four Inches; and whereof, the Orifice is incircled with a lip of Glass, almost an Inch high: For the making of which lip, it was requisite (to mention that upon the by, in case your Lordship should have such another Engine made for you) to have a hollow and taper∣ing Pipe of Glass drawn out, whereof the Orifice above men∣tioned was the Basis, and then to have the Cone cut off with an hot Iron, within about an Inch of the Points (BC.)

The use of the lip, is to sustain the cover delineated in the second Figure; where (DE) points out a brass Ring, so cast, as that it doth cover the lip (BC) of the first Figure, and is ce∣mented on, upon it, with a strong and close Cement. To the inward tapering Orifice of this Ring (which is about three

Inches over) are exquisitely ground the sides of the Brass stop∣ple (FG;) so that the concave superficies of the one, and the convex of the other, may touch one another in so many pla∣ces, as may leave as little access, as possible, to the external Air: And in the midst of this cover is left a hole (HI) of about half an Inch over, invironed also with a Ring or Socket of the same Metal, and fitted likewise with a Brass stopple (K) made in the form of the Key of a Stop-cock, and exactly ground into the hole (HI) it is to fill; so as that, though it be turn'd round in the cavity it possesses, it will not let in the air, and yet may be put in or taken out at pleasure, for uses to be hereafter mentioned. In order to some of which, it is perforated with a little hole, (8) traversing the whole thickness of it at the lower end; through which, and a little Brass Ring (L) fastned to one side (no matter which) of the bottom of the stopple (FG) a string (8, 9, 10.) might pass, to be imploy'd to move some things in the capacity of the empty'd Vessel, without any where unstopping it.

The last thing belonging to our Receiver, is the Stop-cock, designed in the first Figure by (N,) for the better fastening of which to the neck, and exacter exclusion of the Air, there was soder'd on to the shank of the Cock (X) a Plate of Tin, (MTUW) long enough to cover the neck of the Receiver. But be∣cause the cementing of this was a matter of some difficulty, it will not be amiss to mention here the manner of it; which was, That the cavity of the Tin Plate was fill'd with a melted Ce∣ment, made of Pitch, Rosin, and Wood ashes, well incorpora∣ted; and to hinder this liquid Mixture from getting into the O∣rifice (Z) of the shank (X,) that hole was stop'd with a Cock, to which was fastned a string, whereby it might be pull'd out at the upper Orifice of the Receiver; and then, the Glass neck of the Receiver being well warm'd, was thrust into this Cement, and over the shank, whereby it was effected, that all the space betwixt the Tin Plate and the Receiver, and betwixt the inter∣nal superficies of the Receiver, and the shank of the Cock, was fill'd with the Cement; and so we have dispatch'd the first upper part of the Engine.

The undermost remaining part consists of a Frame, and of a sucking Pump, or as we formerly call'd it, an Air Pump, sup∣ported by it: The Frame is of Wood, small, but very strong, consisting of three legs, (111) so plac'd, that one side of it may stand perpendicular, that the free motion of the hand may not be hindered. In the midst of which frame, is transversly nail'd a board, (222) which may not improperly be call'd a Midriff, upon which rests, and to which is strongly fastned, the main part of the Pump it self, which is the only thing remain∣ing to be described.

The Pump consists of four parts, a hollow Cylinder, a Suc∣ker, a handle to move that Sucker, and a Valve.

The Cylinder was (by a pattern) cast of Brass; it is in length about 14 Inches, thick enough to be very strong, notwithstand∣ing the Cylindrical cavity left within it; this cavity is about three Inches Diametre, and makes as exact a Cylinder as the Artificer was able to bore. This hollow Cylinder is fitted with a Sucker, (4455) consisting of two parts; the one (44) some∣what less in Diametre than the Cavity of the Cylinder; upon which is nail'd a good thick piece of tann'd Shoe-leather, which will go so close to the Cylinder, that it will need to be very forcibly knock'd and ram'd in, if at any time it be taken out; which is therefore done, that it may the more exactly hinder the Air from insinuating it self betwixt it and the sides of the Cy∣linder whereon it is to move.

To the midst of this former part of the Sucker is strongly fa∣stned the other; namely, a thick and narrow plate of Iron (55) somewhat longer than the Cylinder, one of whose edges is smooth, but at the other edge it is indented (as I may so speak) with a row of Teeth, delineated in the Scheme, into whose in∣tervals are to be fitted, the Teeth of a small Iron Nut, (αβ) (as Tradesmen call it) which is fastned by two staples (22) to the underside of the formerly mention'd transverse board (222) on which the Cylinder rests, and is turn'd to and fro by the third piece of this Pump, namely, the handle or Manubrium,

(7) of which the Figure gives a sufficient description.

The fourth and last part of this Cylinder, is the Valve, (R) consisting of a hole bored through at the top of the Cylinder, a little tapering towards the cavity; into which hole is ground a tapering Peg of Brass, to be thrust in, and taken out at pleasure.

The Engine being thus describ'd, it will be requisite to add, that something is wont to be done before it be set on work, for the more easie moving of the Sucker, and for the better exclusi∣on of the outward Air: which, when the Vessel begins to be exhausted, is much more difficult to be kept out, than one would easily imagine.

There must then be first pour'd in at the top of the Receiver, a little sallad Oyl, partly to fill up any small intervals that may happen to be betwixt the contiguous surfaces of the internal parts of the Stop-cock: And partly, that it may be the more ea∣sie to turn the Key (S) backwards and forwards. Pretty store of Oyl must also be pour'd into the Cylinder, both that the Sucker may slip up and down in it the more smoothly and free∣ly, and that the Air might be the better hindred from getting in between them: And for the like reasons, a little Oyl is to be used also about the Valve. Upon which occasion, it would not be omitted (for it is strange) that oftentimes, when neither the pouring in of Water, nor even of Oyl it alone, prov'd capable to make the Sucker move easily enough in the Cylinder; a mixture of both those Liquors would readily (sometimes even to admiration) perform the desired effect. And lastly, the Brass cover of the Receiver, being put into the Brass ring for∣merly describ'd, that no Air may get between them, it will be very requisite to plaister over very carefully the upper edges of both, with the Plaister formerly mentioned, or some other as close, which is to be spread upon the edges with an hot Iron; that, being melted, it may run into and fill up all the cranies, or other little cavities, at which the Air might otherwise get entrance.

All things being thus fitted, and the lower shank (O) of the

Stop-cock being put into the upper Orifice of the Cylinder (and) into which it was exactly ground; the Experimenter is first, by turning the handle, to force the Sucker to the top of the Cylinder, that there may be no Air left in the upper part of it: Then shutting the Valve with the Plug, and turning the other way, he is to draw down the Sucker to the bottom of the Cy∣linder; by which motion of the Sucker, the Air that was for∣merly in the Cylinder being thrust out, and none being per∣mitted to succeed in its room, 'tis manifest that the cavity of the Cylinder must be empty in reference to the Air. So that if thereupon the Key of the Stop-cock be so turn'd, as that through the perforation of it, a free passage be opened betwixt the Cylinder and the Receiver, part of the Air formerly con∣tain'd in the Receiver, will nimbly descend into the Cylinder. And this Air being, by the turning back of the Key, hinder'd from the returning into the Receiver, may, by the opening of the Valve, and forcing up of the Sucker to the top of the Cy∣linder again, be driven out into the open Air. And thus by the repetition of the motion of the Sucker upward and down∣ward, and by opportunely turning the Key, and stopping the Valve, as occasion requires, more or less Air may be suck'd out of the Receiver, according to the exigency of the Experiment, and the intention of him that makes it.

Your Lordship will, perhaps, think that I have been unne∣cessarily prolix in this first part of my Discourse: But if you had seen how many unexpected difficulties we found to keep out the external Air, even for a little while, when some consi∣derable part of the internal had been suck'd out; You would peradventure allow, that I might have set down more circum∣stances than I have, without setting down any, whose know∣ledge, he that shall try the Experiment, may not have need of. Which is so true, that, before we proceed any further, I cannot think it unseasonable to advertise Your Lordship, that there are two chief sorts of Experiments, which we design'd in our En∣gine to make tryal of: The one, such as may be quickly dis∣patch'd,

and therefore may be try'd in our Engine, though it leak a little, because the Air may be faster drawn out, by nim∣bly plying the Pump, than it can get in at undiscern'd leaks; I say at undiscern'd leaks, because such as are big enough to be discover'd, can scarce be uneasie to be stopt. The other sort of Experiments consist of those that require, not only that the internal Air be drawn out of the Receiver, but that it be like∣wise for a long time kept out of it. Such are the preservation of Animal and other Bodies therein, the germination and growth of Vegetables, and other trials of several sorts, which it is ap∣parent cannot be well made, unless the external Air can, for a competent while, be excluded: Since, even at a very small leak, there may enough get in, to make the Vacuum soon lose that name; by which I here declare once for all, that I under∣stand not a space wherein there is no Body at all, but such as is either altogether, or almost totally devoid of Air.

Now this distinction of Experiments I thought fit to premise to the ensuing Narratives, because, upon trial, we found it so exceeding (and scarce imaginably) difficult a matter, to keep out the Air from getting at all in at any imperceptible hole or flaw whatsoever, (in a Vessel immediately surrounded with the compressed Atmosphere,) that in spight of all our care and dili∣gence, we never were able totally to exhaust the Receiver, or keep it when it was almost empty, any considerable time, from leaking more or less: although (as we have lately intimated) by unwearied quickness in plying the Pump, the internal Air can be much faster drawn out than the external can get in, till the Receiver come to be almost quite empty. And that's enough to enable Men to discover hitherto unobserved Phae∣nomena of Nature.

The Experiments therefore of the first sort, will, I fear, prove the only ones wherewith my Avocations will allow me to entertain Your Lordship in this Letter. For till your fur∣ther Commands shall engage me to undertake, by God's per∣mission, such an Employment, and more leasure shall better fit

me for it, I know not whether I shall be in a condition to try what may be done, to enable me to give you some account of the other sort of Experiments also.

EXPERIMENT I.

TO proceed now to the Phaenomena, exhibited to us by the Engine above described; I hold it not unfit to begin with what doth constantly and regularly offer it self to our observa∣tion, as depending upon the Fabrick of the Engine it self, and not upon the nature of this or that particular Experiment which 'tis employed to try.

First, then, upon the drawing down of the Sucker (the Valve being shut) the Cylindrical space, deserted by the Sucker, is left devoid of Air; and therefore, upon the turning of the Key, the Air contained in the Receiver rusheth into the emptied Cylinder, till the Air in both those Vessels be brought to about an equal measure of dilatation. And therefore, upon shutting the Receiver by re-turning the Key, if you open the Valve, and force up the Sucker again, you will find, that after this first exsuction you will drive out almost a whole Cylinder full of Air: But at the following exsuctions, you will draw less and less of Air out of the Receiver into the Cylinder, because there will still remain less and less Air in the Receiver it self; and consequently, the Particles of the remaining Air, having more room to extend themselves in, will less press out one another. This you will easily perceive, by finding, that you still force less and less Air out of the Cylinder; so that when the Recei∣ver is almost exhausted, you may force up the Sucker almost to the top of the Cylinder, before you will need to unstop the Valve to let out any Air: And if at such time, the Valve being shut, you let go the handle of the Pump, you will find the Sucker forcibly carried up to the top of the Cylinder, by the protrusion of the external Air; which, being much less rarifi∣ed than that within the Cylinder; must have a more forcible pressure upon the Sucker, than the internal is able to resist:

And by this means you may know how far you have emptied the Receiver. And to this we may add, on this occasion, that constantly upon the turning of the Key to let out the Air from the Receiver, into the emptied Cylinder, there is immediate∣ly produced a considerably brisk noise, especially whilst there is any plenty of Air in the Receiver.

For the more easie understanding of the Experiments triable by our Engine; I thought it not superfluous, nor unseasonable in the recital of this first of them, to insinuate that notion by which it seems likely that most, if not all of them, will prove explicable. Your Lordship will easily suppose, that the No∣tion I speak of is, That there is a Spring, or Elastical power in the Air we live in. By which 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 or spring of the Air, that which I mean is this: That our Air either consists of, or at least abounds with, parts of such a nature; that in case they be bent or compress'd by the weight of the incumbent part of the Atmosphere, or by any other Body, they do endeavour, as much as in them lieth, to free themselves from that pressure, by bearing against the contiguous Bodies that keep them bent; and, as soon as those Bodies are remov'd or reduced to give them way, by presently unbending and stretching out themselves, either quite, or so far forth as the contiguous Bodies that resist them will permit, and thereby expanding the whole parcel of Air, these elastical Bodies compose.

This Notion may perhaps be somewhat further explain'd, by conceiving the Air near the Earth to be such a heap of little Bo∣dies, lying one upon another, as may be resembled to a Fleece of Wooll. For this (to omit other likenesses betwixt them) consists of many slender and flexible Hairs; each of which may indeed, like a little Spring, be easily bent or rouled up; but will also, like a Spring, be still endeavouring to stretch it self out again. For though both these Hairs, and the Aereal Corpu∣scles to which we liken them, do easily yield to external pres∣sures; yet each of them (by virtue of its structure) is endow'd with a Power or Principle of self-Dilatation; by virtue where

of, though the hairs may by a Man's hand be bent and crouded closer together, and into a narrower room than suits best with the nature of the Body, yet, whilst the compression lasts, there is in the fleece they compose an endeavour outwards, where by it continually thrusts against the hand that opposes its Ex∣pansion. And upon the removal of the external pressure, by o∣pening the hand more or less, the compressed Wool doth, as it were, spontaneously expand or display itself towards the reco∣very of its former more loose and free condition, till the Fleece hath either regain'd its former Dimensions, or at least, ap∣proach'd them as near as the compressing hand (perchance not quite open'd) will permit. This Power of self-Dilatation, is somewhat more conspicuous in a dry Spunge compress'd, than in a fleece of Wool. But yet we rather chose to employ the lat∣ter, on this occasion, because it is not like a Spunge, an intire Body, but a number of slender and flexible Bodies, loosely complicated, as the Air it self seems to be.

There is yet another way to explicate the Spring of the Air, namely, by supposing with that most ingenious Gentleman, Monsieur Des Cartes, That the Air is nothing but a Congeries or heap of small and (for the most part) of flexible Particles; of several sizes, and of all kind of Figures which are rais'd by heat (especially that of the Sun) into that fluid and subtle Ethereal Body that surrounds the Earth; and by the restless agitation of that Celestial matter wherein those particles swim, are so whirld round, that each Corpuscle endeavours to beat off all others from coming within the little Sphere requisite to its motion a∣bout its own Centre; and (in case any, by intruding into that Sphere, shall oppose its free Rotation) to expel or drive it away: So that according to this doctrine, it imports very little, whether the particles of the Air have the structure requisite to Springs, or be of any other form (how irregular soever) since their Elastical power is not made to depend upon their shape or structure, but upon the vehement agitation, and (as it were) brandishing mo∣tion, which they receive from the fluid Ether that swiftly flows

between them, and whirling about each of them (independent∣ly from the rest) not only keeps those slender Aëreal Bodies seperated and stretcht out (at least, as far as the Neighbouring ones will permit) which otherwise, by reason of their flexible∣ness and weight, would flag or curl; but also makes them hit against, and knock away each other, and consequently require more room, than that, which, if they were compress'd, they would take up.

By these two differing ways, my Lord, may the Springs of the Air be explicated. But though the former of them be that, which by reason of its seeming somewhat more easie, I shall for the most part make use of in the following Discourse: yet am I not willing to declare peremptorily for either of them, against the other. And indeed, though I have in another Treatise en∣deavoured to make it probable, that the returning of Elastical Bodies (if I may so call them) forcibly bent, to their former po∣sition, may be Mechanically explicated: Yet I must confess, that to determine whether the motion of Restitution in Bodies, proceed from this, That the parts of a Body of a peculiar Struc∣ture are put into motion by the bending of the Spring, or from the endeavor of some subtle ambient Body, whose passage may be oppos'd or obstructed, or else it's pressure unequally resisted by reason of the new shape or magnitude, which the bend∣ing of a Spring may give the Pores of it: To determine this, I say, seems to me a matter of more difficulty, than at first sight one would easily imagine it. Wherefore I shall decline medling with a Subject, which is much more hard to be ex∣plicated, than necessary to be so, by him, whose business it is not, in this Letter, to assign the adequate cause of the Spring of the Air, but only to manifest, That the Air hath a Spring, and to relate some of its effects.

I know not whether I need annex that, though either of the a∣bove-mention'd Hypotheses, and perhaps some others, may af∣ford us an account plausible enough of the Air's Spring; yet I doubt, whether any of them gives us a sufficient account of its

Nature. And of this doubt, I might here mention some Rea∣sons, but that, peradventure, I may (God permitting) have a fitter occasion to say something of it elsew here. And therefore I shuold now proceed to the next Experiment, but that I think it requisite, first, to suggest to your Lordship what comes into my thoughts, by way of Answer to a plausible Objection, which I foresee you may make against our propos'd Doctrine, touching the Spring of the Air. For it may be alledged, that though the Air were granted to consist of springy Particles (if I may so speak) yet thereby we could only give an account of the Dila∣tation of the Air in Wind Guns, and other pneumatical Engines wherein the Air hath been compress'd, and its springs violently bent by an apparent external force; upon the removal of which, 'tis no wonder that the Air should, by the motion of restitution expand it self till it hath recovered its more natural dimensions: whereas in our above-mentioned first Experiment, and in almost all others triable in our Engine, it appears not, that any compres∣sion of the Air preceded its spontaneous Dilatation or Expansion of it self. To remove this difficulty, I must desire Your Lord∣ship to take notice, that of whatever nature the Air, very remote from the Earth, may be, and whatever the Schools may confi∣dently teach to the contrary, yet we have divers Experiments to evince, that the Atmosphere we live in, is not (otherwise than comparatively to more ponderous Bodies) light, but heavy: And did not their gravity hinder them, it appears not why the streams of the Terraqueous Globe, of which our Air in great part consists, should not rise much higher, than the Refractions of the Sun, and other Stars give men ground to think, that the Atmosphere, (even in the judgment of those Rescent Astronomers, who seem willing to enlarge its bounds as much as they dare,) doth reach.

But lest you should expect my seconding this Reason by Ex∣perience; and lest you should object, That most of the Experi∣ments that have been propos'd to prove the gravity of the Air, have been either barely propos'd, or perhaps not accurately tri'd;

I am content, before I pass further, to mention here. That I found a dry lambs-bladder containing near about two thirds of a pint, and compress'd by a packthred tied about it, to lose a grain and the eighth part of a grain of its former weight, by the recess of the Air upon my having prickt it: And this with a pair of Scales, which, when the full bladder and the correspondent weight were in it, would manifestly turn either way with the 32 part of a grain. And if it be further objected, That the Air in the Bladder was violently compress'd by the packthred and the sides of the Bladder, we might probably (to wave prolix answers) be furnish'd with a Reply, by setting down the differing weight of our Receiver, when empti'd and when full of uncompress'd Air, if we could here procure Scales fit for so nice an Experiment; since we are informed, that in the German Experiment, commended at the beginning of this Letter, the ingenious Triers of it found, That their Glass Vessel, of the capacity of 32 measures, was lighter when the Air had been drawn out of it, than before, by no less than one ounce and 3/10 that is, an ounce and very near a third: But of the gravity of the Air, we may elsewhere have occasion to make further mention.

Taking it then for granted that the Air is not devoid of weight, it will not be uneasie to conceive, That that part of the Atmo∣sphere wherein we live, being the lower part of it, the Corpus∣cles that compose it, are very much compress'd by the weight of all those of the like nature that are directly over them; that is, of all the Particles of Air, that being pil'd up upon them, reach to the top of the Atmosphere. And though the height of this Atmosphere, according to the famous Kepler, and some others, scarce exceeds eight common miles; yet other eminent and la∣ter Astronomers, would promote the confines of the Atmosphere to exceed six or seven times that number of miles. And the dili∣gent and learned Ricciolo makes it probable, that the Atmo∣sphere may, at least in divers places, be at least fifty miles high. So that according to a moderate estimate of the thickness of the Atmosphere, we may well suppose, that a Column of Air, of

many miles in height, leaning upon some springy Corpuscles of Air here below, may have weight enough to bend their little springs, and keep them bent: As, (to resume our former compa∣rison,) if there were fleeces of Wooll pil'd up to a mountainous height, upon one another, the hairs that compose the lowermost Locks which support the rest, would, by the weight of all the Wool above them, be as well strongly compress'd, as if a Man should squeeze them together in his hands, or employ any such other moderate force to compress them. So that we need not wonder, that upon the taking off the incumbent Air from any parcel of the Atmosphere here below, the Corpuscles, whereof that undermost Air consists, should display themselves, and take up more room than before.

And if it be objected, That in Water, the weight of the up∣per and of the lower part is the same: I answer, That, (besides that it may be well doubted whether the observation, by rea∣son of the great difficulty, hath been exactly made,) there is a manifest disparity betwixt the Air and Water: For I have not found, upon an Experiment purposely made, (and in another Treatise Recorded) that Water will suffer any considerable compression; whereas we may observe in Wind-Guns, (to men∣tion now no other Engines) that the Air will suffer it self to be crouded into a comparatively very little room; in so much, that a very diligent Examiner of the Phaenomena of Wind-Guns would have us believe, that in one of them, by conden∣sation, he reduc'd the Air into a space at least eight times nar∣rower than it before possest. And to this, if we add a noble Phaenomenon of the Experiment De Vacuo; these things put to∣gether, may for the present suffice to countenance our Doctrine. For that noble Experimenter, Monsieur Pascal (the Son) had the commendable Curiosity to cause the Torricellian Experiment to be tri'd at the foot, about the middle, and at the top of that high Mountain (in Auvergne, if I mistake not) commonly call'd Le Puy de Domme; whereby it was found, That the Mer∣cury in the Tube fell down lower, about three inches, at the top

of the Mountain than at the bottom. And a Learned Man a while since inform'd me, That a great Virtuose, friend to us both, hath, with not unlike success, tried the same Experiment in the lower and upper parts of a Mountain in the west of England. Of which, the reason seems manifestly enough to be this, That upon the tops of high Mountains, the Air which bears against the restagnant Quick-silver, is less press'd by the less ponderous incumbent Air; and consequently is not able to∣tally to hinder the descent of so tall and heavy a Cylinder of Quick-silver, as at the bottom of such Mountains did but maintain an AEquilibrium with the incumbent Atmosphere.

And if it be yet further Objected against what hath been pro∣pos'd touching the compactness and pressure of the inferiour Air; That we find this very Air to yield readily to the motion of little Flies, and even to that of Feathers, and such other light and weak Bodies; which seems to argue, that the parti∣cles of our Air are not so compress'd as we have represented them, especially, since by our former Experiment it appears, that the Air readily dilated it self downward, from the Recei∣ver into the Pump, when 'tis plain, that it is not the incum∣bent Atmosphere, but only the subjacent Air in the brass Cy∣linder that hath been remov'd: If this, I say, be objected, we may reply, That, when a man squeezeth a fleece of Wool in his hand, he may feel that the Wool incessantly bears against his hand, as that which hinders the hairs it consists of, to recover their former and more natural extent. So each parcel of the Air about the Earth, doth constantly endeavour to thrust away all those contiguous Bodies, (whether. Aëreal or more gross,) that keep it bent, and hinder the expansion of its parts, which will dilate themselves, or fly abroad towards that part, (whe∣ther upwards or downwards,) where they find their attemp∣ted Dilatation of themselves less resisted by the neighbouring Bodies. Thus the Corpuscles of that Air we have been all this while speaking of, being unable, by reason of their weight, to ascend above the Convexity of the Atmosphere, and by reason

of the resistance of the surface of the Earth and Water, to fall down lower, they are forced, by their own gravity and this re∣sistance, to expand and diffuse themselves about the Terrestrial Globe; whereby it comes to pass, that they must as well press the contiguous Corpuscles of Air that on either side oppose their Dilatation, as they must press upon the surface of the Earth, and, as it were recoyling thence, endeavour to thrust away those upper particles of Air that lean upon them.

And, as for the easie yielding of the Air to the Bodies that move in it, if we consider that the Corpuscles whereof it con∣sists, though of a springy nature, are yet so very small, as to make up (which 'tis manifest they do) a fluid Body, it will not be difficult to conceive, that in the Air, as in other Bodies that are fluid, the little Bodies it consists of, are in an almost restless motion, whereby they become (as we have more fully discoursed in another Treatise) * 1.1 very much disposed to yield to other Bodies, or easie to be displac'd by them; and that the same Corpuscles are likewise so variously mov'd, as they are intire Corpuscles, that if some strive to push a Body plac'd among them towards the right hand (for instance) others, whose motion hath an op∣posite determination, as strongly thrust the same Body to∣wards the left; whereby neither of them proves able to move it out of its place, the pressure on all hands being reduced as it were to an AEquilibrium: So that the Corpuscles of the Air must be as well sometimes considered under the notion of lit∣tle Springs, which remaining bent, are in their entire bulk transported from place to place; as under the notion of Springs displaying themselves, whose parts fly abroad, whilst, as to their entire bulk they scarce change place: As the two ends of a Bow, shot off, fly from one another, whereas the Bow it self may be held fast in the Archer's hand; and that it is the equal pressure of the Air on all sides upon the Bodies that are in it, which causeth the easie Cession of its parts, may be ar∣gu'd from hence: That if by the help of our Engine the Air

be but in great part, though not totally, drawn away from one side of a Body without being drawn away from the other, he that shall think to move that Body to and fro, as easily as before, will find himself much mistaken.

In verification of which we will, to divert your Lordship a little, mention here a Phaenomenon of our Engine, which even to divers ingenious persons hath at first sight seem'd very wonderfull.

EXPERIMENT II.

THe thing that is wont to be admired, and which may pass for our second experiment is this, That if, when the Re∣ceiver is almost empty, a By-stander be desired to lift up the brass Key (formerly described as a stopple in the brass Cover) he will find it a difficult thing to do so, if the Vessel be well exhausted; and even when but a moderate quantity of Air hath been drawn out, he will, when he hath lifted it up a little, so that it is some∣what loose from the sides of the lip or socket, which (with the help of a little oyl) it exactly filled before, he will (I say) find it so difficult to be lifted up, that he will imagine there is some great weight fastned to the bottom of it. And if (as sometimes hath been done for merriment) onely a Bladder be tied to it, it is pleasant to see how men will marvail that so light a Body, filled at most but with Air, should so forcibly draw down their hand as if it were fill'd with some very ponderous thing: Whereas the cause of this pretty Phaenomenon seems plainly enough to be only this, That the Air in the Receiver, being very much dilated, its Spring must be very much weakn'd, and consequently it can but faintly press up the lower end of the stopple, whereas the Spring of the external Air being no way debilitated, he that a little lifts up the stopple must with his hand support a pressure equal to the disproportion betwixt the force of the internal expanded Air, and that of the Atmosphere in∣cumbent upon the upper part of the same key or stopple: And so men being unused to find any resistance, in lifting things up,

from the free Air above them, they are forward to conclude that that which depresseth their hands must needs be some weight, though they know not where plac'd, drawing be∣neath it.

And, that we have not mis-assign'd the cause of this Phae∣nomenon, seems evident enough by this, That as Air is suffered by little and little to get into the Receiver, the weight that a man fancieth his hand supports, is manifestly felt to decrease more and more, the internal Air by this recruit approaching more to an AEquilibrium with the external, till at length the Receiver growing again full of Air, the stopple may be lifted up without any difficulty at all.

By several other of the Experiments afforded us by our En∣gine, the same notion of the great and equal pressure of the free Air upon the Bodies it environs, might be here manifest∣ed, but that we think it not so fit to anticipate such Experi∣ments: And therefore shall rather employ a few lines to clear up the difficulty touching this matter, which we have observ'd to have troubled some even of the Philosophical and Mathema∣tical Spectators of our Engine, who have wonder'd that we should talk of the Air exquisitely shut up in our Receiver, as if it were all one with the pressure of the Atmosphere; whereas the thick and close body of the Glass, wholly impervious to the Air, doth manifestly keep the incumbent Pillar of the At∣mosphere from pressing in the least upon the Air within the Glass, which it can no where come to touch. To elucidate a little this matter, let us consider, That if a man should take a fleece of Wooll, and having first by compressing it in his hand re∣duc'd it into a narrower compass, should nimbly convey and shut it close up into a Box just fit for it, though the force of his hand would then no longer bend those numerous springy Bodies that compose the Fleece, yet they would continue as strongly bent as before, because, the Box they are inclos'd in, would as much resist their re-expanding of themselves, as did the hand that put them in. For thus we may conceive, that the

Air being shut up, when its parts are bent by the whole weight of the incumbent Atmosphere, though that weight can no lon∣ger lean upon it, by reason it is kept off by the Glass, yet the Corpuscles of the Air within that Glass continue as forcibly bent, as they were before their inclusion, because the sides of the Glass hinder them from displaying or stretching out them∣selves. And if it be objected that this is unlikely, because even Glass bubbles, such as are wont to be blown at the flame of a Lamp, exceeding thin, and Hermetically seal'd, will not break; whereas it cannot be imagin'd that so thin a Prison of Glass could resist the Elastical force of all the included Air, if that Air were so compress'd as we suppose: It may be easily reply'd, That the pressure of the inward Air against the Glass, is counter∣vail'd by the equal pressure of the outward against the same Glass. And we see in bubbles, that by reason of this, an ex∣ceeding thin film of Water is often able, for a good while, to hinder the eruption of a pretty quantity of Air. And this may be also more conspicuous in those great Spherical bubbles, that Boyes sometimes blow with Water, to which Sope hath gi∣ven a Tenacity. But that, if the pressure of the ambient Air were remov'd, the internal Air may be able to break thicker Glasses, than those lately mention'd, will appear by some of the following Experiments; to which, we shall therefore now hasten, having, I fear, been but too prolix in this Excursion, though we thought it not amiss to annex to our first Experi∣ments some general Considerations touching the Spring of the Air, because (this Doctrine being yet a stranger to the Schools) not only we find not the thing it self to be much taken notice of; but of those few that have heard of it, the greater part have been forward to reject it, upon a mistaken perswasion, that those Phaenomena are the effects of Natures abhorrency of a Vacuum, which seem to be more fitly ascribable to the weight and spring of the Air.

EXPERIMENT III.

WE will now proceed to observe, that though, by the help of the handle, the Sucker be easily drawn down to the bottom of the Cylinder; yet, without the help of that Lea∣ver, there would be required to the same effect, a force or weight great enough to surmount the pressure of the whole Atmosphere: since otherwise the Air would not be driven out of its place, when none is permitted to succeed into the place deserted by the Sucker. This seems evident, from the known Torricellian Experiment, in which, if the inverted Tube of Mercury be but 25 Digits high, or somewhat more, the Quick∣silver will not fall, but remain suspended in the Tube, because it cannot press the subjacent Mercury with so great a force, as doth the incumbent Cylinder of the Air, reaching thence to the top of the Atmosphere: Whereas, if the Cylinder of Mer∣cury were three or four digits longer, it would over-power that of the external Air, and run out into the Vessel'd Mercury, till the two Cylinders came to an AEquilibrium, and no further. Hence we need not wonder, that though the Sucker move ea∣sily enough up and down in the Cylinder by the help of the Manubrium; yet if the Manubrium be taken off, it will require a considerable strength to move it either way. Nor will it seem strange, that if, when the Valve and Stop-cock are well shut, you draw down the Sucker, and then let go the Manubrium; the Sucker will, as it were of it self, re-ascend to the top of the Cylinder, since the spring of the external Air findeth no∣thing to resist its pressing up the Sucker. And for the same rea∣son, when the Receiver is almost evacuated, though, having drawn down the Sucker, you open the way from the Recei∣ver to the Cylinder, and then intercept that way again by re∣turning the Key; the Sucker will, upon the letting go the Ma∣nubrium, be forcibly carried up almost to the top of the Cy∣linder: Because the Air within the Cylinder, being equally di∣lated and weakned with that of the Glass, is unable to with∣stand

the pressure of the external Air, till it be driven into so little space, that there is an AEquilibrium betwixt its force and that of the Air without. And congruously hereunto we find, that in this case, the Sucker is drawn down with little less difficulty, than if the Cylinder, being devoid of Air, the Stop∣cock were exactly shut: We might take notice of some other things, that depend upon the Fabrick of our Engine it self; but to shun prolixity, we will, in this place, content our selves to mention one of them, which seems to be of greater moment than the rest, and it is this; that when the Sucker hath been impell'd to the top of the Cylinder, and the Valve is so careful∣ly stopp'd, that there is no Air left in the Cylinder above the Sucker: If then the Sucker be drawn to the lower part of the Cylinder, he that manageth the Pump findeth not any sensi∣bly greater difficulty to depress the Sucker, when it is nearer the bottom of the Cylinder, than when it is much farther off. Which circumstance we therefore think fit to take notice of, because an eminent Modern Naturalist hath taught, that, when the Air is sucked out of a Body, the violence wherewith it is wont to rush into it again, as soon as it is allow'd to re-enter, proceeds mainly from this; That the pressure of the ambient Air is strengthened upon the accession of the Air suck'd out; which, to make it self room, forceth the neighbouring Air to a violent-subingression of its parts: which, if it were true, he that draweth down the Sucker, would find the resistance of the external Air increas'd as he draweth it lower, more of the displaced Air being thrust into it to compress it. But, by what hath been discours'd upon the first Experiment, it seems more probable, that without any such strengthening of the pressure of the outward Air, the taking quite away or the debilitating of the resistance from within, may suffice to produce the effects under consideration. But this will perhaps be illustrated by some or other of our future Experiments, and therefore shall be no longer insisted on here.

EXPERIMENT IV.

HAving thus taken notice of some of the constant Phaenomena of our Engine it self, let us now proceed to the Experiments triable in it.

We took then a Lambs Bladder large, well dry'd, and very lim∣ber, and leaving in it about half as much Air as it could contain, we caus'd the neck of it to be strongly try'd, so that none of the in∣cluded Air, though by pressure, could get out. This Bladder being convey'd into the Receiver, and the Cover luted on, the Pump was set on work, and after two or three exsuctions of the ambient Air (whereby the Spring of that which remain'd in the Glass was weaken'd) the Imprison'd Air began to swell in the Bladder, and, as more and more of the Air in the Receiver was, from time to time, drawn out; so did that in the Bladder more and more expand it self, and display the folds of the formerly flaccid Bladder: So that before we had exhausted the Receiver near so much as we could, the Bladder appear'd as full and stretched, as if it had been blown up with a Quill.

And that it may appear that this plumpness of the Bladder pro∣ceeded from the surmounting of the debilitated Spring of the am∣bient Air remaining in the Vessel, by the stronger Spring of the Air remaining in the Bladder; we return'd the Key of the Stop∣cock, and by degrees allow'd the external Air to return into the Receiver: Whereupon it happen'd, as was expected, that as the Air came in from without, the distended Air in the Bladder, was proportionably compress'd into a narrower room, and the sides of the Bladder grew flaccid, till the Receiver having re-admitted its wonted quantity of Air, the Bladder appear'd as full of wrin∣kles and cavities as before.

This Experiment is much of the same nature with that which was, some years ago, said to be made by that eminent Geometri∣cian Monsieur Roberval, with a Carps Bladder empty'd and con∣vey'd into a Tube, wherein the Experiment De Vacuo was after∣wards try'd, which ingenious Experiment of his, justly deserveth the thanks of those that have been, or shall be solicitous to disco∣ver the nature of the Air.

But to return to our Experiment, we may take notice of this Circumstance in it, That after the Receiver hath been in some measure empty'd, the Bladder doth, at each exsuction, swell much more conspicuously than it did at any of the first Exsuctions; in∣somuch that towards the end of the pumping, not only a great fold or cavity in the surface of the Bladder may be made even, by the stretching of the inward self-expanding Air: But we have sometimes seen, upon the turning of the Key to let the ambient Air pass out of the Receiver into the Cylinder, we have seen (I say) the Air in the Bladder suddenly expand it self so much and so briskly, that it manifestly lifted up some light Bodies that lean'd upon it, and seem'd to lift up the Bladder it self.

Now because it hath, by very learned Men, been doubted, whether the swelling of the Bladder may not have proceeded (not from the Dilatation of the included Air,) but from the Texture of the Fibres, which, being wont to keep the Bladder extended when the Animal (to whom it belong'd) was alive, may be suppos'd in our Experiment to have return'd, like so many Springs to their wonted extent, upon the removal of the ambient Air that compress'd and bent them: Because this, I say, hath been doubted, we thought fit to make this further trial.

We let down into the Receiver with the fore-mentioned Blad∣der two other much smaller, and of the same kind of Animal; the one of these was not ty'd up at the neck that there might be liberty left to the Air that was not squeez'd out (which might amount to about a fifth part of what the Bladder held before) to pass out into the Receiver: The other had the sides of it stretch'd out and press'd together, almost into the form of a Cup, that they might inter∣cept the less Air betwixt them, and then was strongly ty'd up at the neck: This done, and the Air being in some measure suck'd out of the Pneumatical Glass (if I may so call it) the Bladder, men∣tion'd at the beginning of our Experiment, appear'd extended eve∣ry way to its full Dimensions; whereas neither of the two others did remarkably swell, and that, whose neck was not ty'd, seem'd very little, if at all less wrinkl'd than when it was put in.

We made likewise a strong Ligature about the middle of a long

Bladder partly empty'd, and upon the drawing the Air out of the Receiver, could observe no such swelling betwixt the Ligature and the neck of the Bladder, which had been purposely left open, as betwixt the same Ligature and the bottom of the Bladder, whence the included Air could no way get out.

But a farther and sufficient manifestation whence the intumes∣cence of the Bladder proceeds, may be deduc'd from the follow∣ing Experiment.

EXPERIMENT V.

TO try then at once both what it was that expanded the Blad∣der, and what a powerfull Spring there is ev'n in the Air we are wont to think uncompress'd: We caus'd a Bladder dry, well ty'd and blown moderately full, to be hung in the Recei∣ver by one end of a string, whose other end was fastned to the inside of the Cover: and upon drawing out the ambient Air, that press'd on the Bladder; the internal Air not finding the won∣ted resistance, first swell'd and distended the Bladder, and then broke it, with so wide and crooked a rent, as if it had been forcibly torn asunder with hands. After which a second Bladder being convey'd in, the Experiment was repeated with like success: And I suppose it will not be imagin'd that in this case the Blad∣der was broken by its own Fibres, rather than by the Impri∣son'd Air.

And of this Experiment these two Phaenomena may be taken notice of: The one, that the Bladder at its breaking gave a great report, almost like a Cracker: And the other, That the Air con∣tain'd in the Bladder, had the power to break it with the men∣tion'd Impetuosity, long before the ambient Air was all, or near all, drawn out of the Receiver.

But, to verifie what we say in another Discourse, where we show, That even true Experiments may, by reason of the easie mi∣stake of some unheeded Circumstance, be unsuccessfully try'd; we will Advertise, on this occasion, that we did oftentimes in vain try the breaking of Bladders, after the manner above mention'd: Of which the cause appear'd to be this, That the Bladders we could

not break, having been brought us ready blown from those that sold them, were grown dry before they came to our hands: whence it came to pass, that, if we afterwards ty'd them very hard, they were apt to fret and so become unserviceable; and if we ty'd them but moderately hard, their stifness kept them from being clos'd so exactly, but that when the included Air had in the exhausted Re∣ceiver distended them as much as easily it could, it would in part get out between the little wrinkles of the Sphincter of the Neck: Whence also it usually happen'd, that, upon the letting in the Air from without, the Bladders appear'd more flaccid and empty than before they were put in; whereas when the Bladders were brought us moist from the Butchers, we could, without injuring them, tie their necks so close, that none of the Air once blown in, could get out of them, but by violently breaking them.

It would not be amiss on this occasion to point at something which may deserve a more deliberate Speculation than we can now afford it; namely that the Elastical Power of the same Quan∣tity of Air may be as well encreas'd by the Agitation of the Aëri∣al Particles (whether only moving them more swiftly and scat∣tering them, or also extending or stretching them out, I deter∣mine not) within an every way inclosing and yet yielding Body; as display'd by the withdrawing of the Air that press'd it with∣out. For we found that a Bladder, but moderately fill'd with Air and strongly ty'd, being a while held near the Fire, not only grew exceeding turgid and hard, but afterwards, being brought nearer to the Fire, suddenly broke with so loud and vehement a noise, as stony'd those that were by, and made us for a while after, al∣most deaf.

EXPERIMENT VI.

HAving thus seen that the Air hath an Elastical Power, we were next desirous to know in some measure how far a par∣cel of Air might by this its own Spring be dilated. And though we were not provided of Instruments fit to measure the dilatati∣on of the Air any thing accurately, yet because an imperfect mea∣sure of it was more desirable than none at all, we devis'd the fol∣lowing method as very easily practicable.

We took a limber Lambs Bladder which was thorowly wetted in fair Water, that the sides of it being squeez'd together, there might be no Air left in its folds: (as indeed we could not afterwards upon trial discern any) The neck of this Bladder was strongly tied about that of a small Glass, (capable of holding five full drachmes of Water) the Bladder being first so compress'd, that all the included Air was only in the Glass, without being press'd there; then the Pump being set on work after a few exsuctions, the Air in the little Viol began to dilate it self and produce a small Tu∣mor in the neck of the Bladder; and as the ambient Air was more and more drawn away, so the included Air penetrated farther and farther into the Bladder, and by degrees listed up the sides and dis∣play'd its folds, till at length it seem'd to have blown it up to its full extent: Whereupon the external Air, being permitted to flow back into the Receiver, repuls'd the Air that had fill'd the Blad∣der, into its former narrow receptacle, and brought the Bladder to be again flaccid and wrinkled as before: Then taking out the Blad∣der, but without severing it from the Glass, we did, by a hole made at the top of the Bladder, fill the Vessel, they both made up, with Water, whose weight was five Ounces five Drachmes and a half: Five Drachmes whereof were above-mention'd to be the contents of the Bottle. So that in this Experiment, when the Air had most extended the Bladder, it possess'd in all above nine times as much room as it did when it was put into the Receiver. And it would probably have much inlarg'd its bounds, but that the Bladder by its weight and the sticking together of its sides did somewhat resist its expansion: And which was more considerable, the Bladder ap∣pear'd tumid enough, whilst yet a pretty deal of Air was left in the Receiver, whose exsuction would according to our former Obser∣vation, probably have given way to a farther expansion of the Air, especially supposing the dilatation not to be restrain'd by the Bladder.

SInce we wrote the other day the former Experiment, we have met with some Glasses not very unfit for our purpose; by means of which we are now able, with a little more trouble, to

measure the expansion of the Air a great deal more accurately than we could by the help of the above-mention'd Bladder, which was much too narrow to allow the Air its utmost distention.

We took then first a Cylindrical Pipe of Glass, whose bore was about a quarter of an Inch in Diameter: This Pipe was so bent and doubled, that, notwithstanding its being about two foot in length, it might have been shut up into a smaller Receiver, not a Foot high: But by misfortune it crack'd in the cooling, whereby we were reduced to make use of one part which was straight and intire, but exceeded not six or seven Inches. This little Tube was open at one end; and at the other, where it was Hermetically seal'd, had a small Glass bubble to receive the Air whose dilatation was to be measur'd.

Along the side of this Tube was pasted a straight narrow piece of Parchment, divided into twenty six equal parts, marked with black Lines and Figures, that by them might be measur'd both the included Air and its dilatation. Afterwards we fill'd the Tube with Water, almost to the top; and stopping the open end with the Finger, and inverting the Tube, the Air was permitted to as∣cend to the above mention'd Glass bubble. And by reason this ascent was very slow, it gave us the opportunity to mark how much more or less than one of the twenty six divisions this Air took up. By this means, after a trial or two, we were inabled to convey to the top of the Glass a bubble of Air equal enough, as to sight, to one of those Divisions: Then the open end of the Tube being put into a small Viol, whose bottom was cover'd with Water, about half an Inch high; we included both Glasses into a small and slender Receiver, and caused the Pump to be set on work. The event was, That at the first exsuction of the Air there appear'd not any expansion of the bubble, comparable to what appear'd at the second, and that upon a very few exsuctions the bubble reaching as low as the surface of the subjacent Water, gave us cause to think, That if our Pipe had not been broken, it would have expanded it self much farther: Wherefore we took out the little Tube, and found that besides the twenty six divisions formerly mention'd, the Glass bubble and some part of the Pipe

to which the divided Parchment did not reach, amounted to six divisions more. Whereby it appears that the Air hath take up one and thirty times as much room as before, and yet seem'd capa∣ble of a much greater expansion, if the Glass would have permit∣ted it. Wherefore after the former manner, we let in another bubble, that by our guess was but half as big as the former, and found, that upon the exsuction of the Air from the Receiver, this little bubble did not only fill up the whole Tube, but (in part) break through the subjacent Water in the Viol, and thereby manifest it self to have prossessed sixty and odd times its former room.

These two Experiments are mention'd to make way for the more easy belief of that which is now to follow. Finding then that our Tube was too short to serve our turn, we took a slender Quill of Glass which happen'd to be at hand, though it were not so fit for our purpose as we could have wished, in regard it was three or four times as big at one end as the other. This Pipe which was thirty Inches long, being Hermetically seal'd at the slender end, was almost filled with water; and after the above-related manner a bubble was convey'd to the top of it, and the open extreme was put into a Viol that had a little fair Water at the bottom: Then the Cover, by means of a small hole purposely made in it for the Glass Pipe to stand out at, was cemented on to the Receiver, and the Pump being set on work, after some exsuctions, not only the Air manifestly appear'd extended below the surface of the subja∣cent Water; but one of the By-standers affirms, that he saw some bubbles come out at the bottom of the Pipe and break through the Water. This done, we left off Pumping, and observ'd how at the unperceiv'd leaks of the Receiver the Air got in so fast, that it very quickly impell'd up the Water to the top of the Tube, excepting a little space whereinto that bubble was repuls'd, which had so lately possess'd the whole Tube; this Air at the slender end appear'd to be a Cylinder of ⅚ parts of an Inch in length, but when the Pipe was taken out and turn'd upside down, it appear'd at the other end inferiour in bulck to a Pea.

These things being thus done we took (to make the Experi∣ment

the more exactly) a small pair of Scales, such as Gold-Smiths use to weigh Cold Coyn in; and weighing the Tube and Water in it, we found them to amount to one Ounce thirty Grains and an half: Then we pour'd in as much Water as serv'd to fill up the Tube, wherein before we had left as much space unfill'd up as was possess'd by the bubble, and weighing again the Pipe and Water, we found the weight increas'd onely by one Grain. Lastly, pouring out the Water, and carefully freeing the Pipe from it (which yet we could not perfectly doe) we weighed the Glass alone, and found it to want two Drachmes and thirty two Grains of its for∣mer weight: So that the bubble of Air taking up the room but of one Grain in weight of Water, it appear'd that the Air by its own 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 was so rarified, as to take up one hundred fifty two times as much room as it did before: Though it were then compress'd by nothing but the ordinary pressure of the contiguous Air. I know not whether it be requisite to take notice, that this Experiment was made indeed in a moist Night, but in a Room, in whose Chimney there was burning a good Fire, which did perhaps some∣what rarifie the Air of which the bubble consisted.

It hath seem'd almost incredible which is related by the Industri∣ous Mersennus, That the Air by the violence of heat, though as great as our Vessels can support without fusion, can be so dilated as to take up seventy times as much room as before: Wherefore because we were willing to have a confirmation of so strange a Phae∣nomenon; we once more convey'd into the Tube a bubble of the bigness of the former, and prosecuting the Experiment as before with the same Water, we observed that the Air did manifestly stretch it self so far, as to appear several times a good way below the surface of the Water in the Viol, and that too with a surface very convex toward the bottom of the Pipe. Nay, the Pump being ply'd a little longer, the Air did manifestly reach to that place where the bottom of the Tube leaned upon the bottom of the Viol, and seemed to knock upon it and rebound from it: Which Circumstances we add, partly that the Phaenomenon we have been relating may not be imputed to the bare subsiding of the Water that filled the Tube, upon the taking off the pressure of the ambi∣ent

Air. And partly also that it may appear that if our Expe∣riments have not been so accurately made as with fitter Instru∣ments might perhaps be possible; yet the expansion of the Air is likely to be rather greater than lesser than we have made it: Since the Air was able to press away the Water at the bottom of the Pipe, though that were about two Inches below the surface of the Water that was then in the Viol, and would have been at least as high in the Pipe, if the Water had onely subsided and not been depressed: So that it seems not unlikely that if the Expe∣riment could be so made, as that the expansion of the Air might not be resisted by the Neighbouring Bodies, it would yet enlarge its bounds, and perhaps stretch it self to two hundred times its former bulk, if not more. However, what we have now tryed will, I hope, suffice to hinder divers of the Phaenomena of our En∣gine from being distrusted: Since in that part of the Atmosphere we live in, that which we call the free Air (and presume to be so uncompressed) is crouded into so very small a part of that space, which if it were not hindred it would possess. We would gladly have tryed also whether the Air at its greatest expansion could be farther rarified by heat; but doe what we could, our Receiver leaked too fast to let us give our selves any satisfaction in that particular.

EXPERIMENT VII.

TO discover likewise by the means of that pressure of the Air, both the strength of Glass, and how much interest the Figure of a Body may have in its greater or lesser Resistance to the pressure of other Bodies, we made these farther tryals.

We caus'd to be blown with a Lamp, a round Glass bubble, capable of containing, by guess, about five Ounces of Water, with a slender neck about the bigness of a Swan's Quill, and it was purposely blown very thin, as Viols made with Lamps are wont to be, that the thinness of the matter might keep the roundness of the Figure from making the Vessel too strong. Then having moderately emptied the Receiver, and taken it out of the Pump, we speedily applied to the Orifice of the bot∣tom

of it, the Neck of the newly mention'd Glass, carefully stop∣ping the Crannies with melted Plaister, that no Air might get in at them: And after turning the Key of the Stop-cock, we made a free passage for the Air to pass out of the bubble into the Receiver: Which it did with great celerity, leaving the bubble as empty as the Receiver it self; as appear'd to us by some Cir∣cumstances not now to be insisted on. Notwithstanding all which, the Vessel, continuing as intire as before, gave us cause to wonder that the bare roundness of the Figure should enable a Glass, almost as thin as Paper, to resist so great a pressure as that of the whole incumbent Atmosphere. And having reiterated the Experiment, we found again that the pressure of the ambient Body, thrusting all the parts inwards, made them, by reason of their arched Figure, so support one another, that the Glass re∣main'd as whole as at first.

Now that the Figure of the Glass is of great moment in this matter, may be evinced by this other Experiment.

EXPERIMENT VIII.

WE took a Glass Helmet or Alembick (delineated by the seventh Figure) such as Chymists use in Distillations, and containing by conjecture between two and three Pints: The Rostrum or Rose of it mark'd with (c) was Hermetically closed; and at the top of it was a hole, into which was fitted and ce∣mented one of the Shanks of a middle-siz'd Stop-cock; so that the Glass being turn'd upside-down, the wide Orifice (which in common Glass-Helmets is the onely one) was upwards; and to that wide Orifice was fitted a cast cover of Lead, which was carefully cemented on to the Glass: Then the other Shank of the Stop-cock being with cement likewise fasten'd into the upper part of the Pump, the exsuction of the Air was endeavoured. But it was not long before, the remaining Air being made much too weak to ballance the pressure of the Ambient Air, the Glass was (not without a great noise) crack'd almost half round, along that part of it where it began to bend inwards: As if in the Fi∣gure, the crack had been made according to the Line (a b,) and

upon an endeavour to pump out more of the Air, the crack once begun, appear'd to run on farther; though the Glass where it was broken seem'd to be (by conjecture) above ten, some thought above twenty times, as thick as the bubble mentioned in the foregoing Experiment.

This will perhaps make it seem strange, that having taken another Glass bubble blown at the same time, and like for ought we discerned for size, thickness and Figure, to that thin one for∣merly mentioned; and having sealed it up Hermetically, and suspended it in the Receiver, the exsuction of the ambient Air did not enable the imprisoned Air to break, or in the least to crack the bubble; though the Experiment were laboriously tried, and that several times with bubbles of other sizes: But that per∣haps the heat of the Candle or Lamp wherewith such Glasses are Hermetically sealed, (not to mention the warmth of his hands that seal'd it) might so rarefy the contained Air, as much to weaken its Spring, may seem probably by the following Expe∣riments.

EXPERIMENT IX.

WE took a Glass Viol able to hold three or four Ounces of Water, and of the thickness usual in Glasses of that size; into the Neck of this was put a moderately slender Pipe of Glass, which was carefully fastened with a mixture of equal parts of Pitch and Rosin to the Neck of the Viol, and which reached almost to the bottom of it, as the sixth Figure declareth.

This Viol being, upon a particular design, filled with Water, till that came up in it, a pretty deal higher than the lower end of the Pipe, was put into one of our small Receivers, (contain∣ing between a Pint and a Quart) in such manner as that the Glass Pipe, passing through a hole made purposely for it in the Leaden-Cover of the Receiver, was for the most part of it without the Vessel, which being exactly closed, the Pump was set on work: But at the very first exsuction, and before the Sucker was drawn to the bottom of the Cylinder, there flew out of the Viol a piece of Glass half as broad as the Palm of a Man's Hand, and it was

thrown out with such violence, that hitting against the Neigh∣bouring side of the Receiver, it not onely dashed it self to pieces, but cracked the very Receiver in many places, with a great noise that much surprised all that were in the Room. but it seemed, that in so little a Receiver, the Air about the Viol be∣ing suddenly drawn out, the Air imprisoned in the Vessel, ha∣ving on it the whole pressure of the Atmosphere (to which by the Pipe open at both ends, It and the Water were exposed) and not having on the other side the wonted pressure of the Ambient Air to ballance that other pressure, the resistance of Glass was finally surmounted, and the Viol once beginning to break where it was weakest, the external Air might rush in with violence enough to throw the cracked parcel so forcibly a∣gainst the Neighbouring side of the Receiver, as to break that too.

And this may be presumed sufficient to verify what we deli∣vered in that part of our Appendix to the first Experiment where we mentioned the almost equal pressure of the Air on either side of a thin Glass Vessel, as the cause of its not being broken by the forcible spring of the contained Air. But yet that it be not suspected that chance had an interest in so odd an Experiment as we have been relating, we will add that for farther satisfaction we reiterated it in a round Glass contain∣ing by Guess about six ounces of Water: This Viol we put into such a small Receiver as was lately mentioned, in such manner as that the bottom of it rested upon the lower part of the Pneumatical Glass, and the Neck came out through the Leaden-cover of the same at a hole made purposely for it. But being made circumspect by the foregoing mischance, we had put the Viol into a Bladder, before we put it into the Re∣ceiver to hinder this last-named Glass from being endangered by the breaking of the other. Then the Pneumatical Vessel being closed so that no way was left for the outward Air to get into it, but by breaking through the Viol, into whose ca∣vity it had free access by the mouth of it, (which was pur∣posely left open,) the Sucker being nimbly drawn down, the

external Air immediately pressed forcibly as well upon the Lea∣den-cover as the Viol; and the Cover happening to be in one place a little narrower than the edge of the Pneumatical Glass, was depressed, and thrust into it so violently by the incumbent Air, that getting a little within the tapering Lip of the Glass, it did (like a kind of Wedge,) thrust out that side where it was depressed, so as, (though the Receiver was new,) to split it. This accident being thus mentioned upon the bye to con∣firm what we formerly said touching the fitness or unfitness of Glasses of some Figures to resist the pressure of the Atmosphere; We will proceed to relate the remaining part of the Experiment, namely, That having fitted on a wider Cover to the same Re∣ceiver, and closed both that and the crack with Cement, we prosecuted the Experiment in the manner above related, with this success: That upon the quick depressing of the Sucker, the external Air burst the Body of the Viol into above an hundred pieces, many of them exceeding small, and that with such vio∣lence, that we found a wide rent, besides many holes, made in the Bladder it self.

And to evince that these Phaenomena were the effects of a li∣mited and even moderate force, and not of such an abhorrency of a Vacuum as that to avoid it, many have been pleased to think that Nature must, upon occasion, exercise an almost boundless power; we afterwards purposely try'd this Experiment with se∣veral Glasses somewhat thicker than those Viols, and found the event to verify our conjecture, that it would not succeed: For the Glasses were taken out as intire as they were put in.

And here, My Lord, I hold it not unfit, upon occasion of the mention that hath been made of our having employ'd small Re∣ceivers, and one of them, notwithstanding its being crack'd, to annex these two Advertisements.

First then, besides the great Pneumatical Glass so often mentioned, and the proportionate Stop-cock, we thought fit to provide our selves with some small Receivers blown of Cry∣stalline Glass, of several Shapes, and furnished with smaller Stop-cocks purposely made; and this we did upon hopes, that

when we had surmounted the difficulties to be met with in Ce∣menting the Glasses to the Stop-cocks, and the Pneumatical Ves∣sels to the Pump, so exquisitely as is requisite for our purpose, we should from the smallness of our Receivers receive a four-fold Advantage. The first, that by reason of the slenderness of the Vessels, and their being made of much purer and clearer metal, (as the Glass-men speak,) than the great Receiver, we might have a more perfect view of every thing happening within them. The next, that such small Vessels might be emptied with less labour and in much less time. The third, that this nimble ex∣suction of the ambient Air would make many changes in the Bo∣dies shut up in these Glasses more sudden and conspicuous than otherwise they would prove. And the last, that we should be able to draw and keep out the Air much more perfectly from such small Vessels than from our large Receiver, But though we were not much disappointed in the expectation of the three first advantages, yet we were in our hopes of the fourth. For besides the great difficulty we found in fitting together the Glasses, the Stop-cocks, and the Covers; besides this I say, we found our selves seldom able to draw, and keep out the Air so far as to make the remaining Air in these Receivers weaker than the remaining Air in our great Receiver. For though sometimes the Leaks of some of these little Receivers may be much (either fewer or smal∣ler) than those of the larger Vessel; yet a little Air getting into one of these, wherein it had but little room to expand and dis∣play it self, might press as much upon all parts of the internal surface of the Vessel, and upon the included Bodies, as a greater quantity of the Air in a Vessel in whose capacity it might find more room to expand it self.

The other thing that we were to advertise, is, That 'tis not every small crack that can make such a Receiver as is of a roun∣dish Figure altogether useless to our Experiment, in regard that upon the exsuction of the internal Air, the ambient Air on all sides pressing the Glass inwards or towards the middle, doth consequent∣ly thrust the Lips of the crack closer, and so rather close than in∣crease it.

This I mention partly because Receivers fit for our turn are more easily cracked than procured, and therefore ought not to be unnecessarily thrown away as unserviceable: And partly be∣cause I think it becomes one that professeth himself a faithfull Relator of Experiments, not to conceal from Your Lordship, that after a few of the foregoing Experiments were made, there happened in the great Receiver a crack of about a Span long, be∣ginning at the upper Orifice, and occasion'd, as it seem'd, by the excessive heat of too large an Iron that was employ'd to melt the Cement about that Orifice. But having laid upon this crack a broad Plaister, (which in one of our Essays written some years since to your ingenious and hopefull Cousin Jones, we extoll for the mending of crack'd Receivers, and other Chymical Glasses;) and having afterwards thickly overlaid this Plaister with Diachy∣lon, we neither could then, nor can yet perceive that the Vessel leaks sensibly at that crack.

The Plaister was made of good quick Lime finely poudred, and nimbly ground with a Pestle in a Mortar, with a quantity (I know not how much precisely, not having those Essays in this place) of scrapings of Cheese and a little fair Water, no more than is just necessary to bring the mixture to a somewhat soft Paste, which when the Ingredients are exquisitely incorporated, will have a strong and stincking smell: Then it must be im∣mediately spread upon a Linnen Cloath of three or four fingers breadth, and presently apply'd, lest it begin to harden. But if your Lordship had seen how we mended with it Receivers even for the most subtle Chymical Spirits. You would scarce wonder at the service it hath done in our Pneumatical Glass.

EXPERIMENT X.

WE took a Tallow-candle of such a size that eight of them make about a pound, and having in a very commodious Candlestick let it down into the Receiver, and so suspended it, that the Flame burnt almost in the middle of the Vessel, we did in some two minutes exactly close it up: and upon pumping ve∣ry nimbly, we found, that, within little more than half a mi∣nute

after, the Flame went out, though the Snuff had been pur∣posely left of that length we judged the most convenient for the lasting of the Flame.

But the second time having put in the same Candle into the Receiver, (after it had by the blasts of a pair of Bellows been freed from Fumes) the Flame lasted about two minutes from the time the Pumper began to draw out the Air; upon the first ex∣suction whereof, the Flame seem'd to contract it self in all its di∣mensions. And these things were farther observable, that after the two or three first exsuctions of the Air, the Flame (except at the very top) appear'd exceeding blew, and that the Flame still receded more and more from the Tallow, till at length it ap∣pear'd to posses onely the very top of the Week, and there it went out.

The same Candle being lighted again was shut into the Re∣ceiver, to try how it would last there without drawing forth the Air, and we found that it lasted much longer than former∣ly; and before it went out, receded from the Tallow towards the top of the Week, but not neer so much as in the former Experiment.

And having an intention to observe particularly what the mo∣tion of the Smoke would be in these Experiments: We took no∣tice that when the Air was not drawn out, there did, upon the extinction of the Flame, a considerable part of the Week remain kindled, which (probably by reason of the Circulation of the Air) in the Vessel, occasion'd by the heat) emitted a Steam, which ascended swiftly and directly upwards in a slender and un∣interrupted Cylinder of smoke, till it came to the top, whence it manifestly recoil'd by the sides to the lower part of the Vessel. Whereas when the Flame went out upon the exsuction of the Air one time (when the Flame retir'd very leasurely to the top) we perceived it not to be follow'd by any smoke at all. And at ano∣ther time the upper part of the Week remaining kindled after the extinction of the Flame, the slender steam of Fumes that did arise ascended but a very little way, and then after some uncertain mo∣tions this and that way, did, for the most part, soon fall down∣wards.

Being desirous also to try whether there would be any diffe∣rence as well in our Receiver, as there is wont to be elsewhere be∣twixt Candles made of Wax and those made of Tallow, as to their duration; we took slender Tapers of white Wax, (commonly called Virgins Wax) that being found to burn with much less smoke than common yellow Wax. Six of these of like bigness, and each of them of about the thickness of a Swan's Quill, we press'd together into one Candle: and having lighted all the Weeks, we let in the above-mention'd Wax-candle into the Re∣ceiver, and made what haste we could to close it up with Cement. But, though in the mean while we left open the Valve of the Cylinder, the hole of the Stop-cock, and that in the Cover of the Receiver, that some Air might get in to cherish the Flame, and the Smoke might have a vent; Yet for so great a Flame the Air sufficed not so much as till the Cover could be perfectly lu∣ted on: So that before we were quite ready to imploy the Pump, the Candle was extinguished. Wherefore we took but one of the above mention'd Tapers, and having lighted it, clos'd it up in the Receiver, to try how long a small Flame with a proportio∣nable smoke would continue in such a quantity of Air: but we found upon two several tryals, that from the beginning of pump∣ing, the Flame went out in about a minute of an hour. It ap∣pear'd indeed to us that the swinging of the Wier to and fro (in the Engine shaken by pumping) hasten'd the vanishing of the Flame, which seem'd by that motion to be cast sometimes on one side of the Week and sometimes on the other. But though once we purposely refrain'd pumping after a very few exsuctions of the Air, that the Flame might not be agitated, yet it lasted not much longer than the newly-mention'd time. And lastly, clo∣sing up the same Taper, lighted again, to discover how long it would last without drawing out of the Air, we found that it burnt for a while vividly enough, but afterwards began to be lessen'd more and more in all its dimensions. And we observ'd that the Flame did not, as before, retire it self by little and little towards the top, but towards the bottom of the Week (from which yet it did a little withdraw upwards just before it went out)

so that the upper part of the Week-appear'd for a pretty while manifestly above the top of the Flame, which having lasted about five minutes, was succeeded by a directly ascending stream of Smoke.

EXPERIMENT XI.

THere was taken a Wier, which being bent almost in the form of a Screw, constituted such an Instrument, to contain Coals and leave them every way accessible to the Air, as the tenth Figure declareth; the breadth of this Vessel was no less than that it might with ease be convey'd into the Receiver: And having fill'd it to the height of about five Inches with throughly kindled Wood-coals, we let it down into the Glass; and speedily closing it, we caus'd the Pumper to ply his work, and observ'd that upon the very first exsuction of the Air (though perhaps not because of that onely) the Fire in the Coals began to grow very dim, and though the agitation of the Vessel did make them swing up and down (which in the sree Air would have retarded the extinction of the Fire) yet when we could no longer discern any redness at all in any of them, casting our eyes upon a minute Watch we kept by us on this occasion, we found that from the beginning of the Pumping (which might be about two minutes after the Coals had been put in glowing) to the total dis-appearing of the Fire, there had passed but three minutes.

Whereupon, to try the Experiment a little farther, we pre∣sently took out the Coals, in which it seems there had remained some little parcels of Fire, rather cover'd than totally quench'd: For in the open Air the Coals began to be re-kindled in several places, wherefore having by swinging them about in the Wier, throughly lighted them the second time, we let them down again into the Receiver, and clos'd it speedily as before; and then waiting till the Fire seem'd totally extinct without medling with the Pump, we found that from the time the Vessel was clos'd, till that no Fire at all could be perceiv'd, there had pas∣sed about four minutes: Whereby it seem'd to appear that the

drawing away of the ambient Air made the Fire go out sooner than otherwise it would have done; though that part of the Air that we drew out left the more room for the stifling steams of the Coals to be received into.

Lastly, Having taken out the Wier and put other Coals into it, we did, in the same Room where the Engine stood, let it hang quietly by a string in the open Air, to try how long the Fire would last without agitation, when no Air was kept from it, And we found that the Fire began to go out first at the top and outsides of the Coals; but inwards and near the bottom the Fire continu'd visible for above half an hour, a great part of the Coals, especially those next the bottom, being burnt to ashes before the Fire went out.

We caus'd likewise a piece of Iron to be forg'd, of the bigness of a middle siz'd Char-coal, and having made it red-hot through∣out; we caus'd it in the lately mention'd Wier, to be speedily convey'd and shut up into the Receiver, being desirous to try what would become of a glowing Body, by reason of its texture more vehemently hot than a burning Coal of the same bigness, and yet unlike to send forth such copious and stifling Fumes: But we could not observe any manifest change upon the exsuc∣tion of the Air. The Iron began indeed to lose its fiery redness at the top, but that seem'd to be because it was at the upper end somewhat more slender than at the lower: The redness, though it were in the day time, continued visible about four minutes; and then, before it did quite disappear, we turn'd the Key of the Stop-cock, but could not discern any change of the Iron up∣on the rushing in of the Air. Yet some little remainders of Wax that stuck to the Wier, and were turn'd into Fumes by the heat of the neighbouring Iron, seem'd to afford a more plen∣tifull, or at least a much more expanded Smoke when the Air was suck'd out, than afterwards; though allowance was made for the decreasing heat of the Iron. And lastly, notwithstanding a considerable exsuction of the ambient Air, though not by far so great a one as might have been made by the Engine; and notwithstanding the inconsiderable dissipation of the parts of the

Iron; the surrounding sides of the Receiver were sensibly, and almost offensively heated by it; insomuch that a pretty while after the Iron was taken out, the sides of the Glass manifestly re∣tain'd a warmth: which would not be unfit to be consider'd by a Person at more leasure than I am now.

EXPERIMENT XII.

BEing willing to try after this something that would not che∣rish much Fire at once, and would keep Fire much longer than a Coal: We took a piece of Match, such as Souldiers use, of the thickness of a Man's little Finger, or somewhat thicker; and this being well lighted at one end, was by a string suspen∣ded with that end downwards in the cavity of the Receiver which was immediately clos'd: And yet by that time it could well be so, the copious Fumes of the Match had near fill'd and darken'd the Receiver. Wherefore, lest the Vessel should be endanger'd, the Pump was nimbly ply'd, and a great deal of Air and Smoke mixt together was drawn out, whereby the Re∣ceiver growing more clear, we could discern the Fire in the Match to burn more and more languidly: and notwithstanding that by the diligence us'd in pumping, it seem'd to have room enough allow'd it to throw out Fumes; yet, after no long time, it ceas'd from being discernable either by its Light or its Smoke. And, though by that we were invited to suppose it quite extin∣guished, yet we continu'd pumping a-while, in prosecution of another Experiment we were trying at the same time: And this we did the more willingly, because of a suspicion, the Ex∣periment about the Coals, might easily suggest, and which the event declar'd not to have been altogether groundless. For up∣on the admission of the external Air, the Fire, that seem'd to have gone out a pretty while before, did presently revive; and being as it were refresh'd by the new Air, and blown by the Wind made by that Air in rushing in, it began again to shine and dissipate the neighbouring Fuel into Smoke as formally.

EXPERIMENT XIII.

A While after we let down into the Receiver together with a lighted piece of Match, a great Bladder well tyed at the Neck, but very lank, as not containing actually much (if any thing) above a Pint of Air, but being capable of containing ten or twelve times as much.

Our scope in this Experiment was partly to try whether or no the smoke of the Match, replenishing the Receiver, would be able to hinder the dilatation of the inward Air, upon the ex∣suction of the ambient: And partly to discover whether the ex∣tinction of the Fire in the Match did proceed from want of Air, or barely from the pressure of its own Fumes, which for want of room to expand themselves in, might be suppos'd to recoyl upon the Fire, and so to stifle it.

The event of our tryal was, That at the beginning of our pumping the Match appear'd well lighted, though it had al∣most fill'd the Receiver with its plentifull Fumes: But by de∣grees it burnt more and more dimly, notwithstanding, that by the nimble drawing out the Air and Smoke, the Vessel were made less opacous, and less full of compressing matter; as ap∣pear'd by this, That the longer we pump'd, the less Air and Smoke came out of the Cylinder at the opening of the Valve, and con∣sequently the less came into it before; yet the Fire in the Match went but slowly out. And when afterwards, to satisfy our selves of its expiration, we had darken'd the Room, and in vain endeavoured to discover any spark of Fire, (as we could not for some time before by the help of Candles discern the least rising of Smoke,) we yet continued pumping six or seven times; and after all that, letting in the Air, the seemingly dead Fire quickly revived, and manifested its recovery by Light and store of Smoke, with the latter of which it quickly began to re∣plenish the Receiver. Then we fell to pumping afresh, and conti∣nued that labour so long, till the re kindled Match went out again: and thinking it then fit not to cease from pumping so soon as before, we found that in less than half a quarter of an hour the

Fire was got out for good and all, and past the possibility of be∣ing recover'd by the re-admitted Air.

Some Circumstances, besides those already mention'd, oc∣curr'd in the making of the Experiment, of which these are the principal.

First, When the Receiver was full of Smoke, if the Cylinder were emptied, immediately upon the turning of the Stop-cock, the Receiver would appear manifestly darken'd to his eye that look'd upon the light through it: and this darkness was much less when the Receiver was much less fill'd with Fumes: It was also instantaneous, and seem'd to proceed from a sudden change of place and situation in the exhalations, upon the vent sudden∣ly afforded them and the Air they were mixt with, out of the Receiver into the Cylinder.

The next thing we observed was, a kind of Halo that ap∣pear'd a good while about the Fire, and seem'd to be produced by the surrounding Exhalations.

And lastly, it is remarkable, That even when the Fumes seemed most to replenish the Receiver, they did not sensibly hinder the Air included in the Bladder from dilating it self after the same manner (for ought we could discern) as it would have otherwise done: So that before the Fire or the Match was quite extinct, the Bladder appear'd swell'd at least to six or seven times its former capacity.

Since the writing of these last Lines, we took a small Recei∣ver, capable of containing (by guess) about a pound and a half of Water; and in the midst of it we suspended a lighted Match, but though within one minute of an hour (or there abouts) from the putting in of the Match, we had cemented on the Cover, yet we could not make such haste, but that be∣fore we began to pump, the Smoke had so fill'd that small Re∣ceiver, as for ought we discern'd, to choke the Fire. And ha∣ving again and again reiterated the Experiment, it seem'd still as at first, that we could not close up the Vessel, and pump out all the Fumes time enough to rescue the Fire from extinction, whereupon we made use of this Expedient: Assoon as we had

pump'd once or twice, we suddenly turn'd the Key, and there∣by gave access to the excluded Air, which rushing violently in, as if it had been forced thorow a pair of Bellows, did both drive away the ashes, fill the Glass with fresh Air, and by blowing the almost extinguish'd Fire, re-kindl'd it, as appear'd by the Matches beginning again to smoke, which before it had ceas'd to do; we having by this means obtained a lighted Match in the Receiver, without being reduced to spend time to close it up, commanded the Air to be immediately pump'd out, and found that upon the exsuction of it, the Match quickly left smo∣king, as it seem'd, by reason of the absence of the Air; and yet if some urgent occasions had not hinder'd us, we would for greater security have try'd, whether or no the Match rekindled as formerly, would smoke much longer, in case of no exsuction of the ambient Air.

EXPERIMENT XIV.

TO try diverse things at once, and particularly whether Fire, though we found it would not long last, might not be produced in our evacuated Receiver: We took a Pistol of about a foot in length, and having firmly tyed it to a stick almost as long as the Cavity of the Receiver, we very carefully prim'd it with well dry'd Gunpowder, and then cocking it, we ty'd to the Tricker, one end of a string, whose other end was fasten'd to the Key formerly mention'd to belong to the Cover of our Receiver. This done, we convey'd the Pistol, together with the annexed Staff, into the Vessel which being clos'd up, and empty'd aster the usual manner, we began to turn the Key in the Cover; and thereby shortning the string that reach'd from it to the Pistol, we pull'd aside the Tricker, and observ'd, that according to our expectation the force of the Spring of the Lock was not sensibly abated by the absence of the Air: (from whose impetus yet some Modern Naturalists would derive the cause of the motion of Restitution in solid Bodies) For the Cock falling with its wonted violence upon the Steel, struck out of it as ma∣ny, and as conspicuous parts of Fire, as, for ought we could

perceive, it would have done in the open Air. Repeating this Experiment diverse times, we also observed whether or no there would appear any considerable diversity in the Motion of the shining Sparks in a place where the remaining Air was so much rarefied, but could not perceive but that they moved some of them upwards, as well as some of them downwards, and some of them side-ways, as they are wont to do, when upon such collisions they fly out in the open Air.

We likewise caus'd a piece of Steel to be made of the form and bigness of the Flint, in whose place we put it, and then the Pistol being cock'd and conveyed into the Receiver, the Tricker was pull'd after the Air was drawn out: And though the place were purposely somewhat darken'd, yet there appear'd not up∣on the striking of the two Steels against each other the least spark of Fire: Nor did we expect any (having before in vain attempted to strike Fire this way in the open Air) though we thought fit to make the Experiment, to undeceive those who fancy in rarefied Air, I know not what strange disposition, to take fire upon a much slighter occasion than this Experiment afforded. We have indeed found, that by the dextrous Colli∣sion of two harden'd pieces of Steel, store of sparks may be struck out: But that was done with such vehement percussion of the edges of the two Steels, as could not well be compass'd in our Receiver.

But the chief thing we design'd to doe with our Pistol, was, To observe whether Gun-powder would take Fire in our empty'd and closely stop'd Glass? Whether the expansion of the Flame would be considerably varied by the absence of so much of the ambient Air as was drawn out of the Receiver? And whether the Flame would diffuse it self upward, as it is wont, notwith∣standing its not having about it the usual proportion of Air to force it up? And though most of our Attempts to fire the Gun-powder in the Pan of the Pistol succeeded not, because we were fain to let it hang almost perpendicular in the Receiver, where∣by the Powder was shaken down before the sparks could reach it: yet once the Experiment succeeded, and the kindled Powder

seem'd to make a more expanded Flame than it would have done in the open Air, but mounted upwards according to its wont, whether by reason of that little portion of Air, which in spight of our pumping remained in the Receiver, or for any other cause, we have not now the leasure to consider. But we must not forget, that upon the extinction of the Flame the Receiver appear'd darken'd with smoke, which seem'd to move freely up and down, and upon the letting in the Air at the Stop-cock be∣gan to circulate much ••aster than before. We would have made more observations concerning this Flame, but that of two or three attempts we afterwards made to repeat the kindling of the Powder, not any one succeeded; and we have not the leasure to dwell long upon one kind of Trials.

EXPERIMENT XV.

TO these Experiments concerning Fire we added another, which though it succeeded not, may perhaps without impertinency be recorded: partly, because that (as we have in another Treatise amply declar'd) it is usefull to recite what Experiments miscarry as well as succeed. And partly also, be∣cause it is very possible that what we endeavoured in vain, may be performed by Your Lordship, or some other Vertuoso that shall have stancher Tessels than we had, and more Sunny days than the present Winter allows us.

We convey'd then into one of our small Receivers a piece of matter combustible, dry and black (experience declaring things of that colour to be most easily kindled) and carefully closing the Vessel, we brought it to a Window at which the Sun, not very far from the Meridian, shone in very freely: then drawing out the Air with speed we united the Sun beams with a Burning-glass upon the combustible matter, which began immediate∣ly to send forth a smoke that quickly darkned the Receiver, but notwithstanding all our care and diligence the external Air got in so fast, that after divers trials we were fain to leave off the Experiment in that Glass, and induc'd to make trial of it in our great Receiver.

Having then after some difficulty lodg'd the combustible mat∣ter in the cavity of this Vessel in such manner, as that it was al∣most contiguous to that side thereof that was next the Sun, we did endeavour with a pretty large Burning-glass to kindle it, but found, as we fear'd, That, by reason of the thickness of the Glass, (which was also of a less pure and less Diaphanous matter than the other) the Sun-beams thrown in by the Burning-glass, were in their passage so dislocated and scattered (not now to mention those many that being reflected, could not pierce into the cavity of the Receiver) that we could not possibly unite enough of them to kindle the matter, nor so much as to make it sensibly smoke. Yet we hope that the seeing whether Bodies (other than Gun-powder) may be kindled, and what would happen to them when set on fire, in a place in great measure de∣void of Air, may prove so Lucilerous an Experiment, that when the Season is more favourable we shall, God permitting, make farther trial of it, and acquaint your Lordship with the Event, if it prove prosperous. In the mean time we shall pass on to other Experiments, as soon as we have advertis'd Your Lordship that we have forborn to make such Reflexions upon the several Expe∣riments we have set down concerning Fire, as the matter would have easily afforded, and Your Lordship may perhaps have ex∣pected. But I made the less scruple to forbear the annexing of Speculations to these Recitals, because Carneades and Eleutherius have in some Dialogues concerning Heat and Flame, (which were last year seen by some Friends, and may be, when you please, commanded by You,) mention'd divers of my Thoughts and Experiments concerning Fire,

EXPERIMENT XVI.

WE designed to try whether or no divers Magnetical Expe∣riments would exhibit any unusual Phaenomena, being made in our Evacuated Receiver instead of the open Air: But for want of leasure and conveniency to prosecute such Trials, we were induced to reserve the rest for another time, and to content our selves with making that which follows. We con∣vey'd

into the Receiver a little Pedestal of Wood, in the midst of which was perpendicularly erected a slender Iron, upon whose sharp point an excited Needle of Steel purposely made, and of about five Inches long, was so placed, that hanging in an AEquilibrium it could move freely towards either hand. Then the Air being after the usual manner pumped out, we apply'd a Load-stone moderately vigorous to the outside of the Glass, and found that it attracted or repell'd the ends of the Needle, ac∣cording to the Laws Magnetical, without any remarkable dif∣ference from what the same Load-stone would have done, had none of the Air been drawn away from about the Needle, which, when the Load-stone was removed, after some tremulous Vi∣brations to and fro, rested in a position, wherein it look'd North and South.

EXPERIMENT XVII.

PRoceed we now to the mention of that Experiment, where∣of the satisfactory trial was the principal fruit I promis'd my self from our Engine, It being then fufficiently known, that, in the Experiment De Vacuo, the Quick-silver in the Tube is wont to remain elevated, above the surface of that whereon it leans, about 27 digits: I considered, that, if the true and only rea∣son why the Quick-silver falls no lower, be, that at that Altitude, the Mercurial Cylinder in the Tube is in an AEquilibrium with the Cylinder of Air, suppos'd to reach from the adjacent Mer∣cury to the top of the Atmosphere: then if this Experiment could be try'd out of the Atmosphere, the Quick-silver in the Tube would fall down to a level with that in the Vessel, since then there would be no pressure upon the subjacent, to resist the weight of the Incumbent Mercury. Whence I inferr'd (as easily I might) that if the Experiment could be try'd in our Engine, the Quick-silver would subside below 27 Digits, in proportion to the exsuction of Air, that should be made out of the Receiver. For, as when the Air is shut into the Receiver, it doth (according to what hath above been taught) continue there as strongly com∣press'd, as it did whilst all the incumbent Cylinder of the At∣mosphere

lean'd immediately upon it; because the Glass, where∣in it is pen'd up, hinders it to deliver it self, by an expansion of its parts, from the pressure wherewith it was shut up. So if we could perfectly draw the Air out of the Receiver, it would conduce as well to our purpose, as if we were allow'd to try the Experiment beyond the Atmosphere.

Wherefore (after having surmounted some little difficulties which occurr'd at the beginning) the Experiment was made after this manner. We took a slender and very curiously blown Cylin∣der of Glass, of near three foot in length, and whose bore had in Diameter a quarter of an Inch, wanting a hairs breadth: This Pipe being Hermetically seal'd at one end, was, at the other, fill'd with Quick-silver, care being taken in the filling, that as few bub∣bles as was possible should be left in the Mercury: Then the Tube being stopt with the Finger and inverted, was open'd, according to the manner of the Experiment, into a somewhat long and slender Cylindrical Box (instead of which we now are wont to use a Glass of the same form) half fill'd with Quick-silver: And so, the liquid metal being suffered to subside, and a piece of Pa∣per being pasted on level with its upper surface, the Box and Tube and all were by strings carefully let down into the Recei∣ver: And then, by means of the hole formerly mentioned to be left in the Cover, the said Cover was slipt along as much of the Tube as reached above the top of the Receiver; And the Inter∣val, left betwixt the sides of the Hole and those of the Tube, was very exquisitely filled up with melted (but not over hot) Dia∣chylon, and the round chink, betwixt the Cover and the Recei∣ver, was likewise very carefully closed up: Upon which clo∣sure there appeared not any change in the height of the Mercu∣rial Cylinder; no more, than if the interposed Glass Receiver did not hinder the immediate pressure of the ambient Atmos∣phere upon the inclosed Air; which hereby appears to bear upon the Mercury, rather by virtue of its spring than of its weight: since its weight cannot be supposed to amount to above two or three Ounces, which is inconsiderable in comparison of such a Cylinder of Mercury as it would keep from subsiding.

All things: being thus in a readiness, the Sucker was drawn down; and, immediately upon the egress of a Cylinder of Air out of the Receiver, the Quick silver in the Tube did, according to expectation, subside: And notice being carefully taken (by a mark fastened to the outside) of the place where it stopt, we caused him that managed the Pump to pump again, and marked how low the Quick-silver fell at the second exsuction; but continuing this work, we were quickly hindred from accurately marking the Sta∣ges made by the Mercury in its descent, because it soon sunk below the top of the Receiver, so that we could henceforward mark it no other ways than by the eye. And thus, continuing the labour of pumping for about a quarter of an hour, we found our selves unable to bring the Quick-silver in the Tube totally to subside; because, when the Receiver was considerably emptyed of its Air, and consequently that little that remained grown unable to resist the Irruption of the External, that Air would (in spight of what∣ever we could doe) press in at some little Avenue or other; and though much could not thereat get in, yet a little was sufficient to counterballance the pressure of so small a Cylinder of Quick-silver, as then remained in the Tube.

Now (to satisfy our selves farther, that the falling of the Quick-silver in the Tube to a determinate height, proceedeth from the AEquilibrium, wherein it is at that height with the external Air, the one gravitating, the other pressing with equal force upon the sub∣jacent Mercury) we returned the Key and let in some new Air; up∣on which the Mercury immediately began to ascend (or rather to be impelled upwards) in the Tube, and continued ascending, till having returned the Key, it immediately rested at the height which it had then attained: And so, by turning and returning the Key, we did several times at pleasure impell it upwards, and check its as∣cent. And lastly, having given a free egress at the Stop-cock to as much of the external Air as would come in, the Quick-silver was impelled up almost to its first height: I say almost, because it ftopt near a quarter of an Inch beneath the Paper mark formerly men∣tioned; which we ascri••ed to this, That there was (as is usual in this Experiment) some little Particles of Air engaged among those

of the Quick-silver; which Particles, upon the descent of the Quick-silver, did manisestly rise up in bubbles towards the top of the Tube, and by their pressure, as well as by lessening the Cylin∣der by as much room as they formerly took up in it, hindred the Quick-silver from regaining its first height.

This Experiment was a few days after repeated in the presence of those excellent and deservedly Famous Mathematick Profes∣sors, Dr. Wallis, Dr. Ward, and Mr. Wren, who were pleased to honour it with their Presence: And whom I name, both as just∣ly counting it an Honour to be known to them, and as being glad of such Judicious and illustrious Witnesses of our Experi∣ment; and'twas by their guess, that the top of the Quick-silver in the Tube was defined to be brought within an Inch of the sur∣face of that in the Vessel.

And here, for the Illustration of the foregoing Experiment, it will not be amiss to mention some other particulars relating to it.

First then, When we endeavoured to make the Experiment with the Tube closed at one end with Diachylon instead of an Herme∣tical Seal; we perceived, that upon the drawing of some of the Air out of the Receiver, the Mercury did indeed begin to fall, but continued asterwards to subside, though we did not continue pum∣ping. When it appeared, that though the Diachylon that stopt the end of the Tube, were so thick and strong, that the external Air could not press it in (as experience taught us that it would have done, if there had been but little of it) yet the subtler parts of it were able (though slowly) to insinuate themselves through the very body of the Plaister, which it seems was not of so close a Texture, as that which we mentioned our selves to have suc∣cessfully made use of in the Experiment De Vacuo some years ago. So that now we begin to suspect, that perhaps one reason, why we cannot persectly pump out the Air, may be, that when the Vessel is almost empty, some of the subtler parts of the exter∣nal Air may, by the pressure of the Atmosphere, be strained through the very body of the Diachylon into the Receiver. But this is only conjecture.

Another Circumstance of our Experiment was this, That, if (when the Quick-silver in the Tube was fallen low) too much in∣gress were, at the hole of the Stop-cock, suddenly permitted to the external Air; it would rush in with that violence, and bear so forcibly upon the surface of the subjacent Quick-silver, that it would impell it up into the Tube rudely enough to endanger the breaking of the Glass.

We formerly mention'd, that the Quick-silver did not in its descent fall as much at a time after the two or three first exsuctions of the Air, as at the beginning. For, having marked its several Stages upon the Tube, we found, that at the first suck it descended an Inch and ⅜, and at the second an Inch and ⅜; and when the Ves∣sel was almost emptied, it would scarce at one exsuction be drawn down above the breadth of a Barly-corn. And indeed we found it very difficult to measure in what proportion these decrements of the Mercurial Cylinder did proceed: Partly because (as we have already intimated) the Quick-silver wassoon drawn below the top of the Receiver; and partly because, upon its descent at each ex∣suction, it would immediately re-ascend a little upwards; either by reason of the leaking of the Vessel at some imperceptible hole or other, or by reason of the motion of restitution in the Air, which, being somewhat compresled by the fall as well as weight of the Quick-silver, would repell it a little upwards, and make it vibrate a little up and down, before they could reduce each other to such an AEquilibrium as both might rest in. But though we could not hitherto make observations accurate enough concerning the measures of the Quick-silver's descent, to reduce them into any Hypothesis, yet would we not dis∣courage any from attempting it; since, if it could be reduc'd to a certainty, 'tis probable that the discovery would not be unusefull.

And, to illustrate this matter a little more, we will add, That we made a shift to try the Experiment in one of our above-menti∣on'd small Receivers, not containing a Quart; but (agreeably to what we formerly observed) we found it as difficult to bring this to be quite empty as to evacuate the greater; the least exter∣nal

Air that could get in (and we could not possibly keep it all perfectly out) sufficing in so small a Vessel to display a consi∣derable pressure upon the surface of the Mercury, and there∣by hinder that in the Tube from falling to a level with it. But this is remarkable, that having two or three times try'd the Experiment in a small Vessel, upon the very first Cylinder of Air that was drawn out of the Receiver, the Mercury fell in the Tube 18 Inches and a half, and at another trial 19 Inches and a half.

But on this occasion, I hold it not unfit to give your Lordship notice that I hop'd from the descent of the Quick-silver in the Tube upon the first suck, to derive this advantage: that I should thence be enabled to give a near guess at the proportion of force betwixt the pressure of the Air (according to its various states, as to Density and Rarefraction) and the gravity of Quick-silver, than hitherto hath been done. For in our Experiment there are di∣vers things given, that may be made use of towards such a dis∣covery. For first we may know the capacity of the Receiver wherein the Experiment is made, since, by filling it with wa∣ter, we may easily compute how many Quarts, or Measures of any other denomination, it containeth of Air; which Air, when shut up in the Vessel may be suppos'd to have a pressure equal to that of the Atmosphere; since it is able to keep the Quick-silver in the Tube from falling any lower than it did in the free and open Air. Next here is given us the capacity of the brass Cy∣linder empty'd by the drawing down of the Sucker (its bore and height being mention'd in the description of our Pump) where∣by we may come to know how much of the Air contain'd in the Receiver is drawn out at the first-suck. And we may also easily define, either in weight or cubick measures, the Cylinder of Quick silver that answers to the Cylinder of Air lately mention'd (that Mercurial Cylinder being in our Engine computable by de∣ducting from the entire altitude of that Cylinder of Quick-silver, the altitude at which it rests upon the first exsuction.) But though, if this Experiment were very watchfully try'd in Ves∣sels of several sizes, and the various descents of the Quick-silver

compar'd among themselves, 'tis not improbable, that some such things, as we hop'd for, may thereby be discovered. Yet be∣cause not only the solid contents of as much of the Glass-tube as remains within the concave surface of the Receiver, and (which is more difficult) the varying contents of the Vessel containing the Mercury, and of as much of the Mercury it self as is not in the Tube, must be deducted out of the capacity of the Recei∣ver, but there must also an allowance be made for this, that the Cylinder that is empty'd by the drawing down of the Sucker, and comes to be fill'd upon the letting of the Air out of the Re∣ceiver into it, is not so replenish'd with Air as the Receiver it self at first was: because there passeth no more Air out of the Receiver into the Cylinder, than is requisite to reduce the Air in the cavity of the Cylinder, and in that of the Receiver to the same measure of dilatation. Because of these (I say) and some other difficulties that require more skill in Mathematicks than I pretend to, and much more leasure than my present occasions would allow me, I was willing to refer the nicer consideration of this matter to some of our Learned and accurate Mathematici∣ans, thinking it enough for me to have given the Hint already suggested.

For farther confirmation of what hath been delivered, we like∣wise tried the Experiment in a Tube of less than two foot long: and, when there was so much Air drawn out of the Vessel, that the remaining Air was not able to counterballance the Mercurial Cylinder, the Quick-silver in the Tube subsided so visibly, that (the Experiment being try'd in the little Vessel lately mention'd) at the first suck it fell above a span, and was afterwards drawn lower and lower for a little while; and the external Air being let in upon it, impell'd it up again almost to the top of the Tube: So little matters it how heavy or light the Cylinder of Quick∣silver to subside is, provided its gravity overpower the pressure of as much external Air as bears upon the surface of that Mer∣cury into which it is to fall.

Lastly we also observ'd, That if (when the Mercury in the Tube had been drawn down, and by an Ingress permitted to the

external Air, impell'd up again to its former height) there were some more Air thrust up by the help of the Pump into the Re∣ceiver, the Quick-silver in the Tube would ascend much above the wonted height of 27 digits, and immediately upon the letting out of that Air would fall again to the height it rest∣ed at before.

Your Lordship will here perhaps expect, that as those who have treated of the Torricellian Experiment, have for the most part maintained the Affirmative, or the Negative of that fa∣mous Question, Whether or no that Noble Experiment infer a Vacuum? so I should on this occasion interpose my Opinion touching that Controversie, or at least declare whether or no, in our Engine, the exsuction of the Air do prove the place de∣serted by the Air suck'd out, to be truly empty, that is, devoid of all Corporeal Substance. But besides, that I have neither the leasure, nor the ability, to enter into a solemn Debate of so nice a Question; Your Lordship may, if you think it worth the trouble, in the Dialogues not long since referr'd to, find the Difficulties on both sides represented; which then made me yield but a very wavering assent to either of the parties contending about the Question: Nor dare I yet take upon me to determine so difficult a Controversie.

For on the one side it appears, that notwithstanding the exsuc∣tion of the Air, our Receiver may not be destitute of all Bodies, since any thing placed in it, may be seen there; which would not be, if it were not pervious to those beams of Light which re∣bounding from the seen Object to our eyes, affect us with the sense of it: And that either these Beams are Corporeal Emana∣tions from some lucid body, or else at least, the light they con∣vey doth result from the brisk motion of some subtle Matter, I could, if I mistake not, sufficiently manifest out of the Dia∣logues above-mention'd, if I thought Your Lordship could seri∣ously imagine that Light could be convey'd without, at least, having, (if I may so speak) a Body for its Vehicle.

By the sixteenth Experiment, it also appears that the close∣ness of our Receiver hinders it not from admitting the Effluvia

of the Load-stone; which makes it very probable that it also free∣ly admits the Magnetical steams of the Earth; concerning which, we have in another Treatise endeavour'd to manifest that num∣bers of them do always permeate our Air.

But on the other side it may be said, That as for the subtle Matter which makes the-Objects enclosed in our evacuated Receiver, visible, and the Magnetical Effluvia of the Earth that may be presum'd to pass thorow it, though we should grant our Vessel not to be quite devoid of them, yet we cannot so reasonably affirm it to be replenish'd with them, as we may suppose, that if they were gather'd together into one place without Intervals between them, they would fill but a small part of the whole Receiver. As in the thirteenth Experiment, a piece of Match was inconsiderable for its bulk, whilst its parts lay close together, that afterwards (when the Fire had scat∣ter'd them into smoke) seem'd to replenish all the Vessel. For (as elsewhere our Experiments have demonstrated) both Light and the Effluvia of the Load-stone, may be readily admitted into a Glass, Hermatically seal'd, though before their Admissi∣on, as full of Air as hollow Bodies here below are wont to be; so that upon the exsuction of the Air, the large space deserted by it, may remain empty, notwithstanding the pretence of those subtle Corpuscles, by which Lucid and Magnetical Bodies pro∣duce their effects.

And as for the Allegations above mention'd, they seem'd to prove but that the Receiver devoid of Air, may be replenish'd with some Etherial matter, as some Modern Naturalists write of but not that it really is so. And indeed to me it yet seems, that as to those spaces which the Vacuists would have to be emp∣ty, because they are manifestly devoid of Air; and all grosser Bodies the Plenists (if I may so call them) do not prove that such spaces are replenish'd with such a subtle matter as they speak of, by any sensible effects, or operations of it (of which divers new Trials purposely made, have not yet shewn me any) but only conclude that there must be such a Body, because there cannot be a Void. And the reason why there cannot be a Void,

being by them taken, not from any Experiments, or Phaenome∣na of Nature, that clearly and particularly prove their Hypo∣thesis, but from their notion of a Body, whose Nature, accor∣ding to them, consisting only in extension (which indeed seems the property most essential to, because inseparable from a Body) to say a space devoid of Body, is to speak in the Schoolmens Phrase, a Contradiction in Adjecto. This reason I say, being thus desum'd, seems to make the Controversie about a Vacuum, rather a Metaphysical, than a Physiological Question; which therefore we shall here no longer debate, finding it very difficult either to satisfie Naturalists with this Cartesian Notion of a Bo∣dy, or to manifest wherein it is erroneous, and substitute a bet∣ter in its stead.

But though we are unwilling to examine any farther the Infe∣rences wont to be made from the Torricellian Experiment, yet we think it not impertinent to present Your Lordship with a couple of Advertisements concerning it.

First, then if in trying the Experiment here or elsewhere, you make use of the English measures that Mathematicians and Tra∣desmen are here wont to employ, You will, unless you be fore∣warn'd of it, be apt to suspect that those that have written of the Experiment have been mistaken. For whereas men are wont generally to talk of the Quick-silver's remaining suspended at the height of between six or seven and twenty Inches; we common∣ly observed, when divers years since we first were solicitous about this Experiment, that the Quick-silver in the Tube rested at about 29 Inches and a half above the surface of the Restag∣nant Quick-silver in the Vessel, which did at first both amaze and perplex us, because though we held it not improbable that the difference of the grosser English Air, and that of Italy and France, might keep the Quick-silver from falling quite as low in this colder, as in those warmer Climates; yet we could not be∣lieve that that difference in the Air should alone be able to make so great an one in the heights of the Mercurial Cylinders; and accordingly upon enquiry we found, that though the various density of the Air be not to be over-looked in this Experiment,

yet the main Reason why we found the Cylinder of Mercury to consist of so many Inches, was this, That our English Inches are somewhat inferiour in length to the digits made use of in Fo∣reign Parts, by the Writers of the Experiment.

The next thing I desire Your Lordship to take notice of, is, That the height of the Mercurial Cylinder is not wont to be found altogether so great as really it might prove, by reason of the negligence or incogitancy of most that make the Experiment. For oftentimes upon the opening of the inverted Tube into the Vessel'd Mercury, you may observe a bubble of Air to ascend from the bottom of the Tube through the subsiding Quick-sil∣ver to the top; and almost always you may, if you look nar∣rowly, take notice of a multitude of small bubbles all along the inside of the Tube betwixt the Quick-silver and the Glass: (not now to mention the Particles of Air that lie concealed in the ve∣ry Body of the Mercury) Many of which, upon the Quick∣silver's forsaking the upper part of the Tube, do break into that deserted space where they find little or no resistance to their ex∣panding of themselves. Whether this be the reason that upon the Application of warm Bodies to the emptied part of the Tube, the subjacent Mercury would be depressed somewhat lower, we shall not determine; though it seem very probable, especially since we found, that, upon the application of Linnen cloaths dipped in Water, to the same part of the Tube, the Quick-sil∣ver would somewhat ascend; as if the cold had condensed the imprisoned Air, (that pressed upon it,) into a lesser room. But that the deserted space is not wont to be totally devoid of Air, we were induced to think by several Circumstances. For when an eminent Mathematician, and excellent Experimenter, had ta∣ken great pains and spent much time in accurately filling up a Tube of Mercury, we found that yet there remained store of inconspicuous bubbles, by inverting the Tube, letting the Quick-silver fall to its wonted height; and by applying (by degrees) a red hot Iron to the outside of the Tube, over a∣gainst the upper part of the Mercurial Cylinder, (for hereby the little unheeded bubbles, being mightily expanded, ascended

in such numbers, and so fast to the deserted space, that the up∣per part of the Quick-silver seemed, to our wonder, to boil.) We farther observed, That in the trials of the Torricellian Ex∣periment we have seen made by others, and (one excepted) all our own, we never found that upon the inclining of the Tube the Quick-silver would fully reach to the very top of the sealed end: Which argued, that there was some Air re∣treated thither that kept the Mercury out of the unreple∣nished space.

If Your Lordship should now demand what are the best expe∣dients to hinder the intrusion of the Air in this Experiment; we must answer, That of those which are easily intelligible with∣out ocular demonstration, we can at present suggest, upon our own trials, no better than these. First, at the open end of the Tube the Glass must not only be made as even at the edges as you can, but it is very convenient (especially if the Tube be large) that the bottom be every way bent inwards, that so the Orifice, not much exceeding a quarter of an Inch in Diameter, may be the more easily and exactly stopped by the Experimen∣ter's finger; between which and the Quick-silver, that there may be no Air intercepted (as very often it happens that there is) it is requisite that the Tube be filled as full as possibly it can be, that the finger which is to stop it, pressing upon the accumula∣ted and protuberant Mercury, may rather throw down some, than not find enough exactly to keep out the Air. It is also an usefull and compendious way not to fill the Tube at first quite of Mercury, but to leave near the top about a quarter of an Inch empty; for if you then stop the open end with your finger, and invert the Tube, that quarter of an Inch of Air will ascend in a great bubble to the top, and in its passage thither, will ga∣ther up all the little bubbles, and unite them with it self into one great one; so that if by reinverting the Tube, you let that bub∣ble return to the open end of it, you will have a much closer Mercurial Cylinder than before, and need but to add a very little Quick-silver more to fill up the Tube exactly. And lastly, as for those lesser and inconspicuous parcels of Air which cannot this

way begleaned up, You may endeavour before you invert the Tube, to free the Quick-silver from them by shaking the Tube, and gently knocking on the outside of it, after every little par∣cel of Quick-silver which you pour in; and afterwards, by for∣cing the small latitant bubbles of Air to disclose themselves and break, by imploying a hot Iron in such manner as we lately men∣tioned. I remember that by carefully filling the Tube, though yet it were not quite free from Air, we have made the Mer∣curial Cylinder reach to 30 Inches and above an eight, and this in a very short Tube: which we therefore mention, because we have found, by Experience, that in short Tubes a little Air is more prejudicial to the Experiment than in long ones, where the Air having more room to expand it self, doth less potently press upon the subjacent Mercury.

And since we are fallen upon the consideration of the Altitude of the Mercurial Cylinder, I must not conceal from Your Lord∣ship an Experiment relating thereunto, which perhaps will set both You and many of your Friends the Vertuosi on thinking; and, by disclosing some things about the Air or Atmosphere, that have scarce hitherto been taken notice of, may afford you some hints conducive to a further discovery of the subject of this Epistle.

EXPERIMENT XVIII.

WE took a Glass Tube, which though it were not much above three Foot long, we made choice of, because it was of a more than ordinarily even thickness. This we fill'd with Mer∣cury, though not with as much care as we could, yet with some∣what more than is wont to be used in making the Torricellian Experiment. Then, having according to the manner inverted the Tube, and open'd the mouth of it beneath the surface of some other Quick-silver, that in the Tube fell down to the wonted height, leaving, as is usual, some little Particles of Air in the space it deserted, as we guest by observing, that upon the Applica∣tion of hot Bodies to the upper part of the Tube, the Quick∣silver would be a little depress'd. Lastly, having put both the

Tube and the Vessel it lean'd on into a convenient Wooden frame to keep them from mischances: we plac'd that Frame in a Win∣dow within my Bed-chamber, that I might both keep the Mercu∣ry from being stirr'd, and have opportunity to watch from time to time the Phaenomena it was to exhibit. For the better disco∣very of which, when the Quick-silver both in the Tube and sub∣jacent Vessel was perfectly at rest, we took notice, by a mark made on the outside of the Glass, how high the included Liquor then reach'd.

During several Weeks that the Tube was kept in that Win∣down (which was very rarely open'd) I had the opportunity to observe, that the Quick-silver did sometimes faintly imitate the Liquor of a Weather-glass, subsiding a little in warm, and rising a little in cold Weather, which we ascribed to the greater or les∣ser pressure of that little Air that remain'd at the top of the Tube, expanded or condens'd by the heat or cold that affected the am∣bient Air. But that which I was chiefly carefull to observe, was this, That oftentimes the Quick-silver did rise and fall in the Tube, and that very notably, without conforming it self to what is usual in Weather-glasses, whose Air is at the top, nay quite contrary thereunto: for sometimes I observ'd it in very cold weather (such as this Winter hath already afforded us good store of) to fall down much lower than at other times, when by reason of the absence of both Frost, Snow, and sharp Winds, the Air was comparatively much warmer. And I farther ob∣serv'd, That sometimes the Quick-silver would for some days together rest almost at the same height; and at other times again it would in the compass of the same day considerably vary its al∣titude, though there appear'd no change either in the Air abroad, or in the temper of the Air within the Room (wherein was con∣stantly kept a good Fire) nor in any thing else, to which either I, or some eminently Learned Men, whom I then acquainted with the Experiment, could reasonably impute such a change: Especially considering that the space wherein the Mercury wan¦dred up and down, within about five Weeks, amounted to full two Inches, of which we found by our several marks whereby

we had taken notice of its several removes, that it had descend∣ed about 9/16 of an Inch from the place where it first setled, and the other Inch and 7/16 it had ascended. And it seems probable that the height of the Mercurial Cylinder would have varied yet more, if the Experiment had been made in the open Air, and in a long Tube, where the Particles of the imprison'd Air by ha∣ving more room to display themselves in, might not have had so strong a Spring to work upon the Quick-silver with. But for want both of time and of a competent quantity of Mercury (which was not to be procur'd where we then happen'd to be) we were unable to make any farther tryals: which therefore chiefly troubled us, because we would gladly have try'd an ingenious Experiment which was suggested unto us by that excellent Mathematician Mr. Wren, who being invited to name any thing he would have us try touching the pressure of the Air, desired us to observe whe∣ther or no the Quick-silver in a long Tube would not a little va∣ry its height according to the Tides, especially about the New and Full Moon; about which times Mariners observe those great Flowings and Ebbs of the Sea, that they call the Spring-Tides. For he sagaciously and plausibly conjectur'd that such observa∣tions, accurately made, would discover the truth or erroneous∣ness of the Cartesian Hypothesis concerning the Ebbing and Flow∣ing of the Sea: which Des Cartes ascribeth to the greater pres∣sure made upon the Air by the Moon, and the Intercurrent Ethereal Substance at certain times (of the Day, and of the Lu∣nary Month) than at others. But in regard we found the Quick-silver in the Tube to move up and down so uncertainly, by rea∣son, as it seems, of accidental mutation in the Air; I somewhat doubt: whether we shall find the Altitude of the Quick-silver to vary as regularly as the Experiment is ingeniously propos'd. The success we shall (God permitting us to make tryal of it) acquaint your Lordship with; and in the mean time take notice, that when we had occasion to take the Tube out of the Frame (after it had staid there part of November and part of December) a good Fire being then in the room, because it was a Snowy day, we found the Quick-silver in the Tube to be above the upper

surface of the subjacent Mercury 29 Inches three quarters.

If Your Lordship should now aske me what are the true causes of this varying altitude of the Mercurial Cylinder; I should not undertake to answer so difficult a question, and should venture to say no more, than that among divers possible causes to which it may be ascribed, it would not be, perhaps, absurd to reckon these that follow.

First then we may consider, that the Air in the upper part of the Tube is much more rarefied, and therefore more weak than the External Air, as may appear by this among other things, That upon the inclining of the Tube, the Quick-silver will readily ascend almost to the very top of it, and so take up eight or nine tenth parts, and perhaps more of that space which it deserted before: which would not happen, if that whole space had been full of unrarefied Air, since that (as tryal may easily satisfie you) would not have suffer'd it self to be thrust into so narrow a room by so weak a pressure. So that although in our Tube when the included Air, was heated, the Quick-silver was somewhat depress'd; yet there is this difference betwixt such a Tube and common Weather-Glasses, that in these the included and the ambient Air are in an AEquilibrium as to pressure, and the weight of the Water that keeps them separate is scarce consider∣able. Whereas in such a Tube as we are speaking of, the Air within, is very much more dilated than that without. And 'tis not so much the spring or resistance of the included Air, as the weight of the Mercurial Cylinder it self, that hinders the Quick-silver from ascending higher: For if we should suppose that de∣serted part of the Tube perfectly devoid of Air, yet would the Quick-silver rise but a little higher in it, and be far from filling it; in regard the outward Air would not be able to impell up such a weight much higher: whereas it may, by our former Ex∣periments appear, that if all the Air in the upper part of the Weather-Glass were away, the Water would be impell'd up to the very top of it, though the Pipe were above thirty foot long.

We may next consider, that this rarefied: Air at the upper part of our Tube being exactly shut up betwixt the Glass and

the Quick-silver, it was scarce subject to any discernable alter∣ations, save those it receiv'd from heat and cold.

And we may farther consider, that yet the external Air or Atmosphere is subject to many alterations, besides them that proceed from either of those Qualities.

For the Experiment that occasion'd this Discourse, seems to make it probable enough, that there may be strange Ebbings and Flowings, as it were, in the Atmosphere, or at least, that it may admit great and sudden Mutations, either as to its Alti∣tude or its Density, from causes, as well unknown to us, as the effects are unheeded by us. And that You may not think that there is nothing in Nature but our Experiment that agrees with this our conjecture, we might put Your Lordship in mind of the Pains and Aches that are often complain'd of by those that have had great Wounds or Bruises, and that do presage great Mu∣tations in the Air oftentimes, whilst to strong and healthy Per∣sons no sign of any such thing appears. And that is also very memorable to this purpose, which I remember I have some∣where read in a Book of the Ingenious Kircherus, who giving a pertinent admonition concerning the various refractions that may happen in the Air, relateth, That during his stay in Malta, he often saw Mount AEtna, though the next day, notwithstanding its being extremely clear, he could not see it; adding, that Vin∣temillius, a very Learned Person, did oftentimes, from a Hill he names, behold the whole Island he calls Luprica protuberant above the Sea, though at other times, notwithstanding a clear Sky, he could not see it. And though perhaps this may be in part ascribed to the various light and position of the Sun, or to the various disposition of the Spectators eye, or peradventure to some other cause; yet the most probable cause seems to be the differing Density of the Air, occasion'd by Exhalations capable to increase the refraction, and consequently bring Beams to the Eye, which otherwise would not fall on it. We have likewise, in another Treatise, mention'd our having often observ'd with Telescopes a plenty of Steams in the Air, which without such a help would not be taken notice of, and which, as they were

not at all times to be seen even through a Telescope, so they did sometimes, especially after a shower of Rain, hastily disap∣pear: and when we have visited those places that abound with Mines, we have several times been told by the Diggers, that even when the Sky seem'd clear, there would, not seldome, suddenly arise, and sometimes long continue, a certain Steam (which they usually call a damp) so gross and thick that it would oftentimes put out their very Candels, if they did not seasonably prevent it. And I think it will easily be granted, that the as∣cension of such Steams into this or that part of the Air, and their mixing with it, are very like to thicken it; as on the other side either heat or the sudden condensation of the Air in another part of the Atmosphere (to mention now no other causes) are capable of rarefying it.

Nor will it very much import the main scope of our Discourse, whether it be suppos'd that the copious Steams the earth sends into the Air, thicken that part of the Atmosphere that receives them, and make it more heavy: Or that sometimes the Fumes may ascend with such celerity, that though the Air be thickn'd yet they rather diminish than encrease its gravitation, in regard that the quickness of their ascent, not onely keeps them from gravitating themselves, but may hinder the pressing downwards of many Aërial Corpuscles that they meet with in their way up∣wards. This I say, is of no great importance to our present Dis∣course, since either way the Terrestrial Steam may here and there considerably alter the gravity or pressure of the Atmosphere.

Your Lordship may also be pleased to remember, That by our seventeenth Experiment it appear'd, that, as when the Air in the Receiver was expanded more than ordinarily, the Quick-silver in the Tube did proportionably subside; so when the Air in the same Receiver was a little more than ordinarily compress'd, it did impell up the Quick-silver in the Tube, above the wonted height of betwixt six and seven and twenty digits.

And if to these things we annex, that for ought we can find by tryals purposely made, the degree of rarity or density of the Air, shut up into our Receiver, doth not sensibly alter its temper∣ature

as to cold or heat. It will not, I hope, appear absurd to conceive, That since the Air, included in the Tube, could but very saintly hinder the ascent of the Quick-silver, or press it downwards; Since too, that included Air could scarce immedi∣ately receive any sensible alteration, save either by heat or cold; And since also, that according to the bare density or rarity of the Air incumbent on the subjacent Quick-silver in the Vessel, that in the Tube was impell'd more or less high; such changes happening in the neighbouring part of the outward Air, either by the ascension of gross or copious exhalations, or by any other cause (of which there may be divers) as were capable to make considerable alterations in the consistence of the Air, as to rarity and density, may be able proportionably to alter the height of the Quick-silver. I rather say, that such alterations may be, than that they are the causes of our Phaenomenon: because I think it sufficient, if I have propos'd conjectures not altogether irration∣al about a new Mystery of Nature, touching which, the chief things I pretend to, is to give occasion to the Curious to enquire farther into it, than I have been yet able to do.

EXPERIMENT XIX.

THe same Reason that mov'd us to conclude, that by the drawing of the Air out of the Receiver, the Mercury would descend in a Tube shorter than six and twenty digits, in∣duc'd us also to expect, that by the same means Water might be brought to subside in Glass Tubes of a moderate length: Though by the noble Experiment, said to have been accurately made in France, by Monsieur Paschal, we are informed that a Tube of no less than about two and thirty Foot; was found requisite to make the Experiment De vacuo succeed with Water instead of Quick-silver: so tall a Cylinder of that lighter Liquor, being it seems, requisite to equal the Weight of a Mercurial Cylinder of six or seven and twenty digits, and surmount the pressure of the Atmosphere.

We took then a Tube of Glass, Hermetically seal'd at one end, of about four foot in length, and not very slender: This,

at the open end, we fill'd with common Water, and then stopt that end till we had inverted the Tube, and open'd it beneath the sur∣face of a quantity of the like Water, contain'd in a somewhat deep and slender Vessel. This Vessel, with the Tube in it, was let down into the Receiver, and the Receiver being clos'd up after the accustom'd manner, the Pump was set on work.

As much of the event as concerns our present purpose, was this, That till a considerable part of the Air was drawn out of the Receiver, the Tube continu'd top-full of Water as when it was put in, it being requisite that a great part of the Air, formerly contain'd in the Receiver, should be drawn out, to bring the remaining Air to an AEquilibrium, with so short and light a Cy∣linder of Water. But when once the Water began to fall in the Tube, then each exsuction of Air made it descend a little lower, though nothing near so much as the Quick-silver at the begin∣ning did in the Experiment formerly mention'd. Nor did there ap∣pear so much inequality in the spaces transmitted by the Water in its descent, as there it did in those observ'd in the fall of the Quick-silver, of which the cause will scarce seem abstruse to him that shall duly reflect upon what hath been already deliver'd. And whereas we drew down the Quick-silver in the Tube so far as to bring it within an Inch of the surface of the other Quick-silver into which it was to fall; the lowest we were able to draw down the Water was, by our conjecture, to about a Foot or more above the surface of that in the Vessel; of which I know not whether it will be needfull to assign so obvious a cause as that, though the little Air remaining in the Receiver could not hinder a Cylinder of above on Inch high of Quick-silver from subsiding; yet it might be very well able, by its pressure, to countervail the weight of a Cylinder of a Foot long or more, of a Liquor so much less ponderous than Quick-silver, as Water is. And in fine, to conclude our Experiment, when the Water was drawn down thus low, we found, that by letting in the outward Air, it might be immediately impell'd up again to the higher parts of the Tube.

We will adde no more concerning this Experiment, save that

having try'd it in one of our small Receivers, we observ'd, That upon the first exsuction of the Air the Water did usually subside divers Inches, and at the second (exsuction) fall down much lower, subsiding sometimes near two Foot; as also that upon the letting in of the Air from without, the Water was impell'd up with very great celerity.

EXPERIMENT XX.

THat the Air hath a notable Elastical power (whencesoever that proceeds) we have, I suppose, abundantly evinc'd, and it Begins to be acknowledg'd by the eminentest Modern Naturalists. But whether or no there be in Water so much as a languid one, seems hitherto to have been scarce consider'd nor hath been yet, for ought I know, determin'd either way by any Writer, which invited us to make the following Experiment.

There was taken a great Glass bubble, with a long neck; (such as Chymists are wont to call a Philosophical Egge) which being fill'd with common Water till the Liquor reach'd about a span a∣bove the bubble, and a piece of Paper being there pasted on, was put unstop'd into the Receiver, and then the Air was suck'd out after the wonted manner. The event was this, that a consider∣able part of the Air, pen'd up in the Receiver, was drawn out, before we discern'd any expansion of the Water; but, continuing the labour of pumping, the Water manifestly began to ascend in the stem of the Glass, and divers bubbles loosening themselves from the lower parts of the Vessel, made their way through the Body of the Water, to the top of it, and there brake into the Receiver: And after the Water once appear'd to swell, then at each time the Stop cock was turn'd to let out the Air from the Receiver into the Pump, the Water in the Neck of the Glass did suddenly rise about the breadth of a Barly-corn in the Neck of the Glass and so attain'd by degrees, to a considerable height above the mark formerly mention'd. And at length (to make the expansion of the Water more evident) the outward Air was sud∣denly let in, and the Water immediately subsided and deserted all the space it had newly gain'd in the Glass.

And, on this occasion, it will not perhaps be amiss to acquaint Your Lordship here (though we have already mention'd it in another Paper, to another purpose) with another Expedient that we made use of two or three years ago, to try whether or no Water had a Spring in it. About that time then, That Great and Learned Promoter of Experimental Philosophy Dr. Wilkins, doing me the Honour to come himself, and bring some of his inquisitive Friends to my Lodging, we there had in readiness a round and hollow Vessel of Pewter, great enough to contain two pounds of Water, and exactly close every where, but at one little hole where it was to be fill'd, then partly by sucking out the Air, and partly by injecting Water with a Syringe, it was (not with∣out some difficulty) fill'd up to the top; and that hole being plac'd directly upwards, there was a little more Water leisurely forc'd in by the Syringe. Upon which, though the Vessel were permitted to rest, and the hole kept in its former posture, yet the compress'd Water leisurely swell'd above the Orifice of the hole, and divers drops ran over along the sides of the Vessel. After this we caus'd a skilfull Pewterer (who had made the Globe) to close it up in our presence with Soder so exquisitely, that none suspected there was any thing left in it besides Water. And lastly, the Vessel thus soder'd up, was warily and often struck in divers places with a Wooden Mallet, and thereby was mani∣festly compress'd, whereby the inclosed Water was crouded into less room than it had before: And thereupon we took a Needle, and with it and the Mallet perforated the Vessel, and drew out the Needle again; the Water (but in a very slender Stream) was sud∣denly thrown after it into the Air, to the height of two or three Feet. As for the other Phaenomena of this Experiment, since they belong not to our present purpose, and are partly mention'd in another of our Papers, we shall, instead of recording them here, give this Advertisement: That as evidently as this Experiment, and that made in our Receiver, seem to prove a power in the Water to expand and restore it self after compression; yet for a reason to be met with ere long, I judged it not safe, to infer that Conclusion from these Premises, till I had made some

of the following tryals, to the mention of which I will there∣fore hasten.

EXPERIMENT XXI.

TO discover whether the Expansion of the Water really pro∣ceeded from an Elastical power in the parts of the Water it self, we thought it requisite to try two things: The one, Whether or no the Atmosphere gravitates upon Bodies under Water; and the other, Whether in case it do gravitate, the In∣tumescence of the Water may not be ascribed to some substance subtler than it self, residing in it. In order to the satisfying my¦self about the first of these, I intended to let down into the Receiver a Vessel of Water, wherein should be immers'd a very small oyl'd Bladder, almost devoid of Air, but strongly ty'd up at the Neck with a string, and detain'd a little under Water by such a weight fasten'd to that string, as should just be able to keep the Bladder from swimming, and no more. For I sup∣pos'd, that if when all things were thus order'd, the Receiver were empty'd, in case there were any such pressure of the At∣mosphere upon Water, as I was inclin'd to believe, the Air with∣in the Bladder, being upon the exsuction of the Air within the Receiver, freed from that pressure, and being press'd onely by the small weight of the incumbent Water, would considerably expand it self; but whilst we were preparing Bladders for this Experiment, there occurr'd an easie way for the making at once both the Discoveries I desir'd.

We took then a Glass Viol, containing by ghess a pound and some ounces of Water, this we fill'd top full, and then we put into the Neck of it a Glass Pipe a pretty deal bigger than a Goose Quill, open at both ends, and of divers Inches in length: One end of this Pipe was so put into the Neck of the Viol, as to reach a little below it, and then was carefully cemented there∣to that no Air might get into the Viol, nor any Water get out of it, otherwise than through the Pipe; and then the Pipe being warily fill'd, about half way up to the top, with more Water, and a mark being pasted over aganst the upper surface of the Liquor; the Viol thus fitted with the Pipe, was, by strings let

down into the Receiver, and according to the wonted manner exquisitely clos'd up in it.

This done, we began to pump out the Air, and when a pret∣ty quantity of it had been drawn away, the Water in the Pipe began to rise higher in the Pipe, at the sides of which some lit∣tle bubbles discover'd themselves. After a little while longer, the Water still swelling, there appear'd at the bottom of the Pipe a bubble about the bigness of a small Pea, which ascending through the Pipe to the top of the Water, stay'd there a while and then broke; but the Pump being nimbly ply'd, the expan∣sion of the Water so encreas'd, that quickly, getting up to the top of the Pipe, some drops of it began to run down along the out-side of it, which oblig'd us to forbear pumping a while, and give the Water leave to subside within less than two Inches of the bottom of the Pipe. After this the Pump being again set on work, the bubbles began to ascend from the bottom of the Pipe, being not all of a size, but yet so big, that estimating one with another, they appear'd to be of the size of the smaller sort of Peas; and of these we reckon'd about sixty which came up one after another, besides store of smaller ones, of which we made no reckoning: And at length, growing weary of recko∣ning and pumping too (because we found, that in spight of all our pains and industry, some undiscern'd Leak or other in the Receiver hinder'd us from being able to empty it altogether) we thought fit to desist for that time, after tryal made of what operation the external Air, being let in upon the expanded Wa∣ter, would have; and accordingly turning the Key to let in the Air, we saw, as we expected, that the Water in the Pipe in a moment fell down almost to the bottom of it.

Now of this Experiment there are two or three Circumstan¦ces yet to be mention'd, which are no less, than those already recited, pertinent to our present purpose.

In the first place then, when the greater part of the Air had been pump'd out of the Receiver, the rising bubbles ascended so very slowly in the Pipe, that their Progress was scarce discerna∣ble; which seem'd to proceed from this, That their bigness

was such, That they could not sufficiently extend themselves in the cavity of the Glass, without pressing on both hands against the sides of it, whereby they became of more difficult extrusion to the Water. And though it may seem strange that these bub∣bles should be of any considerable bulk, since 'tis like they con∣sisted of lesser parcels of the Air lurking in the Water, than those that were vigorous enough to make their way through, long before them: yet they were commonly much larger than be∣fore, some of them being equal in quantity to four or five Peas: whether this their increase of bulk proceeded from the greater decrement of the pressure of the Air, or from the Union of two or three of those numerous bubbles which were then generated below the bottom of the Pipe, where we could not see what was done among them.

Another thing we noted in our bubbles was, That whereas in ordinary ones the Air, together with the thin film of Water that invests and detains it, is wont to swell above the surface of the Water it swims on, and commonly to constitute Hemis∣pherical Bodies with it, the little parcels of Air that came up after the Receiver was pretty well empty'd, did not make pro∣tuberant bubbles, but such whose upper surface was either le∣vel with, or beneath that of the Water, so that the upper sur∣face being usually somewhat convex, the less protuberant parts of it had a pretty quantity of Water remaining above them.

We also farther observ'd, that whereas in the bubbles that first appear'd in the Pipe, the ascending Air did, as in other com∣mon bubbles, make its way upwards, by dividing the Water through which it pass'd, in those bubbles that appear'd at the latter end of our Experiment, when the pressure of the little ex∣ternal Air, remaining in the Receiver, was grown inconsidera∣ble, the ascending parcels of Air having how little more than the weight of the incumbent Water to surmount, were able both so to expand themselves as to fill up that part of the Pipe which they pervaded, and by pressing every way against the sides of it, to lift upwards with them what Water they found above them, without letting any considerable quantity glide

down along the sides of the Glass; So that sometimes we could see a bubble thrust on before it a whole Cylinder of Water of perhaps an Inch high, and carry it up to the top of the Pipe; though as we formerly noted, upon the letting in the external Air, these tumid bubbles suddenly relaps'd to their former in∣conspicuousness.

All these things laid together seem'd sufficiently to confirm that, which the consideration of the thing it self would easily enough perswade, namely, That the Air, and such like Bodies being under Water, may be press'd upon as well by the Atmo∣sphere, as by the weight of the incumbent Water it self.

Hence likewise we may verify what we observ'd at the close of the foregoing Experiment, namely, That from the sole swel∣ling of Water there recorded, it cannot be so safely concluded, that Water, when freed from compression, is endow'd with an Elastical power of expanding it self: since thereby it appears that the Intumescence produc'd by that Experiment, may, (at least in great part) be ascribed to the numerous little bubbles which are wont to be produc'd in Water, from which the pres∣sure of the Atmosphere is in great measure taken off. So apt are we to be mis-led, even by Experiments themselves, into Mistakes, when either we consider not that most Effects may proceed from various Causes, or mind onely those Circumstan∣ces of our Experiment, which seem to comply with our precon∣ceiv'd Hypothesis or Conjectures.

And hence it seems also probable, that in the Pores or invisi∣ble little recesses of Water it self there lie commonly interspers'd many parcels of either Air, or at least something Analagous thereunto, although so very small, that they have not been hi∣therto so much as suspected to lurk there. But if it be deman∣ded how it appears that there is interspers'd through the Body of Water any substance thinner than it self, and why that which produc'd the bubbles abovemention'd should not be resolutely said to be nothing else than a more active and spirituous part of the Water, we shall, in order to the Elucidation of this matter, subjoyn to what was formerly deliver'd the following Experi∣ment.

EXPERIMENT XXII.

WE recited in our ninteenth Experiment, how by draw∣ing most of the Air out of the Receiver, we made the Water subside by degrees in a Glass not four Foot long: We shall now add, that in the like Experiment made in such a Tube, or a greater, it may be observ'd, That when the Water begins to fall, there will appear store of bubbles fasten'd all along to the sides of the Glass; of which bubbles, by the agitation of the Vessel consequent upon pumping, there will arise good num∣bers to the top of the Water, and there break; and as the Cy∣linder of Water is brought to be lower and lower, so the bub∣bles will appear more numerous in that part of the Tube which the Water yet fills; and the nearer the surface of the Water, in its descent, approacheth to these bubbles, the greater they will grow, because having the less weight and pressure upon them, the expansion of that Air which makes them, can be the less resisted by the pressure of the incumbent Water and Air; as seems probable from hence, that upon the letting in a little ex∣ternal Air, those bubbles immediately shrink.

It may indeed, as we lately intimated, be conjectur'd, that these bubbles proceed not so much from any Air pre-existent in the Water, and lurking in the Pores of it, as from the more subtle parts of the Water it self; which by the expansion al∣low'd them upon the diminish'd pressure of the ambient Bodies may generate such bubbles. And indeed, I am not yet so well satisfied that bubbles may not (at least sometimes) have such an origination: but that which makes me suspect that those in our tryals contain real Air, formerly latitant in the Pores of the Water, is this, That upon the inletting of the external Air, the Water was not again impell'd to the very top of the Tube whence it began to fall, but was stopt in its ascent near an Inch beneath the top. And since, if the upper part of the Tube had been devoid of any other than such Ethereal matter as was subtle enough freely to penetrate the pores of the Glass, the external Air would have been able to impel the Water to

the top of a Tube seven or eight times as long as ours was; The Phaenomenon under consideration seem'd manifestly to argue, that the many bubbles that broke at the top of the Water, did contain a real Air, which being collected into one place, and hinder'd by the top of the Glass from receding, was able to with stand the pressure of the outward Air. As we see that if never so little Air remain in the Tube upon the making the Experi∣ment De Vacuo with Quick-silver, no inclining of the Tube, (though a long one, will enable a Man to impell the Mercury up to the very top, by reason (as we formerly noted) of the resistance of the included Air, which will not be compress'd be∣yond a certain degree.

But in order to a farther discovery what our bubbles were, we will, on this occafion, inform Your Lordship, that we try'd the XIX^th Experiment in one of our small Receivers, and found, that upon the drawing down of the Water, so many bubbles disclos'd themselves, and broke into the upper part of the Tube, that having afterwards let in the external Air, the Water was not thereby impell'd to the top of the Tube (three Foot in length) within a little more than half an Inch. And whether or no it were Air that possess'd that space at the top of the Tube which was not fill'd with Water, we took this course to exa∣mine. We drew the second time the Air out of the Receiver, and found, that by reason of the body that possess'd the top of the Tube, we were able not onely to make the Water in the Tube fall to a level with the surface of the Water in the Vessel; But also (by plying the Pump a little longer) a great way be∣neath it: which, since it could not well be ascrib'd to the bare subsiding of the Water, by reason of its own weight, argued that the Water was depress'd by the Air: which was confirm'd by the Figure of the surface of the Water in the Tube, which was much more concave than that of Water in Tubes of that bigness useth to be. And this farther tryal (to add that upon the bye) we made at the same time, That when the Water in the Pipe was drawn down almost as low as the Water without it, we observ'd, that (though we desisted from pumping) by the

bare application of a hand moderately warm to the deserted part of the Tube, the remaining Water would be speedily and nota∣bly depress'd. And having for a while held a kindled Coal to the outside of the Tube, (the Pump being still unimploy'd, be∣cause the Vessel chanced to hold extraordinarily well) the Air was by the heat so far expanded, that it quickly drove the Wa∣ter to the bottom of the Tube, which was divers Inches beneath the surface of the ambient Water. Whereby it appears (by the same way by which we formerly measur'd the dilatation of the Air) that the Air, even when it is expanded to between 90 and 100 times its extent, will yet readily admit of a much far∣ther rarefaction by heat.

I consider'd also that in case the Bubbles we have been speak∣ing of, were produc'd by the parcels of Air latitant in the Wa∣ter, that Air being now got together to the top of the Tube, though the Air were again drawn out of the Receiver, the ta∣king off its pressure would not disclose bubbles as before; and accordingly, the Air being again pump'd out, the Water in the Tube descended as formerly: but for a great while we scarce saw one bubble appear, onely when the Receiver had been ve∣ry much exhausted; and the Water was fallen very low, there appear'd near the bottom of the Tube, certain little bubbles, which seem'd to consist of such parcels of Air as had not, by reason of their smallness, got up to the top of the Water, with the more bulky and vigorous ones. And that which is not in∣considerable, is, That having, by letting in the Air, forc'd up the Water into the Tube, we could not perceive that it ascended near the top, though we permitted the Engine to remain unim∣ploy'd for two or three Nights together, and watch'd whether the Water would swell up and fill the Tube. And on this oc∣casion I remember, that having try'd such an Experiment as this with Quick-silver instead of Water, in a Tube of about a Foot and a half long, wherein it might seem more hopefull to escape bubbles; yet upon the drawing down the Quick-silver as low as we could, and letting in the external Air upon it, we found that some lurking particles of Air were got up to the top

of the Tube, and hinder'd the Quick-silver from being forc'd up again so high. And though the Quick-silver were by this means brought to appear a very close and lovely Metalline Cy∣linder, not interrupted by interspers'd bubbles as before; yet having caus'd the Air to be again drawn out of the Receiver, I could perceive several little bubbles to disclose themselves, fasten'd to the inside of the Tube, near the bottom of it; and having purposely watch'd one or two of the chiefest, I had the pleasure to observe, that though they grew bigger and bigger as the surface of the Mercurial Cylinder fell nearer and nearer to them, so as that at length they swell'd into a conspicuous bulk; yet upon the wary letting in the Air upon them, they did not break, but presently shrunk up into a littleness that render'd them inconspicuous.

Whence it seems very probable, if not certain, that even in the closest and most ponderous Liquors, and therefore much more in Water, there may lurk undiscernable parcels of Air, capable, upon the removal of the pressure of the ambient Air (though but in part) and that of the liquor wherein it lurks, to produce conspicuous bubbles. And consequently, if it seem in∣convenient to admit an Elastical power in the Water, it may be said that the swelling of the compress'd Water in the Pewter Vessel lately mention'd, and the springing up of the Water at the hole made by the Needle, were not the effects of any inter∣nal Elater of the Water, but of the spring of the many little particles of Air dispers'd through that Water, and acting upon it in their sudden recovering themselves to a greater extent, than that to which a violent compression had reduc'd them to.

But though, from all these particulars, it seems manifest that the Bubbles we have been all this while treating of, were pro∣duc'd by such a substance as may be properly enough call'd Air; yet till we shall have had the opportunity of making some far∣ther tryals concerning the nature of the Air, we shall not reso∣lutely determine whether or no Air be a Primogenial Body (if I may so speak) that cannot now be generated or turn'd either

into Water or any other Body. Yet in the mean while (be∣cause it is an important Question, and if rightly determin'd, may much conduce to the knowledge of the nature of the Air) we think it not unfit to make a brief mention of some of the par∣ticulars which at present occur to our thoughts in favor of either part of the Question.

First then, divers Naturalists esteem the Air (as well as other Elements) to be ingenerable and incorruptible. And reasons plausible enough may be drawn to countenance this Opinion from the consideration of that permanency that ought to belong to the corporeal Principles of other Bodies.

Next, Experience may be pleaded to the same purpose, for I have read of some who in vain attempted to turn Air into Water, or Water into Air.

The diligent Schottus tells us, that amongst other rarities to be met with in that great Repository of * 1.2 them, the Musaeum Kercherianum, there is a round Glass with a tapering neck near half full (as one may guess by the Scheme he annexeth) of ordinary Spring-water, which having been hermetically shut up there by Clavius the famous Geometrician, the included Water is to this day preserv'd, not onely clear and pure, as if it were but newly put in: But (as it seems) without (in the least) turn∣ing into Air, notwithstanding its having been kept there these fifty years: For he tells us, That the Water hath continued there all this while without any diminution.

Nor doth it appear in those Glasses, which for Chymical Ex∣periments we usually close with Hermes his Seal (as they call it) that the included Air doth, during its long imprisonment, notwithstanding the alteration it receiveth from various degrees of heat, discernably alter its nature. Whereas we plainly per∣ceive in our Digestions and Distillations, that though Water may be rarefied into invisible Vapors, yet it is not really chang'd into Air, but onely divided by heat, and scatter'd into very mi∣nute parts, which meeting together in the Alembick or in the Receiver, do presently return into such Water as they consti∣tuted

before. And we also see, that even Spirit of Wine, and other subtle and fugitive Spirits, though they easily fly into the Air, and mingle with it, do yet in the Glasses of Chymists easi∣ly lay aside the disguise of Air, and resume the divested form of Liquors. And so volatile Salts, as of Urine, Harts-horn, &c. though they will readily disperse themselves through the Air, and play up and down in the capacity of an Alembick or a Re∣ceiver: yet will they, after a while, fasten themselves to the insides of such Glasses in the form of Salts.

Besides, since Air is confessedly endow'd with an Elastical power that probably proceeds from its Texture, it appears not, what it is, that in such light alterations of Water, as are by many presum'd capable of turning it into Air, can be reasonably suppos'd so to contrive the Particles of Water, as to give them, (and that permanently,) the structure requisite to a Spring. I add the word permanently, because the newly mention'd ob∣servations seem to argue the Corpuscles of Air to be irreducible into Water, whereas the Aqueous Particles may perhaps for a while be so vehemently agitated, as to press almost like Springs upon other Bodies; yet upon the ceasing of the agitation, they quickly, by relapsing into Water, disclcse themselves to have been nothing else whilst they counterfeited the Air.

Lastly, The Experiment formerly made in our Engine with a piece of Match, seems to evince, that even those light and subtle Fumes (for the most part not aqueous neither) into which the Fire it self shatters dry Bodies, have no such Spring in them as the Air, since they were unable to hinder or repress the expansion of the Air included in the Bladder they surrounded.

I remember indeed that the Learned Josephus Acosta, in his History of the West Indies, tells us, * 1.3 That he saw in those parts some Grates of Iron so rusted and consum'd by the Air, that the Metal being press'd between the Fingers, dissolv'd (to use his words) to powder, as if it had been Hay or parched Straw. And I remember too, that the Accurate Varenius * 1.4 tells us, That in the Islands commonly called Azores,

the Air (and Wind) is so sharp, that in a short time it frets not onely Iron Plates, but the very Tiles upon the Roofs of Houses, and reduceth them to dust. And I have elsewhere mention'd some recent Observations of this kind. But it may be said, That the abovemention'd Authors ascribe the recited effects chiefly to the Winds, and that, however the corrosion of the Iron and the Tiles may proceed not from the Air it self, or any of its genuine parts, but from some saline Corpuscles dis∣pers'd through the Air, and driven by the Winds against the Bodies it is presum'd to fret. And that such volatile Salts may copiously ascend into the Air, and yet retain their nature, as doth the more fixt Salt in the Sea-water, the sublimations of Sal-Armoniack may sufficiently evince. Not to mention, that I have shewn some Friends a secret kind of saline Substance in∣comparably subtler than Sal-Armoniack, which did not onely easily enough ascend it self, but carried up with it (and that in a very great proportion) the solid and ponderous Body even of uncalcin'd Gold in the form of subtle exhalations, which did afterwards fasten themselves to the upper parts of the Vessels, and yet manifest themselves to continue Gold. We remember also, that to try whether Water could be turn'd into Air, we once took an AEolipile, into which we had before convey'd some Water, and placing it upon kindled Coals when the heat forc'd out a vehement stream of aqueous Vapors; we ty'd about the Neck of it, that of a Bladder, which we had before empty'd of Air; and finding the AEolipile after a while to blow up the Bladder, we carefully ty'd it again that the included substance might not get away. Then slipping it off from the AEolipile we convey'd it into our Receiver, to try whether or no that which in part distended the Bladder would appear by its Spring to be true Air: whereby we found that upon the exsuction of the ambient Air, the included substance expanded it self and the Bladder, to a very much greater bulk than it was of before. And for farther satisfaction, having again taken out the Blad∣der, we suffer'd it to remain ty'd up till next Morning, to try whether time, and the coldness of the Night, would make the

contain'd substance relapse into Water: But the next Morning we found it little less tumid than before. I remember, I say, that I once made this Experiment; but I might say in answer to it, that the chief reason of my mentioning it, is, To let Your Lordship see, how requisite it is to be circumspect and conside∣rate, when we are to make and to build upon nice Experi∣ments. For though I may seem to have used sufficient caution, yet afterward considering with my self that the AEolipile I had imploy'd was a very large one, and that it required much more care than one that hath not try'd it would imagine, to drive out all the Air from a large AEolipile, I easily suspected that the di∣stension of the Bladder in our pneumatical Vessel, might pro∣ceed not from the watery steams that came out at the narrow mouth of the AEolipile, and had very much wetted the Bladder, but from the rarefied Air which in that sort of Vessels is wont for a good while together to come out with the rarefied Water: and accordingly having reiterated the Experiment, I found it very difficult (by reason of the thrinking of the Bladders (up∣on their being heated) and of other impediments) to make it so accurately as to deduce from it, that Water may be rarefied into true Air.

Against the other four above-mention'd Considerations, we cannot spend time to frame Objections, but must forthwith proceed to the mention of those things that seem to argue that Air (at least such as produc'd our bubbles) may be generated of Water and other Bodies.

First then we have found by Experience that a vapid Air, or Water rarefied into Vapor, may at least for a while emulate the elastical power of that which is generally acknowledg'd to be true Air. For if you take a good AEolipile, with a moderately strong and slender Neck, and filling it with Water, lay it upon quick Coals, you may after a while observe so great a pressure by some of the parts contain'd in the AEolipile upon others, that the Water will sometimes be thrown up into the Air above three or four Foot high; and if you then take the AEolipile al∣most red hot from off the fire, you may perceive that the Water

will for a longer time than one would easily imagine continue to be spouted out in a violent Stream. And if there remains but little Water in the AEolipile when 'tis taken very hot from the Fire, immersing the Neck of it into cold Water, you will find, that after it begins to suck in some Water, there will be made from time to time store of large bubbles in that Water wherein the Neck was plunged. Which bubbles seem mani∣festly to proceed from hence, that for a while the heat in the AEolipile continues strong enough to rarefy part of the Water that is suck'd in, and expel it in the form of Vapors through the Water incumbent on the Pipe. If also when the AEolipile is almost full of Water, and therefore can contain but little Air; you hold a Coal or Brand in that stream of Vapors that issues out of the narrow mouth of it, you will find this vapid or rorid Air, (if I may so call it) to blow the Fire very strongly, and with a roaring noise. And that it be not said that 'tis by the external Air which the aqueous steams drive before them, and not by the Steams themselves, that the Blast is made and the Flame excited; it hath been observ'd, that by approaching the Coal or Brand almost to the mouth of the AEolipile, the Wind appear'd more vehement, than if the Body to be kindled were held some Inches off.

But in regard the elastical power of the Stream, issuing out of an AEolipile, seems manifestly due to the heat that expands and agitates the aqueous Particles whereof that Stream consists, and that such rapid Winds seem to be but water scatter'd into little parts and set a-moving; since we find, that holding a Knife, or any solid, smooth, and close Body against the Stream that issues out of the AEolipile, the Vapors condensing upon it, will pre∣sently cover it with Water: It will be very pertinent to sub∣joyn a notable Experiment that I remember I have met with in the description given us by the Industrious Kircher, of several Musical Engines. And (though it may seem somewhat pro∣lix) we will resite what he delivers in his own words, which are these.

Cum eodem tempore quo haec scripsi, summi Pont. Innocentii X^mi mandato organi hydraulici in horto Qui∣rinali * 1.5 constituendi cura mihi commendata esset, AEoli∣am cameram insigni sanè successu construi jussimus, eâ quae sequitur ratione.

Erat longitudo sive altitudo camerae AH 5 Pe∣dum, Latitudine 3 ferè ex lateribus constructa; in * 1.6 medio duo tenebat Diaphragmata CD & EF in mo∣dum cribri pluribus foraminibus pertusi. Paulo in∣fra canalis G aquam advehens inserebatur in H eidem epistomi∣um parabat exitum. Aqua itaque per canalem G maximo im∣petu ruens vehementissimum ventum mox intus excitabat; qui ventus nimiâ humiditate imbutus, ut purior exiret sicciórque, Diaphragmata illa in cribri modum pertusa, ordinata sunt. In∣tra haec enim aquae vehemens agitatio rupta fractáque Aerem pu∣riorem per A canalem subtiliorémque emittebat: Verum cum po∣stea inventum sit Aerem plus aequo humidum interioribus Organi meatibus maximum detrimentum inferre: Hinc, ut Aer aquosus ficcissimam consistentiam acquireret, ordinavimus canalem plumbe∣um QR in helicem contortum vasi S aliquantulum capaciori in modum Urnae efformato, insertum. Intra Urnam enim plumbeam & canalem tortuosum illisus Aer humidus, ita ab omni aquositate defaecabatur, ut ex furno in Organum derivatus dici potuerit. Urna S canalis tortuosi QR ultimum orificium Z inseritur ane∣mothecae Organi. Et hunc modum Organis hydraulicis omnium aptissimum reperi.

Debet autem camera illa situari in loco quantum fieri potest sic∣ciori, ita ut longo canali aqua intra eam derivetur, ne locus hu∣miditate suâ Organis officiat.

Thus far the Ingenious Kircherus, whom I the rather cite, because although I have been informed of divers Ventiducts (as they call them) by very knowing Travellers that have observ'd them: yet this relation of our Author being very punctual, and deliver'd upon his own particular Experience, hath I confess, made me with I had had the good fortune when I was at Rome, to take notice of these Organs; or that I had now the oppor∣tunity

of examining of such an Experiment. For if upon a strict enquiry I should find that the breath that blows the Organs doth not really upon the ceasing of its unusual agitation by little and little relapse into Water, I should strongly suspect that 'tis possible for Water to be easily turh'd into Air. I remember in∣deed, that we have formerly taught, that there lurks an inter∣spersed Air in the pores of ordinary Water, which may possibly be struck out by the breaking of the Water in its fall into the AEolian Chamber, (as he calls it.) But in regard the Scheme seems to represent that Chamber as closely shut, and thereby forbids us to suppose that any Air is carried into it, but what is latitant in the Water, it will scarce seem probable (to him who remembers how small a proportion of Air, that appear'd to be when its rarefication ceased, which was conceal'd in the Water we freed from bubbles in our Receiver) that so little Air as is commonly dispers'd through Water, should be able, in so little Water as was requisite for so small a room, to make so vehement a Wind as our Author here tells us of. I have sometime there∣fore suspected, that in this case the Wind may be produc'd by small particles of the Water it self, forcibly expell'd out of the Chamber into the Organs. And to the Objection, to which I foresaw this ghess to be liable, namely, That, no heat interve∣ning, there appear'd nothing that should raise the Water into ex∣halations, and give them an impulse. I thought it might be said, that motion alone, if vehement enough, may, without sensible heat, suffice to break Water into very minute parts, and make them ascend upwards, if they can no where else more ea∣sily continue their agitation. For I remember, that travelling betwixt Lyons and Geneva, I saw, not very far out of the way, a place where the River of Rhone, comeing suddenly to be straiten'd betwixt two Rocks, so near each other, that a Man may, (if my Memory fail me not) stand a stride upon both at once: that rapid Stream dashing with great impetuosity against its Rocky Boundaries, doth break part of its Water into such minute Corpuscles, and put them into such a motion, that Pas∣sengers observe at a good distance off, as it were a Mist arising

from that place, and ascending a good way up into the Air. Such, I say, was my suspicion touching the Wind we have been considering, but it seems something odd that aqueous Vapors should, like a dry Wind, pass through so long and tortuous a Pipe of Lead, as that describ'd by our Authour, since we see in the Heads of Stills, and the Necks of AEolipiles, how quickly such Vapors are even by a very little cold recondensed into Wa∣ter. But to this also something may be speciously reply'd; where∣fore contenting my self to have mention'd our Author's Experi∣ment as a plausible, though not demonstrative proof, that Wa∣ter may be transmuted into Air. We will pass on to mention in the third place another Experiment, which we try'd in order to the same enquiry.

We took a clear glass Bubble (capable of containing by guess about three Ounces of Water) with a Neck somewhat long and wide, of a Cylindrical form; this we fill'd with Oyl of Vitriol and fair Water, of each almost a like quantity, and casting in half a dozen small Iron Nails, we stopt the mouth of the Glass (which was top full of Liquor) with a flat piece of Diapalma provided for the purpose, that, accommodating it self to the surface of the Water, the Air might be exquisitely excluded: and speedily inverting the Viol, we put the Neck of it into a small wide-mouth'd Glass that stood ready with more of the same Liquor in it, to receive it. As soon as the Neck had reach'd the bottom of the Liquor it was dipp'd into, there appear'd at the up∣per part (which was before the bottom) of the Viol a bubble, of about the bigness of a Pea, which seem'd rather to consist of small and recent Bubbles, produc'd by the action of the dissol∣ving Liquor upon the Iron, than any parcel of the external Air that might be suspected to have got in upon the inversion of the Glass, especially since we gave time to those little Particles of Air which were carried down with the Nails into the Liquor to fly up again. But whence this first Bubble was produced, is not so material to our Experiment, in regard it was so small: For soon after we perceiv'd the Bubbles produc'd by the action of the Menstruum upon the Metal, ascending copiously to the

Bubble already named, and breaking into it, did soon excee∣dingly encrease it, and by degrees depress the Water lower and lower, till at length the substance contain'd in these Bubbles pos∣sessed the whole cavity of the glass Viol, and almost of its Neck too, reaching much lower in the Neck than the surface of the ambient Liquor, where with the open-mouth'd Glass was by this means almost replenished. And because it might be suspected that the depression of the Liquor might proceed from the agita∣tion whereinto the exhaling and imprison'd Steams were put, by that heat which is wont to result from that action of corrosive salts upon Metals, we suffered both the Viol and the open∣mouth'd Glass to remain as they were, in a Window, for three or four days and nights together; but looking upon them se∣veral times during that while, as well as at the expiration of it, the whole cavity of the glass Bubble, and most of its Neck, seem'd to be possess'd by Air, since by its spring it was able for so long to hinder the expell'd and ambient Liquor from regain∣ing its former place. And it was remarkable, that just before we took the glass Bubble out of the other Glass, upon the ap∣plication of a warm hand to the convex part of the Bubble; the imprison'd substance readily dilated it self like Air, and broke through the Liquor in divers bubbles, succeeding one another.

Having also another time try'd the like Experiment with a small Viol, and with Nails dissolv'd in Aquafortis, we found no∣thing incongruous to what we have now deliver'd. And this Circumstance we observ'd, that the newly generated Steams did not onely possess almost all the whole cavity of the Glass, but divers times without the assistance of the heat of my hand, broke away in large bubbles through the ambient Liquor into the open Air: So that these Experiments with corrosive Li∣quors, seem'd manifestly enough to prove, though not that Air may be generated out of the Water, yet that in general Air may be generated anew.

Lastly, To the foregoing Arguments from Experience we might easily subjoyn the Authority of Aristotle, and of (his

Followers) the Schools who are known to have taught, that Air and Water being symbolizing Elements (in the quality of moisture) are easily transmutable into one another. But we shall rather to the foregoing Argument add this, drawn from Reason, That if, as Leucippus, Democritus, Epicurus and others, follow'd by divers modern Naturalists, have taught, that the difference of Bodies proceeds but from the various Magnitudes, Figures, Motions, and Textures of the small parts they consist of, all the qualities that make them differ, being deducible from thence) there appears no reason why the minute parts of Wa∣ter, and other Bodies, may not be so agitated or connected as to deserve the name of Air. For if we allow the Cartesian Hy∣pothesis, according to which, as we noted at the beginning of this Letter, the Air may consist of any terrene or aqueous Cor∣puscles, provided they be kept swimming in the interfluent Ce∣lestial Matter; it is obvious that Air may be as often generated as Terrestrial Particles, minute enough to be carried up and down, by the Celestial Matter, ascend into the Atmosphere. And if we will have the Air to be a congeries of little slender Springs, it seems not impossible, though it be difficult, that the small parts of divers Bodies may by a lucky concourse of causes be so connected, as to constitute such little Springs, since (as we note in another Treatise) Water in the Plants it nourisheth is usually contriv'd into springy Bodies, and even the bare alter'd position and connexion of the parts of a Body may suffice to give it a Spring that it had not before, as may be seen in a thin and flexible Plate of Silver; unto which, by some strokes of a Hammer, you may give a Spring, and by onely heating it red∣hot, you may make it again flexible as before.

These, My Lord, are some of the Considerations at present occurring to my thoughts, by which it may be made probable, that Air may be generated anew. And though it be not impos∣sible to propose Objections against these, as well as against what hath been represented in favour of the contrary Doctrine; yet having already almost tired my self, and I fear more than al∣most tired Your Lordship with so troublesome an Enquiry

after the nature of Bubbles, I shall willingly leave Your Lord∣ship to judge of the Arguments alledged on either side, and I should scarce have ventur'd to entertain You so long concerning such empty things as the Bubbles, which have occasioned all this Discourse, but that I am willing to invite You to take notice with me of the obscurity of things, or the dimness of our crea∣ted Intellects (which yet of late too many so far presume upon, as either to deny or censure the Almighty and Omniscient Crea∣tor himself) and to learn hence this Lesson, That there are very many Things in Nature that we disdainfully overlook as obvious or despicable, each of which would exercise our Understandings, if not pose them too, if we would but attentively enough con∣sider it, and not superficially contemplate, but attempt satis∣factorily to explicate the nature of it.

EXPERIMENT XXIII.

SInce the writing of the twenty first and twenty second Ex∣periments (and notwithstanding all that hath been on their occasion deliver'd concerning Bubbles) we made some farther trials in prosecution of the same inquiry whereto they were designed.

We chose then, amongst those Glasses which Chymists are wont to call Philosophical Eggs, one that containing about nine Ounces of Water, had a Neck of half an Inch in Diameter at the top, and as we guest, almost an Inch at the bottom; which breadth we pitched upon for a reason that will by and by ap∣pear: then filling it up with common Water to the height of about a Foot and an half, so that the upper part remained empty, we shut it into the Receiver, and watch'd what would follow upon pumping, which proved that a great part of the Air being drawn out, the Bubbles began to discover themselves at the bot∣tom and sides of the Glass; and increasing, as the Air was more and more drawn away, they did from time to time ascend co∣piously enough to the top of the Water, and there quickly break: but by reason that the wideness of the Glass allow'd them free

passage through the Water, they did not appear as in the former Experiments to make it swell: The Water scarce ever rising at all above the mark affixt to its upper surface, when it was put in, and upon the return permitted to the outward Air, and consequently the shrinking in of the remaining bubbles, the Water seem'd to have lost of his first extent, by the avolation of the formerly interspers'd Air.

Being willing likewise to try whether distilled Water were, by having been divided into minute parts, and then re-united, more or less dispos'd to expand it self than Water not distill'd: We took out of our Laboratory some carefully distill'd Rain-wa∣ter, and put about two Ounces of it into a round Glass-bubble, with a very small Neck (not exceeding the sixth part of an Inch in diameter) which we filled half way to the top, and then convey'd it into the Receiver; the issue was, that though we drew out more Air than ordinary, yet there appeared not the least intumescence of the Water, nor any ascending bubbles.

But suspecting that either the small quantity of the Water or the figure of the Vessel might have an interest in this odd Phae∣nomenon, we took the lately mentioned Philosophical Egg, and another not much differing from it; the former we fill'd up with distill'd Rain-water to the old mark, and into the latter we put a long Cylinder or Rod of solid Glass to straiten the cavity of the Neck by almost filling it up; and then pouring some distil∣led Water into that also, till it reach'd within some Fingers breadth of the top, the Eggs were let down into the Receiver. In this Experiment the Air was so far drawn forth, before there appeared any bubble in either of the Glasses, that the disparity betwixt this and common Water was manifest enough. But at length, when the Air was almost quite pump'd out, the bubbles began to disclose themselves, and to increase as the pressure of the Air in the Receiver decreas'd. But whereas in the first mentioned Philosophical Egg the bubbles were very small, and never able to swell the Water, that we took notice of, at all above the mark: In the other, whose Neck, as we lately

said, was straitned, and their passage obstructed, great num∣bers of them, and bigger, fastned themselves to the lower end of the Glass-rammer (if we may so call it) and gather'd in such numbers between that and the sides of the Neek, that the Water swell'd about a Finger's breadth above the mark, though upon the admitting of the external Air it relapsed to the former mark, or rather fell somewhat below it. And although there∣upon in the first named Vessel all the bubbles presently disap∣peared, yet in the other we observed, that divers remained fastned to the lower part of the Glass-rammer, and continued there somewhat to our wonder, for above an hour after, but contracted in their dimentions.

Moreover, having suffered the Glasses to remain above twen∣ty four hours in the Receiver, we asterwards repeated the Ex∣periment, to try what change the exsuction of the external Air would produce in the Water, after the internal and latitant Air had (as is above recited) in great measure got away in bubbles, and whether or no the Water would by standing re admit any new particles of Air in the room of those that had forsaken it. But though we exhausted the Receiver very diligently, yet we scarce saw a bubble in either of the Glasses, not with standing which, we perceiv'd the Water to rise about the breadth of a Barly-corn, or more, in the Neck of that Glass wherein the so∣lid Cylinder had been put; the Liquor in the other Glass not sensibly swelling.

And lastly upon the letting in of the Air, the Water in the straitned Neck soon subsided to the mark above which it had swollen, which whether it ought to be ascrib'd to the same small expansion of the parts of the Water it self, or to the rarifaction of some yet latitant Air broken into such small particles, as to escape our observation, seems not easily determinable, without such farther tryals, as would perhaps prove tedious to be recited as well as to be made; though I was content to set down those already mentioned, that it might appear how requisite it is in nice Experiments to consider variety of Circumstances.

EXPERIMENT XXIV.

AFter having thus discovered what operation the exsuction of the ambient Air had upon Water, we thought good to try also what changes would happen in other Liquors upon the like taking off the pressure of the external Air. We took then a glass Egg, somewhat bigger than a Turkey Egg, which had a long Neck or Stem of about a ⅓ part of an Inch in diame∣ter; and filling it up with Sallet-oyl untill it reach'd above half way to the top of the Neck, we inclos'd it in the Receiver to∣gether with common Water in a resembling Vessel; that we might the better compare together the operation of the exsuc∣tion of the Air upon those two Liquors. The Pump being set on work, there began to appear bubbles in the Oyl much sooner than in the Water, and afterwards they also ascended much more copiously in the former Liquor than in the latter: Nay, and when by having quite tired the Pumper, and almost our own Patience, we gave over, the Bubbles rose almost (if not alto∣gether) in as great numbers as ever, insomuch that none of the various Liquors we tried either before or since, seemed to abound more with Aerial Particles than did this Oyl. In which it was farther remarkable, that between the time it was set into the Receiver, and that, at which we could get ready to pump, it subsided notably (by ghess about half an Inch) below the mark it reached before it was put in.

After this express'd Oyl, we made tryal of a distill'd one, and for that purpose made choice of the common Oyl or Spirit (for in the Shops where it is sold, the same Liquor is promis∣cuously called by either name) of Turpentine, because 'twas one∣ly of that Chymical Oyl, we had a sufficient quantity: which, being put into a small glass Bubble with a slender Neck, so as to fill it about two Inches from the top, did, upon the evacua∣ting of the Receiver, present us with great store of bubbles, most of which rising from the bottom, expanded themselves exceedingly in their ascent, and made the Liquor in the Neck to swell so much by degrees, that at length it divers times ran

over at the top: by which means, we were hindred from be∣ing able to discern upon the letting in of the Air, how much the subsidence of the Oyl below the first mark was due to the recess of the Bubbles.

Having likewise a mind to try whether, as strong a solution of Salt of Tartar in fair Water as could be made (we having then no Oyl of Tartar per deliquium at hand) though it be ac∣counted, Quick-silver excepted, the heaviest of Liquors, would afford us any bubbles; we put in a glass Egg full of it at the same time, with other Liquors, and found that they did long yield store of bubbles before any discovered themselves in the Liquor of Tartar; and having pursued the Experiment, it ap∣pear'd, That of all the Liquors we made trial of, this afforded the fewest and smallest bubbles.

Spirit of Vineger being tried after the same manner, exhibi∣ted a moderate number of bubbles, but scarce any thing else worth the mentioning.

Nor could we in Red Wine, try'd in a glass Egg, take no∣tice of any thing very observable. For though upon the ex∣suction of the Air the bubbles ascended in this Liquor, as it were in sholes, and shifted places among themselves in their as∣cent; yet the intumescence of the whole bulk of the Liquor was scarce at all sensible, the bubbles most commonly breaking very soon after their arrival at the top, where during their stay, they composed a kind of shallow froth, which alone appeared higher in the Neck of the Glass, than was the Wine when it was let down. Neither yet did Milk, conveyed into our Pneu∣matical Vessel, present us with any thing memorable save that (as it seem'd by reason of some unctuousness of the Liquor) the bubbles not easily breaking at the top, and thrusting up one another, made the Intumescence appear much greater than that of common Water.

We likewise conveyed Hens Eggs into the Receiver, but af∣ter the exsuction of the Air, took them out whole again. That which invited us to put them in, was, That (as perhaps we mention in other papers) we had among other Experiments

of cold, made Eggs burst, by freezing them within doors with Snow and Salt: The Ice, into which the aqueous parts of the Egg were turned by the cold, so distending (probably by reason of the numerous bubbles wont to be observable in Ice) the out∣ward parts of the Egg, that it usually crack'd the Shell, though the inner Membrane that involv'd the several Liquors of the Egg, because it would stretch and yield, remain'd unbroken. And hereupon we imagin'd that in our Engine it might appear, whether or no there were any considerable Spring, either in any of the Liquors, or in any other more spirituous substance in∣cluded in the Egg.

We took also some Spirit of Urine, carelesly enough defleg∣med, and put it into the same Glass (first carefully scour'd and cleansed) wherein we had put the Oyl olive above-mentioned We took also another Glass, differing from a Glass egg, onely in that its bottom was flat, and fill'd it up to about ⅔ of the Neck (which was wider than that of the Egg) with rectified Spirit of Wine.

We took also another Glass egg, and having fill'd it with common Water till it reached to the middle of the Neck, we poured to it of the same Spirit of Wine, till it reached about an Inch higher.

These three Glasses having marks set on them, over against the edges of the contain'd Liquors were put into the Receiver, and that beginning to be evacuated, the bubbles in all the three Liquors began to appear. The mixture of the Spirit of Wine and Water disclos'd a great store of bubbles, especially to∣wards the top; but scarce afforded us any thing worth the re∣membring. The Spirit of Urine appear'd to swell near an Inch and an half above the mark; and besides that, sent forth store of bubbles, which made a kind of froth at the upper part of it. And above that spume, there appear'd eight or ten great bubbles one above another, in a very decent order, each of them con∣stituting, as it were, a Cylinder of about half an Inch high, and as broad as the internal cavity of the Neck: So that all the upper part of the Neck (for these bubbles reach'd to the top) seem'd

to be divided into almost equal parts by certain Diaphragmes, consisting of the coats of the bubbles, whose edges appeared like so many Rings suspended one above another.

In the Spirit of Wine there did arise a great multitude of bub∣bles, even till weariness did make us give over the Experiment. And in these bubbles two or three things were remarkable; as first, That they ascended with a very notable celerity: Next, That being arrived at the top, they made no stay there: and yet, notwithstanding the great thinness and spirituousness of the Li∣quor, did, before they broke, lift up the upper surface of it, and for a moment or two form thereof a thin film or skin which ap∣peared protuberant above the rest of the superficies like a small Hemisphere. Thirdly, That they ascended streight up, whereas those produced at the lower part of the Vessel, containing the mixture of the Water and Spirit of Wine, ascended with a wa∣vering or wrigling motion, whereby they described an indented Line. Lastly, it was observable in the Spirit of Wine (and we took notice of the like in the Oyl of Turpentine lately men∣tioned) that not onely the bubbles seemed to rise from certain determinate places at the bottom of the Glass, but that in their ascension they kept an almost equal distance from each other, and follow'd one another in a certain order, whereby they seem'd part of small Bracelets, consisting of equally little incontiguous Beads: the lower end of each Bracelet, being as it were, fastned to a certain point at the bottom of the Glass.

The Air being sparingly let into the Receiver, the great bub∣bles formerly mentioned as incumbent upon one another, in that Glass that contained the Spirit of Urine, were by orderly de∣grees lessened, till at length they wholly subsided. Notwith∣standing the recess of so many bubbles as broke on the top of the Spirit of Urine, during all the time of the Experiment; yet it scarcely appear'd at all to be sunk below the mark: Nor did the mixture of Spirit of Wine and Water considerably subside. But that is nothing to what we observ'd in the Spirit of Wine, for not onely it conspicuously expanded it self in the Neck of the Vessel that contain'd it; notwithstanding the largeness of it,

and that the Bubbles were wont to break at the top of it almost as soon as they arriv'd there: But upon the readmission of the external Air, the Spirit of Wine retain'd its newly acquired ex∣pansion. And though we let it alone for near an hour together, in expectation that it might subside; yet when we took it out, we found it still swell'd between a quarter and half an Inch above the mark; and although it was not easily imaginable how this Phaenomenon could proceed from any mistake in trying the Ex∣periment, yet the strangeness of it invited me to repeat it with fresh Spirit of Wine. Which, swelling in the Neck as formerly, I left all night in the Receiver, allowing free access to the ex∣ternal Air at the Stop-cock, and the next day found it still ex∣panded as before, save that it seem'd a little lower: which de∣crement perhaps proceeded from the avolation of some of the fugitive parts of so voiatile a Liquor. And for better satisfaction having taken out the Glass, and consider'd it in the open Air, and at a Window, I could not find that there was any remain∣ing bubbles that could occasion the persevering and admir'd ex∣pansion.

EXPERIMENT XXV.

BEing desirous to discover what difference there might be as to gravity and levity, between Air expanded under Water, and it self before such expansion; we took two very small Viols, such as Chymical Essences (as they call them) are wont to be kept in, and of the size and shape expressed by the eighth Fi∣gure: into one of these we put so much of a certain ponderous Mercurial mixture (hapning to be then at hand) that the mouth being stopt with a little soft Wax, the Glass would just sink in Water and no more; this we let fall to the bottom of a wide∣mouth'd Christal Jar, fill'd with about half a pint of common Water, and into the same Vessel we sunk the other Essence∣glass unstop'd, with as much water in it as was more than suf∣ficient to make it subside. Both these sunk with their mouths downwards, the former being about three quarters full of Air, the latter containing in it a bubble of Air that was guess'd to be

of the bigness of half a Pea: This done, the wide mouth'd Glass was let down into the Receiver, and the way of employ∣ing the Engine was carefully made use of.

The success was, That having drawn out a pretty quantity of Air, the bubbles began to disclose themselves in the Water, as in the former Experiments; and though for a good while af∣ter the bubbles ascended in swarms from the lower parts of the Water, and hastily broke at the top; yet we prosecuted the Ex∣periment so long without seeing any effect wrought upon the Essence-bottles, that we began to despair of seeing of them rise. But continuing to ply the Pump, that little Glass, whose mouth was open'd, came to the top of the Water, being, as it were, boy'd up thither by a great number of bubbles that had fastned themselves to the sides of it; swimming thus with the mouth downward, we could easily perceive that the internal Air above∣mention'd had much dilated it self, and thereby seem'd to have contributed to the emerging of the Glass, which remain'd floa∣ting, notwithstanding the breaking and vanishing of most of the contiguous bubbles: being hereby incouraged to persist in pumping, we observed with some pleasure, that at each time we turn'd the Key, the Air in the little Glass did manifestly ex∣pand it self and thrust out the Water, generally retaining a very protuberant surface where it was contiguous to the remaining Water. And when after divers exsuctions of the Air in the Re∣ceiver, that in the Viol so dilated it self as to expel almost all the Water, it turn'd up its mouth towards the surface of the Water in the Jar, and there deliver'd a large bubble, and then relapsed into its former floating posture. And this Experiment taught us, among other things, that it was a work of more time and labour than we imagin'd, to exhaust our Engine as much as it may be exhausted: for although before the emerging of the small Viol, we did (as hath been touch'd already) think we had very considerably emptied the Receiver, because there seem'd to come out but very little or almost no sensible Air at each exsuction into, and out of the Cylinder; yet afterwards, at each drawing down the Sucker, the Air included in the Viol

did manifestly dilate it self, so long, that it did no less than nine times turn its mouth upwards, and discharge a bubble by con∣jecture about the bigness of a Pea, after the manner newly re∣cited. But as for that Viol which had the weight in it, it rose not at all. So that being not able by quick pumping to gain another bubble from the Air in the swimming Glass, which proceeded from some small leak in the Vessel, though it held in this Experiment more stanch than was usual, we thought fit to let in leasurely the Air from without, upon whose admission that within the Viol shrinking into a very narrow compass, the Glass did, as we expected, fall down to the bottom of the Jar.

But being desirous before we proceed to any new Experi∣ment, to try once more whether the little Glass, that had the weight in it, might not also be rais'd: After we had suffer'd the Engine to remain clos'd as it was, for five or six hours, the Pump was again ply'd with so much obstinacy, that not onely about the upper part of the Jar there appear'd a good number of bubbles (but very much smaller than those we saw the first time) but afterwards, there came from the bottom of the Jar, bubbles about the bigness of small Peas: which the Pump being still kept going, follow'd one another to the number of forty, coming from the stopp'd Viol; whose mouth, it seems, had not been shut so strongly and closely, but that the inclu∣ded Air, dilating it self by its own spring, made it self some little passage betwixt the Wax and the Glass, and got away in these bubbles; after which, the unstopt Glass began to float again, the Air shut up in it being manifestly so dilated as to ex∣pel a good part of the Water, but not so much as to break quite thorough. And at length, when our expectation of it was al∣most tired out, the heavier of the two Viols began to come alost, and immediately to subside again; which appear'd to be oc∣casion'd by the Air within it, whose bulk and spring being weaken'd by the recess of the forty bubbles before-mention'd, it was no longer able, as formerly, to break forcibly through the incumbent Water; but forming a bubble at the mouth of the Glass, boyed it up towards the top; and there getting away,

left it to sink again till the pressure of the Air in the Receiver being farther taken off, the Air in the Viol was permitted to expand it self farther, and to create another bubble, by which it was again for a while carried up. And it was remarkable, that though after having emptied the Receiver as far as well we could, we ceased from pumping; yet the Vessel continuing more stanch than it was wont, this ascent and fall of the Viol was repeated to the ninth time; the included Air, by reason of the smallness of the vent at which it must pass out, being not able to get away otherwise than by little and little; and consequent∣ly, in divers such parcels as were able to constitute bubbles, each of them big enough to raise the Viol and keep it alost untill the avolation of that bubble. Whereby it may appear, that the grand rule in Hydrostaticks, That a Body will swim in the Wa∣ter, in case it be lighter than as much of the Water as equals it in bulk, will hold likewise when the pressure of the Atmosphere is in very great measure, if not when it is totally taken off from the Liquor and the Body: though it were worth inqui∣ring what it is that so plentifully concurs to fill the bubbles made in our Experiment by the so much expanded Air. For to say with the old Peripatetick Schools, That the Air in rarefaction, may acquire a new extent, without the admission of any new substance, would be an account of the Phaenomenon very much out of date, and which, I suppose, our Modern Naturalists would neither give nor acquiesce in.

I know not whether it may be requisite to add, that in this Experiment, as in the former, the outward Air, being let in, did soon precipitate the floating Viol. But I think it will not be amiss to note, that (congruously to what hath been above recorded of the vast expansion of the Air) the Water which in the heavier Viol, succeeded in the room of those forty odd, if not fifty great bubbles of Air, which at several times got out of it, amounted but to a very inconsiderable bigness.

EXPERIMENT XXVI.

IT having been observ'd by those that have consider'd what belongs to Pendulums (a Speculation that may, in my poor judgment, be highly usefull to the Naturalists) that their Vi∣brations are more slowly made, and that their motion lasts less in a thicker, than in a thinner Medium: We thought it not amiss to try if a Pendulum would swing faster, or continue swinging longer in our Receiver, in case of exsuction of the Air, than otherwise. Wherefore we took a couple of round and polish'd Pendulums of Iron or Steel, of equal bigness, as near as we could get the Artificer to make them, and weighing each of them twenty Drachmes, wanting as many Grains. One of these we suspended in the cavity of the Receiver by a very slender silken string, of about seven Inches and a half in length from the Cover of the Receiver to which it is fasten'd. Then (by inclining the Engine) we made the Pendulum swing to and fro in it, and describe as long Arches as in the capacity of so brittle a Vessel we thought safe and convenient. And one of the Assistants telling the recursions of the other Pendulum hang∣ing in the free Air, by a string of about the same length, we shortned and lengthned this other Pendulum, till it appear'd to keep the same pace in its Vibrations, with that shut up in the Receiver. Then having carefully drawn away the Air, we did again set the Pendulum in the Receiver a vibrating; and giving the other Pendulum such a motion as made it describe an Arch, according to ones ghess, equal to that of the included Pendulum; we reckon'd, one of us, the Recursions of that Pendulum which was swinging within the Receiver; and another of us, that which was moving in (that which one would think a much more resisting medium) the Air. But once, one of us reckon'd near two and twenty Recursions of the included Pendulum, whilst the other reckon'd but twenty of the Pendulum that vi∣brated without. And another time also, the former of these Pendula was reckon'd to have made one and twenty Recursions, wherein the other made but twenty; Yet this Experiment

seem'd to teach us little, save that the difference betwixt the motion of such a Pendulum in the common Air, and in one ex∣ceedingly rarefied, is scarce sensible in Vessels no bigger than our Receiver; especially, since though during this Experiment it held very well, yet we could not suppose it to be altogether devoid of Air. We observed also, that when the Receiver was full of Air, the included Pendulum continued its Recursions about fifteen minutes (or a quarter of an hour) before it left off swing∣ing; and that after the exsuction of the Air, the vibration of the same Pendulum (being fresh put into motion) appear'd not (by a minutes Watch) to last sensibly longer. So that the event of this Experiment being other than we expected, scarce afforded us any other satisfaction, than that of our not having omitted to try it. And whether, in case the trial be made with a Pendulum much less disproportionate to the Air than Steel is, the event will much better answer expectation, experience may be consulted.

EXPERIMENT XXVII.

THAT the Air is the medium whereby sounds are con∣vey'd to the Ear, hath been for many Ages, and is yet the common Doctrine of the Schools. But this Received Opi∣nion hath been of late oppos'd by some Philosophers upon the account of an Experiment made by the Industrious Kircher, and other Learned Men: who have (as they assure us) observ'd, That if a Bell, with a Steel Clapper, be so fasten'd to the inside of a Tube, that upon the making the Experiment De Vacuo with that Tube, the Bell remain'd suspended in the deferted space at the upper end of the Tube: And if also a vigorous Load-stone be apply'd on the outside of the Tube to the Bell, it will attract the Clapper, which upon the removal of the Load-stone falling back, will strike against the opposite side of the Bell, and thereby produce a very audible sound; Whence divers have concluded, That 'tis not the Air, but some more subtle Body that is the medium of sounds. But because we conceiv'd that, to invali∣date such a consequence fro m this ingenious Experiment (though

the most luciferous, that could well be made without some such Engine as ours) some things might be speciously enough alledg'd; we thought fit to make a trial or two, in order to the discove∣ry of what the Air doth in conveying of sounds, reserving di∣vers other Experiments triable in our Engine concerning sounds, till we can obtain more leasure to prosecute them. Conceiving it then the best way to make our trial with such a noise as might not be loud enough to make it difficult to discern slighter variations in it; but rather might be, both lasting, (that we might take notice by what degrees it decreas'd;) and so small, that it could not grow much weaker without becoming im∣perceptible. We took a Watch, whose Case we open'd, that the contain'd Air might have free egress into that of the Re∣ceiver. And this Watch was suspended in the cavity of the Ves∣sel onely by a Pack-thread, as the unlikeliest thing to convey a sound to the top of the Receiver: And then closing up the Ves∣sel with melted Plaister, we listen'd near the sides of it, and plainly enough heard the noise made by the ballance. Those also of us, that watch'd for that Circumstance, observ'd, that the noise seem'd to come directly in a streight Line, from the Watch unto the Ear. And it was observable to this purpose, that we found a manifest disparity of noice, by holding our Ears near the sides of the Receiver, and near the Cover of it: which difference seem'd to proceed from that of the Texture of the Glass, from the structure of the Cover (and the Cement) through which the sound was propagated from the Watch to the Ear. But let us prosecute our Experiment. The Pump after this being imploy'd, it seem'd that from time to time the sound grew fainter and fainter; so that when the Receiver was empty'd as much as it us'd to be for the foregoing Experiments, neither we, nor some Strangers that chanc'd to be then in the Room, could, by applying our Ears to the very sides, hear any noise from within; though we could easily perceive that by the moving of the hand which mark'd the second minutes, and by that of the ballance, that the Watch neither stood still, nor re∣markably varied from its wonted motion. And to satisfy our

selves farther that it was indeed the absence of the Air about the Watch that hinder'd us from hearing it, we let in the external Air at the Stop-cock, and then, though we turn'd the Key and stopt the Valve, yet we could plainly hear the noise made by the ballance, though we held our Ears sometimes at two Foot distance from the outside of the Receiver. And this Experi∣ment being reiterated into another place, succeeded after the like manner. Which seems to prove, that whether or no the Air be the only, it is at least, the principal medium of Sounds. And by the way it is very well worth noting, that in a Vessel so well clos'd as our Receiver, so weak a pulse as that of the ballance of a Watch should propagate a motion to the Ear in a Physical∣ly streight Line, notwithstanding the interposition of so close a Body as Glass, especially Glass of such thickness as that of our Receiver: since by this it seems that the Air imprison'd in the Glass, must, by the motion of the ballance, be made to beat against the concave part of the Receiver, strongly enough to make its convex part beat upon the contiguous Air, and so propagate the motion to the Listners Ears. I know this can∣not but seem strange to those, who, with an eminent Modern Philosopher, will not allow that a Sound, made in the cavity of a Room, or other place so clos'd, that there is no intercourse betwixt the external and internal Air, can be heard by those without, unless the sounding Body do immediately strike against some part of the inclosing Body. But not having now time to handle Controversies, we shall onely annex, That after the foregoing Experiment, we took a Bell of about two Inches in Diameter at the bottom, which was supported in the mid'st of the cavity of the Receiver by a bent stick, which by reason of its Spring press'd with its two ends against the opposite parts of the inside of the Vessel: in which, when it was clos'd up, we observed that the Bell seemed to sound more dead than it did when just before it sounded in the open Air. And yet, when afterwards we had (as formerly) emptyed the Receiver, we could not discern any considerable change (for some said they observ'd a small one) in the loudness of the sound. Whereby it

seemed that though the Air be the principal medium of sound, yet either a more subtle matter may be also a medium of it, or else an ambient Body that contains but very few particles of Air, in comparison of those it is easily capable of, is sufficient for that purpose. And this, among other things, invited us to consider, whether in the above-mentioned Experiment made with the Bell and the Load-stone, there might not in the deser∣ted part of the Tube remain Air enough to produce a sound: since the Tubes for the Experiment De Vacuo (not to mention the usual thinness of the Glass) being seldom made greater than is requisite, a little Air might bear a not inconsiderable propor∣tion to the deserted space: And that also, in the Experiment De Vacuo, as it is wont to be made, there is generally some little Air that gets in from without; or at least store of bubbles that arise from the Body of the Quick-silver, or other Liquor it self, Observations heedfully made have frequently informed us: And it may also appear, by what hath been formerly deli∣vered concerning the Torricellian Experiment.

On the occasion of this Experiment concerning sounds, we may add in this place, That when we tried the Experiment for¦merly mentioned, of firing Gun-powder with a Pistol in our evacuated Receiver, the noise made by the striking of the Flint against the Steel, was exceeding languid in comparison of what it would have been in the open Air. And on divers other oc∣casions it appeared that the sounds created within our exhausted Glass, if they were not lost before they reach'd the Ear, seem'd at least to arrive there very much weaken'd. We intended to try whether or no the Wire-string of an Instrument shut up in∣to our Receiver, would, when the ambient Air was suck'd out, at all tremble, if in another Instrument held close to it, but with out the Receiver, a string tun'd (as Musicians speak, how pro∣perly I now examine not) to an Unison with it, were briskly toucht, and set a Vibrating. This, I say, we purpos'd to try to see how the motion made in the Air without, would be propa∣gated through the cavity of our evacuated Receiver. But when the Instrument wherewith the tryal was to be made came to

be imploy'd, it prov'd too big to go into the Pneumatical Vessel: and we have not now the conveniency to have a fitter made.

We thought likewise to convey into the Receiver a long and slender pair of Bellows, made after the fashion of those usually employ'd to blow Organs, and furnished with a small Musical instead of an ordinary Pipe. For we hop'd, that by means of a string fastned to the upper part of the Bellows, and to the moveable stopple that makes a part of the Cover of our Recei∣ver, we should, by frequently turning round that stopple, and the annexed string, after the manner already often recited, be able to lift up and distend the Bellows; and by the help of a competent weight fastned to the same upper part of the Bellows, we should likewise be able, at pleasure, to compress them: and by consequence, try whether that subtler matter than Air (which, according to those that deny a Vacuum, must be sup∣pos'd to fill the exhausted Receiver) would be able to produce a sound in the Musical Pipe; or in a Pipe like that of ordinary Bellows, to beget a Wind capable to turn or set on moving some very light matter, either shap'd like the Sails of a Wind-Mill, or of some other convenient form, and exposed to its Orifice. This Experiment, I say, we thought to make, but have not yet actually made it for want of an Artificer to make us such a pair of Bellows as it requires.

We had thoughts also of trying whether or no, as Sounds made by the Bodies in our Receiver become much more languid than ordinary, by reason of the want of Air: so they would grow stronger, in case there were an unusual quantity of Air crouded and shut up in the same Vessel. Which may be done (though not without some difficulty) by the help of the Pump, provi∣ded the Cover and Stopple be so firmly fasten'd (by binding and Cement, or otherwise) to the Glass and to each other, that there be no danger of the condensed Airs blowing of either of them away, or its breaking through the junctures. These thoughts, My Lord, as I was saying, we entertain'd; but for

want of leasure, as, of as good Receivers as ours, to substitute in its place, in case we should break it before we learn'd the skill of condensing the Air in it, we durst not put them in practice: Yet, on this occasion, give me leave to advertise Your Lordship once for all, That though for the reasons newly inti∣mated, we have, Only in the seventeenth Experiment, taken notice, that by the help of our Engine the Air may be con∣dens'd as well as rarefied; yet there are divers other of our Ex∣periments, whose Phaenomena it were worth while to try to vary, by means of the compression of the Air.

EXPERIMENT XXVIII.

WE taught, among divers other things, when we dis∣coursed of our first Experiment, That the Air shut up in our Receiver, presseth as strongly upon the Bodies shut up with it, as if they were exposed to the pressure of the whole Atmosphere. That this was not inconsiderately propounded, we hope Your Lordship hath gather'd from divers of the things already recited: But yet perhaps it will not be amiss to subjoin, by way of farther confirmation of the same truth, the follow∣ing Experiment: which would have accompanied the 20th, but the Paper wherein the one was written chanced not to be at hand, when the other was sent away.

We convey'd into the Receiver a new Glass Viol, capable of holding about 6 or 7 ounces of Water, into which we had before put 2 or 3 Spoonfulls of that Liquor, and stopt it close with a fit Cork. The Pneumatical Vessel being emptyed, there ap∣pear'd not any change in the inclos'd Water, the Air imprison∣ed with it, not having the force to blow out the stopple. Which event, though it were no other than we expected, was differing from what we desir'd. For we would gladly have seen what change would have appeared in the Water upon the Bottles be∣ing suddenly unstopp'd, in a place where the ambient Body was so differing from our common Air. Wherefore we did again put in the Viol, but less strongly clos'd than formerly, though as strongly stopt as seem'd requisite on ordinary occasions:

But when the Air was pumped out of the Receiver, that with∣in the Viol did quickly, as we expected, find or make it self little passages to get out at: as we argued, from this, That where∣as when the Viol was put in the time before, the Water re∣mained all the while perfectly free from bubbles; at this time the bottom of the Glass appear'd all covered with them, and they, upon the egress of the excluded Air into the Receiver, did presently flag and shrink up.

From these trials it seem'd deducible enough, that whilst the Viol continued to be well stopt, the included Water did, from the Air, shut up with it, sustain a pressure equal to that of the Atmosphere; since till the Air could get out of the Glass, there appeared no bubbles in the Water, notwithstanding the want of pressure in the ambient Body.

But to be sure to reach the chief end of our Experiment, we made use of this other expedient: We caused a convenient quantity of Water to be put, and Hermetically shut up into a Glass Egg, whose long Neck (which was purposely made of an unequal thickness) was fastened to one end of a string, whose other end was tied to the Cover of our Receiver, after the manner elsewhere mentioned already: Then the Egg being conveyed into the Pneumatical Vessel, and that being evacu∣ated, we did, by turning the brass Stopple formerly describ'd amongst the parts of our Engine, so shorten the string as to break the Glass; whereby liberty being given to the Air im∣prisoned in the Egg, to pass into the cavity of the Receiver, the sudden recess of the Air made the bubbles in a trice appear so numerous, and ascend so swiftly in the Water, that their mo∣tion look'd like that of a violent shower of Rain; save that the bubbles did not, like the drops of Rain, tend downwards, but upwards. Which made me resemble this Phaenomenon to what I have seen happen in the dissolution of Seed-Pearl in some acid Menstruum, inwhich, if a good quantity of the little Pearls be cast whole, they will at first, if the Menstruum be sharp enough, be carried in swarms from the bottom to the top of the Liquor. We will add, that without sealing up the Glass, this Expe∣riment

may be tryed in one of our smallest Receivers. For there the exsuction of the ambient Air may be performed so nimbly, that immediately the bubbles lurking in the Water are allowed to display themselves, and ascend in throngs; inso∣much, as having in such a Receiver try'd the Experiment with Wine as a more spirituous Liquor) instead of Water, the Red-Wine appeared all cover'd, with a copious, but vanishing white Froth, almost as if a Vessel full of bottl'd drink had been unwarily opened.

EXPERIMENT XXIX.

IT may not a little conduce to the clearer explication of divers Points in the Doctrine of Meteors, and perhaps of some other Physiological difficulties, to discover what the Air doth to the motion of those Steams or Exhalations that ascend into it, namely, Whether they mount upwards by virtue of any such positive levity (as some Peripateticks speak) acquir'd together with their Aërial nature, as inables them to pierce through part of the Atmosphere, and over-come its resistance. Or else, whe∣ther these steams being once raised above the Earth by their agi∣tation, have their ascent and sustentation aloft, rather promo∣ted than hindred by the Air: as the inferior parts of that, being thicker and heavier than the superior, the steams can more easily continue for a while their agitation upwards than downwards; And afterwards are by the same fluidity and thickness of the Air, carried to and fro in it, and kept from relapsing to the Earth: as in the Sea-Water the saline parts are kept from subsiding by those aqueous ones wherewith they are associated.

We hop'd to illustrate this matter, by observing the motion of the smoke, proceeding from kindled or flaming Bodies in our exhausted Receiver. But as we formerly noted, upon the exsuction of the Air, the smoking of those Bodies presently ceas'd. We had thoughts also of conveying into our Pneumatical Glass a hot Iron, with some Bodie easie to be dissipated into smoke set upon it, but consider'd, that neither was that way free from inconveniencies; especially this, that the hot Body

would make the Imprisoned Air circulate within the Receiver, and consequently make it questionable whether the ascent of the steams would not be due to the new and acquired motion of the Air.

Wherefore I bethought my self of another way to satisfie in some measure my curiosity, to wit, by means of a certain Li∣quor, which I call'd to mind that some years ago I had (for a de∣sign that belongs not to our present purpose) prepar'd; which, I suppose, I shew'd Your Lordship, and which had the luck to be taken notice of by divers very Ingenious and Famous Men. For this Liquor, though most of its Ingredients be Metals, and all of them ponderous enough, is yet of that nature, that whilst the Viol wherein it is kept is stopt (how slight a Cover soever) both the Liquor and the Glass are transparent; and so is that upper half of the Glass to which the Liquor reacheth not: But as soon as ever the stopple is taken out, and full access is given to the external Air, both the inward part of the Cork, and the Liquor it self, do presently send upwards, and scatter abroad a¦sume as thick and white, as if there were a quantity of Alaba∣ster-dust thrown up into the Air: And this smoaking of the Li∣quor lasts till my unwillingness to waste it invites me to stop it again, and then the ascension of the fumes suddenly ceaseth, till the Viol be again unstop'd.

This fuming Liquor then I thought would much conduce to the discovery I desir'd to make, since it sav'd me the need of con∣veying any hot Body with it into the Receiver, and would not darken it with fumes before the time. Wherefore having ty'd to the Viol a great weight of Lead, to keep it from being lifted up by the drawing out of the Cork; and having ty'd to the stopple one end of a string, of which the other end was made fast to the Cover of the Pneumatical Glass, the Liquor was carefully clos'd up after the wonted manner; then the Air being diligently pump'd out, the Viol was unstop'd in the empty'd Receiver. And though immediately, upon the drawing out of the Cork, there appear'd to be as it were thrown up some white fumes, which seem'd to proceed from the Air before imprison'd

in the Viol, and diffusing it self suddenly into the capacity of the Receiver: Yet we afterward observ'd, as we expected, That the fumes did not amount and disperse themselves as they used to do in the open Air; but that, when by reason of the agitati∣on of the Corpuscles of the Liquor, which could not continue their motion in so narrow a space as the Viol afforded them, and were therefore reduc'd to thrust one another out of it; when, I say, by these assistances the fumes were ascended to the lip of the Viol, they mounted no higher, but ran down along the out∣side of the Viol to the bottom of it; and thence along, a long and inclining piece of Lead, on which the Viol rested, like a little Stream (not very much bigger than a Swans Quill) whose nature they seem'd to emulate so well, that it quitted not the Viol till it was come to the bottom of it, and then forsook it in such a manner'a as stream of Water of the same bigness would have done. And this stream lasted a pretty while, and would probably have lasted longer, but that being loath to waste my Liquor, I let in at the Stop-cock a pretty deal of the external Air; notwithstanding which, finding after a while that the stream did run afresh, though, as it seem'd not altogether so copious as before; I let as much more Air, as would come in: and found (somewhat to my wonder) that though the stream formerly mention'd dis-appear'd, yet there appear'd not any white fumes to arise, either from the Cork, or out of the Viol it self, no not when the Cover was remov'd from the Receiver; though not on∣ly after a while there ascended white fumes from the Receiver: but having forthwith taken out the Viol into the open Air, it emitted white exhalations as before; and having presently after unstopp'd it in an open Window, we found both it and the Cork immediately to send forth a yet much more plentifull smoak: Though it be now divers years since this Numerical Liquor was prepared, after the manner mention'd either by Carneiades or Eleu∣therius (for I do not well remember which) in those Dialogues concerning Heat and Flame that have above been mention'd.

More circumstances concerning these Fumes we might have observ'd, had we not been deterr'd by an Indisposition in point

of health, from having much to do with steams of so dange∣rous a nature, as by that of the Ingredients of this Liquor these seem likely to be of.

The reflexions that may be made upon this Experiment, we have not now the leasure to prosecute, and therefore shall con∣tent our selves to recommend the several circumstances of it to Your Lordship's serious consideration; and to take notice (en passant) that steams in an ambient Body, or a medium thinner than themselves, may both tend downwards, and otherwise emulate the nature of a Liquor; which I therefore point at, that it may appear the less strange, if we sometimes speak of the At∣mosphere as of a kind of Liquor, in comparison of that more thin and subtle Celestial matter that surrounds it.

And though it might perchance suffice to have on this occasion intimated thus much; yet, lest this way of speaking of the At∣mosphere should be thought too bold and extravagant, I am con∣tent to borrow an Experiment of the discourse formerly men∣tion'd (touching fluidity and firmness) and subjoyn it here with alterations suitable to the contrivance of our Engine; and this the rather, because I hope it may conduce to the discovery of the nature of the Atmosphere: for which reason it might have been annext to what hath been noted either upon the first, or eighteenth Experiment, but that when they were written and sent away, it came not into my mind. The Experiment then as we try'd in our Engine, was as follows.

EXPERIMENT XXX.

WE took one of the small Receivers, often mention'd already, and into it we convey'd a piece of well lighted Match; and letting it remain there till it had fill'd the Receiver with smoak, we took it out and hastily clos'd again the Receiver, that the smoak might not get away. Then staying awhile to let these fumes leisurely subside, we found, as we expected, that af∣ter some time they setled themselves in the lower half of the Receiver; in a darkish Body, leaving the upper half of the Re∣ceiver transparent, and as to sight, full of nought but clear

Air. Now to manifest that this smoak thus setled emulated a Liquor, we inclin'd the Engine that contain'd it, sometimes to one side, and sometimes to the other; and observ'd the smoak to keep its surface almost Horizontal, notwithstanding the stoo∣ping of the Vessel that held it, as Water, or another liquor would in the like case have done. And if by a quicker rocking of the Engine the smoak were more swiftly shaken, it would, like Water, either vibrate to and fro from one side to the other of the Glass, or else have its surface manifestly curl'd with Waves, but preserve its self in an entire and distinct Body from the incum∣bent Air; and being permitted to rest a while, would soon re∣cover its former smooth and level Superficies. If also the Key were turn'd and the Valve unstopp'd, so that there was a free, though but a narrow passage open'd betwixt the external Air and the cavity of the Receiver, then would some of this smoak fall down, as it were, in a stream into the subjacent Cylinder, and a proportionate quantity of the outward Air, would manifestly ascend through it into the incumbent Air, much after the same manner as if you invert a Viol with a long neck, and well fill'd with Red-Wine, into a Glass full of fair Water, you shall see the Water and Wine by degrees mingle with one another; the one falling down as it were in little colour'd streams, and the other as∣cending in its room in the like curled streams, sometimes prece∣ded by round parcels of Water, which, by reason of their tran∣sparency, look almost like bubbles. The other circumstances of this Experiment, belonging not all of them to our present purpose, we shall content our selves with taking notice of one which seems the most important, and may illustrate and confirm some things formerly delivered. And it was, That if, when the superficies of our smoak lay smooth and Horizontal, a hot Iron were held near the outside of the Receiver, the neighbou∣ring part of the included fumes (for the rest did not very much alter their former superficies) being rarified by the heat, would readily ascend in a large Pillar of smoak to the very top of the Receiver, yet without seeming to lose a distinct superficies, or to be confounded with Air; below which, upon the recess of

the adventitious heat that by agitating it impell'd it upward, it would again subside.

All which being added to the late Experiment of the smoak∣ing Liquor, and to what may be from that which hath been elsewhere said, gather'd to the same purpose, will, I hope, keep it at least from appearing absur'd. If, since we see that there is so great an inequality in the density and weight of Liquors, that Water is near fourteen times thinner or lighter than Quick-silver of the same bulk; and well dephlegm'd spirit of Wine, yet much lighter than Water, we venture to speak sometimes of the Atmos∣phere, as if it were a peculiar kind of thin and halitious Liquor (if I may so call it) much lighter than Spirit of Wine.

To these things I know not whether it will be requisite to add, That as we lately took notice of conspicuous Waves that appear'd upon the superficies of our agitated smoak: So some such thing may not absurdly be conjectur'd to happen on the su∣perficies of the Atmosphere, by those strange ruggednesses that appear (especially in the Spring and Fall, when Exhalations and Vapours are wont to ascend most plentifully) upon the limb or edge of the Rising and Setting Sun. I speak thus disfidently upon this occasion, because I know, that by the Fluctuation or Boyling of the Suns own superficies, divers eminent Mathe∣maticians have plausibly enough (but how truly, I leave Your Lordship to judge) endeavour'd to give an account of it. But if we will joyn with those that have ascrib'd of late this Phaeno∣menon, to the refraction the Sun-beams suffer in our vapid air, we may, as hath been intimated, promote their Doctrine, by deducing from it, That probably the surface of the Atmos∣phere is oftentimes (if not always) exceedingly curl'd or wav'd. And certainly it is somewhat wonderfull, as well as very plea∣sant to behold, how, to him that looks upon the setting Sun through a long and excellent Telescope, there will not only appear strange inequalities in the edge of it (insomuch that I have often seen it more indented than a Saw) but those inequali∣ties will vanish in one place, and presently appear in another, and seem perfectly to move like Waves succeeding and destroying

one another, save that their motion oftentimes seems to be quickest; as if in that vast Sea they were carried on by a Cur∣rent, or at least by a Tide. And this (as we elsewhere note) appears to the Eye, not only when it looks directly through the Telescope upon the Sun; but also when a large and well defin'd Image of the Sun is by the same Telescope brought into a Room and cast upon a sheet of white Paper. But to insist on this were to digress: and therefore I will proceed to Experiments of another kind.

EXPERIMENT XXXI.

IT hath been admir'd by very ingenious Men, that if the exqui∣sitely polish'd surfaces of two flat pieces of Marble, be so con∣gruous to each other, that from their mutual application there will result an immediate contact, they will stick so fast together, that he that lifts up the uppermost, shall, if the undermost be not exceeding heavy, lift up that too, and sustain it alost in the free Air. A probable cause of this so close adhesion, we have elsewhere endeavoured to deduce from the unequal pressure of the Air upon the undermost stone; For the lower superficies of that stone being freely expos'd to the Air, is press'd upon by it, whereas the uppermost surface, being contiguous to the superior stone, is thereby defended from the pressure of the Air; which conse∣quently pressing the lower stone against the upper, hinders it from falling, as we have elsewhere more fully declar'd. Upon these grounds we conjectur'd, that in case we could procure two Mar∣bles exactly ground to one another, and in case we could also suf∣ficiently evacuate our Receiver; the lower stone would, for want of the wonted and sustaining pressure of the Air, fall from the upper. But the farther trial of this Experiment we must, unless Your Lordship think it worth Your making at Paris, put off till a fit∣ter opportunity. For where we now are, we cannot procure Mar∣bles so exactly ground, that they will sustain one another in the Air above a minute or two, which is a much shorter time than the emptying of our Receiver requires. We did indeed try to make our Marbles stick close together, by moistening their polish'd sur∣faces

with rectifi'd spirit of Wine, in regard that liquor, by its sudden avolation from Marble, if pour'd thereon, without leaving it moist or less smooth, seem'd unable to sustain them together after the manner of a glutinous Body, and yet seem'd sufficient to exclude and keep out the Air. But this we try'd to little pur∣pose, for having convey'd into the Receiver two black square Marbles (the one of two Inches and a third in length or breadth, and somewhat more than half an Inch in thickness: The other of the same extent, but not much above half so thick) fasten'd together by the intervention of pure spirit of Wine; and ha∣ving suspended the thicker by a string from the cover, we found not that the exsuction of the ambient Air would separate them, though a weight amounting to four Ounces were fasten'd to the lowermost Marble to facilitate its falling of.

I would gladly have the Experiment try'd with Marble, so well polish'd, as to need no Liquor whatsoever to make them cohere, and in a Vessel out of which the Air may be more persectly drawn than it was out of ours. But in the mean time, though we will not determine whether the spirit of Wine did contri∣bute to the strong cohesion of these stones, otherwise than by keeping ev'n the subtlest parts of the Air from getting in be∣tween them: yet it seemed that the not falling down of the lowermost Marble, might, without improbability, be ascrib'd to the pressure of the Air remaining in the Receiver; which, as we formerly noted, having been able to keep a Cylinder of Wa∣ter, of above a Foot in height, from falling to the bottom of the Tube, may well enough be suppos'd capable of keeping so broad a flat Marble from descending. And though this may seem a strange proof of the strength of the spring of the Air, ev'n when rarefied, yet it will scarce seem incredible to him that hath observ'd how exceeding strong a cohesion may be made betwixt broad Bodies, only by their immediate touching one another. A notable instance of which, I met with in this short Narra∣tive of the Learned Zucchius. Juveni (saith he) lacertorum suorum robur jactanti proposit a * 1.7 semel est lamina aerea, per ansam in medio ex∣tantem

apprehensam elevanda è tabula marmorea, cui optime con∣gruebat: qui primo tanquam rem ludicram puero committendam contempsit: tum instantibus amicis manum utrámque admovens, cum luctatus diu haerentem non removisset, excusavit impotentiam, objecta peregrini & potentissimi glutinis interpositione, quo fortissi∣me copulante nequiret divelli; donec vidit ab alio per tabulam facilimè laminam deduci, & ad extrema productam, & actam in transversum inde deportari. But that we may learn from our, own Engine, that two Bodies, though they touch each other but in a small part of their surfaces, may be made to cohere very strongly, only by this, That the Air presses much more forcibly upon the inferiour superficies of the lowermost Body, than upon the upper surface of the same: We will hereunto annex the following Experiment, though out of the order wherein they were made.

EXPERIMENT XXXII.

I Remember I have, in a Discourse touching Fluidity and Firm∣ness, made mention of my having, by the exsuction of the Air out of a Glass Vessel, made that Vessel take up, or suck up (to speak in the common Language) a Body weighing divers Ounces; but our Engine affording us the opportunity of making considerabler Experiments of that kind, We thought fit to make a further trial of the force of the Atmosphere's pressure upwards, after the following manner.

The Receiver having been exquisitely clos'd as we have of∣ten taught already, and the Air being in a good measure drawn out of it, it was remov'd from off the Pump: and to the lower branch of the Stop-cock, there was speedily apply'd a tapering Valve of brass, such as is described in the 9th Figure, made fit to go with its narrower end into the cavity of the branch, and to fill the Orifice of that cavity with its broader part. And that the Air might not get in at the little intervals, left here and there between the convex surface of the stopple and the inter∣nal edge of the branch, those intervals were stopt with a little Diachylon. And to the door, or, (if you please) that part of

the Valve which was to move to and fro, and in this Experi∣ment hung perpendicular to the Horizon, there was, at a but∣ton of brass belonging to the Valve, fasten'd a broad scale wherein weights were to be put. This done, the Key of the Stop-cock was turn'd, and the external Air beating like a forcible stream upon the Valve to get in there, it did suddenly both shut the Valve and keep it shut so strongly, that we had time to cast in divers weights one after another into the Scale; till at length the weight overpowering the pressure of the Atmosphere, drew down the Valve by the strings that tied the Scale to it, and gave liberty to the outward Air to rush into the Receiver. Though another time, when the Valve had but little weight hanging at it, being, by I know not what accident, drawn down beneath its former place, it was by the impetuous current of the out∣ward Air suddenly impell'd up into it again, and kept there. But in the former Experiment it is remarkable, That though the Receiver were not well exhausted, and though it leak'd whilst the rest of the Experiment was in prosecution: and though the Valve whereon the Cylinder of the Atmosphere could press, were not above an Inch and a half in Diameter, yet the weight kept up by suction, or rather supported by the Air, (namely the Valve, the Scale and what was cast out of it,) being sent to be weigh'd, amounted to about ten of our common Pounds, consisting of sixteen Ounces a piece: So that we doubted not but that, had the Experiment been made with favourable circumstances, the Air endeavouring to press in at the Orifice of the Stop-cock, would have kept a very much greater weight from falling out of it; I say the Air, because we found, by trial purposely made, that neither the imperfect contact of the Valve and the Stop-cock, nor the Diachylon that was employ'd to fill up the little Crannies left betwixt them, were considerable in this Experiment. By which it may, among other things, appear, that I did not without cause in the above-named Discourse touching Fluidity and Firmness, ascribe a great force, even to such Pillars of. Air as may be supposed to begin at the top of the Atmosphere, and recoyling from the ground, to terminate on the Bodies on which

they press: since in the present Experiment such a weight was supported by so slender a Cylinder of Air, rebounding from the Earth to the Valve whereon it did bear.

EXPERIMENT XXXIII.

BUt in regard we have not yet been able to empty so great a Vessel as our Receiver, so well as we can the Cylinder it self; our Pump alone may afford us a nobler instance of the force of the Air we live in, insomuch, that by help of this part of our Engine, we may give a pretty near ghess at the strength of the Atmosphere, computed as a weight. And the way may be this; First, the Sucker being brought to move easily up and down the Cylinder, is to be impelled to the top of it: Then the Receiver must be taken off from the Pump, that the upper Orifice of the Cylinder remaining open, the Air may freely succeed the Suc∣ker, and therefore readily yield to its motion downwards. This done, there must be fasten'd to one of the Iron Teeth of the Sucker, such a weight as may just suffice to draw it to the bot∣tom of the Cylinder. And having thus examin'd what weight is necessary to draw down the Sucker, when the Atmosphere makes no other than the ordinary resistance of the Air against its descent; the Sucker must be again forc'd to the top of the Cylinder, whose upper Orifice must now be exactly closed; and then (the first weight remaining) we easily may, by hanging a Scale to the above-mention'd Iron (that makes part of the Suc∣ker) cast in known weights so long, till in spight of the reluc∣tancy of the Atmosphere the Sucker be drawn down. For to these weights in the Scale, that of the Scale it self being added, the sum will give us the weight of a Column of Air, equal in Diameter to the Sucker, or to the cavity of the Cylinder, and in length to the height of the Atmosphere.

According to this method we did, since the writing of the last Experiment, attempt to measure the pressure of the At∣mosphere, but found it more difficult than we expected, to per∣sorm it with any accurateness; for though by the help of the Manubrium the Sucker moved up and down with so much ease,

that one would have thought that both its convex surface, and the concave one of the Cylinder were exquisitely smooth, and as it were slippery; yet when the Sucker came to be moved onely with a dead weight or pressure (that was not (like the force of him that pumped) intended as occasion required) we found that the little rufnesses or other inequalities, and per∣haps too, the unequal pressure of the Leather against the ca∣vity of the Cylinder, were able, now and then, to put a stop to the descent or ascent of the Sucker, though a very little ex∣ternal help would easily surmount that impediment; and then the Sucker would, for a while, continue its formerly interrup∣ted motion, though that assistance were withdrawn. But this discouragement did not deter us from prosecuting our Experi∣ment, and endeavouring, by a carefull trial, to make it as in∣structive as we could. We found then that a Leaden Weight, of 28 pounds (each consisting of sixteen Ounces) being fastned to one of the teeth of the Sucker, drew it down closely enough, when the upper Orifice of the Cylinder was left open: though by the help of Oyl and Water, and by the frequent moving the Sucker up and down with the Manubrium, its motion in the Cylinder had been before purposely facilitated. This done, the upper Orifice of the Cylinder was very carefully and closely stop∣ped, the Valve being likewise shut with its wonted Stopple well oyl'd, after the Sucker had been again impell'd up to the top of the Cylinder. Then to the precedent twenty eight pound, we added a hundred and twelve pounds more; which forcing down the Sucker, though but leisurely, we took off the twenty eight pound weight; and being unable to procure just such weights as we would have had, we hung on, instead of it, one of four∣teen pound: but found that, with the rest, unable to carry down the Sucker. And to satisfie our selves, and the Spectators, that it was the resistance of the ambient Air that hinder'd the descent of so great a weight, after that we had try'd that upon unstopping the Valve, and thereby opening an access to the external Air, the Sucker would be immediately drawn down. After this, I say, we made this farther Experiment, That having by a Man's strength

forcibly depress'd the Sucker to the bottom of the Cylinder, and then fastned weights, to the above-named Iron that makes part of that Sucker, the pressure of the external Air finding little or nothing in the cavity of the evacuated Cylinder to resist it, did presently begin to impell the Sucker, with the weights that clogg'd it, towards the upper part of the Cylinder; till some such accidental Impediment, as we formerly mention'd, check'd its course. And when that rub, (which easily might be,) was taken out of the way, it would continue its ascent to the top, to the no small wonder of those By-standers, that could not comprehend how such a weight could ascend, as it were, of it self; that is, without any invisible force, or so much as Suction to list it up. And indeed it is very considerable, that though possibly there might remain some particles of Air in the Cy∣linder, after the drawing down of the Sucker; yet the pressure of a Cylinder of the Atmosphere, somewhat less than three Inches in Diameter (for, as it was said in the description of our Engine, the cavity of the Cylinder was no broader) was able, uncompress'd, not only to sustain, but even to drive up a weight of an hundred and odd pounds: for besides the weight of the whole Sucker it self, which amounts to some pounds, the weights annexed to it made up an hundred and three pounds, besides an Iron Bar, that by conjecture weighed two pounds more; and yet all these together fall somewhat short of the weight which we lately mention'd, the resistance of the Air, to have held suspended in the cavity of the Cylinder.

And though (as hath been already acknowledg'd (we can∣not peradventure, obtain by the recited means so exact an account as were to be wish'd, of what we would discover: Yet, if it serve us to ground conjectures more approaching to the Truth, than we have hitherto met with, I hope it will be consider'd (which a famous Poet judiciously says)

Est quoddam prodire tenus, si non datur ultra.

Peradventure it will not be impertinent to annex to the other circumstances that have been already set down concerning this

Experiment, That it was made in Winter, in Weather neither Frosty nor Rainy, about the change of the Moon, and at a place whose latitude is near about 51 degrees and a half: For perhaps the force or pressure of the Air may vary, according to the Seasons of the Year, the temperature of the Weather, the elevation of the Pole, or the phases of the Moon; all, or even any of them seeming capable to alter either the height or consistence of the incumbent Atmosphere: And therefore it would not be amiss if this Experiment were carefully tried at several times and places, with variety of circumstances. It might also be tried with Cy∣linders of several Diameters, exquisitely fitted with Suckers, that we might know what proportion several Pillars of the Atmos∣phere bear to the weights they are able to sustain or lift up; and consequently, whether the increase or decrement of the resis∣tance of the ambient Air, can be reduced to any regular pro∣portion to the Diameters of the Suckers: These, and divers other such things which may be try'd with this Cylinder, might most of them be more exactly try'd by the Torricellian Experi∣ments, if we could get Tubes so accurately blown and drawn, that the cavity were perfectly Cylindrical.

To dwell upon all the several Reflexions, that a speculative Wit might make upon this and the foregoing Experiment, (I mean the thirty third and thirty second) would require almost a Volume; whereas our occasions will scarce allow us time to touch upon three or four of the chief Inferences that seem deducible from them, and therefore we shall content our selves to point at those few.

And first, as many other Phaenomena of our Engine, so espe∣cially, the two lately mention'd Experiments, seem very much to call in question the received Opinion of the nature or cause of Suction. For it's true indeed, that when men suck, they commonly use some manifest endeavour by a peculiar motion of their Mouths, Chests, and some other conspiring parts, to convey to them the body to be suck'd in. And hence perhaps they have taken occasion, to think that in all Suction there must be some endeavour or motion in the sucking to attract the

sucked Body. But in our last Experiment it appears not at all how the upper part of the empty'd Cylinder that remains moveless all the while, or any part of it, doth at all endea∣vour to draw to it the depressed Sucker and the annexed weights. And yet those that behold the ascension of the Sucker, without seriously considering the cause of it, do readily conclude it to be raised by something that powerfully Sucks or attracts it, though they see not what that may be or where it lurks. So that it seems not absolutely necessary to Suction, that there be in the Body, which is said to suck, an endeavour or motion in order thereunto, but rather that Suction may be at least for the most part reduced to Pulsion, and its effects ascrib'd to such a pressure of the neighbouring Air upon those Bodies (whether Aë∣rial, or of other natures) that are contiguous to the Body that is said to attract them, as is stronger, than that substance, which possesseth the cavity of that sucking Body, is able to resist. To object here, that it was some particles of Air remaining in the emptied Cylinder that attracted this weight to obviate a Vacuum, will scarce be satisfactory; unless it can be clearly made out by what little hooks, or other grappling Instruments, the internal Air could take hold of the Sucker; how so little of it obtained the force to lift up so great a weight; and why also, upon the letting in of a little more Air into one of our evacuated Vessels, the attraction is, instead of being strengthened, much weakned; though, if there were danger of a Vacuum before, it would re∣main, notwithstanding this ingress of a little Air. For that still there remained in the capacity of the exhausted Cylinder store of little rooms, or spaces empty or devoid of Air, may appear by the great violence wherewith the Air rusheth in, if any way be open'd to it. And that 'tis not so much the decrement of the Vacuum within the cavity of the vessel that debilitates the attra∣ction, as the Spring of the included Air (whose presence makes the decrement) that doth it by resisting the pressure of the exter∣nal Air, seems probable, partly from the Disability of vacuities, whether greater or lesser, to resist the pressure of the Air; and partly by some of the Phaenomena of our Experiments, and par∣ticularly

by this Circumstance of the Three and Thirtieth, that the Sucker was, by the pressure of the Ambient Air, im∣pell'd upwards with its weight hanging at it, not onely when it was in the bottom of the Cylinder, and consequently left a great Vacuum in the cavity of it; but when the Sucker had been already impell'd almost to the top of the Cylinder, and consequently, when the Vacuum that remain'd was become very little in comparison of that which preceded the beginning of the Sucker's ascension.

In the next place, these Experiments may teach us, what to judge of the vulgar Axiom received for so many Ages as an un∣doubted Truth in the Peripatetick Schools; That Nature ab∣hors and flyeth a Vacuum, and that to such a degree, that no humane power (to go no higher) is able to make one in the Universe; wherein Heaven and Earth would change places, and all its other Bodies rather act contrary to their own Na∣ture, than suffer it. For, if by a Vacuum we will understand a place perfectly devoid of all corporeal Substance, it may indeed then, as we formerly noted, be plausibly enough maintained that there is no such thing in the world; but that the generality of the Plenists, (especially till of late years some of them grew more wary) did not take a Vacuum in so strict a sense, may ap∣pear by the Experiments formerly, and ev'n to this day imploy'd by the Deniers of a Vacuum, to prove it impossible that there can be any made. For when they alledge (for Instance) that when a man sucks Water through a long Pipe, that heavy Li∣quor, contrary to its Nature, ascends into the Sucker's mouth, only, to fill up that room made by the Dilatation of his Breast and Lungs, which otherwise will in part be empty. And when they tell us, that the reason why if a long Pipe exactly clos'd at one end be filled top-full of Water, and then inverted, no Liquor will fall out of the open Orifice; Or, to use a more sa∣miliar Example, when they teach, that the cause, why in a Gar∣diner's watering Pot shaped conically, or like a Sugar-Loaf, fill'd with Water, no Liquor falls down through the numerous holes at the bottom, whilst the Gardiner keeps his Thumb upon the

Orifice of the little hole at the top, and no longer; must be that if in the case proposed the Water should descend, the Air being unable to succeed it, there would be le••t at the upper and deserted part of the Vessel a Vacuum, that would be avoided if the hole at the top were open'd. When (I say) they al∣ledge such Experiments, the tendency of them seems plainly to import, that they mean, by a Vacuum, any space here be∣low that is not filled with a visible body, or at least with Air though it be not quite devoy'd of all Body whatsoever. For why should Nature, out of her detestation of a Vacuum, make Bodies act contrary to their own tendency, that a place may be fill'd with Air, if its being so were not necessary to the avoi∣ding of a Vacuum.

Taking then a Vacuum in this vulgar and obvious sense, the common opinion about it seems lyable to several Excep∣tions, whereof some of the chief are suggested to us by our Engine.

It will not easily then be intelligibly made out, how hatred or aversation, which is a passion of the Soul, can either for a Vacuum, or any other object, be supposed to be in Water, or such like inanimate Body, which cannot be presumed to know when a Vacuum would ensue; if they did not bestir themselves to prevent it: nor to be so generous as to act contrary to what is most conducive to their own particular preservation for the publique good of the Universe. As much then of intelligible and probable Truth, as is contain'd in this Metaphorical Expres∣sion, seems to amount but to this; That by the Wise Authour of Nature (who is justly said to have made all things in number, weight and measure,) the Universe, and the parts of it, are so contriv'd, that it is as hard to make a Vacuum in it, as if they studiously conspir'd to prevent it. And how far this it self may be granted, deserves to be farther consider'd.

For in the next place, our Experiments seem to teach, that the supposed Aversation of Nature to a Vacuum is but accidental, or in consequence, partly of the Weight and Fluidity, or, at least, Fluxility of the Bodies here below; and partly, and per∣haps

principally, of the spring of the Air, whose restless en∣deavour to expand it self every way, makes it either rush in it self, or compel the interposed Bodies into all spaces, where it finds no greater resistance than it can surmount. And that in those mo∣tions which are made ob fugam Vacui (as the common phrase is) Bodies act without such generosity and consideration, as is wont to be ascrib'd to them, is apparent enough in our 32d Experi∣ment, where the torrent of Air, that seem'd to strive to get into the empty'd Receiver, did plainly prevent its own design by so impelling the Valve, as to make it shut the only Orifice the Air was to get out at. And if afterwards either Nature, or the in∣ternal Air, had a design the external Air should be attracted, they seem'd to prosecute very unwisely by continuing to suck the Valve so strongly; when they found that by that Suction the Valve it self could not be drawn in: Whereas by forbearing to suck, the Valve would by its own weight have fallen down, and suffer'd the excluded Air to return freely, and to fill again the exhausted Vessel.

And this minds me to take notice of another deficiency, poin∣ted at by our Experiments in the common Doctrine of those Plenists we reason with; for many of those unusual motions in Bodies, that are said to be made to escape a Vacuum, seem ra∣ther made to fill it. For why, to instance in our newly mention'd Experiment, as soon as the Valve was depressed by the weight we hung at it, should the Air so impetuously and copiously rush into the cavity of the Receiver; if there were before no vacant room there to receive it? and if there were, then all the while the Valve kept out the Air, those little spaces in the Receiver, which the corpuscles of that Air afterwards fill'd, may be concluded to have remain'd empty. So that the seeming violence, imploy'd by Nature on the occasion of the evacuating of the Vessel, seems to have come too late to hinder the making of Vacuities in the Receiver, and only to have, as soon as we permitted, fill'd up with Air those that were already made.

And as for the care of the publique good of the Universe as∣crib'd to dead and stupid Bodies, we shall only demand, why

in our 19^th Experiment, upon the Exsuction of the ambient Air, the Water deserted the upper half of the Glass-Tube; and did not ascend to fill it up, till the external Air was let in upon it: whereas by its easie and sudden regaining that upper part of the Tube, it appeared both that there was there much space devoid of Air, and that the Water might with small or no resistance have ascended into it, if it could have done so without the im∣pulsion of the re-admitted Air; which, it seems, was necessary to mind the Water of its formerly neglected Duty to the Uni∣verse.

Nay, for ought appeareth, even when the excluded Air, as soon as 'twas permitted, rush'd violently into our exhausted Re∣ceiver, that flowing in of the Air proceeded rather from the determinate Force of the Spring of the neighbouring Air, than from any endeavour to fill up, much less to prevent vacuity's. For though when as much Air as will, is gotten into our Re∣ceiver our present Opponents take it for granted that it is full of Air; yet if it be remembred that when we made our 17^th Expe∣riment we crouded in more Air to our Receiver than it usually holds; and if we also consider (which is much more) that the Air of the same consistence with that in our Receiver may in Wind-guns, as is known, and as we have tryed, be compressed at least into half its wonted room (I say at least, because some affirm, that the Air may be thrust into an 8^th, or a yet smaller part of its ordinary extent) it seems necessary to admit either a notion of condensation and rarefaction that is not intelligible, or that in the capacity of our Receiver when presumed to be full of Air, there yet remain'd as much of space as was taken up by all the Aërial corpuscles, unpossessed by the Air. Which seems plainly, to infer that the Air that rush'd into our empty'd vessel did not doe it precisely to fill up the Vacuities of it, since it left so many un∣fill'd, but rather was thrust in by the pressure of the contiguous Air: which as it could not, but be always ready to expand it self, where it found least resistance, so was it unable to fill the Receiver any more, than untill the Air within was reduc'd to the same measure of Compactness with that without.

We may also from our two already often mention'd Experi∣ments farther deduce, that, (since Natures hatred of a Vacuum is but Metaphorical and Accidental, being but a consequence or result of the pressure of the Air and of the Gravity, and partly also of the Fluxility of some other Bodies) The power she makes use of to hinder a Vacuum, is not (as we have else-where also noted) any such boundless thing as men have been pleased to imagine. And the reasons why in the former Experiments, mentioned in favour of the Plenists, Bodies seem to forget their own Natures to shun a Vacuum, seems to be but this; That in the alledged cases the weight of that Water that was either kept from falling or impell'd up, was not great enough to surmount the pressure of the contiguous Air; which, if it had been, the Water would have subsided, though no Air could have succeeded. For not to repeat that Experiment of Monsieur Paschal (formerly mention'd to have been tryed in a Glass exceeding 32. Foot) wherein the inverted Pipe being long enough to contain a com∣petent-weight of Water, that Liquor freely ran out at the lower Orifice: Not to mention this (I say) we saw in our nineteenth Experiment, that when the pressure of the ambient Air was suf∣ficiently weakn'd, the Water would fall out apace at the Orifice even of a short Pipe, though the Air could not succeed into the room deserted by it. And it were not amiss if tryal were made on the tops of very high Mountains, to discover with what case a Vacuum could be made near the confines of the Atmosphere, where the Air is probably but light in comparison of what it is here below. But our present (three and thirtieth) Experiment seems to manifest, not onely that the power, exercis'd by Na∣ture, to shun or replenish a Vacuum, is limitted, but that it may be determin'd even to Pounds and Ounces: Insomuch that we might say, such a weight Nature will sustain or will lift up to resist a Vacuum in our Engine; but if an Ounce more be added to that weight, it will surmount Her so much magnifi'd detesta∣tion of Vacuities. And thus, My Lord, our Experiments may not onely answer those of the Plenists, but enable us to retort their Arguments against themselves: since, if that be true which

they alleadge, that, when Water falls not down according to its nature, in a Body wherein no Air can succeed to fill up the place it must leave, the suspension of the Liquor is made Ne detur Vacuum, (as they speak) it will follow, that if the Water can be brought to subside in such a case, that deserted space may be deem'd empty, according to their own Doctrine; especially, since Nature (as they would perswade us) bestirs her self so mightily to keep it from being deserted.

I hope I shall not need to remind Your Lordship, that I have all this while been speaking of a Vacuum, not in the strict and Philosophical sense, but in that more obvious and familiar one that hath been formerly declar'd.

And therefore I shall now proceed to observe in the last place, that our 33^d Experiment affords us a notable proof of the un∣heeded strength of that pressure which is sustain'd by the Cor∣puscles of what we call the free Air, and presume to be uncom∣pressed. For, as fluid and yielding a Body as it is, our Experi∣ment teacheth us, That ev'n in our Climate, and without any other compression than what is (at least here below) Natural, or (to speak more properly) ordinary to it, it bears so strongly upon the Bodies whereunto it is contiguous, that a Cylinder of this free Air, not exceeding three Inches in Diameter is able to raise and carry up a weight, amounting to between sixteen and seventeen hundred Ounces. I said even in our Climate, because that is temperate e∣nough; * 1.8 and as far as my observations assist me to conjecture, the Air in many other more Northern Countries may be much thicker, and able to support a greater weight: which is not to be doubted of, if there be no mistake in what is Recorded concern∣ing the Hollanders, that were forc'd by the Ice to Winter in Nova Zembla, namely, That they found there so condens'd an Air, that they could not make their Clock goe, ev'n by a very great addition to the weights that were wont to move it.

I suppose Your Lordship will readily take notice, that I might very easily have discoursed much more fully and accurately than I have done, against the common opinion touching Suction, and touching natures hatred of a Vacuum. But I was willing to keep my self to those considerations touching these matters, that might be verified by our engine it self, especially, since, as I said at first, it would take up too much time to insist particularly upon all the Reflexions that may be made even upon our two last Experiments. And therefore passing to the next, I shall leave it to Your Lordship to consider how far these tryals of ours will either confirm or disfavour the new Doctrine of several eminent Naturalists, who teach, That in all motion there is necessarily a Circle of Bodies, as they speak, moving together; and whether the Circles in such motion be an Accidental or Consequential thing or no.

EXPERIMENT XXXIIII.

'TIs a known thing to those that are conversant in the Hy∣drostaticks, That two Bodies which in the Air are of e∣qual weight, but of unequal bulk, as Gold, for instance and Iron, being afterwards weighed in Water, will lose their AEqui∣librium upon the change of the ambient Body: so that the Gold will sink lower than the Iron; which, by reason of its greater bulk, hath more Water to lift or displace, that it may sink. By Analogy to this Experiment, it seemed probable, that if two weights did in our Engine ballance each other, when the Glass was full of Air; upon the exsuction of a great part of that Air, so notable a change in the consistence of the ambient Body, would make them lose their AEquilibrium.

But being desirous at the same time to make a tryal, for a certain Design that needs not here be mention'd, we took for one of our weights a dry Bladder, strongly tyed at the Neck, and about half fill'd with Air (that being a weight both slight, and that would expand it self in the evacuated Glass) and fastn∣ing that to one part of our formerly mentioned exact ballance (which turns with the 32^d part of a Grain) we put a Metalline

counterpoise into the opposite Scale; and so the two weights being brought to an AEquilibrium, the ballance was convey'd into the Receiver, and suspended from the Cover of it.

But before we proceed farther, we must note, That presently after the laying on of the Cover, the Bladder appear'd to pre∣ponderate, whereupon the Scales being taken out, and reduc'd very near to an AEquilibrium, yet so, that a litle advantage remained on that side to which the Metalline weight belonged; they were again let down into the Receiver, which was pre∣sently made fast with Plaister, and a hot Iron: Soon after which before the Pump was employ'd, the Bladder seem'd again a little to preponderate. Afterwards the Air in the Glass being begun to be drawn out, the Bladder began (according to the formerly mention'd Observations) to expand it self, and mani∣festly to outweigh the opposite weight, drawing down the Scale to which it was fastned very much beneath the other, especially when the Air had swell'd it to its full extent.

This done, we very leisurely let in the external Air; and ob∣serv'd, that upon the flagging of the Bladder, the Scale whereto it was fastned, not onely by degrees return'd to an AEquilibrium with the other, but at length was a little outweighed by it.

But because we suspected there might have interven'd some unheeded Circumstance in this last part of the Experiment we would not presently take out the Scales, nor meddle with the Cover, but leaving things as they were, we perceiv'd, that af∣ter a little while the Bladder began again to preponderate, and by degrees to sink lower and lower for divers hours, wherefore, leaving the Vessel closed up all night, we repair'd to it next Morning, and found the Bladder fallen yet lower. As if the very substance of it, had imbibed some of the moisture wherewith the Air (the Season being very rainy) did then abound: As Lutestrings, which are made likewise of the Membranous parts of Guts, strongly wreath'd, are known to swell so much oftentimes as to break in rainy and wet weather. Which con∣jecture is the more to be regarded, because congruously unto it one of the company having a little warm'd the Bladder, found

it then lighter than the opposite weight. But this must be look'd upon as a bare conjecture, till we can gain time to make farther tryals about it. In the mean while we shall adde, that without removing the Scales or the Cover of the Receiver, we again caused the Air to be drawn out (the weather continuing very moist) but found not any manifest alteration in the ballance; whether because the AEquilibrium was too far lost to let a small change appear, we determine not.

But to make the Experiment with a Body less apt to be altered by the temperature of the Air, than was the Bladder; we brought the Scales again to an AEquilibrium with two weights, whereof the one was of Lead, the other of Cork. And having evacuated the Receiver, we observed, that both upon the ex∣suction, and after the return of the Air, the Cork did manifestly preponderate, and much more, a while after the Air had been let in again, than whilst it was kept out. Wherefore, in the room of the Cork, we substituted a piece of Char-coal, as less likely to imbibe any moisture from the Air, but the event proved much the same with that newly related: So that this Experiment seems more liable to Casualties than any, excepting one we have made in our Engine. And as it is difficult to prevent them, so it seems not very easie to discover the causes of them, whereof we shall therefore at present forbear mentioning our Conjectures.

EXPERIMENT XXXV.

SOme Learned Mathematicians have of late ingeniously endea∣voured to reduce Filtres to Siphons; but still the true cause of the ascension of Water, and other Liquors both in Siphons and in Filtration, needing (for ought we have yet found) a clearer Discovery and Explication, we were desirous to try whether or no the pressure of the Air might reasonably be supposed to have either the principal, or at least a considerable Interest in the rai∣sing of those Liquors. But because we found that we could not yet so evacuate our Receiver, but that the remaining Air though but little in comparison of the exhausted, would be able to im∣pell the Water to a greater height than is usual in ordinary Fil∣trations:

we resolved instead of a List of Cotton, or the like Filtre, to make use of a Siphon of Glass, delineated in the third Figure, consisting of three pieces, two streight, and the third crooked to joyn them together; whose Junctures were diligent∣ly clos'd that no Air might find entrance at them. One of the Legs of this Siphon was (as it should be) somewhat longer than the other, and was pervious at the bottom of it onely, by a hole almost as slender as a hair, that the Water might but very leasurely drop out of it, lest it should all run out before the Ex∣periment were compleated. The other and shorter Leg of the Siphon was quite open at the end, and the same wideness with the rest of the Pipe, whose bore was about ¼ of an Inch. The whole Siphon made up of these several pieces put together, was design'd to be about a Foot and a half long; that the remaining Air, when the Vessel was exhausted after the wonted manner, might not be able to impell the Water to the top of the Siphon; which being inverted, was fill'd with Water, and of which the Shorter leg being let down two or three Inches deep into a Glass Vessel full of Water, and the upper parts of it being fasten'd to the inside of the Cover of the Receiver, we proceeded to close first, and then to empty the Vessel.

The effect of the tryal was this, That till a pretty quantity of Air had been drawn out, the Water dropp'd freely out at the low∣er end of the lower leg of the Siphon, as if the Experiment had been performed in the free Air. But afterwards, the Bubbles (as had been apprehended) began to disclose themselves in the Water, and ascending to the top of the Siphon, imbodyed them∣selves there into one, which was augmented by little and little, by the rising of other bubbles that from time to time broke in∣to it, but much more by its own dilatation, which increas'd proportionably to the exsuction that was made of the Air out of the Receiver. So that at length the Water in the shorter Leg of the Siphon was reduc'd, partly by the extraction of the ambi∣ent Air, and partly by the expansion of the great Bubble at the upper part of the Siphon, to be but about a Foot high, if so much; whereby it came to pass, that the course of the Water

in the Siphon was interrupted, and that which remain'd in the longer Leg of it, continu'd suspended there without dropping any longer. But upon the turning of the Stop-cock, the out∣ward Air (being let into the Receiver) got into the Siphon, by the little hole at which the Water formerly dropt out; and tra∣versing all the incumbent Cylinder of Water, in the form of Bubbles, joynd it self with that Air that before possess'd the top of the Siphon.

To prevent the inconveniences arising from these Bubbles, two Glass Pipes, like the former, were so placed, as to terminate together in the midst of the Belly of a Glass Viol, into whose Neck they were carefully fasten'd with Cement; and then both the Viol and the Pipes being (which was not done without dif∣ficulty) totally fill'd with Water, the Siphon describ'd in the fifth Figure, was plac'd with its shorter Leg in the Glass of Wa∣ter as formerly; and the Experiment being prosecuted after the same manner, much more Air than formerly was drawn out, before the bubbles, disclosing themselves in the water, were able to disturb the Experiment; because that in the capacity of the Viol there was room enough for them to stretch themselves, without depressing the Water below the ends of the Pipes; and during this time, the Water continued to drop out of the propending Leg of the Siphon. But at length the Receiver being very much empty'd, the passage of the Water through the Siphon ceas'd, the upper ends of the Pipes beginning to appear a little above there∣maining Water in the Viol, whose dilated Air appear'd likewise to press down the Water in the Pipes, and fill the upper part of them.

And hereby the continuity of the Water, and so the Experi∣ment it self being interrupted we were invited to let in the Air a∣gain, which, according to its various proportions of pressure to that of the Air in the Viol and the Pipes, did for a good while exhibite a pleasing variety of Phaenomena, which we have not now the leasure to recite. And though upon the whole matter there seem'd little or no cause to doubt, but that, if the Bubbles had not disturb'd the Experiment, it would manifestly enough have appear'd that the course of Water through Siphons depends

upon the pressure of the Air: yet we resolv'd, at our next lea∣sure and conveniency, to try the Experiment again, with a quantity of Water before freed from Bubbles by the help of the same Engine.

This occasion I have had to take notice of Siphons, puts me in mind of an odde kind of Siphon that I caus'd to be made ā pretty while ago; and which hath been since, by an Ingenious Man of Your acquaintance, communicated to divers others. The occa∣sion was this: An eminent Mathematician told me one day, that some inquisitive French Men (whose Names I know not) had observ'd, That in case one end of a slender and perforated Pipe of Glass be dip'd in Water, the liquor will ascend to some height in the Pipe, though held perpendicular to the plain of the Water. And, to satisfie me that he mis-related not the Experi∣ment, he soon after brought two or three small Pipes of Glass, which gave me the opportunity of trying it: though I had the less reason to distrust it, because I remember I had often, in the long and slender Pipes of some weather Glasses, which I had caus'd to be made after a somewhat peculiar fashion, taken notice of the like ascension of the Liquor, though (presuming it might be casual) I had made but little reflexion upon it. But after this tryal, beginning to suppose, that though the Water in these Pipes that were brought me, rise not above a quarter of an Inch, (if near so high) yet, if the Pipes were made slender enough, the Water might rise to a very much greater height; I caus'd se∣veral of them to be, by a dexterous Hand, drawn out at the flame of a Lamp, in one of which that was almost incredibly slender we found that the Water ascended (as it were of it self) five Inches by measure, to the no small wonder of some famous Ma∣thematicians, who were Spectators of some of these Experi∣ments. And this height the Water reach'd to, though the Pipe were held in as erected a posture as we could: For if it were in∣clin'd, the Water would fill a greater part of it, though not rise higher in it. And we also found, that when the inside of the Pipe was wetted beforehand, the Water would rise much better than otherways: But we caus'd not all our slender Pipes to be

made streight, but some of them crooked, like Siphons: And having immers'd the shorter Leg of one of these into a Glass that held some fair Water, we found, as we expected, that the Wa∣ter arising to the top of the Siphon, though that were high enough, did of it self run down the longer Leg, and continue running like an ordinary Siphon. The cause of this ascension of the Wa∣ter, appear'd to all that were present so difficult, that I must not stay to enumerate the various Conjectures that were made at it, much less to examine them; especially having nothing but bare Conjectures to substitute in the room of those I do not ap∣prove. We try'd indeed, by conveying a very slender Pipe and a small Vessel of Water into our Engine, whether or no the ex∣suction of the ambient Air would assist us to find the cause of the ascension we have been speaking of: But though we imploy'd red Wine instead of Water, yet we could scarce certainly per∣ceive thorow so much Glass, as was interpos'd betwixt our eyes and the Liquor, what happen'd in a Pipe so slender that the red∣ness of the Wine was scarce sensible in it. But as far as we could discern, there happen'd no great alteration to the Liquor: which seem'd the less strange, because the spring of that Air that might depress the Water in the Pipe, was equally debilitated with that which remain'd to press upon the surface of the Water in the little Glass. Wherefore, in favor of his Ingenious Conjecture who ascrib'd the Phaenomenon under consideration, to the greater pressure made upon the water by the Air without the Pipe, than by that within it, (where so much of the Water (consisting per∣haps of Corpuscles more pliant to the internal surfaces of the Air) was contiguous to the Glass) it was shown, that in case the little Glass Vessel that held the water, of which a part ascended into the slender Pipe, were so clos'd, that a Man might with his mouth suck the Air out of it, the water would immediately subside in the small Pipe. And this would indeed infer, that it ascended before onely by the pressure of the incumbent Air; But that it may (how justly I know not) be objected, That peradventure this would not happen, in case the upper end of the Pipe were in a Vacuum: And that 'tis very probable the

water may subside, not because the pressure of the internal Air is taken off by Exsuction, but by reason of the spring of the external Air, which impels the Water it findes in its way to the cavity deserted by the other Air, and would as well impel the same water upwards, as make it subside, if it were not for the accidental posture of the Glasses. However, having not now leisure to examine any farther this Matter, I shall onely mind Your Lordship, that if You will prosecute this Specula∣tion, it will be pertinent to find out likewise, Why the surface of water (as is manifest in Pipes) useth to be concave, being de∣press'd in the middle, and higher on every side? and why in Quick∣silver on the contrary, not onely the surface is wont to be very convex, or swelling, in the middle; but if you dip the end of a slender Pipe in it, the surface of the Liquor (as 'tis call'd) will be lower within the Pipe, than without. Which Phaenomena, whether, and how far, they may be deduc'd from the Figure of the mercurial Corpuscles, and the Shape of the springy Parti∣cles of the Air, I willingly leave to be consider'd.

EXPERIMENT XXXVI.

SEveral ways we have met with propos'd, partly by the ex∣cellent Galileo, and partly by other ingenious Writers, to manifest that the Air is not devoid of weight; some of these re∣quire the previous absence of the Air to be weighed; and others, the violent condensation of it. But if we could list a pair of Scales above the Atmosphere, or place them in a Vacuum, we might there weigh a parcel of Air it self, as here we do other Bodies in the Air, because it would there be heavier than that which surrounds it, as are grosser Bodies we commonly weigh, than the medium or ambient Air. Wherefore, though we have above declin'd to affirm, that our Receiver, when emptyed, de∣serves the name of a true Vacuum, and though we cannot yet perfectly free it from Air it self, yet we thought fit to try how far the Air would manifest its gravity in so thin a medium, as we could make in our. Receiver, by evacuating it. We caus'd then to be blown at the Flame of a Lamp, a Glass bubble of

about the bigness of a small Hen-egge, and of an Oval form, save that at one end there was drawn out an exceeding slender Pipe, that the Bubble might be sealed up, with as little rarefaction as might be, of the Air included in the great or Oval Cavity of it. This Glass being sealed, was fastened to one of the Scales of the exact pair of Ballances formerly mention'd; and being counter∣pois'd with a weight of Lead, was convey'd into the Receiver, and clos'd up in it. The Beam appearing to continue Horizon∣tal, the Pump was set on work, and there scarce past above two or three Exsuctions of the Air, before the Ballance lost its Equi∣librium, and began to incline to that side on which the Bubble was; which, as the Air was farther and farther drawn out, did manifestly more and more preponderate, till he that pumped began to grow weary of his Imployment: after which the Air being leisurely let in againe, the Scales by degrees returned to their former Equilibrium. After that we took them out, and casting into that Scale to which the lead belonged three quarters of a grain, we conveyed the ballance into the Receiver, which being closed up, and exhausted as before, we observ'd, that as the Air was drawn out more and more, so the Glass bubble came nearer and nearer to an Equilibrium with the other weight, till at length the Beam was drawn to hang Horizontal; which (as we had found by another tryal) we could not bring it to do, when a quarter of a Grain more was added to the Scale, to which the Lead belong'd: though it seem'd questionless, that if we could have perfectly empty'd the Receiver of the contain'd Air, that included in the bubble would have weighed above a Grain, notwithstanding its having been probably somewhat rarefied by the flame, by the help of which, the bubble was seal'd up. Let us adde, That on the regress of the excluded Air, the Lead, and the weight cast into the same scale, did again very much pre∣ponderate.

We likwise convey'd into the Receiver, the same bubble, open'd at the end of the slender Pipe above-mention'd, but ha∣ving drawn out the Air, after the accustomed manner, we found not as before, the bubble to out-weigh the opposite Lead: so

that by the help of our Engine we can weigh the Air, as we weigh other Bodies, in its natural or ordinary consistence, with∣out at all condensing it: Nay, which is remarkable, having con∣vey'd a Lambs bladder about half full of Air into the Receiver, we observed, that though upon the drawing out of the ambient Air, the imprisoned Air so expanded it self, as to distend the Bladder so, as to seem ready to Break it; yet this rarefied Air did manifestly depress the Scale whereunto it was annexed.

Another thing we must not forget to mention, that happened to us, whilst we were making tryals concerning the weight of the Air; namely, that having once caus'd the Pump to be some∣what obstinately ply'd, to discover the better what may be ex∣pected from the thinness of the medium in this Experiment; the Imprison'd Air broke its brittle Prison, and throwing the greatest part of it against the side of the Receiver, dash'd it against that thick Glass into a multitude of pieces. Which accident I men∣tion, partly that it may confirm what we deliver'd in our Re∣flexions, upon the first Experiment, where we considered what would probably be done by the spring of the Air Imprison'd in such Glasses, in case the ballancing pressure of the ambient Air were withdrawn; and partly, that we may thence discern of how close a Texture Glass is, since so very thin a film of Glass (if I may so call it) prov'd so impervious to the Air, that it could not get away through the Pores, but was forc'd to break the Glass in pieces to free it self; and this, notwithstanding the time and advantage it had to try to get out at the Pores. And this I mention, that neither our Experiments, nor those of divers Learn∣ed Men, might receive any prejudice from an Experiment which I happen'd to make divers years ago, and which, having been so much taken notice of by curious Men, may be drawn to coun∣tenance their erroneous Opinion, who would fain perswade us, That Glass is penetrable by Air properly so called. Our Experi∣ment was briefly this: We were distilling a certain Substance, that much abounded with subtle Spirits and volatile Salt, in a strong Earthen vessel of an unusual shape, to which was luted a large Receiver, made of the course sort of Glass (which the

Trades-men are wont to call green Glass) but in our absence, the Fire, though it were to be very strong, was, by the negligence or mistake of those we appointed to attend it, so excessively in∣creas'd, that when we came back to the Fornace, we found the spirituous and saline Corpuscles pour'd out (if I may so call it) so hot, and so copiously into the Receiver, that they made it all opacous, and more likely to flie in pieces, than fit to be touch'd. Yet, being curious to observe the effects of a Distillation, prose∣cuted with so intense and unusual a degree of heat, we ventur'd to come near, and observ'd, among other things, that on the out∣side of the Receiver, at a great distance from the juncture, there was setled a round whitish Spot or two, which at first we thought might be some stain upon the Glass; but after, finding it to be in divers Qualities like the Oyl and Salt of the Concrete we were Distilling, we began to suspect that the most subtle and fugitive parts of the impetuously ascending Steams, had pe¦netrated the substance (as they speak) of the Glass, and by the cold of the ambient Air were condensed on the surface of it. And though we were very backward to credit this suspition, and therefore call'd in an Ingenious Person or two, both to assist us in the Observation, and have Witness of its event, we continu∣ed a while longer to watch the escape of such unctuous Fumes; and upon the whole matter unanimously concluded that (all things consider'd) the subtle parts of the distill'd matter being violently agitated, by the excessive heat that pass'd through the Pores of the Glass, widn'd by the same heat. But this having never happen'd but once in any of the Distillations we have either made or seen, though these be not a few, it is much more reasonable to suppose, that the perviousness of our Receiver to a Body much more subtle than Air, proceeded partly from the looser Texture of that particular parcel of Glass the Receiver was made of (for Experience hath taught us, that all Glass is not of the same compactness and solidity) and partly from the enor∣mous heat, which, together with the vehement agitation of the penetrant Spirits, open'd the Pores of the Glass; than to imagine that such a substance as Air, should be able to permeate the Body

of Glass contrary to the testimony of a thousand Chymical and Mechanical Experiments, and of many of those made in our Engine, especially that newly recited: Nay, by our fifth Ex∣periment it appears that a thin Bladder will not at its Pores give passage even to rarefied Air. And on this occasion we will an∣nex an Experiment, which hath made some of those we have acquainted with it, doubt, whether the Corpuscles of the Air be not less subtle than those of Water.

But without examining here the reasonableness of that doubt, we will proceed to recite the Experiment it self, which seems to teach, That though Air, when sufficiently compressed, may perchance get entrance into narrower holes and crannies than Water; yet unless the Air be forc'd in at such very little holes, it will not get in at them, though they may be big enough to let Water pass through them.

The Experiment then was this: I took a fair Glass Siphon, the lower end of whose longest Leg was drawn by degrees to such a slenderness, that the Orifice, at which the Water was to fall out, would hardly admit a very small Pin: This Siphon be∣ing inverted, the matter was so order'd, that a little Bubble of Air was intercepted in the slenderest part of the Siphon, betwixt the little hole newly mention'd, and the incumbent Water, upon which it came to pass, that the Air being not to be forc'd through so narrow a passage, by so light a Cylinder of Water, (though amounting to the length of divers Inches,) as lean'd upon it, hindered the farther efflux of the Water, as long as I pleased to let it stay in that narrow place: whereas, when by blowing a little at the wider end of the Siphon, that little parcel of Air was forced out with some Water, the remaining Water, that before continu'd suspended, began freely to drop down again as former∣ly. And if you take a Glass Pipe, whether it be in the form of a Siphon, or no, that being for the most part of the thickness of a Mans Finger, is yet towards one end so slender, as to termi∣nate in a hole almost as small as a Horse-hair; and if you fill this Pipe with Water, you will find that Liquor to drop down free∣ly enough thorow the slender Extream: But if you then invert

the Pipe, you will find that the Air will not easily get in at the same hole through which the Water passed. For in the sharp end of the Pipe, some Inches of water will remain suspended, which, 'tis probable, would not happen, if the Air could get in to succeed it, since if the hole were a little wider, the Water would immediately subside. And though it be true, that if the Pipe be of the length of many Inches, a great part of the Water will run down at the wider Orifice: yet that seems to happen for some other reason, than because the Air succeeds it at the upper and narrow Orifice, since all the slender part of the Pipe, and perhaps some Inches more, will continue full of Water.

And on this occasion I remember, that whereas it appears by our fifth Experiment, That the Aërial Corpuscles (except per∣haps some that are extraordinarily fine) will not pass thorow the Pores of a Lambs Bladder, yet Particles of Water will, as we have long since observ'd, and as may be easily try'd, by very closely tying a little Alcalizate Salt (we us'd the Calx of Tartar made with Nitre) in a fine Bladder, and dipping the lower end of the Bladder in Water; for if you hold it there for a compe∣tent while, you will find that there will strain thorow the Pores of the Bladder, Water enough to dissolve the Salt into a Liquor.

But I see I am slip'd into a Digression, wherefore I will not examine, whether, the Experiment I have related, proceeded from hence, That the springy Texture of the Corpuscles of the Air, makes them less apt to yield and accommodate themselves easily to the narrow Pores of Bodies, than the more flexible Particles of Water; or whether it may more probably be ascrib'd to some other Cause. Nor will I stay to consider how far we may hence be assisted to ghess at the cause of the ascension of Water in the slender Pipes, and Siphons formerly mention'd, but will return to our Bubble; and take notice, That we thought fit also to endeavor to measure the capacity of the Bubble we had made use of, by filling it with Water, that we might the better know how much Water answer'd in weight to ¾ of a Grain of Air, but notwithstanding all the diligence that was used to preserve so brittle a Vessel, it broke before we could perfect

that we were about, and we were not then provided of another Bubble fit for our turn.

The haste I was in, My Lord, when I sent away the last Sheet, made me forget to take notice to you of a Problem that occurr'd to my thoughts, upon the occasion of the slow breaking of the Glass Bubble in our evacuated Receiver. For it may seem strange, since by our sixth Experiment it appears, that the Air, when permitted, will by its own internal Spring expand it self twice as much as Mersennus was able to expand it, by the heat even of a candent AEolipile: Yet the Elater of the Air was scarce able to break a very thin Glass Bubble, and utterly unable to break one somewhat thicker, within whose cavity it was impri∣son'd; whereas Air pen'd up and agitated by heat is able to per∣form so much more considerable effects, that (not to mention those of Rarefaction that are more obvious) the Learned Jesuit Cabaeus (he that writ of the Load-stone) relates, That he saw a Marble Pillar (so vast, that three men to∣gether * 1.9 with display'd arms could not imbrace it, and that 1000 Yoke of Oxen drawing it several ways with all their strength, could not have torn it assunder) quite broken off in the midst, by reason of some Wood, which happening to be burnt just by the Pillar the heat proceeding from the neigh∣bouring Fir, so rarefied some Air or Spirituous Matter which was shut up in the cavities of the Marble, that it broke through the solid Body of the Stone to obtain room to expand it self.

I remember I have taken notice that probably the reason why the included Air did not break the hermetically seal'd Bubbles that remain'd intire in our emptyed Receiver, was, That the Air, being somewhat rarefied by the flame imploy'd to close the Glass, its Spring, upon the recess of the heat, grew weaker than before. But though we reject not that ghess, yet it will not in the present case serve the turn, because that much smaller Glass bubbles exactly clos'd, will, by the included Air (though agitated by the heat of a very moderate Fire) be made to fly in pieces. Whether we may be assisted to salve this Problem, by consider∣ing that the heat doth from within vehemently agitate the Cor∣puscles

of the Air, and add its assistance to the Spring they had before, I shall not now examine: since I here but propose a Pro∣blem, and that chiefly that by this memorable Story of Cabae∣us, notice may be taken of the prodigious power of Rarefaction, which hereby appears capable of performing stranger things than any of our Experiments have hitherto ascrib'd to it.

We should hence, My Lord, immediately proceed to the next Experiment, but that we think it fit, on this occasion, to ac∣quaint You with what some former tryals (though not made in our Engine) have taught us, concerning what we would have discover'd by the newly mention'd Bubble that broke. And this the rather, because (a great part of this Letter supposing the gravity of the Air) it will not be impertinent to determine more particularly than hitherto we have done, what gravity we ascribe to it.

We took then an AEolipile made of Copper, weighing six ounces, five drachms, and eight and forty grains: this being made as hot as we durst make it, (for fear of melting the mettle, or at least the Sodar) was removed from the fire and immediately stopped with hard Wax that no Air at all might get in at the lit∣tle hole, wont to be left in AEolipiles for the fumes to issue out at: Then the AEolipile being suffer'd leasurely to cool, was again weighed together with the Wax that stopt it, and was found to weigh (by reason of the additional weight of the Wax) six oun∣ces, six drachms, and 39 grains. Lastly, the Wax being per∣forated without taking any of it out of the Scale, the external Air was suffered to rush in (which it did with some noise) and then the AEolipile and Wax, being again weighed amounted to six ounces, six drachms, and 50 grains. So that the AEoli∣pile freed as far as our fire could free it, from its Air, weighed less than it self when replenished with Air, full eleven grains. That is, the Air containable within the cavity of the AEolipile amoun∣ted to eleven grains and somewhat more; I say somewhat more, because of the particles of Air, that were not driven by the fire out of the AEolipile. And by the Way (if there be no mistake in the observations of the diligent Mersennus) it may seem strange

that it should so much differ from 2 or 3 of ours; in none of which we could rarefie the Air in our AEolipile (though made red hot almost all over, and so immediately plung'd into cold Wa∣ter) to half that degree which he mentions, namely to 70 times its natural extent, unless it were that the AEolipile he imploy'd was able to sustain a more vehement heat than ours (which yet we kept in so great an one, that once the Soder melting, it fell asunder into the two Hemispheres it consists of.)

The fore-mentioned way of weighing the Air by the help of an AEolipile, seems somewhat more exact than that which Mer∣sennus used, In that in ours the AEolipile was not weighed, till it was cold; whereas in his, being weighed red hot, it is subject to lose of its substance in the cooling, for (as we have else∣where noted on another occasion) Copper heated red hot, is wont in the cooling to throw off little thin seales in such plenty, that having purposely watched a Copper AEolipile during its refrige∣ration, we have seen the place round about it almost covered with those little scales it had every way scatter'd: which, how∣ever they amount not to much, ought not to be over-looked, when 'tis so light a Body as Air, that is to be weighed. We will not examine whether, the AEolipile in cooling may not receive some little increment of weight, either from the vapid or saline Steams that wander up and down in the Air: But we will rather mention, that (for the greater exactness) we imployed to weigh our AElipile, both when fill'd only with Air and when re∣plenish'd with Water, a pair of Scales that would turn (as they speak) with the fourth part of a grain.

As to the proportion of weight betwixt Air and Water, some learned men have attempted it by ways so unaccurate that they seem to have much mistaken it. For (not to mention the im∣probable accounts of Kepler and others.) The learned and dili∣gent Ricciolus, having purposely endeavoured to investigate this proportion by means of a thin bladder, estimates the weight of the Air to that of the Water to be as one to ten thousand, or there abouts. And indeed I remember that having formerly, on a certain occasion, weighed a large bladder full of Air, and found

it when the Air was all squeesed out, to have contained fourteen grains of Air. I found the same bladder afterwards fill'd with Water to contain very near 14 pound of that liquor: according to which account, the proportion of Air to Water was almost as a grain to a pound, that is, as one, to above 7600. To this we may add, that on the other side, Galileo himself using ano∣ther, (but an unaccurate way too,) defined the Air to be in weight to Water, but as one to 4 hundred. But the way formerly propo∣sed of weighing the Air by an AEolipile, seems by great odds more exact; and (as far as we could ghess) seemed to agree well enough with the Experiment made in our Receiver. Wherefore it will be best to trust our AEolipile in the enquiry we are about. And according to our observations the water it contained amoun∣ting to one and twenty ounces and an half, and as much Air as was requisite to fill it weighing eleven grains, the proportion in gravity of Air to Water of the same bulk will be as one to 938. And though we could not fill the AEolipile with water, so exactly as we would, yet in regard we could not neither as perfectly as we would, drive the Air out of it by heat, we think the propor∣tion may well enough hold: but those that are delighted with round numbers (as the phrase is) will not be much mistaken if they reckon Water to be near a thousand times heavier than Air. And (for farther proof that we have made the proportion be∣twixt these two Bodies rather greater than lesser than indeed it is: and also to confirm our former observation of the weight of the Air) we will add, That, having another time put some Wa∣ter into the AEolipile before we set it on the fire, that the copi∣ous vapours of the rarefied liquor might the better drive out the Air, we found, upon tryal carefully made, that when the AEo∣lipile was refrigerated, and the included vapours were by the cold turned again into Water (which could not have happen'd to the Air, that the preceding Steams expelled) the Air, when it was let in, increas'd the weight of the AEolipile as much as before, namely, Eleven Grains; though there were already in it twelve Drachms and a half, besides a couple of Grains of Water, which remained of that we had formerly put into it to drive out the Air.

Mersennus indeed tells us, that by his account Air is in weight to Water, as 1 to 1356. And adds, that we may, without any danger, believe that the gravity of Water to that of Air of a like bulk, is not less than of 1300 to 1. And consequently that the quantity of Air to a quantity of Water equiponderant thereto, is as 1300 to 1. But why we should relinquish our own carefully repeated tryals, I see not. Yet I am unwilling to reject those of so accurate and usefull a Writer: And therefore shall propose a way of reconciling our differing Observations, by presenting, that the discrepance between them may probably a∣rise from the differing consistence of the Air at London and at Pa∣ris: For our Air being more cold and moist, than that which Your Lordship now breaths, may be suppos'd also to be a fourth or fifth part more heavy. I leave it to be consider'd, whether it be of any moment that our Observations were made in the midst of Winter, whereas his were perhaps made in some warmer time of the Year. But I think it were not amiss, that, by the method formerly propos'd, the gravity of the Air were observ'd both in several Countries, and in the same Country, in the several Sea∣sons of the Year and differing Temperatures of the Weather. And I would give something of value to know the weight of such an AEolipile as ours full of Air, in the midst of Winter in Nova Zembla, if that be true which we formerly ••ook notice of, namely, That the Hollanders, who Wintered there, found that Air so thick that their Clock would not go.

If Your Lordship should now ask me, if I could not by the help of these, and our other Observations, decide the Contro∣versies of our Modern Mathematicians about the height of the Air or Atmosphere, by determining how high it doth indeed reach: I should answer, That though it seems easie enough to shew that divers Famous and Applauded Writers have been mi∣staken in assigning the height of the Atmosphere: Yet it seems very difficult precisely to define of what height it is. And be∣cause we have hitherto but lightly touch'd upon a matter of such importance, we presume it will not be thought imperti∣nent, upon this occasion, to annex something towards the Elu∣cidation of it.

What we have already try'd and newly set down, allows us to take it for granted, that (at least about London) the proportion of gravity betwixt Water and Air, of equal bulk, is as of a thou∣sand to one.

The next thing therefore that we are to enquire after, in order to our present design, is the difference in weight betwixt Water and Quick-silver: And though this hath been defin'd already by the Illustrious Verulam, and some other inquisitive Persons, that have compared the weight of several Bodies, and cast their Ob∣servations into Tables, yet we shall not scruple to annex our own tryals about it: Partly, because we find Authors considerably to disagree; partly, because we used exacter Scales, and a some∣what more wary method than others seem to have done: And partly also, because having prosecuted our inquiry by two or three several ways; the small difference between the events may assure us that we were not much mistaken.

We took then a Glass Pipe, of the form of an inverted Siphon, whose shape is delineated in the sixteenth Figure: And pouring into it a quantity of Quick-silver, we held it so, that the super∣ficies of the Liquor, both in the longer and shorter leg, lay in a Horizontal Line, denoted in the Scheme by the prick'd Line E F; then pouring Water into the longer Leg of the Siphon, till that was almost fill'd, we observ'd the surface of the Quick-silver in that Leg to be, by the weight of the Water, depressed, as from E to B; and in the shorter Leg, to be as much impell'd up∣wards as from F to C: Whereupon having formerly stuck marks, as well at the point B, as at the opposite point D, we measur'd both the distance D C to have the height of the Cylinder of Quick-silver, which was raised above the point D (level with the surface of the Quick-silver in the other Leg) by the weight of the Water, and the distance B A which gave us the height of the Cylinder of Water. So that the distance D C amounting to 2 13\54 Inches, and the height of the Water amounting 30 45\54 In∣ches; and the whole numbers on both sides, which the annexed Fractions being reduc'd to improper Fractions of the same deno∣mination, the proportion, appear'd to be (the denominators

being left out as equal on both sides) as 121 to 1665; or by re∣duction, as one to 92/121.

Besides this unusual way of determining the gravity of some things, we measur'd the proportion betwixt Quick-silver and Water, by the help of so exact a ballance, as looseth its AEqui∣librium by the hundredth part of a Grain. But because there is wont to be committed an oversight in weighing Quick-silver and Water, especially if the Orifice of the Vessel wherein they are put be any thing wide, in regard that men heed not that the surface of Water in Vessels will be concave, but that of Quick-silver notably convex or protuberant: To avoid this usual oversight (I say) we made use of a Glass bubble, blown very thin at the Flame of a Lamp, that it might not be too heavy for the Ballance, and terminating in a very slender neck wherein the concavity or con∣vexity of a Liquor could not be considerable: This Glass weigh∣ing 23½ Grains, we fill'd almost with Quick-silver, and fastning a mark over against the middle of the protuberant Superficies as near as our Eyes could judge, we found that the Quick-silver a∣lone weighed 299 7/12 Grains; Then the Quick-silver being pour'd out, and the same Glass being fill'd as full of common Water, we found the Liquor to weigh 21⅞ Grains. Whereby it appear'd the weight of Water to Quick-silver, is as one to 13 19/28: Though our Illustrious Verulam (questionless not for want of Judgment or Care, but of exact Instruments) Makes the proportion betwixt those two Liquors to be greater than of 1 to 17. And to add, that upon the bye, since Quick-silver and well rectified Spirit of Wine, are (how justly I say not) accounted, the one the heaviest, and the other the lightest of Liquors; we thought to fill the same Glass, and with the same Scales to observe the difference betwixt them, which we found to be as of 1 to 16 641/1084; whereby it ap∣pear'd, That the difference betwixt Spirit of Wine, that may be made to burn all away, (such as was ours) and common Wa∣ter, is as betwixt 1 and 1 44/171.

We might here take occasion to admire, that though Water (as appear'd by the Experiment formerly mention'd of the Pewter Vessel) seems not capable of any considerable condensation,

and seems not to have interspersed in it any store of Air; yet Quick-silver, of no greater bulk than Water, should weigh near fourteen times as much. But having only pointed at this as a thing worthy of consideration, we will proceed in our inquiry af∣ter the height of the Atmosphere: And to avoid the trouble of Fractions, we will assume, that Quick-silver is fourteen times as heavy as Water, since it wants so little of being so.

Wherefore, having now given us the proportion of Air to Water, and Water to Quick-silver, it will be very easie to find the proportion betwixt Air and Quick-silver, in case we will suppose the Atmosphere to be uniformly of such a consistence as the Air we weighed here below. For since our Engine hath sufficiently manifested that 'tis the AEquilibrium with the exter∣nal Air, that in the Torricellian Experiment keeps the Quick-silver from subsiding; And since, by our accurate Experiment formerly mention'd, it appears that a Cylinder of Mercury, able to ballance a Cylinder of the whole Atmosphere, amoun∣ted to near about thirty Inches; and since, consequently we may assume the proportion of Quick-silver to Air to be as four∣teen thousand to one; it will follow, that a Cylinder of Air, capable to maintain an AEquilibrium, with a Mercurial Cylin∣der of two Foot and an half in height, must amount to 35000 Feet of our English measure; and consequently (reckoning five Foot to a Geometrical Pace, and one thousand such Paces to a Mile) to seven full Miles.

But this (as we lately intimated) proceeds upon the supposi∣tion, that the Air is every where of the same consistence that we found it near the surface of the Earth; but that cannot with any safety be concluded, not only for the reason I find to have been taken notice of by the Ancients, and thus exprest in Seneca. Omnis Aër (says he) quo propior est terris hoc cras∣sior; quemadmodum in aqua & in omni humore faex * 1.10 ima est, ita in Aëre spississima-quae{que} desidunt, but much more, because the springy Texture of the Aerial Corpuscles; makes them capable of a very great compression, which the weight of the incumbent part of the Atmosphere is very suffi∣cient

to give those that be undermost and near the surface of the Earth. And if we recall to mind those former Experiments, whereby we have manifested, That Air, much rarefied with∣out heat, may easily admit a farther rarefaction from heat, and that the Air, even without being expanded by heat, is capable of being rarefied to above one hundred and fifty times the ex∣tent it usually possesseth here below; How can it be demonstra∣ted that the Atmosphere may not, for ought we know, or at least for ought can be determin'd by our Statical and Mechanical Experiments, rise to the height of Five and twenty German Leagues, if not of some hundred of common Miles?

And this conjecture it self may appear very injurious to the height whereunto Exhalations may ascend, if we will allow that there was no mistake in that strange Observation made at Tolouse in a clear Night in August, by the diligent Mathematician Ema∣muel Magnan, and thus Recorded by Ricciolus, for I have not at hand the Author's own Book: Vidit (says he) ab hora undecima post meridiem * 1.11 usque ad mediam noctem Lunâ infra hori∣zontem positâ, nubeculam quandam lucidam prope Meridianum fere usque ad Zenith diffusam quae consideratis omnibus non poterat nisi à sole illuminari; ideoque altior esse de∣buit tota umbra terrae. Addit (continues Ricciolus) simile quid evenisse Michaeli Angelo Riccio apud Sabinos versanti nempe viro in Mathesi eruditissimo.

Various Observations made at the feet, tops, and interjacent parts of high Mountains, might perchance somewhat assist us to make an estimate in what proportion, if in any certain one, the higher Air is thicker than the lower, and ghess at the difform con∣sistence, as to laxity and compactness of the Air at several distan∣ces from us. And if the difficulties about the refractions of the Celestial Lights, were satisfactorily determin'd, that might also much conduce to the placing due limits to the Atmosphere (whose, Dimensions those Observations about Refractions seem hitherto much to contract.) But for the present we dare not pronounce any thing peremptorily concerning the height of it,

but leave it to farther inquiry: contenting our selves to have manifested the mistake of divers eminent Modern Writers, who will not allow the Atmosphere to exceed above two or three Miles in height (as the Famous Kepler will not the Aër refractivus) and to have rendred a reason why in the mention we made in the Notes upon the first Experiment touching the height of the Atmosphere, we scrupled not to speak of it, as if it might be many Miles high.

EXPERIMENT XXXVII.

WE will now proceed to recite a Phaenomenon, which, though made amongst the first, we thought fit not to mention till after many others, that we might have the opportunity to observe as many Circumstances of it as we could, and so present Your Lordship at once, most of what we at several times have taken notice of concerning so odd a Phaenomenon.

Our Engine had not been long finish'd, when, at the first lei∣sure we could steal from our occasions to make trial of it, we caused the Air to be pump'd out of the Receiver; and whilst I was busied in entertaining a Learned Friend that just then came to visit me, an Ingenious By-stander, thought he perceiv'd some new kind of Light in the Receiver, of which giving me hasti∣ly notice, my Friend and I presently observ'd, that when the Sucker was drawn down, immediately upon the turning of the Key, there appear'd a kind of Light in the Receiver, almost like a faint flash of Lightning in the Day-time, and almost as sud∣denly did it appear and vanish. Having, not without some amaze∣ment, observ'd divers of these apparitions of Light, we took notice that the Day was clear, the hour about ten in the Morning, that the only Window in the Room faced the North; and also, that by interposing a Cloak, or any opacous Body between the Recei∣ver and the Window, though the rest of the Room were suffi∣ciently enlightned, yet the flashes did not appear as before, un∣less the opacous Body were removed. But not being able on all these Circumstances to ground any firm Conjecture at the cause of this surprising Phaenomenon, as soon as Night

was come, we made the Room very dark; and plying the Pump, as in the Morning, we could not, though we often try'd, find, upon the turning of the Key, so much as the least glimmering of Light; whence we inferred, that the flash appearing in the Receiver, did not proceed from any new Light generated there, but from some reflexions of the light of the Sun, or other Lu∣minous Bodies plac'd without it; though whence the Reflexion should proceed, it pos'd us to conjecture.

Wherefore the next Morning, hoping to inform our selves better, we went about to repeat the Experiment, but though we could as well as formerly exhaust the Receiver, though the place wherein we made the trial was the very same; and though other Circumstances were resembling, yet we could not discover the least appearance of Light all that Day, nor on divers others on which trial was again fruitlesly made; nor can we to this very time be sure a Day before-hand that these Fla∣shes will be to be seen in our great Receiver. Nay, having once found the Engine in a good humour (if I may so speak) to shew this trick, and sent notice of it to our Learned Friend Dr. Wallis, who express'd a great desire to see this Phaenomenon, though he were not then above a Bow-shoot off, and made haste to fatisfie his Curiosity; yet by that time he was come, the thing he came for was no longer to be seen; so that having vainly endeavour∣ed to exhibit again the Phaenomenon in his prefence, I began to apprehend what he might think of me, when unexpectedly the Engine presented us a flash, and after that a second, and as ma∣ny more, as suffic'd to satisfie him that we might very well con∣fidently relate, that we have our selves seen this Phaenomenon, though not confidently promise to shew it others.

And this unsuccessfulness whereto our Experiment is liable, being such, that by all our watchfulness and trials, we could ne∣ver reduce it to any certain Rules or Observations; since in all constitutions of the Weather, times of the Day, &c. It will sometimes answer, and sometimes disappoint our expectations; We are much discourag'd from venturing to frame an Hypothe∣sis to give an account of it: which if the Experiment did con∣stantly

succeed, might the more hopefully be attempted; by the help of the following Phaenomena laid together: some of them produc'd upon trials purposely made to examine the validity of the conjectures, other trials had suggested.

First then we observ'd, that the Apparition of Light may be made as well by Candle-light, as by Day-light; and in what∣ever position the Candle be held, in reference to the Receiver, as on this or that hand of it, above it, beneath it, or any other way, provided the beams of Light be not hinder'd from falling upon the Vessel.

Next, we noted that the flash appears immediately upon the turning of the Key, to let the Air out of the Receiver into the emptied Cylinder, in so much that I remember not that when at any time in our great Receiver, the Stop-cock was open'd be∣fore the Cylinder was exhausted (whereby it came to pass that the Air did rather descend, than rush into the Cylinder) the of∣ten mentioned flash appear'd to our eyes.

Yet, we farther observ'd, that when instead of the great Re∣ceiver we made use of a small Glass, not containing above a pound and a half of Water, the Phaenomenon might be exhibit∣ed though the Stop-cock were open, provided the Sucker were drawn nimbly down.

We noted too, that when we began to empty the Receiver, the appearances of Light were much more conspicuous than to∣wards the latter end, when little Air at a time could pass out of the Receiver.

We observed also, that when the Sucker had not been long before well Oyl'd, and instead of the great Receiver, the smaller Vessel above-mention'd was emptied; We observ'd, I say, that then, upon the opening of the Stop-cock, as the Air descended out of the Glass into the emptied Cylinder, so at the same time there ascended out of the Cylinder into the Vessel a certain steam, which seem'd to consist of very little Bubbles, or other minute Corpuscles thrown up from the Oyl, rarefied by the attrition it suffered in the Cylinder. For at the same time that these Steams ascended into the Glass, some of the same kind manifest∣ly

issued out like a little Pillar of Smoke at the Orifice of the Valve, when that was occasionally opened. And these Steams frequently enough presenting themselves to our view, we found, by exposing the Glass to a clear Light, that they were wont to play up and down in it, and so by their whitishness, to emulate in some measure the apparition of Light.

For we likewise sometimes found, by watchfull observation, that when the Flash was great, not only at the very instant the Receiver lost of its transparency, by appearing full of some kind of whitish substance; but that for some short time after the sides of the Glass continued somewhat opacous, and seem'd to be darken'd, as if some whitish Steam adher'd to the inside of them.

He that would render a Reason of the Phaenomenon, whereof all these are not all the Circumstances, must do two things; whereof the one is difficult, and the other little less than im∣possible: For he must give an account not only whence the ap∣pearing whiteness proceeds, but wherefore that whiteness doth sometimes appear, and sometimes not.

For our part, we freely confess our selves at a loss about ren∣dering a Reason of the less difficult part of the Problem: And though Your Lordship should ev'n press us to declare what Con∣jecture it was, that the above recited Circumstances suggested to us, we should propose the thoughts we then had, no other∣wise than as bare Conjectures.

In case then our Phaenomenon had constantly and uniformly appear'd, we should have suspected it to have been produc'd af∣ter some such manner as follows.

First, we observ'd that, thought that which we saw in our Re∣ceiver seem'd to be some kind of Light, yet it was indeed but a whiteness which did (as hath already been noted) opacate (as some speak) the inside of the Glass.

Next we consider'd, that our common Air abounds with Par∣ticles, or little Bodies, capable to reflect the beams of Light. Of this we might easily give divers proofs, but we shall name but two: The one, that vulgar observation of the Motes that appear

in multitudes swimming up and down in the Air, when the Sun∣beams shooting into a Room, or any other shady place, discover them, though otherwise the Eye cannot distinguish them from the rest of the Air: The other proof we will take from what we (and no doubt very many others) have observ'd, touching the Illumination of the Air in the Night. And we particularly re∣member, that, being at some distance from London one Night, that the People, upon a very welcome occasion, testified their Joy by numerous Bon-fires; though, by reason of the Interposi∣tion of the Houses, we could not see the Fires themselves, yet we could plainly see the Air all enlighten'd over and near the City; which argu'd, that the lucid Beams shot upwards from the fires, met in the Air with Corpuscles opacous enough to reflect them to our Eyes.

A third thing that we considered, was, That white may be produc'd (without excluding otherways, or denying invisible Pores in the solidest Bodies) when the continuity of a Diaphanous Body happens to be interrupted by a great number of surfaces, which, like so many little Looking-glasses, do confusedly repre∣sent a multitude of little and seemingly contiguous Images of the lucid Body. We shall not insist on the explanation of this, but refer You for it to what we have said in another Paper (touch∣ing Colours.) But the Instances that seem to prove it are obvi∣ous: For Water or whites of Eggs beaten to froth, do lose their transparency and appear white. And having out of one of our lessers Receivers carefully drawn out the Air, and so order'd it, that the hole by which the Water was to get in, was exceeding small, that the Liquor might be the more broken in its passage thorow it, we observ'd with pleasure, That, the Neck being held under Water, and the little hole newly mention'd being open'd, the Water that rushed in was so broken, and acquired such a multitude of new Surfaces, that the Receiver seem'd to be full rather of Milk than Water. We have likewise found out, That by heating a lump of Crystal to a certain degree, and quenching it in fair Water, it would be discontinu'd by such a multitude of Cracks, (which created new Surfaces within it) that

though it would not fall asunder, but retain its former shape, yet it would lose its transparency, and appear white.

Upon these Considerations, My Lord, and some others, it seem'd not absur'd to imagine, That upon the rushing of the Air out of the Receiver into the empty'd Cylinder, the Air in the Receiver being suddenly and vehemently expanded, the Tex∣ture of it was as suddenly alter'd, and the parts made so to shift places (and perhaps some of them to change postures) as during their new and vehement motion and their varied situation, to di∣sturb the wonted continuity, and so the Diaphaneity of the Air; which (as we have already noted) upon its ceasing to be a tran∣sparent Body, without the interposition of colour'd things, must easily degenerate into white.

Several things there were that made this Conjecture seem the less improbable. As first, That the whiteness always appear'd greater when the exsuction began to be made, whilst there was store of Air in the Receiver, than when the Air was in great part drawn out. And next, That, having exhausted the Receiver, and apply'd to the hole in the Stop-cock a large bubble of clear Glass, in such a manner, that we could at pleasure let the Air pass out at the small Glass into the great one, and easily fill the small one with Air again, We observ'd with pleasure, That, upon the opening the passage betwixt the two Glasses, the Air in the smal∣ler having so much room in the greater to receive it, the Dissili∣tion of that Air was so great, that the small Viol seem'd to be full of Milk; and this Experiment we repeated several times. To which we may add, That, having provided a small Recei∣ver, whose upper Orifice was so narrow that I could stop it with my Thumb, I observ'd, that when, upon the exsuction of the Air, the capacity of the Glass appear'd white, if, by a sudden re∣moval of my Thumb, I let in the outward Air, that whiteness would immediately vanish. And whereas it may be objected, That in the Instance formerly mention'd, Water turning from perspicuous to white, there intervenes the Air, which is a Body of a Heterogeneous nature, and must turn it into Bubbles to make it lose its transparency. We may borrow an Answer from an

Experiment we deliver in another Treatise, where we teach, how to make two very volatile Liquors, which being gently put together, are clear as Rock-water, and yet will almost in a moment, without the sub-ingression of Air to turn them into Bubbles, so alter the disposition of their insensible parts, as to become a white and consistent Body. And this happens not as in the precipitation of Benjamin, and some other Resinous Bodies, which being dissolv'd in spirit of Wine, may, by the effusion of fair Water, be turn'd into a seemingly Milky substance. For this whiteness belongs not to the whole Liquor, but to the Corpuscles of the dissolv'd Gum, which after a while subsiding leave the Liquor transparent, themselves only remain∣ing white: Whereas in our case, 'tis from the vary'd texture of the whole formerly transparent fluid Body, and not from this or that part, that this whiteness results: For the Body is white throughout, and will long continue so; and yet may, in process of time, without any addition, be totally reduc'd into a tran∣sparent Body as before.

But besides the Conjecture insisted on all this while, we ground∣ed another upon the following Observation, which was, That ha∣ving convey'd some smoke into our Receiver plac'd against a Window, we observ'd, that upon the exsuction of the Air, the Corpuscles that were swimming in it, did manifestly enough make the Receiver seem more opacous at the very moment of the rushing out of the Air: For considering that the whiteness, whose cause we enquire of, did but sometimes appear, it seem'd not impossible but that at such times the Air in the Receiver might abound with Particles, capable of reflecting the Light in the manner requisite to exhibite a white colour, by their being put into a certain unusual Motion. As may be in some mea∣sure illustrated by this, That the new motion of the freshly men∣tion'd Fumes, made the inside of the Receiver appear somewhat darker than before: And partly by the nature of our formerly mention'd smoking Liquor, whose parts, though they seem'd tran∣sparent whilst they compos'd a Liquor, yet when the same Cor∣puscles, upon the unstopping of the Glass, were put into a new

motion, and dispos'd after a new manner, they did opacate that part of the Air they mov'd in, and exhibited a greater white∣ness than that which sometimes appears in our Pneumatical Ves∣sel. Nor should we content our selves with this single Instance, to manifest, That little Bodies, which being rang'd after one manner, are Diaphanous and Colour-less, may, by being bare∣ly agitated, dispers'd, and consequently otherways rang'd, ex∣hibit a colour, if we were not unwilling to rob our Collec∣tion of Experiments concerning Colours.

But, My Lord, I foresee You may make some Objections against our proposed ghess, which perhaps I shall scarce be able to answer, especially, if You insist upon having me render a Reason why our Phaenomenon appears not constantly.

I might indeed answer, that probably it would do so, if in∣stead of our great Receiver we use such a small Viol as we have lately mention'd, wherein the Dissilition of the Air being much greater, is like to be the more conspicuous: Since I remember not that we ever made our trial with such small Vessels, without finding the expected whiteness to appear. But it would remain to be explicated, why in our great Receiver the Phaenomenon should sometimes be seen, and oftentimes not appear. And though that Conjecture which we last made should not be re∣jected, yet if we were farther press'd to assign a reason why the Air should abound with such Particles, as we there suppose, more at one time than another, we are not yet provided of any better Answer, than this general one, That the Air about us, (and much more that within the Receiver,) may be much al∣ter'd by such causes as few are aware of: For, not to repeat those probable Arguments of this Assertion which we have oc∣casionally mention'd here and there in the former part of this Epistle, we will here set down two or three Instances to verifie the same Proposition. First, I find that the Learned Josephus Acosta, among other Judicious Observations he made in Ame∣rica, hath this concerning the effects of some * 1.12 Winds: There are (saith he) Winds which naturally trouble the Water of the Sea, and

make it green, and black; others, clear as Crystal. Next, we have observ'd, That though we convey'd into the Receiver our Scales, and the Pendula formerly mention'd, clean and bright; yet aster the Receiver had been empty'd, and the Air let in again, the gloss or lustre both of the one, and of the other, ap∣pear'd tarnish'd by a beginning rust. And in the last place, we will subjoyn an Observation we made some Years ago, which hath been heard of by divers Ingenious Men, and seen by some of them: We had, with pure Spirit of Wine, drawn a Tincture out of a certain Concrete which useth to be reckon'd among Mineral Bodies; And this Tincture being very pure and tran∣sparent, we did, because we put a great value upon it, put into a Crystal Viol which we carefully stopp'd, and lock'd up in a Press among some other things that we specially priz'd. This Li∣quor being a Chymical Rarity, and besides very defecate, and of a pleasing Golden colour; we had often occasion to look upon it, and so to take notice, that one time it seem'd to be very much troubled, and not clear as it was wont to be: Whereupon we imagined, that though it would be something strange, yet it was not impossible, that some Precipitation of the Mineral Corpus∣cles was then happening, and that thence the Liquor was opaca∣ted. But, finding after some days that though the expected Pre∣cipitation had not been made, yet the Liquor, retaining its for∣mer vivid Colour, was grown clear again as before; we some∣what wondered at it, and locking it up again in the same Press, we resolved to observe, both whether the like changes would a∣gain appear in our Tincture; and whether in case they should appear, they would be ascribable to the alterations of the Wea∣ther. But though, during the greatest part of a Winter and a Spring, we took pleasure to observe, how the Liquor would of∣ten grow turbid, and after a while clear again: Yet we could not find that these Mutations depended upon any that were mani∣fest in the Air, which would be often dark and clouded, when the Tincture was clear and transparent; as on the other side, in clear Weather the Liquor would appear sometimes troubled, and more opacous. So that being unable to give an account of

these odd changes in our Tincture (which we suppose we have not yet lost, though we know not whether it hath lost its fickle Nature) either by those of the Air, or any thing else that oc∣curr'd to our thoughts; we could not but suspect, that there may be in divers Bodies, as it were Spontaneous Mutations, that is, such changes as depend not upon manifest Causes. But, My Lord, what hath been all this while said concerning our Phae∣nomenon, is offer'd to You, not as containing a satisfactory ac∣count of it, but to assist You to give Your self one.

EXPERIMENT XXXVIII.

WE took a Glass Vessel, open at the top, and into it we put a mixture of Snow and common Salt, (such a mixture as we have in another Treatise largely discoursed of) and into the midst of this mixture we set a Glass, of a Cylindrical form, closely stopp'd at the lower end with Plaister, and open at the upper, at which we fill'd it with common Water. These things being let down into the Receiver, and the Pump being set on work, the Snow began to melt somewhat faster than we expect∣ed; Whether upon the account of the exsuction of the Air, or because there was but little of the Snow, or whether for any other Reason, it appear'd doubtfull. But however, by that time the Receiver had been considerably exhausted, which was done in less than ¼ of an hour, we perceived the Water near the bot∣tom of the Glass Cylinder to Freeze, and the Ice by a little long∣er stay, seem'd to encrease, and to rise somewhat higher than the surface of the surrounding Liquor, whereinto almost all the Snow and Salt were resolv'd. The Glass being taken out, it appear'd that the Ice was as thick as the inside of the Glass it fill'd, though into that I could put my Thumb. The upper sur∣face of the Ice was very concave, which whether it were due to any unheeded accident, or to the exsuction of the Air, we leave to be determin'd by farther trial. And lastly, the Ice held against the Light, appear'd not destitute of Bubbles, though some By-standers thought they were fewer than would have been found if the Water had been frozen in the open Air. The

like Experiment we try'd also another time in one of our small Receivers, with not unlike success.

And on this occasion, My Lord, give me leave to propose a Problem, which shall be this: Whence proceeds that strange force that we may sometimes observe in frozen Water, to break the Bodies that imprison it, though hard and solid? That there is such a force in Water expos'd to Congelation, may be gather∣ed not only from what may be often observ'd in Winter, of the bursting of Glasses too close stopp'd, fill'd with Water or a∣queous Liquors, but by Instances as much more considerable as less obvious. For I remember, that an Ingenious Stone-cutter not long since complain'd to me, That sometimes, through the negligence of Servants, the Rain being suffered to soak into Marble Stones, the supervening violent Frosts would burst the Stones, to the Possessour's no small damage. And I remem∣ber another Trades-man, in whose House I had Lodgings, was last Winter complaining, that even Implements made of Bell∣metal, being carelesly expos'd to the wet, have been broken and spoil'd by the Water, which, having gotten into the little Cavities and Crannies of the Metal, was there afterwards fro∣zen and expanded into Ice. And to these Relations, we can add one of the formerly mention'd Cabaeus's, whereby * 1.13 they not only may be confirm'd; but are surpass'd: For he tells us, That he saw a huge Vessel of exceeding hard Marble, split asunder by congeal'd Water, whose rarefaction, saith our Author, prov'd so vehement, that the hardness of the Stone yielded to it; and so a vessel was broken, which would not have been so by 100 Yoke of Oxen drawing it several ways. I know, My Lord, that to solve this Problem, it will be said, That Congelation doth not (as is commonly, but erroneously pre∣sum'd) reduce Water into less room than it possess'd before, but rather makes it take up more. And I have elsewhere prov'd by particular Experiments, That whether or no Ice may be truly said to be Water rarefi'd (for that seems questionable) it may be said to take up more room than the Water did before Glaciation. But though we grant that freezing makes Water

swell, yet, how cold (which in Weather-Glasses manifestly con∣denseth the Air) should expand either the Water, or the inter∣cepted Air so forcibly, as to perform such things as we have newly related, will yet remain a Problem.

EXPERIMENT XXXIX.

WE took an Oval Glass, clear and (lest it should break) pretty strong, with a short Neck at the obtuser end; through this Neck, we thrust almost to the bottom, a Pipe of Glass, which was closely cemented to the newly mention'd Neck, the upper part of which Pipe, was drawn in some places more slender than a Crows Quill, that the changes of the Air in that Glass Egg might be the more conspicuous; Then there was con∣vey'd into the Glass five or six Spoon-fulls of Water, part of which, by blowing Air into the Egg, was rais'd into the above∣mention'd slender part of the Pipe, so that the Water was inter∣pos'd between the external Air, and that included in the Egg. This Weather glass (delineated in the fourteenth Figure) was so plac'd, and clos'd up in the cavity of one of our small Receivers, that only the slender part of the Pipe, to the height of four or five Inches, passing thorow a hole in the Cover remain'd expos'd to the open Air.

The Pump being set a work, upon the exsuction of the Air, the Water in the Pipe descended about a quarter of an Inch, and this upon two or three reiterated trials; which seem'd sufficient∣ly to argue, that there was no heat produc'd in the Receiver up∣on the exsuction of the Air: For even a little heat would proba∣bly have been discover'd by that Weather-glass, since upon the bare application of my hand to the outside of the Receiver, the warmth having after some time been communicated or propaga∣ted through both the Glasses, and the interval betwixt them, to the imprison'd Air, did so rarefie that, as to inable it, by pressing upon the subjacent Water, to impel that in the Pipe very many times as far as it had fallen downwards upon the ex∣suction of the Air.

Yet shall not we conclude, that in the cavity of the Receiver

the cold was greater after the exsuction of the Air than be∣fore.

For if it be demanded what then could cause the fore-men∣tion'd subsiding of the Water? it may be answered, That pro∣bably it was the reaching of the Glass Egg, which, upon the ex∣suction of the ambient Air, was unable to resist altogether as much as formerly the pressure of the included Air, and of the Atmosphere, which, by the intervention of the Water, press'd upon its concave surface: Which seem'd probable, as well by what was above deliver'd, in the Experiment about the breaking of the Glass by the force of the Atmosphere; as by this notable Circumstance (which we divers times observ'd) That when by drawing the Air out of the Receiver, the Water in the Pipe was subsided, upon the re-admission of the external Air, to press against the convex surface of the Egg, the Water was pre∣sently re-impell'd to its former height: Which would perhaps appear less strange to Your Lordship, if You had yet seen, what we have heretofore taught in another Treatise, concerning the Spring that may be discover'd in Glass, as rigid and inflexible a Body as it is generally esteem'd. And in the mean while it may serve the turn, to cause a Glass Egg to be blown exceeding thin; and then, having broken it, try how far you can by degrees bend some narrow parts of it; and how readily, upon the re∣moval of what kept it bent, it will restore it self to its former state or posture. But to return to our Experiment: From thence it seems probable, either that there succeeds no Body in the room of the Air drawn out of our Receiver; or that it is not every Matter that is suotle enough readily to pass through the Pores of Glass, that is always agitated enough to produce Heat where ever it is plentifully found. So that if no Vacuum be to be admitted, this Experiment seems to invite us to allow a great disparity, either as to bulk, or as to agitation, or as to both, be∣twixt some parts of the Etherial substance, and those that are wont here below to produce Heat and Fire.

We try'd also what Operation the drawing out of the Air would have upon Camphire, that being a Body, which, though not a

Liquor, consists of such Volatile or Fugitive parts, that without any greater agitation than that of the open Air it self, they will copiously flie away. But we sound not that even this loose Body was sensibly alter'd by the exsuction of the ambient Air.

EXPERIMENT XL.

IT may seem well worth trying, whether or no in our exhau∣sted Glass the want of an ambient Body, of the wonted thickness of Air, would disable even light and little Animals, as Bees, and other winged Insects, to fly. But though we easily foresaw how difficult it would be to make such an Experiment; yet not to omit our endeavours: We procur'd a large Flesh Fly, which we convey'd into a small Receiver. We also another time shut into a great Receiver a Humming Bee, that appear'd strong and lively, though we had rather have made the trial with a Butter-fly, if the cold Season would have permitted us to find any. * 1.14 The Fly, after some exsuctions of the Air, dropp'd down from the side of the Glass whereon she was walking: But, that the Experiment with the Bee might be the more instructive, we convey'd in with her a bundle of Flowers, which remain'd sus∣pended by a string near the upper part of the Receiver: And having provok'd the Bee, we excited her to flie up and down, the capacity of the Vessel, till at length, as we desir'd, she lighted upon the Flowers; whereupon we presently began to draw out the Air, and observ'd, That though for some time the Bee seem'd to take no notice of it, yet with∣in a while after she did not flie, but fall down from the Flow∣ers; without appearing to make any use of her Wings to help her self. But whether this fall of the Bee, and the other Insect, proceeded from the mediums being too thin for them to flie in, or barely from the weakness, and as it were swooning of the Animals themselves, you will easily gather from the following Experiment.

EXPERIMENT XLI.

TO satisfie our selves in some measure, about the account upon which Respiration is so necessary to the Animals, that Nature hath furnished with Lungs, we took (being then unable to procure any other lively Bird, small enough to be put into the Receiver) a Lark, one of whose Wings had been bro∣ken by a shot, of a Man that we had sent to provide us some Birds for our Experiment; but notwithstanding this hurt, the Lark was very lively, and did, being put into the Receiver, divers times spring up in it to a good height. The Vessel being hastily, but carefully clos'd, the Pump was diligently ply'd, and the Bird for a while appear'd lively enough; but upon a greater exsuction of the Air, she began manifestly to droop and appear sick, and very soon after was taken with as violent and irregular Convulsions, as are wont to be observ'd in Poultry, when their heads are wrung off: For the Bird threw her self over and over two or three times, and dyed with her Breast upward, her Head downwards, and her Neck awry. And though upon the appearing of these Convulsions, we turn'd the Stop-cock, and let in the Air upon her, yet it came too late; whereupon casting our Eyes upon one of those accurate Dyals that go with a Pendulum, and were of late ingeniously invented by the No∣ble and Learned Hugenius, we found that the whole Tragedy had been concluded within ten Minutes of an hour, part of which time had been imploy'd in cementing the Cover to the Receiver. Soon after we got a Hen-sparrow which being caught with Bird-lime was not at all hurt; when we put her into the Receiver, almost to the top of which she would briskly raise her self, the Experiment being try'd with this Bird, as it was with the former, she seemed to be dead within seven minutes, one of which were imployed in cementing on the Cover: But upon the speedy turning of the Key, the fresh Air flowing in, began slowly to revive her, so that aster some pantings she opened her eyes, and regain'd her feet, and in about a ¼ of an hour after, threatned to make an escape at the top of the Glass,

which had been unstopped to let in the fresh Air upon her: But the Receiver being closed the second time, she was killed with violent Convulsions, within five Minutes from the begin∣ning of the Pumping.

A while after we put in a Mouse, newly taken, in such a Trap as had rather affrighted than hurt him; whilst he was leaping up very high in the Receiver, we fasten'd the Cover to it, ex∣pecting that an Animal used to live in narrow holes with very little fresh Air, would endure the want of it better than the lately mentioned Birds: But though, for a while after the Pump was set a work, he continued leaping up as before; yet, 'twas not long ere he began to appear sick and giddy, and to stagger: after which he fell down as dead, but without such violent Con∣vulsions as the Bird died with. Wherepon, hastily turning the Key, we let in some fresh Air upon him, by which he recovered, after a while, his senses and his feet, but seemed to continue weak and sick: But at length, growing able to skip as formerly, the Pump was plyed again for eight minutes, about the middle of which space, if not before a very little Air by a mischance got in at the Stop-cock; and about two minutes after that, the Mouse divers times leap'd up lively enough, though after about two minutes more he fell down quite dead, yet with Convulsions far milder than those wherewith the two Birds expired. This alacrity so little before his death, and his not dying sooner than at the end of the eighth minute, seemed ascribable to the Air (how little soever) that slipt into the Receiver. For the first time, those Convulsions (that, if they had not been suddenly re∣medied, had immediately dispatch'd him) seised on him in six mi∣nutes after the Pump began to be set a work. These Experiments seemed the more strange, in regard that during a great part of those few minutes the Engine could but considerably rarefie the Air (and that too, but by degrees) and at the end of them there remained in the Receiver no inconsiderable quantity; as may appear by what we have formerly said of our not being able to draw down Water in a Tube, within much less than a Foot of the bottom: With which we likewise consider'd, that by the

exsuction of the Air and interspersed Vapours, there was left in the Receiver a space some hundreds of times exceeding the bigness of the Animal, to receive the fuliginous Steams, from which, expiration discharges the Lungs; and, which in the other cases hitherto known, may be suspected, for want of room, to stifle those Animals that are closely pen'd up in too nar∣row Receptacles.

I forgot to mention, that having caus'd these three Creatures to be open'd, I could, in such small Bodies, discover little of what we sought for, and what we might possibly have found in larger Animals; for though the Lungs of the Birds appear'd very red, and as it were inflam'd, yet that colour being usual enough in the Lungs of such winged Creatures, deserves not so much our notice, as it doth, That in almost all the destructive Experiments made in our Engine, the Animals appear'd to die with violent Convulsive motions: From which, whe∣ther Physicians can gather any thing towards the discovery of the Nature of Convulsive Distempers, I leave to them to consider.

Having proceeded thus far, though (as we have partly intimated already) there appear'd not much cause to doubt, but that the death of the fore-mention'd Animals proceeded rather from the want of Air, than that the Air was over∣clogg'd by the steams of their Bodies, exquisitely pen'd up in the Glass; yet I, that love not to believe any thing upon Conjectures, when by a not over-difficult Experiment I can try whether it be true or no, thought it the safest way to obviate Objections, and remove Scruples, by shutting up another Mouse as close as I could in the Receiver, wherein it lived about three quarters of an hour; and might probably have done so much lon∣ger, had not a Virtuoso of quality, who in the mean while chanc'd to make me a Visit, desir'd to see whether or no the Mouse could be kill'd by the exsuction of the ambient Air whereupon we thought fit to open, for a little while, an intercourse betwixt the Air in the Receiver, and that without it, that the Mouse might thereby (if it were needfull

for him) be refresh'd, and yet we did this without uncemen∣ting the Cover at the top, that it might not be objected, that perhaps the Vessel was more closely stopp'd for the exsuction of the Air than before.

The Experiment had this event, that after the Mouse had liv'd ten Minutes, (which we ascrib'd to this that the Pump, for want of having been lately Oyled, could move but slowly, and could not by him that manag'd it, be made to work as nimbly as it was wont) at the end of that time he dy'd with Convulsive Fits, wherein he made two or three bounds into the Air, before he fell down dead.

Nor was I content with this, but for Your Lordships far∣ther satisfaction, and my own, I caused a Mouse, that was very hungry, to be shut in all Night, with a Bed of Paper for him to rest upon: And to be sure that the Receiver was well clos'd, I caus'd some Air to be drawn out of it, where∣by, perceiving that there was no sensible leak, I presently re∣admitted the Air at the Stop-cock, lest the want of it should harm the little Animal; and then I caused the Engine to be kept all Night by the Fire side, to keep him from being de∣stroyed by the immoderate cold of the Frosty Night. And this care succeeded so well, that the next Morning I found that the Mouse not only was alive, but had devour'd a good part of the Cheese that had been put in with him. And ha∣ving thus kept him alive full twelve hours, or better, we did, by sucking out part of the Air, bring him to droop, and to appear swell'd; and by letting in the Air again, we soon reduc'd him to his former liveliness.

A Digression containing some Doubts touching Respiration.

I Fear Your Lordship will now expect, that to these Experi∣ments I should add my Reflexions on them, and attempt, by their assistence, to resolve the difficulties that occur a∣bout Respiration; since at the beginning I acknowledg'd a far∣ther enquiry into the Nature of that, to have been my design in the related Tryals. But I have yet, because of the inconve∣nient season of the Year, made so few Experiments, and have been so little satisfied by those I have been able to make, that they have hitherto made Respiration appear to me rather a more, than a less Mysterious thing, than it did before. But yet, since they have furnished me with some such new Considerations, concer∣ning the use of the Air, as confirms me in my Diffidence of the truth of what is commonly believ'd touching that matter; That I may not appear sullen or lazy, I am content not to decline employing a few hours in setting down my Doubts, in present∣ing Your Lordship some Hints, and in considering whether the Tryals made in our Engine, will at least assist us to discover wherein the Deficiency lies that needs to be supplyed.

And this, My Lord, being all my present Design, I suppose You will not expect that (as if You knew not, or had forgotten what Anatomists are wont to teach) I should entertain You with a needless Discourse of the Organs of Respiration, and the vari∣ety of their Structure in several Animals; though if it were ne∣cessary, and had not been perform'd by others I should think, with Galen, that by treating of the Fabricks of living Bodies, I might compose Hymns to the wise Author of Nature, who, in the excellent contrivance of the Lungs, and other parts of (those admirable Engines) Animals, manifests himself to be indeed what the Eloquent Prophet most justly speaks him, Won∣derfull in Councel, and excellent in working.

Nor shall we any farther meddle with those Controversies so much agitated among the Moderns, namely, Whether the motion of the Lungs in Respiration be their own, or but consequent to the motion of the Thorax, Diaphragme, and (as some Learned Men would have it) the Abdomen; And, Whence it is that the Air swells the Lungs in Inspiration, any farther than they may re∣ceive light from our Engine: But that it may appear what kind of service it is that may be expected from it on this occasion, we must premise a few Words to shew wherein the strength of the Objection we are to answer, lies: In favour then of those that would have the Lungs rather passive than active in the business of Respiration, it may against the common opinion be alledg'd, That as the Lungs being destitute of Muscles and of Fibres, are unfit to dilate themselves; so it appears, that without the mo∣tion of the Thorax they would not be fill'd with Air. Since as our Learned Friend Dr. Highmore hath well (and congruously, to what our selves have purposely tried) observed, if a live Dog have a great wound made in his Chest, the Lobes of the Lungs on that side of the Mediastinum will subside and lie still; the Thorax and the Lobes on the other side of the Mediasti∣num, continuing their former motion. And if suddenly at once the Muscles of the Chest be on both sides dissected, up∣on the Ingress of the Air, the whole Lungs, though untouch'd, will remain moveless, at least, as to any expansion or contra∣ction of their substance.

To which we may add the Observation of the diligent Bar∣tholinus, who affirms the like of the Diaphragme also, namely, That it being wounded, the Lungs will fall together, and the Respiration cease, which my Experiments oppose not, provi∣ded the Wound be any thing great. And indeed the Diaphragme seems the principal Instrument of ordinary and gentle Respi∣ration, although to restrained Respiration (if I may so call it) the intercostal Muscles, and perhaps some others may be allow∣ed eminently to concur. But the chief of the Controversies for∣merly pointed at, is not yet decided, namely, what it is that conveys the Air into the Lungs. For when, to counterballance all that

hath been alledg'd, those that plead for the Lungs demand what it is that should bring the Air into the Lungs, if themselves do not attract it, their Antagonists disagree about the Reply. For when to this question some of the best Modern Philosophers answer, That by the dilatation of the Chest the contiguous Air is thrust away, and that pressing upon the next Air to it, and so onwards, the Propulsion it continued till the Air be driven into the Lungs, and so dilate them: When this (I say) is an∣swered, it is Objected even by Bartholine himself, as a convin∣cing Reply, that, according to this Doctrine, a Man could not fetch his Breath from a great Vessel full of Air, with a slender Neck, because, that when his Mouth covers the Orifice of the Neck, the dilatation of his Thorax could not propell the Air in the Vessel into his Lungs, by reason of its being separated by the inclosing Vessel from the ambient Air; and yet, say they, Experience witnesseth, that out of such a Vessel a Man may suck Air. But of this difficulty our Engine furnisheth us with an ea∣sie Solution, since many of: the former Experiments have mani∣fested, That in the case proposed, there needs not be made any (though 'tis true that in ordinary Respiration there is wont to be made some) propulsion of the Air by the swelling Thorax or Abdomen into the Lungs; since upon the bare Dilatation of the Thorax, the Spring of that internal Air, or halituous substance that is wont to possess as much of the cavity of the Chest as the Lungs fill not up, being much weaken'd, the external and contiguous Air must necessarily press in at the open Wind pipe into the Lungs, as finding there less resistance than any where else about it.

And hence (by the way) we may derive a new assistance to judge of that famous Controversie disputed among Naturalists and Physicians, ever since Galen's time, some maintaining that the Chest, with the contained Lungs, may be resembled to a pair of Bellows, which comes therefore to be fill'd because it was dilated: And others pleading to have the comparison made to a Bladder, which is therefore dilated because it is fill'd. For as to the Thorax, it seems evident from what hath been lately said, that

it, like a pair of Bellows, happens to be partly fill'd with Air, but because it was dilated: But as for the Lungs themselves, who want Fibres to distend them, they may fitly enough be compar'd to a Bladder; since they are dilated by being fill'd, namely, by that Air which rusheth into them upon the dilatation of the Chest, in whose increased cavity it finds (as we freshly noted) less resist∣ance to its Spring than elsewhere. And this brings into my mind that strange Observation of Nicolaus Fontanus, a Physician at Amsterdam, who testifieth, That in a Boy of the same Town, four years old, there was found, instead of Lungs, a certain Membra∣nous Bladder; which being fill'd with Wind, and furnish'd with little Veins, had its origination from the Wind-Pipe it self; which being suppos'd true, how well it will agree with most of the Opi∣nions touching Respiration, I leave to be consider'd.

And thus may the grand Objection of Bartholine, and others, be answered: But I leave to Anatomists to consider what is to be said to some Observations that seem to contradict those Anatomi∣cal Experiments already mention'd: Such was particularly that which I remember I have read in Sennertus (from the obser∣vation of his Father-in-law Schato) of a Melancholy Student, who having stabb'd himself, and pierced the Diaphragme in the thinner or tendonous part (call'd by many the Nervous Circle) lived seven Months after he had wounded himself, though af∣ter his death (preceded by violent Vomitings) the Wound (perchance dilated by those strainings) appear'd so great, that the whole Stomach was found to have got in by it into the left side of the Thorax. And such also was the accident that hap∣pen'd to a Noble Man, whom I remember I have seen, and who is yet alive, in whose Chest there hath, for these many years, remain'd a hole so great, that the motion of his Heart may be perceiv'd by it. These (I say) and some other Ob∣servations, I shall now forbear to insist on, because I hold it not unfit, before we come to consider the use of Respiration, that we acquaint Your Lordship with an Ingenious Conjecture, that was made at the cause of the hasty death of the Animals our Engine kill'd: namely, That it was not the want of Air that

destroy'd them, but the Pressure of the innate Air in the cavity of the Chest; as if the spring of the Air being no longer coun∣terballanc'd by the ambient Air, was thereby become so strong, that it kept the Thorax forcibly distended, and hinder'd its wont∣ed contraction; and so compress'd the Lungs and their Vessels, as to obstruct the circulation of the Blood. And this Conjecture, as it is specious enough, so I might have admitted it for true; but that I consider'd, that (not to mention that one, especially of the Animals kill'd in our Engine, seemed manifestly for a pretty while, and not long before he dy'd, to move his Thorax, as if he exercis'd Respiration) the diligent Wallaeus relates, that he divers times observed, in the dissection of live Bodies, that the Mem∣brane that invests the Lungs, had Pores in it as big as the larger sort of Peas, which agreeth with the Observations of Chyrur∣gions and Physicians, viz. That Matter collected in the Thorax, hath penetrated into the Lungs, and been discharged by cough∣ing. And I remember too, that most of the Animals we kill'd in our Engine were Birds, of whose Lungs Harvey somewhere informs us, That he observ'd them very manifestly to open at their extremities into the Abdomen: And by such perforitions we may well'suppose the passage free betwixt the external Air, and that in the Abdomen: But this Conjecture may be farther consider'd. Besides, to show that the Animals that died in our Glasses, need not be supposed to have been kill'd by the want of Air, we foresee another Argument that we must deal so in∣geniously with Your Lordship, as not to conceal. You very well know, that besides the generality of the Schools, there are many new Philosophers who, though they dissent from the old Peripateticks in other things, do, as they, deny the possibi∣lity of a Vacuum; and hold, that those spaces which are devoid of Air, and other grosser Bodies, are all of them exactly re∣plenished with a certain Etherial Matter, so thin and subtle, that it can freely permeate the Pores of the compactedst and closest Bodies, and ev'n of Glass it self. Now some of those Naturalists that are of this perswasion may object, That the Animals that died in our Receiver, did so, not so much for lack

of Air, as by reason that the Air that was pump'd out was ne∣cessarily succeeded by an Etherial substance; which consisting of parts vehemently agitated, and so very small, as without resist∣ance to pass in and out through the very Pores of Glass; it may well be supposed, that a considerable quantity of this rest∣less and subtle Matter, meeting together in the Receiver, with the excessive heat of it, may be quickly able to destroy a little Animal, or at least, make the Air too intemperately hot to be fit for Respiration.

But though this be a Difficulty not so easily to be resolved without the assistance of our Engine, yet I suppose we have al∣ready answer'd the Objection by our 38^th and 39^th Experiments; which, though we made partly for other purposes, yet we pre∣mis'd them only to clear up the difficulty proposed.

Another suspicion we should have entertain'd concerning the death of our Animals, namely, That upon the sudden removal of the wonted pressure of the ambient Air, the warm blood of those Animals was brought to an Effervescence or Ebullition, or at least so vehemently expanded, as to disturb the circulation of the Blood, and so disorder the whole Oeconomy of the Body. (This (I say) I should have had some suspicion of) but that Ani∣mals of a hot Constitution are not the sole ones that cannot in our exhausted Engine exercise the Function of Life. But I must not now dwell upon matters of this nature, because I think it high time to proceed to the consideration of the principal subject of our Engine, namely, the use of Respiration; or rather, The use of the Air in Respiration. For whereas of the divers uses of it men∣tioned by Anatomists the most, such as the Production and Modulation of the Voice by the Elision of the Air, the Larynx, &c. the expulsion of Excrements by Coughing, the conveying in of Odours by Inspiration, and some others, rather convenient for the well being of an Animal, than absolutely necessary to his Life: Whereas (I say) the other uses are such as we have said, The great Hippocrates himself gives this notable Testimony to the use of the Air, as to Animals endow'd with Lungs: Mortali∣bus (saith he) hic (spiritus) tum vitae, tum morborum aegrotis causa

est. Tantáque corporibus omnibus spiritûs inest necessitas, ut fi∣quidem aliis omnibus & cibis & potionibus, quis abstineat, duos tamen aut tres, vel plures dies possit vitam ducere: At si quis spiritus in corpus vias intercipiat, vel exiguâ diei parte, homini pereundum fit; Adeo necessarius est usus spiritûs in corpore. Ad haec quoque, quum omnibus aliis actionibus homines quiescant, quod mutationibus innumeris vita sit exposita, ab hâc tamen solâ actione nunquam desistant animantia, quin aut spiritum adducant, aut reddant.

But touching the account upon which the Inspiration and Ex∣spiration of Air (both which are comprehended in 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, Re∣spiration) is so necessary to Life, both Naturalists and Physici∣ans do so disagree, that it will be very difficult either to reconcile their Opinions, or determine their Controversies.

For first, Many there are who think the chief (if not sole) use of Respiration to be the cooling and tempering of that Heat in the Heart and Blood, which otherwise would be immoderate: And this Opinion, not only seems to be most received amongst Scholastick Writers, but divers of the new Philosophers, Cartesians, and others, admitted with some variation; teach∣ing. That the Air is necessary, by its coldness, to condense the Blood that passeth out of the right Ventricle of the Heart into the Lungs, that thereby it may contain such a consistence, as is requisite to make it fit Fewel for the vital fire or flame, in the left Ventricle of the Heart. And this Opinion seems fa∣vour'd by this, That Fishes, and other cold Creatures, whose Hearts have but one cavity, are also unprovided of Lungs, and by some other considerations. But though it need not be deny'd, that the inspir'd Air may sometimes be of use by refrigerating the Heart; yet (against the Opinion that makes this Refrigeration, the most genuine and constant use of the Air) it may be Ob∣jected, That divers cold Creatures (some of which, as particu∣larly Frogs, live in the Water) have yet need of Respiration, which seems not likely to be needed for Refrigeration by them that are destitute of any sensible heat, and besides, live in the cold Water: That even decrepid old Men, whose natural Heat is

made very languid, and almost extinguish'd by reason of Age, have yet a necessity of frequent Respiration: That a temperate Air is fittest for the generality of breathing Creatures; and as an Air too hot, so also an Air too cold, may be inconvenient for them (especially, if they be troubled with an immoderate degree of the same quality which is predominant in the Air:) That in some Diseases the natural heat is so weaken'd, that in case the use of Respiratic were to cool, it would be more hurt∣full than beneficial to Breath; and the suspending of the Respi∣ration, may supply the place of those very hot Medicines that are wont to be employ'd in such Distempers: That Nature might much better have given the Heart but a moderate heat, than such an excessive one, as needs to be perpetually cool'd, to keep it from growing destructive; which the gentle, and not the burning heat of an Animal's Heart,. seems not intense e∣nough so indispensably to require. These, and other Objecti∣ons, might be oppos'd, and press'd against the recited Opinion: But we shall not insist on them, but only add to them, That it appears not by our foregoing Experiments (I mean the 38^th and 39^th) that in our exhausted Receiver, where yet Animals die so suddenly for want of Respiration, the ambient Body is sensibly hotter than the common Air.

Other Learned Men there are, who will have the very substance of the Air to get in by the Vessels of the Lungs, to the left Ven∣tricle of the Heart, not only to temper its heat, but to provide for the generation of Spirits. And these alledge for themselves the authority of the Ancients, among whom Hippocrates seems manifestly to favour their Opinion; and both Aristotle and Galen do sometimes (for methinks they speak doubtfully e∣nough) appear inclineable to it. But for ought ever I could see in Dissections, it is very difficult to make out, how the Air is convey'd into the left Ventricle of the Heart, especially the Sy∣stole and Diastole of the Heart and Lungs being very far from being Synchronical: Besides, that the Spirits seeming to be but the most subtle and unctuous Particles of the Blood, appear to be of a very differing Nature from that of the lean and incom∣bustible

Corpuscles of Air. Other Objections against this Opi∣nion have been proposed, and press'd by that excellent Anato∣mist, and my Industrious Friend, Dr. Highmore, to whom I shall therefore refer you.

Another Opinion there is touching Respiration, which makes the genuine use of it to be Ventilation not of the Heart, but of the Blood, in its passage through the Lungs; in which pas∣sage, it is dis-burthened of those Excrementitious Steams proceeding, for the most part, from the superfluous Serosities, of the Blood, (we may add) and of the Chyle too, which (by those new Conduits of late very happily detected by the Fa∣mous Pecquet) hath been newly mix'd with it in the Heart.) And this Opinion is that of the Industrious Maebius, and is said to have been that of that excellent Philosopher Gassendus; and hath been in part an Opinion almost vulgar: But this Hypothe∣sis may be explicated two ways: For first, The necessity of the Air in Respiration, may be suppos'd to proceed from hence; That as a Flame cannot long burn in a narrow and close place, because the Fuliginous Steams it uncessantly throws out, can∣not be long receiv'd into the ambient Body; which, after a while, growing too full of them to admit any more, stifles the flame: So that the vital Fire in the Heart requires an ambient Body, of a yielding nature, to receive into it the superfluous Serosities, and other Recrements of the Blood, whose season∣able Expulsion is requisite to depurate the Mass of Blood, and make it fit both to circulate, and to maintain the vital heat re∣siding in the Heart. The other way of explicating the above∣mentioned Hypothesis, is, by supposing, that the Air doth not only, as a Receptacle, admit into its Pores the Excrementiti∣ous vapours of the Blood, when they are expell'd through the Wind-pipe, but doth also convey them out of the Lungs, in re∣gard that the inspired Air, reaching to all the ends of the Aspe∣ra Ateria, doth there associate it self with the exhalations of the circulating Blood, and when 'tis exploded, carries them away with it self: as we see that Winds speedily dry up the surfaces of wet Bodies, not to say any thing of what we for∣merly

observed touching our Liquor, whose fumes were strangely elevated upon the ingress of the Air.

Now of these two ways of Explicating the use of Respira∣tion, our Engine affords us this Objection against the first; That upon the exsuction of the Air, the Animals die a great deal sooner than if it were left in the Vessel; though by that ex∣suction the ambient space is left much more free to receive the Steams that are either breathed out of the Lungs of the Ani∣mal, or discharg'd by insensible Transpiration through the Pores of his Skin.

But if the Hypothesis propos'd, be taken in the other sense, it seems congruous enough to that grand observation, which partly the Phaenomena of our Engine, and partly the relations of Travellers, have suggested to us: namely, That there is a certain consistence of Air requisite to Respiration; so that if it be too thick, and already over-charged with Vapours, it will be unfit to unite with, and carry off those of the Blood, as Wa∣ter will dissolve, and associate to it self but a certain proportion of saline Corpuscles; and if it be too thin or rarefied, the num∣ber or size of the Aërial Particles is too small to be able to as∣sume and carry off the halituous Excrements of the Blood, in such plenty as is requisite.

Now that Air too much thicken'd (and as it were clogg'd) with Steams, is unfit for Respiration, may appear by what is wont to happen in the Lead-Mines of Devonshire, (and for ought I know, in those too of other Countries, though I have seen Mines where no such thing was complain'd of) for I have been informed by more than one credible Person (and particularly by an Ingenious Man, that hath often, for curiosity, digg'd in those Mines, and been imploy'd about them) that there often riseth Damps, as retaining the Germane Word by which we call them) which doth so thicken the Air, that unless the Work-men speedily make signs to them that are above, they would (which also sometimes happens) be presently stifled for want of Breath, and though their Companions do make haste to draw them up, yet frequently, by that time they

come to the free Air, they are, as it were in a swoon, and are a good while before they come to themselves again. And that this swooning seems not to proceed from any Arsenical or Poy∣sonous Exhalation contain'd in the Damp, as from its over∣much condensing the Air, seems probable from hence; That the same Damps oftentimes leisurely extinguish the flames of their Candles or Lamps; and from hence also that it appears (by many Relations of Authentical Authors) that in those Cel∣lars where great store of new Wine is set to work, Men have been suffocated by the too great plenty of the Steams exhaling from the Must, and too much thickning the Air: As may be gather∣ed from the custom that is now used in some hot Countries, where those that have occasion to go into such Cellars, carry with them a quantity of well kindled Coals, which they hold near their Faces; whereby it comes to pass, that the Fire dis∣cussing the Fumes, and rarefying the Air, reduceth the ambient Body to a consistence fit for Respiration.

We will add (by way of Confirmation) the following Ex∣periment: In such a small Receiver, as those wherein we kill'd divers Birds, we carefully clos'd up one, who, though for a quarter of an hour he seem'd not much prejudiced by the close∣ness of his Prison, afterwards be••••n first to pant very vehement∣ly, and keep his Bill very open, and then to appear very sick; and last of all, after some long and violent strainings, to cast up some little matter out of his Stomach: which he did several times, till growing so sick, that he stagger'd and gasp'd, as being just ready to die. We perceiv'd, that within about three quarters of an hour from the time that he was put in, he had so thickened and tainted the Air with the Steams of his Body, that it was become altogether unfit for the use of Respiration: Which he will not much wonder at, who hath taken notice in Sanctorius his Statica Medicina, how much that part of our Aliments, which goeth off by insensible Transpiration, exceeds in weight all the visible and grosser Excrements both solid and liquid.

That (on the other side) an Air too much dilated is not ser∣viceable for the ends of Respiration, the hasty death of the

Animal we kill'd in our exhausted Receiver, seems sufficiently to manifest. And it may not irrationally be doubted, whether or no, if a Man were rais'd to the very top of the Atmosphere, he would be able to live many minutes, and would not quickly dye for want of such Air as we are wont to breath here below. And that this Conjecture may not appear extravagant, I shall on this occasion subjoyn a memorable Relation that I have met with in the Learned Josephus Acosta, who tells us, That when he himself past the high Mountains of Peru, (which they call Pariacaca) to which, he says, That the Alps themselves seem'd to them but as ordinary Houses, in regard of high Towers, he and his Companions were surprised with such extreme Pangs of Straining and Vomiting, (not without casting up Blood too) and with so violent a Distemper, that he concludes he should un∣doubtedly have died, but that this lasted not above three or four hours, before they came into a more convenient and natural temperature of Air: To which our Learned Author adds an In∣ference, which being the principal thing I design'd in mention∣ing, the Narrative I shall set down in his own words: I there∣fore (says he) perswade my self, That the Element of the Air is there so subtle and delicate, as it is not proportionable with the breathing of Man, which req••••••es a more gross and temperate Air; and I believe it is the cause that doth so much alter the Sto∣mach, and trouble all the Disposition. Thus far our Author, whose Words I mention, that we may ghess by what happens somewhat near the Confines of the Atmosphere (though pro∣bably far from the surface of it) what would happen beyond the Atmosphere. That, which some of those that treat of the height of Mountains, relate out of Aristotle, namely, That those that ascend to the top of the Mountain Olympus, could not keep themselves alive, without carrying with them wet Spun∣ges, by whose assistance they could respire in that Air, otherwise too thin for Respiration: (That Relation (I say) concerning this Mountain) would much confirm what hath been newly recited out of Acosta, if we had sufficient reason to believe it: But I confess, I am very diffident of the truth of it; partly be∣cause

cause when I pass'd the Alps, I took notice of no notable change betwixt the consistence of the Air at the top and the bottom of the Mountain; partly because in a punctual Relation made by an English Gentleman, of his ascension to the top of the Pike of Tenariff (which is by great odds higher than Olympus) I find no mention of any such difficulty of breathing; and partly also because the same Author tells us out of Aristotle, That upon the top of Olympus there is no motion of the Air, insomuch, that Letters traced upon the dust, have been, after many years, found legible and not discompos'd; whereas that Inquisitive Busbequius (who was Embassadour from the German to the Turkish Emperour) in one of his eloquent Epi∣stles, * 1.15 tells us, upon his own knowledge, That Olympus may be seen from Constantinople, blanch'd with perpetual Snow; which seems to argue, That the top of that, as well as of di∣vers other tall Hills, is not above that Region of the Air where∣in Meteors are formed. Though otherwise, in that memora∣ble Narrative which David Fraelichius, made of his ascent to the top of the prodigiously high * 1.16 Hungarian Mountain Carpathus: He tells us, That when, having pass'd through very thick Clouds, he came to the very top of the Hill, he found the Air so calm and subtle, that not a hair of his head mov'd, whereas in the lower Stages of the Mountain he felt a vehement Wind. But this might well be casual, as was his, having a clear Air where he was, though there were Clouds, not only beneath him, but above him.

But (though what hath been hitherto discours'd, incline us to look upon the Ventilation and Depuration of the Blood, as one of the principal and constant uses of Respiration; yet) me∣thinks it may be suspected that the Air doth something more than barely help to carry off what is thrown out of the Blood in its passage through the Lungs, from the right Ventricle of the Heart to the left. For we see, in Phlegmatick Consti∣tutions and Diseases, that the Blood will circulate tolerably well, notwithstanding its being excessively ferous: And in Asthmatical Persons, we often see, that though the Lungs

be very much stuff'd with tough Phlegm, yet the Patient may live some Months, if not some Years. So that it seems scarce probable, that either the want of throwing out the supefluous Serum of the Blood for a few moments, or the detaining it, du∣ring so short a while, in the Lungs, should be able to kill a per∣fectly sound and lively Animal: I say, for a few moments, be∣cause, that having divers times try'd the Experiment of killing Birds in a small Receiver, we commonly found, that within half a minute of an hour; or thereabout, the Bird would be sur∣pris'd by mortal Convulsions, and within about a minute more would be stark dead, beyond the recovery of the Air, though never so hastily let in. Which sort of Experiments seem so strange, that we were obliged to make it several times, which gain'd it the advantage of having Persons of differing Qualities, Professions and Sexes, (as not only Ladies and Lords, but Doc∣tors and Mathematicians) to witness it. And to satisfie Your Lordship, that it was not the narrowness of the Vessel, but the sudden exsuction of the Air that dispatched these Creatures so soon; we will add, That we once inclos'd one of these Birds in one of these small Receivers, where, for a while, he was so little sensible of his Imprisonment, that he eat very chearfully certain seeds that we conveyed in with him, and not only lived ten minutes, but had probably lived much longer, had not a great Person, that was Spectator of some of these Experiments, rescu'd him from the prosecution of the Trial. Another Bird be∣ing within about half a minute, cast into violent Convulsi∣ons, and reduced into a sprawling condition, upon the exsuction of the Air, by the pity of some fair Lady's related to Your Lordship) who made me hastily let in some Air at the Stop-cock, the gasping Animal was presently recovered, and in a condition to enjoy the benefit of the Lady's compassion. And another time also, being resolved not to be interrupted in our Experi∣ment, we did, at night, shut up a Bird in one of our small Re∣ceivers, and observ'd that for a good while he so little felt theal∣teration of the Air, that he fell asleep with his Head under his Wing; and though he afterwards awak'd sick, yet he continu'd

upon his legs between forty minutes and three quarters of an hour; after which, seeming ready to expire; we took him out, and soon found him able to make use of the liberty we gave him for a compensation of his sufferings.

If to the foregoing Instances of the sudden destruction of Ani∣mals, by the removal of the ambient Air, we should now annex some, that we think fitter to reserve till anon; perhaps Your Lordship would suspect, with me, that there is some use of the Air which we do not yet so well understand, that makes it so continually needfull to the Life of Animals, Paracelsus indeed tells us, That as the Stomach concocts Meat, and makes part of it usefull to the Body, rejecting the other part, so the Lungs consume part of the Air, and proscribe the rest. So that according to our Hermetick Philosopher (as his followers would have him stil'd) it seems we may suppose that there is in the Air a little vital Quintessence (if I may so call it) which serves to the re∣freshment and restauration of our vital Spirits, for which use the grosser and incomparably greater part of the Air being un∣serviceable, it need not seem strange that an Animal stands in need of almost incessantly drawing in fresh Air. But though this Opinion is not (as some of the same Author) absur'd, yet besides that, it should not be barely asserted, but explicated and prov'd; and besides that, some Objections may be fram'd against it, out of what hath been already argu'd against the Transmutation of Air into vital Spirits: Besides these things, it seems not probable, that the bare want of the Generation of the wonted quantity of vital Spirits, for less than one minute, should within that time be able to kill a lively Animal, without the help of any external violence at all.

But yet, on occasion of this Opinion of Paracelsus, perhaps it will not be impertinent, if before I proceed, I acquaint Your Lordship with a Conceit of that deservedly Famous Mechanician and Chymist, Cornelius Drebell, who among other strange things that he perform'd, is affirmed (by more than a few credible Per∣sons) to have contrived for the late Learned King James, a Vessel to go under Water; of which, trial was made in the Thames,

with admired success, the Vessel carrying twelve Rowers, besides Passengers; one of which is yet alive, and related it to an ex∣cellent Mathematician that inform'd me of it. Now that for which I mention this Story, is, That having had the curiosity and opportunity to make particular enquiries among the Rela∣tions of Drebell, and especially of an Ingenious Physician that married his Daughter, concerning the grounds upon which he conceived it feasible to make men unaccustomed to continue so long under Water without suffocation, or (as the lately men∣tion'd Person that went in the Vessel affirms) without inconve∣nience. I was answer'd that Drebell conceiv'd, that 'tis not the whole body of the Air, but a certain Quintessence (as Chy∣mists speak) or spirituous part of it, that makes it fit for Re∣spiration, which being spent, the remaining grosser body, or carcase (if I may so call it) of the Air, is unable to cherish the vital flame residing in the Heart: So that (for ought I could gather) besides the Mechanical contrivance of his Vessel he had a Chymical liquor, which he accounted the chief Secret of his submarine Navigation. For when from time to time he percei∣ved, that the finer and purer part of the Air was consumed, or over-clogg'd by the Respiration, and steams of those that went in his Ship, he would, by unstopping a Vessel full of this Liquor, speedily restore to the troubled Air such a proportion of Vital parts, as would make it again for a good while fit for Respira∣tion, whether by dissipating, or precipitating the grosser Exha∣lations, or by some other intelligible way, I must not now stay to examine, contenting my self to add, that having had the op∣portunity to doe some service to those of his Relations, that were most Intimate with him, and having made it my business to learn what this strange Liquor might be, they constantly af∣firm'd that Drebell would never disclose the Liquor unto any, nor so much as tell the matter whereof he had made it, to above one Person, who himself assured me what it was.

This account of Drebell's performance, I mention, not that I any farther assent to his opinion than I have already intimated, but because the Man, and the Invention being extraordinary, I

suppose Your Lordship will not be displeas'd to know the ut∣most I could learn about it; especially not having found it men∣tioned by any Writer. Wherefore I have been sometimes in∣clin'd to favourable thoughts of their opinion, who would have the Air necessary to ventilate, and cherish the vital slame, which they do suppose to be continually burning in the Heart. For we see, that in our Engine the flame of a Lamp will last al∣most as little after the exsuction of the Air, as the life of an Animal: Nay, I remember, that though I devis'd a more pro∣mising way, to make a fire last in our exhausted Receiver, yet it would not succeed: We took a hard body made in the form of a Clove, but twice as long, and proportionably thick, this body being made of such a Composition, that if it be kindl'd at the upper end, it will most certainly burn away to the very bottom, much better than a Match; we convey'd it divers times kindl'd at the upper end, into one of our small Receivers, but still found, that though presently upon the exsuction of the Air, it would leave smoking, and seem quite gone out, and again begin to smoke as soon as the Air was let in upon it; yet if the Air were kept out but four or five minutes, the fire would be totally, and irrevocably extinguish'd. To which we will add, that though we convey'd into a great Receiver, a small lamp with rectifi'd spirit of Wine, that being so pure as not to smut the Cotten week, or so much as a piece of white Paper held over it; yet we could not by divers trials make the flame last a couple of minutes after the Air was begun to be drawn out. But though our Engine thus shews us a new kind of resemblance betwixt Fire and Life: Yet the opinion we have last mentioned is not free from Difficulties. For, though in the hearts of ma∣ny Animals, Blood be a warm liquor, and in some even a hot one; yet it is not easie to conceive either how the Air (in sub∣stance) can get thither, or how, in case it could, it were able to increase the heat. Since, however, the Air may encrease the heat of a Coal by blowing off the ashes, and making the active Corpuscles pierce farther into the kindled body, and shat∣ter it the more, yet we see hot Liquors have their heat allayed,

and not augmented, by having Air blown on them. And whereas some Eminent Naturalists think it not inconvenient, to make the heat residing in the Heart to be a true flame, provided they add, that 'tis such a temperate, and almost insensible fire, as the flame of spirit of Wine, which will long burn upon fine white Linnen or Paper without consuming either: Give me leave to wish that they had been more curious to make differing tri∣als with that liquor. For (as we observe in another Treatise) the reason why a Linnen cloth, dipped in common Spirit of Wine, is not burnt by the flame of it, is, because the Phlegm of the Liquor defends the Cloth: And the Flame of Spirit of Wine is so far from being too weak to burn a piece of Paper, or of Linnen, that I have us'd it in Lamps to distill Liquors out of tall Cucurbites, and found that the Spirit burned away indeed much faster than Sallet Oyl, but gave at least as great a heat: Nay, I have, for curiosity sake, melted crude Gold, and that readily enough, with the bare Flame of pure Spirit of Wine.

But not to press this any farther, we will, on this occasion, venture to subjoyn an odd Observation, which may perhaps in∣vite to a farther Enquiry into the Opinion we have for Discourse sake oppos'd. Our English Democritus, Dr. Harvey, proposeth this difficult and noble Problem to Anatomists, Why a foetus, even out of the Womb, if involv'd in the secundines, may live a good while without Respiration; but in case after having once began to breath, its Respiration be stopp'd, it will presently die. We are far from pretending to solve so hard a Problem, but this we try'd in relation to it; We took a Bitch that was said to be almost ready to whelp, and having caused her to be hang'd, we presently open'd her Abdomen, and found four Puppeys in her Womb; one of these we took out, and having freed him from the Teguments that involved him, and from the Liquor he swam in, we observed that he quickly opened his Mouth very wide, moved his Tongue, and exercised Respiration; then we opened both his Abdomen and his Chest, and cut assun∣der the Diaphragme, notwithstanding which, he seemed often

to endeavour Respiring, and mov'd in a notable manner, both the Inter costal Muscles, part of the Diaphragme, the Mouth and the Tongue: But that which we mention this Puppy for, was this, That being desirous to try whether the other young ones that had not yet breath'd at all, would long survive this or no; we took them also out of the Womb, and having open'd them found none of them so much alive, as to have any perceptible motion in his heart, whereas the heart of that Puppy which had once enjoy'd the benefit of Respiration, continued beating so long, that we our selves observ'd the Auricle to beat, after five or six hours; and a Servant that staid-up and watch'd it after we were gone to Bed, affirm'd, That he saw the Pulsa∣tion continue about two hours longer. I shall leave it to others to make Reflexions upon this Observation, compar'd with Dr. Harvey's Problem.

It is much doubted, whether Fishes breath under Water, and we shall not take upon us, as yet, to determine the Question either way, because we have not yet been able to procure lit∣tle Fishes alive to make Experiments upon: That such as are not Setaceous (for such manifestly breath) have not Respira∣tion, properly so called, such as is exercised by four footed Beasts, and Birds, may be argu'd from their having no cavity in their Hearts, and from their want of Lungs, whence they are observed to be Mute; unless we say, what is not altoge∣ther absurd, That their Gills seem somewhat Analogous (as to their use) to Lungs. But that on the other side, Air is neces∣sary to the Lives even of Fishes, and that therefore 'tis proba∣ble they have some obscure kind of Respiration, seems mani∣fest by two or three Observations and Experiments, mentioned by divers Authors, who tell us, That Fishes soon die in Ponds and Glasses quite fill'd with Water; if the one be so frozen over, and the other so closely stopp'd, that the Fishes cannot enjoy the benefit of the Air, if we allow them to be true. But because these Relations are not wont to be deliver'd by Writers upon their own Knowledge; as I shall not reject them, so I dare not build upon them, till I have opportunity to examine them by experience.

In the mean time, we will add, That our Engine hath taught us two things that may illustrate the matter in hand: The one, That there is wont to lurk in Water, many little parcels of in∣terspers'd Air, whereof it seems not impossible that Fishes may make some use, either by separating it, when they strain the Water thorow their Gills, or by some other way: The other, what may be collected from the following Experiment.

We took a large Eel, (being able to procure no other Fish alive) and removing it out of the vessel of Water, wherein it was brought us, into our great Receiver, we caus'd the Air to be pump'd out; and observ'd, That the Eel, after some motion to and fro in the Glass, seem'd somewhat discompos'd; and that when we had prosecuted the exsuction of the Air somewhat obstinately, she turn'd up her belly, as dying Fishes are wont to do, and from thence-forward lay altogether moveless, just as if she were stark dead; and though I did not think her so, yet the continuing in that posture, even after the Cover of the Recei∣ver was taken off (whereby the Air was let in) I should have been of the opinion of the By-standers, if the Diffidence I am wont to exercise in trying Experiments (especially such as are not usual) had not invited me to take the Fish out of the Receiver, upon which she shew'd her self, by her vivid motions, as much alive as before.

But that is most strange which we observ'd of a great, gray, House-Snail (as they call it) which being clos'd up in one of our small Receivers, did not only not fall down from the side of the Glass, upon the drawing out of the Air. (For that may be ascrib'd to the tenacity of the Liquor wherewith Snails use to stick themselves, even to the smoothest Bodies) but was not so much as depriv'd of progressive motion by the recess of the Air: Though, except this Snail, we never put any living Creature into our Receiver, whom it did not kill, or at least reduce to seem ready to die. But as we shall not here examine what inter∣est the glutinous, and uneasily dissipable nature of the Juices of Snails, may have on this event; so whether this escape of our Eel be ascrib'd to the particular and vivacious nature of this

sort of Fishes; or to this, That the Air is not indeed necessary to the life of Fishes; or finally to this, That though these Ani∣mals need some Air, yet they need so little, that that which could not be drawn out of the Receiver, might (at least for a while) suffice them, we will not now determine.

Nor are we at leisure to examine that Paradox of Hippocrates, which some Learned Physicians have of late reviv'd, namely, That the Foetus respires in the Womb: For on the one side it seems very difficult to conceive, how Air should traverse the Body of the Mother, and the Teguments of the Child: And since Nature hath, in new-born Babes, contriv'd peculiar and Temporary Vessels, that the Blood may circulate thorow other Passages, than it is wont to doe in the same Individuals when they come to have the free use of their Lungs, it seems unlike∣ly, that Infants in the Womb do properly respire: But then since our Experiments have manifested, That almost all kind of Li∣quors do, as well as Water, abound with interspers'd Corpuscles of Air, it seems not altogether absurd to say, That when the Foetus is grown big, he may (especially the upper part of the involving Amnios, being destitute of Liquor, and fill'd only with an halituous substance) exercise some obscure Respiration; espe∣cially, since 'tis not (as many wise Men think it) a Fable, That Children have been heard to cry in the Mothers Womb: For though it happens exceeding rarely, yet sometimes it hath been observ'd. And I know a young Lady, whose Friends, when she was some years since with Child, complain'd to me, that she was several times much frighted with the Cries of her In∣fant, which, till I disabus'd her, she and her Friends look'd up∣on as Portentous. And such Observations are the more credi∣ble, because not only Houswives, but more judicious Persons, mention it as no very unfrequent thing to hear the Chick pip and cry in the Egg, before the Shell be broken. But this I men∣tion but as a probable, not a cogent Argument, till I can dis∣cover whether an Elision of an halituous Substance, though no true Air, may not at the top of the Larynx produce a Sound, since I find that the Blade of a Knife, held in several postures in

the stream of Vapors (or rarefied Water) that issues out of an AEolipile, will afford various and very audible Sounds.

I had thoughts of conveying into our Receiver young ones, ripped out of the Womb of their Dams, with their involving Coats intire, but could not procure them And I have also had thoughts of trying whether it be not practicable, to make a Receiver, though not of Glass, yet with little Glass windows, so placed, that one may freely look into it, capacious enough to hold a Man, who may observe several things, both touching Respiration, and divers other matters; and who, in case of fainting, may, by giving a sign of his weakness, be immedi∣ately reliev'd, by having Air let in upon him. And it seems not impossible, but that by accustomance, some Men may bring themselves to support the want of Air a pretty while, since we see that divers will live, so much longer than other Men, under Water: that those that dive for Pearls in the West Indies are said to be able to stay a whole hour under Water. And Cardan tells us of one Colanus a Diver in Sicily, who was able to continue (if Car∣dan neither mistake nor impose upon us) three or four times as long. Not to mind Your Lordship, that You have Your self oftentimes seen in England, a corpulent Man, who is wont to descend to the bottom of the Thames, and bring out of deep holes at the bottom of the Banks, large Fishes alive in his hands. And Acosta tells us, he saw in Peru the like manner of fishing, but more difficult, practised by the Indians.

I made mention of some Men, and of Accustomance: because there are but very few, who, though they use themselves to it by degrees, are fit to support, for many minutes, the want of Air. Insomuch that an ingenious Man of my acquaintance, who is very famous for the usefull skill of drawing Goods, and even Ordnance, out of sunk Ships, being asked by me how long he was able to continue at the depth of 50 or 60 foot un∣der Water, without the use of Respiration, confessed to me, that he cannot continue above two minutes of an hour, with∣out resorting to the Air, which he carries down with him in a certain Engine (whereof I can show Your Lordship a descrip∣tion.)

Another thing I also learn'd of him by enquiry, that was not despicable: For asking him, whether he found any use of chawing little Sponges, dipt in Oyl, in his mouth, when he was perfectly under Water, and at a distance from his Engine; he told me, that by the help of these Sponges he could much longer support the want of his wonted Respiration, than he was able to doe without them. The true cause of which, would perhaps, if discovered, teach us some thing pertinent to the Problem touching the Respiration of Fishes.

But the necessity of Air to the most part of Animals unaccu∣stomed to the want of it, may best be judg'd of, by the following Experiments, which we try'd in our Engine, to discover, whe∣ther Insects themselves have not, either Respiration, or some other use of the Air equivalent thereunto.

We took then an humble Bee, one of those common flyes that are call'd Flesh-flies, and one of those hairy Worms that resemble Caterpillars, and are wont to be call'd Palmer-worms: These three we convey'd into one of our small Receivers, and observ'd, to the great wonder of the Beholders, that not only the Bee, and the Fly fell down, and lay with their Bellies upwards; but the Worm it self seem'd to be suddenly struck dead: All of them being reduc'd to lie without motion, or any other dis∣cernable sign of life, within somewhat less (if we mistake not) than one minute of an hour: And this, notwithstanding the smallness of the Animals in proportion to the capacity of the Vessels: Which circumstance we the rather mention, because we found that the Vessel was not free from leaks. And to satis∣fie the Spectators, that't was the absence of the Air that caus'd this great and sudden change: We had no sooner re-admitted the Air at the Stop-cock, than all the three Insects began to shew signs of life, and by little and little to recover. But when we had again drawn out the Air, their motions presently cea∣sed, and they fell down seemingly dead as before, continuing moveless, as long as, by continuing to pump, the vessel was kept exhausted. This invited us thankfully to reflect upon the wise goodness of the Creator, who by giving the Air a spring, hath

made it so very difficult, as Men find it, to exclude a thing so necessary to Animals: And it gave us also occasion to suspect, that if Insects have no Lungs, nor any part analogous thereun∣to, the ambient Air afsects them, and relieves them at the Pores of their skin, it not being irrational to extend to these Crea∣tures that of Hippocrates; who saith, That a living Body is throughout perspirable; or to use his expression, 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, dispos'd to admit and part with what is Spirituous: Which may be somewhat illustrated by what we have elsewhere noted, That the moister parts of the Air readily insinuate themselves into, and recede from the pores of the Beards of wild Oats, and those of divers other wild Plants; which almost continually wreath and unwreath themselves according to, even, the light variations of the temperature of the ambient Air.

This Circumstance of our Experiment we particularly took no∣tice of, that when at any time, upon the ingress of the Air, the Bee began to recover, the first sign of Life she gave, was a vehemen panting, which appear'd near the Tail: Which we therefore men∣tion, because we have observ'd the like in Bees drown'd in Water, when they first come to be reviv'd by a convenient heat: As if the Air were in the one case as proper to set the Spirits, and Ali∣mental Juice moving, as heat is in the other; and this may, perchance, deserve a farther consideration.

We may add, That we scarce ever saw any thing that seem'd so much as this Experiment, to manifest, That even living Crea∣tures (Man always excepted) are a kind of curious Engines, fram'd and contriv'd by nature (or rather the Author of it) much more skilfully than our gross Tools and imperfect Wits can reach to. For in our present Instance we see Animals, vivid and per∣fectly sound, depriv'd immediately of motion, and any discern∣able signs of life, and reduc'd to a condition that dissers from death, but in that it is not absolutely irrecoverable. This (I say) we see perform'd without any, so much as the least external vio∣lence offer'd to the Engine; unless it be such as is offered to a Wind-Mill, when the Wind ceasing to blow on the Sails, all the several parts remain moveless and useless, till a new Breath put them into motion again.

And this was farther very notable in this Experiment; That whereas 'tis known that Bees and Flies will not only walk, but flie for a great while, after their heads are off; and sometimes one half of the Body will, for divers hours, walk up and down, when it is sever'd from the other: Yet, upon the exsuction of the Air, not only the progressive motion of the whole Body, but the very motions of the Limbs do forthwith cease; as if the presence of the Air were more necessary to these Animals, than the presence of their own Heads.

But it seems, that in these Insects, that fluid Body (whether it be a Juice or Flame) wherein Life chiefly resides, is nothing neaŕ so easily dissipable, as in perfect Animals. For whereas we have above-recited, That the Birds we conveyed into our small Receiver were within two minutes brought to be past re∣covery, we were unable (though by trying him that pump'd) to kill our Insects by the exsuction of the Air: For though, as long as the Pump was kept moving, they continued immova∣ble; yet when he desisted from pumping, the Air that press'd in at the unperceiv'd Leaks (did though slowly) restore them to the free exercise of functions of Life.

But, My Lord, I grow troublesome, and therefore shall pass on to other Experiments: Yet without despairing of your par∣don for having entertain'd you so long about the use of Respi∣ration, because it is a subject of that difficulty to be explain'd, and yet of that importance to humane Life, that I shall not regret the trouble my Experiments have cost me, if they be found in any degree serviceable to the purposes to which they were design'd. And though I despair not but that hereafter our Engine may furnish us with divers Phaenomena usefull to illu∣strate the Doctrine of Respiration; yet having not, as yet, had the opportunity to make the other trials, of various kinds, that I judge requisite for my Information: I must confess to Your Lordship, that in what I have hitherto said, I pretend not so much to establish, or over-throw this or that Hypothesis, as to lay together divers of the Particulars that occurr'd to me, in or∣der to a future inquiry. I say, divers of the Particulars, be∣cause

I could add many others, but that I want time, and fear that I shall need Your Lordship's pardon, for having been so pro∣lix in writing; and that of Physicians (which perhaps I shall more easily obtain) for having invaded Anatomy, a Discipline which they challenge to themselves, and indeed have been the almost sole Improvers of. Without denying then that the inspir'd and exspir'd Air may be sometimes very usefull, by condensing and cooling the Blood that passeth through the Lungs; I hold that the depuration of the Blood in that passage, is not only one of the ordinary, but one of the principal uses of Respiration. But I am apt also to suspect, that the Air doth something else in Re∣spiration, which hath not yet been sufficiently explain'd; and therefore, till I have examin'd the matter more deliberately, I shall not scruple to answer the Questions that may be asked me, touching the genuine use of Respiration, in the excellent Words employ'd by the acute St. Austin, to one that ask'd him hard Questions: Mallem quidem (says he) eorum quae à me quaesivi∣sti, habere scientiam quam ignorantiam: sed quia id nondum potui, magis eligo cautam ignorantiam confiteri, quam falsam sci∣entiam profiteri.

EXPERIMENT XLII.

HAving (partly upon the consideration of some of the fore∣going Experiments, and partly upon grounds not now to be insisted on) entertain'd a suspicion, that the action of Cor∣rosive Liquors in the dissolving of Bodies, may be considerably varied by the gravitation or pressure of the incumbent Air, and the removal of it; I thought fit to examine my Conjecture by the following Experiment.

I took whole pieces of red Coral, and cast them into as much spirit of Vineger, as sufficed to swim above an Inch over them: These substances I made choice of, that the Ebullition upon the Solution might not be too great, and that the opera∣tion might last the longer.

Having then put about half a score sprigs of Coral, together with the Menstruum, into a somewhat long neck'd Viol, whereof

they seem'd scarce to fill a third part, we convey'd that Viol into one of our small Pneumatical Glasses, containing by ghess about a Quart of Water; and having fastned on the Cover, after the ac∣custom'd manner, we suffered the Liquor to remain unmov'd a while, to observe whether the Menslruum would work upon the Coral otherwise than besore. But sinding there did only arise, as formerly, a pretty number of small Bubbles, that made there no sensible froth upon the surface of the distill'd Vineger, there were made two or three exsuctions of the Air; upon which, there emerg'd from the Coral such a multitude of Bubbles, as made the whole Body of the Menstruum appear white; and soon aster a Froth, as big as all the rest of the Liquor, was seen to swim upon it: And the Menstruum plainly appear'd to boil in the Glass, like a seething Pot. And though, if we desisted but one minute from pumping, the decrement of the Froth and Ebullition, upon the getting in of a little Air, at some leak or other, seem'd to argue, that the removal of the pressure of the external Air was the cause, or, at least, the occasion of this Ef∣fervescence: Yet to evince this the more clearly, we turn'd the Key, and let in the external Air at the Stop-cock; immediately upon whose entrance the Froth vanish'd, and so many of the Bubbles within the body of the Liquor disappear'd, that it lost its whiteness, and grew transparent again: The Menstruum also working as languidly upon the Coral, as it did before they were put into the Receiver: But when we had again drawn out the Air, first the whiteness re-appear'd, then the Ebullition was re∣new'd, which, (the pumping being a while longer and nimbly pursued,) grew so great, that for 3 or 4 times one aster another, when ever the Air was let out of the Receiver into the emptied Cylinder, the frothy liquor overflow'd the Glass, and ran down by the sides of it: And yet, upon the readmitting of the ex∣cluded Air, the boiling Liquor grew immediately as calm and as transparent as at first: As if indeed the operation of it, up∣on the Coral, had been facilitated by the exsuction of the in∣cumbent Air, which on its recess, lest it more easie sor the more active parts of the liquor to shew themselves such, than it was

whilst the wonted pressure of the Air continued unremoved. It may indeed be suspected, that those vast and numerous Bubbles proceeded, not from the action of the Menstruum upon the Co∣ral, but from the suddain emersion of those many little parcels of Air that (as we formerly observ'd) are wont to be dispers'd in Liquors, without excluding Spirit of Vineger; but having had this suspicion before we try'd the Experiment, we convey'd our distill'd Vineger alone into the Receiver, and kept it a while there, to free it from its Bubbles (which were but very small) before ever we put the Coral into it. It may be suspected like∣wise, that the agitation of the Liquor, necessary following up∣on the shaking of the Glass, by pumping, might occasion the recited Ebullition; but upon trial made, there appear'd not any notable change in the Liquor, or its operation, though the con∣taining Vessel were shaken, provided no Air were suck'd out of it. The former Experiment was another time try'd in another small Receiver, with Coral grosly powdred, and the success was very much alike, scarce differing in any thing, but that the Coral being reduc'd to smaller parts, upon the ebullition of the Liquor, so many little lumps of Coral would be carried and Boy'd up by the emerging Bubbles, as sometimes to darken the Viol, though the same Coraline Corpuscles would be let fall again upon the letting in of the Air.

Some thing also we try'd in our great Receiver, concerning the solution of Metals in Aqua fortis, and other Corrosive Liquors; but partly the stink, and partly some accidents, kept us from ob∣serving any thing peculiar and remarkable about those Solutions.

One thing we must not omit, that when the Spirit of Vineger was boiling upon the Coral, we took off the Cover of the Recei∣ver, and took out the Viol, but could not find, that notwithstan∣ding so very late an Ebullition, the Liquor had any heat great enough to be at all sensible to our hands.

EXPERIMENT XLIII.

WE will now subjoyn an Experiment, which, if the for∣mer did not lessen, the wonder of it would probably ap∣pear

very strange to Your Lordship, as it did to the first Spec∣tators of it.

The Experiment was this: We caus'd Water to be boil'd a pretty while, that by the heat it might be freed from the latitant Air, so often already taken notice of in common Water: Then al∣most filling with it a Glass Viol, capable of containing near four Ounces of that Liquor; we convey'd it, whilst the Water was yet hot, into one of our small Receivers (big enough to hold about a pound of Water) and having luted on the Cover, we caus'd the Air to be drawn out: Upon the two first exsuctions, there scarce appear'd any change in the Liquor, nor was there any notable alteration made by the third; but at the fourth, and afterwards, the Water appear'd to boil in the Viol, as if it had stood over a very quick Fire; for the Bubbles were much greater than are usually found upon the Ebullition of very much more Water than was contain'd in our Viol. And this Effer∣vescence was so great in the upper part of the Water, that the Liquor boyling over the top of the Neck, a pretty deal of it ran down into the Receiver, and sometimes continued (though more languidly) boyling there. Prosecuting this Experiment, we observ'd, that sometimes, after the first Ebullition, we were reduc'd to make divers exsuctions of the Air, before the Liquor would be brought to boil again. But at other times, as often as the Key was turn'd to let the Air pass from the Receiver into the Pump, the Effervescence would begin afresh, though the Pump were ply'd for a pretty while together; which seem'd to argue, that the boyling of the Water proceeded from hence, That upon the withdrawing the pressure of the incumbent Air, either the fiery Corpuscles, or rather the Vapors agitated by the heat in the Water (which last, what we have formerly noted touch∣ing the raresied Water of an AEolipile, manifest to be capable of an Elastical Power) were permitted to expand themselves mightily in the evacuated Receiver; and did, in their tumultuous Dilatation, list up (as the Air is wont to do) the uppermost part of the Water, and turning it into Bubbles, made the Water appear boiling. This conjecture was farther confirm'd by these additional

Circumstances: First, The Effervescence was confin'd to the up∣per part of the Water, the lower remaining quiet, unless the Liquor were but shallow. Next, although sometimes (as is al∣ready noted) the Ebullition began again, after it had ceas'd a pretty while, which seem'd to infer, That some concurrent cause (whatever that were) did a little modifie the operation of heat; yet, when the Water in the Viol could by no pumping be brought to boil any more, the self-same Water, being in the very same Viol warm'd again, and reconvey'd into the Pneumatical Glass, was quickly brought to boil afresh, and that vehemently and long enough; not to mention, that a new parcel, taken out of the same parcel of the boiled Water with the former, and put in cold, could by no pumping be brought to the least shew of Effervescence. Besides, having try'd the Experiment in hot Sallet Oyl, being a much more tenacious Liquor, and requi∣ring a stronger heat to make it boil, could not be brought to an Effervescence in our Receiver; whereas the Chymical Oyl of Turpentine, being thinner and more volatile, was presently made to boil up, till it reach'd four or five times the former height in the Viol, in whose bottom it lay, and continued boil∣ing till it was almost reduc'd to be but luke-warm. Wine also being a more thin and spirituous Liquor than Water, being convey'd in hot, instead of the Oyl, did, as I remember, at the very first exsuction begin to boil so vehemently, that, in a short time that the Pump was kept moving, four parts of five, by our ghess, boil'd over out of the Viol, though it had a pretty long Neck. On which occasion we will add, that even the Water it self, near one half, would sometimes boil over into the Receiver before it became luke-warm. And it was also remar∣kable, that once, when the Air had been drawn out, the Li∣quor did, upon a single Exsuction, boil so long with prodigious∣ly vast Bubbles, that the Effervescence lasted almost as long as was requisite for the rehearsing of a Pater Noster. Now the Experiment having been try'd more than once, and found to succeed as to the main, seems much to countenance the Conjec∣ture we made at the beginning of this Letter, where we told

Your Lordship, That perhaps the pressure of the Air might have an interest in more Phaenomena than Men have hitherto thought. For as we had not then made this Experiment, so now we have made it, it seems to teach, That the Air, by its stronger or weaker pres∣sure, may very much Modefie (as the School-men speak) divers of the Operations of that vehement and tumultuous Agitation of the small parts of Bodies, wherein the nature of heat seems chiefly, if not solely, to consist. Insomuch that if a heated Bo∣dy were convey'd above the Atmosphere, 'tis probable that the heat may have a differing operation, as to the power of dissi∣pating the parts of it, from what it hath here below.

To conclude, This Experiment might have been farther pro∣secuted, but our want of leisure makes us content our selves to add at present; That perhaps it would not be lost labour if this were try'd, not only with other Liquors, but with variety of heated, and especially soft or melted Bodies: But in such cases the Receiver ought to be shap'd, as is most proper to preserve the Ce∣ment where with the Cover must be fastned on, from being melt∣ed by the heat of the included Matter; the inconvenience to be hereby avoided, having befallen us in the use of a Receiver too shallow, though otherwise capacious enough.

The CONCLVSION.

BEing come thus far, My dear Lord, not without thoughts of proceeding farther: The unwelcome Importunity of my oc∣casions becomes so prevalent, that it quite hinders, for the present, my design'd Progress; and reduceth me, not only to reserve for another opportunity that kind of Experiments, which, at some distance from the beginning of this Letter, I call'd (as Your Lord∣ship may remember) Experiments of the second sort; but to leave unessay'd some of the first sort, which I might try in the Engine, as it now is, were it not that my Avocations are grown so urgent, for my remove from the place where the Engine was set up, that I am put to write Your Lordship this Excuse; Weary, and in an Inn which I take in my way to my Dearest Brother Corke: Who being at length arriv'd in England, after I have for

divers years been deprived of his Company, and wish'd for it as long; what ever my other Occasions may be, my first Business must be to wait on Him and Your excellent Mother; in whose gratefull Company I may hope to forget a while those publick Calamities that distress this too unhappy Nation, Since that is in∣dear'd to me, both by their personal Merit; by the near Relation which Nature gives me to Him, Affinity to Her, and Friendship to both; and also by their many Favours, especially that of my owing them My Lord of Dungarvan. But I suffer my self to be transported too far with these delightfull thoughts; To return therefore to our Engine. Though I find this Letter is beyond my expectation swell'd, not only into a Book, but almost into a Vo∣lume; yet the Experiments already mentioned in it, are so far from comprising all those that may be try'd by the help of our Engine, that I have not yet been able to try all those, which, pre∣sently occurring to my thoughts, upon my first seeing the work∣ing of it, I caus'd to be set down in a Catalogue within less than half an hour. But I doubt I have but too much cause to appre∣hend that the Affairs, and other things I complain of, have made it needfull for me to Apologize, as well for the things I have set down, as for those I am necessitated to omit. For as partial as Men use to be to the Children of their own Brains, as well as to those of their Loins, I must not deny that the foregoing Trials are not altogether free from such unaccuratenesses, nor the recital of them from such Imperfections, as I my self can now discern, and could, perhaps, partly mend, if I had the leisure to repeat the Experiments, with the Circumstances that have since offer'd themselves to my Thoughts, as things that might have been worth Observation or Enquiry. But the truth is, that I was re∣duc'd to make these Experiments, when my Thoughts had things that more concern'd me to imploy them, and the same avocations made me set them down, for the most part, as soon as I had made them, and in the same order, and that so fast, that I had not over∣frequently the opportunity to mind any more than the bare Truth of what I set down; without allowing it any of those ad∣vantages that Method, Stile, and decent Embellishments, are

wont to confer on the Composures they are imploy'd to adorn.

But, My Lord, though to invite and encourage You and Your learned Friends at Paris, to make a farther use of this Engine, than I have yet been able to doe, I am thus free to acknowledge the Im∣perfections of the foregoing Letter: Yet, if some Intelligent Persons mistake not, by what hath been done, such as it is, there is a way open'd, whereby Sagacious Wits will be assisted to make such farther Discoveries in some points of Natural Phylosophy, as are yet scarce dream'd of. And I am the more desirous to engage You to that Imployment, because I am apt to think, that if the making and writing of such Experiments shall cost You as much trouble as they have me, You will be inclin'd to excuse me; and if the Discoveries give You as much pleasure as they gave me, You will (perhaps) be invited to thank me. However, I think (My Lord) I may justly pretend, that the things I have set down have been faithfully Recorded, though not elaborately Written; and, I suppose, my former Papers may have long since satisfied You, that though many devise Experiments better than Your Ser∣vant, none perhaps hath related them more carefully and more truly: And particularly of These; sometimes one, sometimes ano∣ther, hath been performed in the presence of Persons, divers of them eminent for their Writings, and all for their Learning. Wherefore, having in the foregoing Narratives made it my busi∣ness to enoble them with the chief Requisites of Historical Com∣posures, Candor, and Truth, I cannot despair that You will either excuse their Imperfections, or, at least, forgive them: Especially, considering that this unpolish'd Letter is as well a Production of Your Lordship's Commands and my Obedience, as a Testimony of my desire to make others beholden to My Lord of Dungarvan, by the same way which I indeavour to express my Self

Beconsfield, this 20th of December, 1659.

His Lordship's Most obedient Servant, and Most affectionate Uncle,

ROBERT BOTLE.

Notes

• * 1.1

  In a Discourse touch∣ing fluidity and firm∣ness.
• * 1.2

  Schottus Me∣cham hydrau∣licopneumat. Part 3. Class. 1.
• * 1.3

  Natural and Moral Hist. of the Indies. Lib. 3. c. 9.
• * 1.4

  Geogr. Gene∣ral. Lib. 1. cap. 19.
• * 1.5

  Kirch. Art. Mag. Con. & Disson. lib. 9. p. 309.
• * 1.6

  See the fif∣teenth Fi∣gure.
• * 1.7

  P. Nic. Zucchius apud Scbot. part. 1. Mec. Hydraulopneum.
• * 1.8

  Aere frigido existente tardi∣us moventar Automata quam aere calido, adeo quidem at Automaton quod Belgae in Nova Zembla agentes in ae∣dibus suis collocaverunt om∣nino à motu cessaverit etsi∣multo majus pondus ei addi∣dissent quam antea serre so∣lebat. Varenius Geo: Gen∣eral. lib. 111. Propo: 7. pag. 648.
• * 1.9

  P: Nicol: Cab: lib: 4. Meteor: A∣ristot:
• * 1.10

  Senec. Nat. quest. lib. 4. cap. 10.
• * 1.11

  Ricciol. Alma. Nov. Tom. 2. lib. 10. sect. 6. prop. 50. Ex Magnan. lib. 1. Perspectivae horariae prop. 38.
• * 1.12

  Joseph. Acosta's Nat. and Mor. Hyst. of the Indies, jib. 3. cap. 9.
• * 1.13

  In lib. 4. Meleor. Arist.
• * 1.14

  Since the writing of this XLth Experiment, we pro∣cur'd a white Butter-Fly, and inclosed it in one of our smaller Receivers, where, though at first he fluttered up and down, yet presently, upon the exsuction of the Air, he fell down as in a swoon, retaining no other motion than some little trem∣bling of the Wings.
• * 1.15

  Epist. 3.
• * 1.16

  Fraelichius' apud Va∣ren. Geogra. Gener. lib. 1. cap. 19.