Tracts written by the Honourable Robert Boyle containing New experiments, touching the relation betwixt flame and air, and about explosions, an hydrostatical discourse occasion'd by some objections of Dr. Henry More against some explications of new experiments made by the author of these tracts : to which is annex't, An hydrostatical letter, dilucidating an experiment about a way of weighing water in water, new experiments, of the positive or relative levity of bodies under water, of the air's spring on bodies under water, about the differing pressure of heavy solids and fluids.

THE FIRST SECTION.

CHAP. I.

THe first Explication of mine, that the Learned Doctor ani∣madverts upon in his 12th Chapter, is, that which I give in the 33th of my Physico-Mechanical Experiments, touching the Spring and Weight of the Air; where I relate, that the Sucker in the Air-Pump of our En∣gine, having been forcibly depress'd to the lower part of the Brass Cylin∣der, which yet was carefully closed at the top, so that the cavity of the Cylinder was empty of Air; this Sucker, I say, would in this case ap∣pear spontaneously to remount to∣wards the top of the Cylinder, though

it were clogg'd with a hundred pound weight to hinder its ascent. Which Phaenomenon I ascrib'd to this, that the Sucker being, by the withdraw∣ing of the Air in the Cylinder, freed from the wonted force of the springy Air that endeavour'd to depress the internal part of it, was not inabled by the appendant weight to resist the pressure of an Atmospherical Cylin∣der equal in diameter to it, which, pressing against its lower or exter∣nal surface, endeavour'd to impel it up.

Now the Doctor having in the two first Paragraphs made a Description of my Engine, (which I shall now pass over) does in the third teach us, that the Corporeal cause, if there be any, of the ascent of the Sucker, must be, either in the Sucker it self, or in the almost exhausted cavity of the Cylinder, or lastly in the exter∣nal

Air: Which premised, he does in the same third Section, and in the fourth, endeavour to prove at large, that the cause is to be derived neither from the one, nor from the other of the two first. And therefore I, that maintain neither of the Opinions he disputes against, shall leave those Pa∣ragraphs of his untouch'd. Nor shall I meddle with the fifth, sixth, and se∣venth, where he argues against the explications of some, that would solve the Phaenomenon upon some Cartesian grounds, and as well amply as par∣ticularly against the solution that he supposes would be given of it con∣gruously to his own Sentiments by the Learned Regius. These Discourses, I say, of the Doctors I leave un∣touch'd; because 'tis at length in the eighth Paragraph, that he im∣pugnes that solution of the Phaeno∣menon, which he ascribes to me, whose

Opinion he first delivers, though not just in the terms I would express it my self; yet I dare say very sincere∣ly, and so near my sence, that I shall forthwith pass from the eighth Secti∣on to the beginning of the ninth, where he begins to propose his Ob∣jections, which he is pleas'd to usher in with a complement to me, that I should be very vain if I looked upon as any thing more than a Comple∣ment.

To his first Objection, propos'd in these words, * 1.1 Primò enim, si haec solutio verè mechanica sit, quae tandem Causa verè mechanica assi∣gnari potest gravitationis singularum particularum, totiúsque atmosphaerae in suis locis? Nam quod materiam subtilem attinet, &c. I answer, that I did not in that Book intend to write a whole Systeme, or so much as the Elements of Natural Philosophy; but

having sufficiently proved, that the Air, we live in, is not devoid of weight, and is endowed with an Ela∣stical Power or springiness, I endea∣vour'd by those two Principles to ex∣plain the Phaenomena exhibited in our Engine, and particularly that now under debate, without recourse to a Fuga Vacui, or the Anima Mun∣di, or any such unphysical Principle. And since such kind of Explications have been of late generally called Mechanical, in respect of their be∣ing grounded upon the Laws of the Mechanicks; I, that do not use to contend about Names, suffer them quietly to be so: And to entitle my now examined Explication to be Me∣chanical, as far as I pretend, and in the usual sence of that expression, I am not obliged to treat of the cause of Gravity in general; since many Propositions of Archimedes, Stevinus,

and those others that have written of Staticks, are confessed to be Mathe∣matically or Mechanically demon∣strated, though those Authors do not take upon them to assign the true cause of Gravity, but take it for granted, as a thing universally ac∣knowledged, that there is such a quality in the Bodies they treat of. And if in each of the Scales of an or∣dinary and just Ballance, a pound weight, for instance, be put; he that shall say, that the Scales hang still in Aequilibrium, because the equal weights counterpoise one another: and in case an ounce be put into one of the Scales, and not into the oppo∣site; he that shall say that the loaded Scale is depress'd, because 'tis urged by a greater weight than the other, will be thought to have given a Me∣chanical Explication of the Aequili∣brium of the Scales, and their losing

it; though he cannot give a true cause, why either of those Scales tends towards the Center of the Earth. Since then the assigning of the true cause of Gravity is not required in the Staticks themselves, though one of the principal and most known of the Mechanical Disci∣plines; Why may not other Pro∣positions and Accounts, that suppose Gravity in the Air, (nay prove it, though not à priori) be look'd on as Mechanical?

CHAP. II.

THe next thing the Doctor op∣poses to my Explication, is a resolute Denial, that there is any such Gravitation, as I pretend, of Bodies, or their Particles, in their

proper places. But because, for the proof of his negation, he refers us to the next Chapter, we shall hereafter have a fitter place than this to con∣sider it in.

Thirdly, he tells us, we may justly doubt of the equal diffusion of the Springy power, or the Pressure of the Air every way. In what sence, in some cases, I admit of a small inaequa∣lity between the pressure of Fluids against differing parts of a surrounded body, I have * 1.2 elsewhere declared, and need not here discourse of; since in the case before us, and in the like, that Pressure is inconsiderable enough to be safely neglected. And whereas our Author thus ar∣gues, * 1.3 Semotâ vi Elasticâ, par∣ticulae tamen Atmosphaerae deorfum tenderent. Est igitur depressio quae∣dam deorsum praeter vim Elasticam

ipsi superaddita; sursum non item sed elastica sola, éstque suppar ratio in pressionious transversis & obliquis. I presume, he did not sufficiently con∣sider our Hypothesis and the nature of the pressure of Fluid Bodies that have weight: For Water, to which no Springiness is ascribed, as there is to Air, but which acts by its weight and fluidity, is able upon the score of those Qualities to buoy up great Ships, that the ebbing Tide often leaves upon the strand.

And whereas the Learned Exami∣ner proposes a fourth Objection in these terms, * 1.4 Quibus omnibus addas, difficile esse intellectu, si unius Cylindri Atmosphaerae pondus ae∣qualis diametri cum Embolo reflectione in fundum Emboli derivetur, cur non quinque alii Cylindri Aeris qui cir∣cumstant Embolum in ejus fundum eo∣dem modo simul agere possunt, ita ut

vis sursum impellens Embolum sextuplo major sit quàm hactenus ab bujus opi∣nionis fautoribus existim ita est. Quod si sit, tunc certe, siquo artificio fieri possit ut unius solius Cylindri actio in Embolum admitteretur, re iquorum quinque exclusa, & pari tamen faci∣litate Embolus ascenderet, manifestum indicium esset, ne unum quidem Cylin∣drum Atsmosphaerae agere in fundum Emboli, sed totam Hypothesin, inge∣niosam tantummodo esse fictionem. I presume, Hydrostaticians will think, this might have been spared. For they will tell him, that there can no more of a fluid press directly upward against the Cylindrical Orifice of a Body immers'd in that fluid, than a Cylinder of that fluid of the same dia∣meter with the Orifice (the lateral pressures bearing against the lateral parts of the Cylinder.) And there∣fore if you invert, for instance, a

Pipe open at both ends, and filled to a certain height with Oyl, into com∣mon water; the Oyl that is kept up by the pressure of the water upwards, will keep at the same height as to sense, whether the Vessel that con∣tains the Water be broad or narrow, provided it be somewhat larger than the Orifice of the Pipe.

And now, to invalidate yet further the precedent Objections, made by the Doctor, I shall add, that it need not be thought incredible, that the Atmosphere by its weight, or the Spring of the Air compress'd by that weight, should be able to raise up fourscore or a hundred pound, hang∣ing at the Sucker: Since I have * 1.5 manifested two or three years ago by a clear and cogent Expe∣riment, that a little air included in a Bladder will by its meer Spring be

able to heave up a weight of a hun∣dred Pound, and this without the help of any rarefaction by heat. By which Experiment may be also con∣firmed, what I deliver'd a while since about the endeavour of the Air, that is wont to be included in our brass Cylinder, by expanding it self to thrust away the Sucker (which, in regard of the structure of the Pump, it can do no other∣wise than downwards,) with a de∣pressing force, aequivalent to the pressure upwards of the Atmosphere against the external part of the same Sucker.

CHAP. III.

BUt I shall not insist upon the foregoing Objections, because the Learned Doctor himself tells us,

that their attempts may seem to be but light skirmishes in comparison of that which follows. Whereunto I shall therefore apply my atten∣tion.

This grand Objection our Learned Adversary takes from the already often-mention'd ascent of the Sucker clogg'd with a hundred pound weight, and recommends by this introdu∣ction. * 1.6 Etenim ex ipsis Phae∣nomeni visceribus robustissimum jam contra omnem mechanicam illius solutionem Argumentum eruo, & quod non solum contra vim aeris elasticam suprà dicto modo explicatam militat, sed etiam contra Cartesianum illum aeris conatum nixúmque, &c. Which premis'd, the Argument it self is thus propos'd: * 1.7 Est enim (says he) juxta hujus experimenti Phaeno∣menon, vis illa aeris elastica (nixus∣que expansorius) major multo quàm

quae fieri potest à rerum natura, quám∣que quotidianis illis Phaenomenis con∣gruit. Nam si nixus hic elasticus tan∣tam vim elasticam haberet ut plus cen∣tum pondo plumbum sursum possit pro∣pellere, omnes profecto rerum terre∣strium compages tantâ violentiâ com∣primerentur, ut nullae, nisi quae ad∣modum firmiter compactae sint, tantae compressioni resistere possent, quin con∣fringerentur, vel partium collisione ita contererentur ut brevi tempore peri∣rent, &c.

Though this Objection be specious enough, yet it presents me with no difficulty, that I was not well aware of; as I presume you will easily per∣ceive by what you will meet with in the following Papers, especially that, which consists of Experiments and Considerations about the differing Pressures of Solids, Weights, and Am∣bient Fluids. The nature of which

Pressure and its aequality (as far as in our controversie 'tis needful to be suppos'd) will, I hope, satisfie you of the invalidity of the propos'd ob∣jections; especially since the Do∣ctrine it impugns, namely the Weight and Pressure of the Atmosphere, is not a bare Hypothesis, but a truth made out by divers Experiments, by which even profess'd Opposers of it have publickly acknowledg'd themselves to be convinced.

CHAP. IV.

IN the next Paragraph (which is the 11th.) the Learned Doctor adds a further Objection, wherein he supposes, that there is laid upon a wooden Scale, of the same diameter with the above-mention'd Sucker, a lump of Butter of the same largeness

with the Scale. Whence he argues, that if our Hypothesis take place, the Butter must be press'd against by two Cylinders of Air, the one pressing it upwards, the other downwards, and the pressure of them both amounting to two hundred pounds. But, sayes he, the Butter is not press'd at all, as appears by this, that no serous hu∣mour is squeez'd out of it towards the edges, not so much as in those parts that lie parallel to the Hori∣zon, whence the Conclusion seems easie to be deduc'd.

But in the 12th Paragraph, the Doctor himself proposes a Solution, which he might easily foresee I would employ to invalidate his Argument; Namely, that the Air pressing, as well against the sides of the Butter, as against the top and bottom, hin∣ders the Mass from horizontally ex∣tending it self. And whereas, by

way of reply to this subterfuge, as 'tis call'd in the margent, he sub∣joynes, * 1.8 Cui respondeo, quòd tamen hoc nihil prohibet quo mi∣nùs in omnes partes horizontales ex∣primatur humor serosus & lacteus, si revera esset ulla hujusmodi pressura elastica qualis fingitur. The Reply is easie, that the pressure of the am∣bient Air, which is a fluid more sub∣til than Butter-milk, will as well hin∣der the starting out of that liquor as of the parts of the Butter it self: As he will easily grant, that attentively considers the nature of the thing, and remembers how Air keeps Water from running out at the little holes of a Gardeners Watering-pot clos'd at the top. What the Objector adds about the extrusion of what he calls a sub∣tiler Element (supposed to be har∣bour'd in the Butter) by the pres∣sure of the Atmosphere, in case it had

any, I think it would not be difficult to answer, if we consider'd, that a great and undeniable pressure ap∣plied to water does not sensibly con∣dense it, or deprive it of its fluidity, because of the grossness and strength of its parts. But the Argument be∣ing but transiently mention'd by the Author, and grounded upon a Car∣tesian supposition that I never em∣ployed, I leave it to those that may think themselves concern'd (which I am not) to make a solemn answer to.

And whereas our Learned Exami∣ner superadds, * 1.9 Quod tametsi butyri massa in disci lignei spe∣ciem reducta, cujus margo centum vi∣cibus areâ sit minor, interque duas laminas ligneas ejusdem formae ac lati∣tudinis posita, filis sus•• enderetur in aere tanquam in lance, ita ut pressura aeris elastica quà ab infra, quà de∣super

ducentis fere vicibus excessura sit pressionem in marginem butyri, buty∣rum tamen nihilo arctiùs comprimetur per vim aeris elasticam, nec aliter hîc afficietur quàm antea: He seems not to have sufficiently consider'd the Laws of the Hydrostaticks, according to which, supposing the pressure of the Atmosphere that he rejects, the Butter ought not to be deprived of its shape. For the pressure of the am∣bient Air, being equal on all sides, if we suppose the superficies of the But∣ter to be distinguish'd into a multi∣tude of little equal portions, each of these, whether they be scituated Ho∣rizontally, or on the edges, can be press'd against but by an Atmosphe∣rical Pillar equal to its Basis; and the Horizontal portions, if I may so call them, cannot be thrust out of place, without there be at the same time squeez'd out some of the Lateral por∣tions,

which yet cannot be so dis∣placed, because they also are with equal force press'd (inwards) by little aerial Pillars, whose Bases are contiguous to them, and bear against them. Which Answer, though of it self sufficient, may be much confirm'd by the Instance, you will hereafter meet with, of a lump of Butter that kept its irregular shape, in spight of a great and manifest pressure of the wa∣ter that surrounded it.

And this Answer may suffice to dis∣prove, what the Doctor annexes in the beginning of the 13th Paragraph, about the vast excess of Pressure, which the Air exercises upon the flat and Horizontal surfaces of the above-mention'd lump of Butter, in com∣parison of the pressure the Marginal parts of its surface can be exposed to. What he adds, and illustrates with a Scheme, about the hands being

assisted with the pressure of the Air, it concerns not me to answer. But whereas among the places where the Elastical power of the Air is under∣stood not to reach, he reckons a Pail full of water, with a lump of butter put in it; he supposes that, which our Hydrostaticks will by no means allow, and which is disproved by se∣veral both of our former Experiments, and by those you will meet with in the following Papers. By which it appears, that the pressure of the At∣mosphere is exercised, as indeed I do not see what should hinder it from being, even upon Bodies that are quite immers'd under water; and by which, added to what has been hi∣therto discours'd in answer to the Learned Doctors Objections, you will easily judge, how deservedly he shuts up the Arguments, we have been examining, with this Conclu∣sion.

* 1.10 Adeo ut extra omnem controversiam positum videa∣tur, quòd nulla est ejusmodi vis ela∣stica in aere, qualem è doctis non∣nulli supponunt, multoque minus tam fortis ut centum librarum pondus su∣peret. Quod erat Demonstrandum.

CHAP. V.

BUt this is not all the Doctor ur∣ges against me in this Chapter; for in the 14^th Paragraph he seconds his former argument by another, drawn from this Experiment of mine, That having taken two round Mar∣bles, whose surfaces, that were to be contiguous, were as well ground ve∣ry flat as carefully polish'd; and ha∣ving placed them one directly upon the other, they did in a horizontal

posture so firmly cohere, without the help of any Glue, * 1.11 or viscous Body, that the upper Marble being pull'd up, would take up the lower, though clogg'd with a weight of fourscore and odd pounds.

This Experiment, when I many years ago first publish'd it, I referr'd to the action of the Atmosphere, which pressing equally and strongly against the surfaces of both the Mar∣bles, except where they were conti∣guous, the higher could not be drawn directly upwards from the lower (and consequently must be follow'd by it) by a less force than that which was equivalent to the weight of as great a Cylinder of the Atmosphere as lean'd upon the upper Marble.

This Experiment thus explain'd, though it hath been judged a very fa∣vourable

one to the Hypothesis on whose behalf I alledged it, does yet to the justly famous Doctor seem a very considerable Argument against it, though for this judgement of his he urges only this reason, That if the force, with which the Air presses the lower Marble against the upper, be able to sustain that Marble, though clogg'd with the great weight above mention'd, the same pressure of Air would much more easily support a Plate of wood brought to a true plain, and not loaded with any weight, if the wooden Plate were substituted to the lower Marble, and instead of it applied to the upper.

But since the Experiment, as I pro∣posed it, did upon tryal succeed ve∣ry well, it had not been amiss if the Learned Examiner had consider'd it as it was really and successfully made, and shewed why the pressure of the

ambient Air was not able to hinder the separation of the Marbles: And his needless substitution of a Wooden plate instead of the lower Marble ea∣sily suggests a suspition, that there may lie some fallacy, though not in∣tended by him, in the variation he proposes of the Experiment. And he seems to have himself had thoughts of this kind, by taking notice, that it may be answer'd on our behalf, that a Wooden Plate cannot be so exactly applied to the upper Marble, but that there will be a little Air intercepted between it and the bottom of that stone. And though having granted that it may be so, he employes two pages to shew, that this intermediate Air could not keep the pressure of the Atmosphere from supporting the un∣clogg'd plate of wood, if it had been That pressure, which, when there was no such intermediate Air, had sustain'd

the lower Marble with all the appen∣dant weight; yet I confess his Proofs seem not to me to be answerable to the Assurance he uses in speaking of them. His Examples taken from Gunpowder and Wind, you will easily judge not to be very proper, where we are not considering a force that acts by a sudden and vanishing Im∣petus, but a constant and equal pres∣sure. And as to his other Instance, which is taken from five men that thrust against the sixth (standing with his back to a Wall) who is but as strong as any one of them: I answer, that neither is this example near e∣nough of kin to our case. For each of these five men is supposed to have an equal power of thrusting, proper to himself, and independent from all or any of the other four. And the sixth man is likewise supposed to re∣sist but by his own single force, with∣out

having his power of reacting in∣creas'd by the force wherewith the o∣thers thrust against him. But in our case the thing is quite otherwise; for supposing that some aerial particles be so placed that a solid Body hinders them to recoil or expand themselves, we are to consider, that, as the conti∣guous corpuscles of air press against them not by their own single weight or pressure, but as they transmit the action of all the other particles of the air which by their weight or pressure thrust them on; so the aerial parti∣cles, contiguous to the solid Body, resist not barely by that force which they would have if they were not com∣press'd, but by vertue of the Sprin∣giness they acquire upon the score of the forcible inflection they sustain from the action of the corpuscles, that either mediately or immediately thrust against them; and consequently, in

proportion to that external force, the Elasticity of these compress'd Parti∣cles will be increased, as we see that a Bow or other Springy body, the more it is bent by an external force, the greater power it has to resist further compression. Upon which grounds it need to be no wonder, that a small portion of Air, being almost included in a solid Body, and having for some (though but very little) time been exposed to the outward air, should be capable of resisting the pressure of as much of the whole Atmosphere, as can come to press against it. For, this pressure of the Atmosphere being continual, if the Springiness of the aerial particles were not now great enough to resist that pressure, they must necessarily have been before∣hand inflected or compress'd by it, till the endeavours of the one and the other were reduced to an Aequipol∣lency.

Of which I shall give you an instance in so obvious a body as a Bubble at the top of water: For though there be but a little Air in∣cluded in a very thin and transparent film of water; yet this little air is so well able to resist the weight of all the Atmosphere that can come to bear a∣gainst it, that all the pressure of it is not able to make the film shrink, or become wrinkled; which it would do, if the corpuscles of the Internal air were not reduced to a Springiness, which makes its power of resisting equal to the endeavour of the Exter∣nal Atmosphere to compress it. And to let you see, that we may well con∣ceive such a Springiness of the air included in the Bubbles, I have else∣where related, how by barely with∣drawing the pressure of the ambient air from Glass-Bubbles hermetically sealed with air in them not compress'd

beyond its usual state, the Spring of the Internal air would make the Bubbles fly in pieces: And this will happen to stronger Glasses than Bub∣bles, as you will find in one of the former Experiments * 1.12. And if we would illustrate what we are debating of by an Example; it should not be by considering, as the Doctor does, the endeavour of five men against the sixth that hath his back to the Wall; but that of five Bladders full of air, pil'd up, and resting upon a sixth. For in this case, whatever force or power of pres∣sing we suppose in the incumbent Bladders, they all bear jointly upon the lower, which continuing at a stand, must thereby be so compress'd as to be able to resist their joint endeavours, as 'tis manifest; because otherwise it would not continue in that state, but

be farther compress'd; which is against the supposition.

This Notion about Pressure and Resistance I have the more particu∣larly deduced, because I found many modern Naturalists, and even Hydro∣staticians themselves to be great stran∣gers to it. For which reason I shall add, that I have evinc'd it by pur∣posely devised Experiments in the Continuation of the Physico-Mecha∣nical Experiments * 1.13 a∣bout the Air. Were it not for this, I should per∣haps have spared my self the labour of setting down these thoughts as not necessary to the solution of the Do∣ctors Objections. For he admits a Layer, or (as he aptly speaks) an Area of Aerial Particles to be inter∣posed between the upper Marble and the Wooden Plate; and therefore the flatness and stiffness of those two Bo∣dies

must keep them from an imme∣diate contact as well at the edges as by the help of the same Area they do elsewhere; and consequently that in∣terposed Air may communicate with the ambient Air. From whence the Laws of the Hydrostaticks (which I have elsewhere shewn) will allow me to conclude, that the weight of the Atmosphere endeavours to depress the upper surface of the wooden Plate; and so what the Examiner urges of the inconsiderable resistance, that the few Aerial Particles interposed be∣tween the flat Bodies can make to the great pressure of the Column of Air that thrusts the Woodden against the Marble Plate, would not conclude, though our former answer could not have been made; since the resistance, made by the interposed Aerial Par∣ticles to the pressure upwards of the Atmosphere, is not in our present sup∣position

made by those Particles a∣lone, but by the weight of the lateral and superior part of the Atmosphere exercised by the intervention of these Particles. Which being so, what the Learned Doctor adds, that the weight of the wooden Plate it self is here of no consideration, must needs be a mi∣stake. For the two equal Atmosphe∣rical Pressures, the one against the upper surface of the woodden Plate, and the other against the lower, coun∣tervailing and consequently frustra∣ting the endeavour of each other, the gravity of the wood it self will suffice to make it fall, as well as if it were press'd against by neither of them. And from this Discourse you will ea∣sily judge, whether the Doctor had reason to say as he does, * 1.14 Quam ab omni ratione (igitur) ab∣sonum est, ut superficies illa sive area aerearum particularum, quae insinuant

se laminam ligneam inter & marmor, solidam columnam hujusmodi particu∣larum, vi elastica sursum enitentium, contra laminam ligneam obnitendo vincat, ipsamque laminam in terram de∣turbet.

CHAP. VI.

WHat he adds in the sixteenth number against those that fancy the Aerial Particles to be en∣dow'd with Perception, and to act with Design pro re nata, does not at all concern me; and what he adds in the next Paragraph, wherewith he concludes his twelfth Chapter, I shall altogether pass by, as far as it con∣cerns the extravagant conceit he op∣poses. But because at the close of the Paragraph, he makes an Inference,

which comprises our Opinion also; since he concludes, that the Experi∣ment by him alledged, * 1.15 Cer∣tissimum est indicium, particulas Aerias nec cum consilio nec sine con∣silio inferius marmor sustinere nec suf∣fulcire: It will not be amiss to shew, that our Opinion is undeservedly in∣cluded in the Inference; which I shall do by briefly solving the Phae∣nomenon the Doctor layes so much weight on. For if we conceive with him, that the two flat Marbles for∣merly mention'd be suspended, and that to the lower of them a flat wood∣den plate of the same shape and extent be applied; I see no cause to wonder, why the two Marbles should stick to∣gether, and not the lower of them to the woodden plate. For, as I lately noted, there being an Area or Bed of Aerial Particles interpos'd be∣twixt the Marble and the Wood, the

weight of the Atmosphere, exercised by the intervention of those Aerial Corpuscles, ought to be aequipollent to the pressure of the Atmospherical Cylinder, that bears against the lower surface of the Plate; which conse∣quently by its own weight must drop down: whereas there being no such Layer of Aerial Particles interposed betwixt the two Marbles, the pres∣sure of the ambient Atmosphere, which touches them every where, save where their polish'd surfaces are contigu∣ous, must keep them strongly cohe∣rent.

I presume I need not mind you, that hitherto I have discours'd upon supposition, that the Doctor experi∣mentally knows, what he delivers concerning the Non-adhesion of an exactly smooth woodden Plate to a Marble one: And upon his conces∣sion, that, because of the want of

sufficient congruity between the sur∣faces of two Bodies, there is a bed of Aerial Corpuscles interposed between them. But now I think, it will not be unfit to take notice to you, that though, to illustrate on this occa∣sion a subject that is generally so little understood, as the exercise of Pression among fluid Bodies, I have answer'd my Learned Adversaries Objections, as if I had nothing more to say for my Explication of the Suspension of coherent Marbles, than what I many years since deliver'd in the little Tract by him cited; yet I have since abundantly confirmed that Explication by the 50th of the Expe∣riments publish'd in my Continua∣tion; which if the Doctor had been pleased to read, perhaps he would have received the same satisfaction that other Learned men have done: since there I experimentally shew,

that the undermost Marble without the accustomed Clog, would, upon the bare withdrawing of the sustain∣ing air, drop off from the upper. And whereas the two Marbles in our Va∣cuum would not cohere; as soon as the formerly excluded Air was let in upon them, it did by its supervening pressure make them stick together ve∣ry strongly.

Notes

• * 1.1

  139.
• * 1.2

  See the Hy∣drostatical Paradoxes, esp. cially Parad. 7.
• * 1.3

  p. 139.
• * 1.4

  p. 139.
• * 1.5

  See Continuat. of New Exper. Physico-Mechan. Exp. 48. p. 165.
• * 1.6

  p. 140.
• * 1.7

  p. 140.
• * 1.8

  p. 142.
• * 1.9

  p. 142.
• * 1.10

  p. 143.
• * 1.11

  See the Hist. of Flu∣idity and Firmness, p. 222. of the second E••ition.
• * 1.12

  See the Tract about the Pres∣sure of the Airs Spring on bo∣dies under wa∣ter.
• * 1.13

  Exper. 25. and elsewhere.
• * 1.14

  p. 146.
• * 1.15

  p. 150.