New experiments physico-mechanical, touching the air

A DEFENCE Of Mr. R. BOYLE's EXPLICATIONS of his Physico-Mechanical EXPERIMENTS, against FRANCISCUS LINUS.

The I. Part. Wherein the Adversaries Objections against the Elaterists are examined.

CHAP. I.

A Newly-published Treatise, De Corporum insepara∣bilitate, being brought to my Hands, I find several Chapters of it employ'd to oppose the Explications I ventur'd to give of some of my new Experiments touching the Spring of the Air. Wherefore though I am very little delighted to be engag'd in Controversies, and though I be not at present without Employments enough (of a private, and of a publick Nature) to make it unseasonable for me, to be by a Work of this sort diverted from them; yet for the Reasons specified in the Preface, I hold it not amiss to examine briefly what is ob∣jected against the thing I have delivered: and the rather, partly, because the learned Author, whoever he be (for 'tis the Title-Page of his Book that first acquainted me with the name of Franciscus Linus) having forborn provoking Language in his Objections, allowes me in answering them to comply with my

Inclinations and Custom of exercising Civility, even where I most dissent in point of Judgment. Besides, the Author himself has somewhat facilitated my Reply to him, by directing me in the ninth Page to some Books and Passages that I had not, when I publisht my Epistle, either seen or taken notice of. As indeed there are besides some of these several other Discourses that treat of the Torrecellian Experiments, which though by the names of their Authors I guess to be learnedly written, I have not to this day had opportunity to peruse, my stay in the remo∣ter part of Ireland (whither Philosophical Books were not, in that time of publick Confusion, brought) having kept me from hearing of divers of them, till they were all bought up. Which I here mention, to excuse my self if I have not taken notice of some things or passages to be met with in these Writings, which their Learned Authors or Inquisitive Readers might justly per∣haps expect I should take some notice of, in case those Writings had fallen into my hands. But to digress no further.

'Tis true indeed, and it somewhat troubles me that it is so, that I can scarce promise my self to make my Adversary a Pro∣selyte, since he without scruple assumes those very things as Principles, that to me seem almost as great Inconveniences as I would desire to shew any Opinion I dislike, to be liable unto. But since whatever Operation the following Discourse may have upon the Person that occasion'd it, I hope it may bring some sa∣tisfaction to those Philosophers who can as little as I understand the Aristotelean Rarefaction, and who will as well as I be back∣ward to admit what they cannot understand; it shall suffice me to defend the Truths I have deliver'd, if I cannot be so happy as to convince my acute Adversary of them; and I shall not believe my labour lost, if this Discourse can contribute to the Establish∣ment of some Notions in Philosophy that I think not inconside∣rable in the minds of those whose clear Principles make me the most respect their Judgements, and for whose sakes I principal∣ly write.

Now though I be not in strictness oblig'd to defend any more than such of my own Explications as the Examiner has thought

fit to question, and those Particulars which I have added by way of Improvement to the two Hypotheses of the Spring and Weight of the Air; yet that I may the more effectually prose∣cute what I lately intimated I aim at in this Writing, and may as well illustrate my Doctrine as defend it, I shall divide the en∣suing Treatise into three Parts; whereof the first is design'd to answer my Adversaries Objections against our Principles; the second shall examine the Funicular Hypothesis he would substitute in their stead; and the third shall contain particular Replyes to what he alledges against some of my particular Explications.

CHAP. II.

ALthough our Author confesses in his second Chapter, that the Air has a Spring as well as a Weight, yet he resolutely denies that Spring to be near great enough to perform those things which his Adversaries (whom for brevities sake we will venture to call Elaterists) ascribe to it. And his whole fourth Chapter, as the Title declares, is imploy'd to prove that the Spring of the Air is unable in a close place to keep the Mercury suspended in the Torrecellian Experiment. The proof of this Assertion he sayes is easie: But alledges two or three Arguments for it, which I think will be more easily answer'd than his Asser∣tion evinc'd.

In the First he sayes that those Experiments concerning the Adhesion of ones finger, &c. which he had mentioned in the foregoing Chapter, eodem modo se habent in loco clauso ac in aper∣to. But the answering of this we shall suspend till anon; partly, because it may then be more conveniently examin'd, and partly, because our Author seems not to build much upon it, his chief Ar∣gument being that which he proposes in these words, Cum tota vis hujus Elaterii pendeat à refutato jam aëris aequi∣pondio cum digitis 29½ argenti vivi, it a ut nec plus, nec * 1.1 minus faciat hoc elaterium in loco occluso, quam fit per il∣lud aequipondium in loco aperto; manifestum est, cum jam ostensum sit fictitium planè esse hujusmodi aequipondium, fictitium quoque esse tale elaterium. Wherefore since all the validity of his Objection

against the Spring of the Air depends upon his former Chap∣ter, wherein he thinks he has disprov'd the Weight of the Air; it will behove us to look back into the former Chapter, and ex∣amine the four Arguments which he there proposes. But I must crave leave to vary from his method, and consider the third in the first place, because the removal of that Objection will faci∣litate and shorten the answer to the rest. His Third Argument therefore is thus set down. Nam si Tubus viginti tantum digi∣torum (quo usi sumus in primo Argumento) non totus impleatur argento, ut prius, sed spacium aliquod inter * 1.2 digitum superiorem & argentum relinquatur in quo sit solus aër; videbimus subtracto inferiore digito superiorem non solum deorsum trahi, ut prius, sed etiam argentum jam descendere, idque nota∣biliter, quantum nimirum extendi potest exiguailla aëris particula à tali pondere descendente. Unde st loco illius aëris ponatur aqua, aliusve liquor qui non tam facilè extenditur, descensus nullus erit.

Hinc, inquam, contra hanc sententiam formatur argumentum: nam st externus ille aër nequeat vel hos viginti digitos argenti à lapsu sustentare, uti jam vidimus, quomodo quaeso sustentabit 29½? Certè haec nullatenus reconciliari possunt.

But to this Argument, which he thinks so irreconcilable with his Adversaries Hypothesis he has himself furnisht them with an Answer in these words, Dices forte ideo argentum in hoc casu de∣scendere, quia deorsum truditur ab aëre illo sese per suum Elaterium dilatante. Which Anfwer I think sufficient for the Objection, notwithstanding the two exceptions he takes at it.

For first, whereas he sayes, that sic deberet digitus potius à tubo repelli, quam eidem affigi, cum non minus sursum quam deorsum fiat bujusmodi dilatatio: He considers not, that though the endea∣vour of the included Air to expand it self be at first every way alike, yet the expansion it self in our case must necessarily be made downward, and not upward; because the Finger that stops the Tube being expos'd on the upper parts and the sides to the external Air, has the whole Weight and pressure of the Atmosphere upon it; and consequently cannot be thrust away

but by a force capable to surmount that pressure: whereas on the lower side of the Included Air there is the Weight of the whole Mercurial Cylinder to assist the Spring of the Air, to sur∣mount the Weight of the Atmosphere that gravitates upon the restagnant Mercury. So that the Air included and endeavouring to expand it self, finding no assistance to expand it self upward, and a considerable one to expand it self downward, it is very natural that it should expand it self that way whence it finds less resistance. As accordingly it will happen, till the Spring of the Air be so far debilitated by its Expansion, that its pressure, together with the weight of the Mercury that remains suspended, will but counter-balance, not overcome, the pressure of the out∣ward Air upon the restagnant Mercury. And this explication may be confirm'd by this trial that I have purposely made, namely, that if in stead of Quicksilver you employ Water, and leave as before in the Tube an Inch of Air, and then inverting it, open it under Water, you will perceive the included Inch of Air not to dilate it self any thing near (for I need not here define the Proportion) half so far as it did when the Tube was almost fill'd with Mer∣cury; because the Weight of so short a Cylinder of Water does but equal that of between an Inch and an Inch and an half onely of Quicksilver, and consequently the inward Air is far less assisted to dilate it self and surmount the pressure of the out∣ward Air by the Cylinder of Water than by that of Mercury. And as for what our Author sayes, that if instead of Air, Water or some other Liquor be left at the top of the Tube, the Quick∣silver will not descend: the Elaterists can readily solve that Phae∣nomenon, by saying that Water has either no Spring at all, or but an exceeding weak one; and so scarce presses but by its Weight, which in so short a Cylinder is inconsiderable. Now the same solution we have given of our Examiners Objection, gives us also an account why the Finger is so strongly fastned to the upper part of the Orifice of the Tube it stops; for the included Air being so far dilated that an Inch, for example, left at first in the upper Part of the Tube, reaches twice or thrice as far as it did before the descent of the Quicksilver, its spring must be pro∣portionably

weakned. And consequently that part of the Finger that is within the Tube will have much les pressure a∣gainst it from the dilated Air within, than the upper part of the same Finger will have from the unrarefi'd Air without. By which means the Pulp of the Finger will be thrust in (which our Author is pleas'd to call suckt in) as we shall ere long have occasion to declare in our Answer to his second Argument.

And having said thus much to our Authors first exception against the solution he foresaw we would give of his third Ar∣gument; we have not much to say at present to this second. For whereas he sayes, Concipi non posse quomodo aër ille sic se dilatet, argentumque deorsum trudat, nisi occupando * 1.3 majorem locum: Quod tamen hi Authores quam maxime refugiunt, asserentes rarefactionem non aliter fieri, quam per corpuscula aut vacuitates: I wish he had more clearly express'd himself, since as his words are couch'd I cannot easily guess what he means, and much less easily discern how they make an Argument a∣gainst his Adversaries. For, sure he thinks them not so absurd, as to imagine that the Air can dilate it self, and thrust down the Mercury, without in some sense taking up more room than it did before: For the very word Dilatation, and the effect they ascribe to the included Air, clearly imply as much; so that I see not why he should say that they are so averse from granting the Air to take up more Place than before, especially since he takes notice in the former Chapter, that we compare the Expansion of the Air to that of compress'd Wooll; and since he here also annexes that we explicate Rarefaction either by Corpuscles or Vacuities. But this later Clause makes me suspect his meaning to be, that the Elaterists do not admit that the same Air may adequately fill more of Place at one time than at another; which I believe to be as true as that the self-same lock of compress'd Wooll has no more Hairs in it, nor does adequately fill more Place with them, when it is permitted to expand it self, than whilst it remain'd compress'd. But against this way of Rare∣faction our Author here has not any Objection, unless it be in∣timated in these words, Concipi non potest: Which if it be,

I shall need onely to mind him in this place, that whereas many of the chiefest Philosophers, both of Ancient and our own times, have profest they thought not the Aristotelean way of Rarefaction conceivable; and he acknowledges (as we shall see anon) that it is not clear; what the ablest of his Party (the mo∣dern Plenists) are wont to object against the way of Rarefaction he dislikes, is, that it is not true, not that it is not intelligible.

CHAP. III.

OUR Authors Second Objection (for so I reckon it) is thus propos'd by him. Si sumatur tubus utrinque apert us sed longior, puta digitorum 40. Argentoque impleatur, eique * 1.4 digitus supernè applicatur ut prius, videbimus subtracto inferiore digito, argentum quidem descendere usque ad consuetam suam statio∣nem; Digitum autem superiorem fortiter intra tubum trahi, eique firmissime, ut prius, adhaerere. Ex quo rursum evidenter conclu∣ditur, argentum, in sua statione constitutum, non ibidem sustentari ab externo aëre, sed à funiculo quodam interno suspendi, cujus su∣perior extremitas, digito affixa, eum sic intra tubum trahit, eique affigit. But this Argument being much of the same nature with that drawn from his third Experiment, the Answer made to that and to his first may be easily apply'd, and will be suffi∣cient for this also; especially because in our present case there is less Pressure against the Pulp of the Finger in the inside of the Tube than in the third Experiment (where some Air is inoluded, though much expanded and weakned;) the Pressure of the At∣mosphere being in the present case kept off from it by the subja∣cent Mercury, whereas there is nothing of that Pressure abated against the other parts of the Finger that kept it off from the de∣serted Cavity of the Tube, save onely that from the Pulp that is contiguous to the Tube, there may be somewhat of that Pres∣sure taken off by the Weight of the Glass it self. But as for that Part of the Finger which immediately covers the hole, whether or no there be any Spring in its own fibres, or other constituent substances, which finding no resistance in the place deserted by the Quicksilver, may contribute to its swelling (for that we will

not now examine) he that has duly consider'd the account al∣ready given of this Intrusion of the Pulp into the Glass, will find no need of our Authors internal Funiculus, which to some seems more difficult to conceive, than any of the Phaenomena in Controversie is to be explain'd without it.

CHAP. IV.

BY what we have already said against our Examiners Third Argument, we may be assisted to answer his first, though he propose it as a very clear Demonstration; and though it be indeed the principal thing in his Book. Sumatur (sayes he) tubus brevior digitis 29½ puta digitorum 20. non tamen clausus altero extremo, (ut hactenus) sed utrinque apertus: * 1.5 Hic Tubus, immerso ejus orificio Argento restagnanti, suppositoque digito, ne effluat Argentum Tubo infundendum, impleatur Argento vivo: alius{que} deinde digitus orificio quo{que} applicetur, illud{que} bene claudat. Quo facto, si subtrahatur inferior digitus, sentietur superior vehementer trahi ac sugi intra tubum, tam{que} pertinaciter ei (vel argento potius, ut postea) adhaerere, ut ipsum tubum cum toto argento incluso facilè elevet teneat{que} in vase pendulum.

Ex quo sane experimento clarissimè refellitur haec sententia: Cum enim, juxta eam, Argentum in tubo hujusmodi 20. tantum digitorum, sursum trudatur à praeponderante aëre externo: nun∣quam profecto per eam explicabitur, quomodo digitus ille sic traha∣tur deorsum, tubo{que} tam vehementer adhaereat; non enim à tru∣dente sursum potest sic deorsum trahi.

Thus far our Authors objection, in answer whereunto I have divers things to represent, to shew, that a good account may be given of this Experiment in the Hypothesis of the Elaterists, which is sufficient to manifest how far the argument is from being so un∣answerable as the proposer of it would perswade his Reader.

I deny then that the Finger is drawn downward, or made by suction to adhere to the Tube; but I explicate that which he calls the suction of the Finger, as I lately did in answer to his third Argument, as we shall more particularly see anon.

He sayes indeed, that the Air which thrust up the Quicksilver

cannot so strongly draw down the Finger. As if the Air were not a fluid body, but a single and entire pillar of some solid matter. But to shorten our Reply to his Objections, the best way perhaps will be briefly to explicate the Phaenomenon thus:

When the Tube is fill'd with Quicksilver, the Finger that stops the upper Orifice is almost equally press'd above and at the sides by the contiguous Air; but when the lower Finger is re∣mov'd, then the Cylinder of Mercury, which before gravitated upon the Finger, comes to gravitate upon the restagnant Mercu∣ry, and by its intervention to press against the outward Air: so that against those parts of the Finger that are contiguous to the Air there is all the wonted pressure of the outward Air; whereas against that Pulp that is contiguous to the Mercury there is not so much pressure as against the other parts of the Finger by two thirds. I say by two thirds, or thereabout, be∣cause the Mercurial Cylinder in this Experiment is suppos'd to be twenty Inches high; and if it were but a little more than thirty Inches high, (which is a third more) then the weight of the Quicksilver would take off not two thirds only, but the whole pressure of the outward Air, from the above-mentioned pulp of the Finger. For in that case the Quicksilver would quite desert it, and settle beneath it. Wherefore since it has appeared by our Answer to the Examiner's third Argument, That the pressure of the outward Air is taken off from the body that remains in the upper part of the Tube, according to the weight of the Liquor suspended in the Tube; and since in our Hypothesis the pressure of the outward Air is able to keep thir∣ty Inches of Quicksilver, or two or three and thirty foot of Water, suspended in a Tube; it need be no great wonder, if a pressure of the ambient Air, equal to the weight of a Cylin∣der of Water of near twenty two foot long, should be able to thrust in the pulp of the Finger at the upper Orifice of the Tube, and make it stick closely enough to the lip of it.

I know the Examiner affirms, That no thrusting or pressure from without can ever effect such an adhesion of the Finger to the Tube. But this should be as well prov'd as said. But, first,

though I am willing to think the Examiner would not know∣ingly relate any thing he is not persuaded of; yet as far as I and another person very well vers'd in these Experiments have pur∣posely tried, I could not find the Adhesion of the Finger to the Tube to be near so strong as our Author hath related. Second∣ly, if you carefully endeavour by pressure and otherwise to thrust the pulp of your Finger into the Orifice of the Tube, you may through the Glass perceive it to be manifestly tumid in the cavity of the Pipe. And if by pressing your Finger against the Orifice of the Tube, you should not make the pulp adhere quite so strongly to the Tube, nor swell quite so much within it, as may happen in some Mercurial Experiments; it is to be consider'd, that the Air being a fluid as well as a heavy body, it does not (as grosser Weights would) press only a∣gainst the upper part of the Finger, but pressing as much of the finger as is expos'd to it almost every where, and almost uni∣formly, as well as strongly, it does by its lateral pressure on every side thrust in the Pulp of the Finger into the hole where there is not any resistance at all, or at least near so much pres∣sure against the Pulp as that of the ambient Air against the parts of the Finger contiguous to it.

By this it may appear that we need not borrow the Objecti∣on our Author offers to lend us; namely, that in the Experi∣ment under consideration the Quicksilver is press'd downward by the Spring of some Air lurking betwixt it and the Finger. (Though I am prone to think that unless the Experiment be made with a great deal of care, such a thing may easily happen, and contribute to the stronger Adhesion of the Finger to the Tube.) This I say may appear not withstanding what our Au∣thor Objects, that the Air expanding it self will thrust away the Finger upwards, since the contrary of that pretence we have lately manifested in the Answer to his Third Argument. And as for what he adds to confirm his Argumentation in these words, Quod vel inde confirmatur, Quia cum prae∣ponderans ille aër succedat (uti asseritur) loco sublati in∣ferioris * 1.6 digiti, id est, eodem modo nunc sustentet Argentum quo

ante ab applicato digito inferiore sustentabatur; manifestum est, non debere, juxta hanc sententiam, magis deorsum trahi digitum superiorem post sublatam inferiorem quam ante. Cum itaque con∣trarium planè doceat experientia, satis liquet sententiam illam esse falsam. We must consider that the Tube being suppos'd per∣fectly full of Mercury, the Finger that stops the lower Orifice is wont to be kept strongly press'd against it, lest any of that ponderous Liquor should get out between the Tube and the Finger. So that although both the lower Finger do indeed keep up the Mercury in the Tube, and the pressure of the out∣ward Air would do so too; yet there is this difference, that the pressure of the Atmosphere depending upon its Weight, can∣not be intended and weakned as we please, as can that of the undermost Finger. And therefore whereas the Atmospherical Cylinder will not keep up a Cylinder of Quicksilver of above thirty Inches high, those that make the Torricellian Experiment do often, upon one occasion or other, keep up with the Finger a Mercurial Cylinder of perhaps forty or fifty Inches or far more: So that whereas in our case, before the removal of the undermost Finger, the Pulp of the uppermost must have about the same pressure against it where it is contiguous to the Mer∣cury, as there is against the other part of the same Finger; af∣ter the removal of the undermost Finger, there is as much of the Atmospherical Pressure, if I may so speak, taken off from the newly mention'd Pulp as counter-balances a Cylinder of Quicksilver of twenty Inches long.

CHAP. V.

THe Examiners Fourth and last Experiment is thus propos'd. Quarto denique (says he) impugnatur: Quia ex eo seque∣retur, Argentum vivum per similem Tubum è vasculo ex∣ugi posse eâdem prorsus facilitate quâ ex eodem exugere∣tur * 1.7 aqua: quod tamen experientiae repugnat, quâ docemur aquam in os sugentis facillimè attrahi; quo tamen Argentum vivum ne toto quidem adhibito conatu perduci queat, imo vix ad Tubi me∣dietatem.

Sequelam autem sic ostendo: Quia cum in hac sententia nihil aliud agendum sit quam hoc, ut per Tubum sic ascendat subject us Liquor, sive Aqua fuerit, sive Argentum, nisi ut sugendo sur sum trahatur aër Tubo inclusus, quo sic attracto ascendit illico sub∣ject us Liquor, protrusus nimirum ab externo aëre jam praepon∣derante (uti docet Pecquettus in dissertatione Anatomica pag. 63.) manifestum est, eadem planè facilitate exugendum sic Ar∣gentum vivum qua exugitur Aqua: Quod quum Experientiae tam aperte repugnat, necesse est sententiam ex qua sequitur fal∣sam esse.

This Experiment I remember I made some years ago, accor∣dingly 'tis alledg'd in the fourth Essay of the Treatise (I was then writing) to prove against the Vulgar Opinion, that Li∣quors do not to prevent a Vacuum spontaneously ascend, which I presume will be so far allow'd of by our Author, who would have Liquors suppos'd to be rais'd by Suction violently drawn up by the contraction of his Funiculus. But to examine this Experiment, as it concerns the present Controversie, we may recal to mind that we formerly shew'd in the Answer to our Author's Third Argument, That when the Mercurial Cy∣linder that leans upon the restagnant Mercury has at the other end of it Air, kept from any entercourse with the Atmos∣phere, that included Air has so much of the Pressure of the external Air taken off from it as counterpoises the Mercurial Cylinder. And the Finger that is expos'd to the whole Pres∣sure of the ambient Air in some of its Parts, and in others but to the much fainter Pressure of the included Air, endures an unusal Pressure from the preponderating power of the Atmosphere.

We may consider also that there is against the Thorax and those Muscles of the Abdomen that are subservient to Respira∣tion the Pressure of the whole ambient Air. Which Pres∣sure, notwithstanding, The Muscles design'd for the use of Res∣piration, are able without any considerable resistance to dilate the Thorax at pleasure; because, as fast as they open the Chest, and by dilating it weaken the Spring of that Air which is then

within the Body, the external Air by flowing in, for want of finding the usual resistance there, keeps that within the Thorax in an AEquilibrium of force with that without. These things premised, 'tis not Difficult in our Hypothesis to give an Answer to our Examiner's Experiment. For we say when a Cylinder of Mercury is rais'd in the Tube to any considerable height, the Pressure of the Air in the Thorax is lessen'd by the whole weight of that Mercurial Cylinder, and consequently the Respiratory Muscles are thereby disabled to dilate the Chest as freely as they were wont, by reason of the prevalency of the undiminish'd Pressure of the external Air against the weakned Pressure of the internal: But if instead of Mercury you substitute Water, so short a Cylinder of that comparatively light Liquor takes off so little of the Pressure of the included Air, that it comes into the Lungs with almost its usual strength, and consequently with almost as much force as the outward Air presses with against the Thorax.

And on this occasion there occurs to my thoughts a noble Experiment of the most Ingenious Monsieur Paschal, which clearly shews, that if we could free the upper part of such a Tube as we are now considering from the Pressure of all inter∣nal Air, it would follow, as the Examiner says it should, that the Quicksilyer would by the Pressure of the outward Air be impell'd up into the Tube as well as Water, till it had attain'd a height great enough to make its Weight not inferiour but equal to that of the Atmosphere. The Experiment it self be∣ing so pertinent and considerable, we shall annex it in the same words wherein it is related by his Country-man and Ac∣quaintance, the Learned and Candid Gassen∣dus. Neque hoc verò solum, sed insuper vitreo * 1.8 Diabete Clysteréve ea qua par fuerit longitudine confecto, & post embolum ad orificium us{que} com∣pulsum, immisso ad normam in subjectum Hydrargyrum, depre∣hendit, ubi embolum sensim deinde educitur, consequi Hydrargv∣rum ascendere{que} ad eandem us{que} duorum pedum & digitorum trium eum semisse altitudinem. To which he immediately subjoyns a

Circumstance very considerable to the present Controversie in the following Clause. Ac ubi deinceps, adhibita licet non ma∣jore vi, Embolum altius educitur, consistere Hydrargyrum, ne{que} amplius consequi, ac fieri interim Inane quod spatium intercipitur ab ipso ad Embolum usque. Thus far he. So that as to the Exa∣miner's Experiment, we may well explicate it in our Hypothesis, by saying, that agreeably to it it happens, that in a more for∣cible Respiration the Mercurial Cylinder is raised higher than in a more languid; because, in the former Case, the Chest be∣ing more dilated, the included Air is also more expanded; whereby its debilitated Spring cannot as before enable the Mer∣curial Cylinder to counterpoise altogether the Pressure of the ambient Air. And that the reason why the Quicksilver is not by Respiration rais'd as high as it is kept suspended in the Torri∣cellian Experiment, is not, that the Pressure of the outward Air is unable to raise it so high, but because, as we have alrea∣dy declar'd, the free Dilatation of the Thorax is opposed by the Pressure of the ambient Air; which Pressure being against so great a Superficies, and being but imperfectly resisted by the debilitated Pressure of the Air within the Thorax, will be easi∣ly imagined to be very considerable by him who considers that in our Engine, the Pressure of the external Air against the Suc∣ker of less than three inches Diameter was, as we relate in the 33. Experiment, able to thrust up a Weight of above a hundred pound. And here we may observe upon the By in confirmation of our former Doctrine, that when we strongly suck up Quick∣silver in a Glass Tube, though the Elevation of the Quicksilver be according to our Author performed likewise by his Funicu∣lus contracting it self every way, and though there be a Communication betwixt the internal surface of the Lungs, and the cavity of the Tube; yet we feel not in our Lungs any endeavour of the shrinking Funiculus to tear off that Membrane they are lin'd with.

And thus we have examin'd our Author's four Arguments, to prove that in the Torricellian Experiment the Quicksilver can∣not be kept suspended by the counterpoise of the external

Air: Against which Opinion he tells us indeed, that other Ar∣guments might be alledg'd) but as it is not probable that if he had thought them better than those he has * 1.9 elected to insist on, he would have omitted them; so 'tis not unlikely that Answers might be as well found for them as for the others; especially since that which he singles out for a Spe∣cimen is, that from his Adversaries Hypothesis it would follow, that the Quicksilver would descend much more (I suppose 'tis a mistake of the Press, for much less) in cold Weather than in hot, because the Air is then thicker and heavier, and therefore ought to impel up the Quicksilver higher. For besides that we shall in its due place question the validity of our Author's Con∣sequence; it will be here sufficient to Reply, that the Obser∣vation on which he grounds it does not constantly hold, as his Objection supposes: Which may appear by that part of our 18. Experiment whence the matter of fact is desum'd, as we shall have occasion to take further notice of when we shall come to the Defence of that Experiment. So that what has been hitherto Discours'd on both sides being duly consider'd, the Reader is left to judge what ground the Examiner had for the 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉 wherewith he is pleas'd to conclude his Third Chapter, Maneat igitur tot Argumentis comprobatum, quorum quodlibet se solo sufficit, Argentum (facto * 1.10 Experimento in loco aperto) per externi aëris gravitatem à lapsu minimè sustentari.

CHAP. VI.

HIs fourth Chapter, wherein the Title promises that he will prove, Argentum in loco occluso non sustentari à lapsu per ipsum aëris Elaterium, is very short, and does not require that we should dwell long upon it. For the proof he brings of his Assertion being this, Cumtota vis hujus Elaterii pen∣deat à refutato jam aëris aequipondio cum digitis 29½ Ar∣genti * 1.11 vivi, ita ut nec plus nec minus faciat hoc elaterium in loco occluso quam fit per illud aequipondium in loco aperto; manifestum est, cum jam ostensum sit fictitium planè esse hujusmodi aequipon∣dium,

fictitium quo{que} esse tale elaterium: This being no new Argument, but an Inference from those he had set down in the former Chapter, by our Answers to them it is become needless for us to make any distinct Reply to this. We shall rather desire the Reader to take notice, that whereas our Author says that according to his Adversaries, Nec plus nec minus faciat hoc Ela∣terium in loco occluso quam fit per illud AEquipondium in loco aper∣to; whatever others may have written, we for our part allow of this Opinion but in some Cases; for in others we have per∣form'd much more by the Spring of the Air, which we can within certain limits increase at pleasure, than can be perform'd by the bare weight, which for ought we know remains always somewhat near the same. And of this advantage that the spring of the Air may have in point of force above the weight of it, we have formerly given an Instance in our 17. Experi∣ment, (where, by compressing the Air in the Receiver, we im∣pell'd the Mercurial Cylinder higher than the station at which the counterpoise of the Air is wont to sustain it) and shall hereafter have occasion to give yet more considerable proofs. To the lately recited words our Examiner subjoyns these; Adde, cum allata jam capite praecedente experimenta de adhaesione digiti, &c. eodem modo se habent in loco * 1.12 clauso ac in aperto, necessarium esse facta ex eis argumenta contra aequipondium, eadem quo{que} contra elaterium vim habere. But though he propose this as a new Argument, yet since 'tis built but upon the adhesion of the Finger (of which we have al∣ready given an account in our Hypothesis) I see not how it requires any new and particular Answer. And whereas he says, that the Experiments he had mentioned concerning the adhesion of ones Finger, &c. eodem modo se habent in loco clau∣so ac in aperto; I could wish he had added what way he took to make the Trials. For he gives no intimation that he did them any other ways than in ordinary rooms. And in such there scarce ever wants a communication betwixt the inward and outward Air, either at the Chimney, or Window, or Door not exactly shut, or at some hole or crevice or other,

by means of which the weight of the Atmosphere has its ope∣ration within the room.

To his second Argument our Author adds not a third, unless we take that for an Argument which he immediately annexes to his last recited words: Et profectò (says he) si secum expenderent hi Authores, quanta sit difficultas explicandi * 1.13 hujusmodi aëris elaterium, nisi idem aër se solo occupet majorem locum (ut paulo ante) credo eos sententiam facilè mutaturos. But this being said gratis, does not exact an Answer; and he must make it more intelligible than any man that I know of has yet done, how the same Air can adequately fill more space at one time than at another, before he perswade me to change my opinion about the Spring of the Air: Especially since he himself allows that the Air has a Spring, * 1.14 whereby it is able, when it has been violently compress'd, to recover its due extension; the manner whereof if he will intelligibly explicate, his Adversaries will have no great diffi∣culty to make out the spring of the Air. But whether his Hypothesis, or ours, be the more intelligible, will be more properly considered in the second part of our Discourse, to which we will therefore now proceed.

The II. Part. Wherein the Adversaries Funicular Hypothesis is examin'd

CHAP. I. What is alledged to prove the Funiculus is consider'd; and some Difficulties are propos'd against the Hypothesis.

THE Hypothesis that the Examiner would, as a better, substitute in the place of ours, is, if I mistake it not, briefly this; That the things we ascribe to the weight or spring of the Air are really perform'd by neither, but by a certain Funiculus, or extremely thin substance, provided in such cases by Nature, ne detur vacuum, which being exceeding∣ly rarefied by a forcible distension, does perpetually and strongly endeavour to contract it self into dimensions more agreeable to the nature of the distended body; and consequently does violently attract all the bodies whereunto it is contiguous, if they be not too heavy to be remov'd by it.

But this Hypothesis of our Authors does to me, I confess, appear liable to such Exceptions, that though I dislik'd that of his Adversaries yet I should not imbrace his, but rather wait till time and further Speculations or tryals should suggest some other Theory, fitter to be acquiesc'd in than this; which seems to be partly precarious, partly unintelligible, and partly insuffi∣cient, and besides needless: though it will not be so conveni∣ent to prove each of these apart, because divers of my Objecti∣ons tend to prove the Doctrine, against which they are alledged, obnoxious to more than one of the imputed Imperfections.

First, then, the Arguments by which our Author endea∣vours to evince his Funiculus, are incompetent for that end.

The Arguments which he proposes in his sixth Chapter, (where he undertakes to make good his Assertion) I there find to be three.

The first he sets down in these words, Constat hoc primò ex¦jam dict is Capite praecedente: nequit enim argentum des∣cendens sic digitum deorsum trahere, tubo{que} affigere, nisi * 1.15 à tali Funiculo suspendatur, eum{que} suo pondere vehementer exten∣dat, ut per se patet. But to this proof answer has been made already in the former Part of this Discourse: onely whereas the Author seems to refer us to the foregoing Chapter, we will look back to it, and take notice of what I find there against the Vacuists. For though I neither am bound, nor intend, in this Discourse to declare my self for, or against a Vacuum; yet since I am now writing against the Funicular Hypothesis, it will much conduce to shew that it is not firmly grounded, if I examine what he here alledges against the Assertors of a Vacuum.

In the next place therefore I consider that according to the Examiner, there can be no Vacuum; and that he makes to be the main reason why Nature in the Torricellian and our Experi∣ments does act after so extraordinary a manner, as is requisite to the production of his Funiculus. For in the 47th. Page, having in his Adversaries name demanded what need there is at the descent of the Quicksilver, that before it falls a superficies should be separated from it, and extended; Respondeo (sayes he) ideo hoc fieri, ne detur vacuum; cum nihil aliud ibi adsit quod loco argenti descendentis possit succedere. To which he imme∣diately subjoyns, (with what cogency I will not now examine) At{que} hinc plane confirmatur commune illud per tot jam elapsa secula usurpatum in Scholis axioma, viz. Naturam à vacuo abhorrere. And though he seem to make his Funiculus the immediate cause of the Phaenomena occurring in the Torricellian and our Experi∣ments: yet that, if you pursue the inquiry a little higher, he resolves them into Natures abhorrency of a Vacuum, himself plainly informs us in the next page; Nam licet (sayes he) imme∣diata ratio cur aqua v. g. ex hydria hortulana superne clausa (quo exemplo utuntur) non descendat, non sit metus va. ui,* 1.16

sed ea quam modo diximus, nempe quod non detur sufficiens pon∣dus ad solvendum illum nexum quo adhaereat aqua clausae hydriae summitati; ad eam tamen rationem tandem necessario veniendum est. But, though as well our Author's Funiculus, as the other scarce conceivable Hypotheses that learned men have devised, to account for the suspension of the Quicksilver otherwise than by the resistance of the external Air, seem to have been exco∣gitated onely to shun the necessity of admitting a Vacuum: yet I see not how our Examiner cogently proves, either that there can be none in rerum naturâ, or that De facto there is none produc'd in these Experiments. For in his fifth Chap∣ter (where he professedly undertakes that task) he has but these two incompetent Arguments. The first is drawn from the attraction, as he supposes, of the Finger into the deserted cavi∣ty of the Tube in the Torricellian Experiment: Quae quidem (sayes he) tam vehemens tractio & adhaesio, cum non nisi à reali aliquo corpore inter digitum & argentum * 1.17 constitutum queat provenire, manifestum est spatium illud vacuum non esse, sed verâ aliquâ substantiâ repletum. But to this Argu∣ment having already given an Answer, let us (without staying to urge, that the Vacuists will perhaps object, that they see not a Necessity, though they should admit of Traction in the case, that the internal substance must therefore perfectly re∣plenish the deserted Cavity; without pressing this, I say, let us) consider his other, which he draws from the Diaphaneity of the deserted part of the Tube, which space (he sayes) were it empty, would appear like a little black Pillar, Eo quod nullae species visuales ne{que} ab eo ne{que} per illud possunt ad oculum pervenire. But (not to engage our selves in Optical Speculations and Con∣troversies) if we grant him somewhat more than perhaps he can prove; yet as the Experiment will not demonstrate that there is nothing of body in any part of the space deserted by the Mercury, so neither will the Argument conclude (as the Pro∣poser of it does twice in this Chapter) That space ver â aliquâ sub∣stantiâ repleri. For according to the Hypothesis of the Epicureans and other Atomists, who make Light to be a corporeal Effluvium

from lucid bodies, and to consist of Atoms so minute, as freely to get in at the narrow Pores of Glass, there will be no cause to deny interspers'd Vacuities in the upper part of the Tube. For the Corpuscles of Light that permeate that space may be so numerous, as to leave no sensible part of it un-inlightned; and yet may have so many little empty Intervals betwixt them, that, if all that is corporeal in the space we speak of were uni∣ted into one lump, it would not perhaps adequately fill the one half (not to say the tenth, or even the hundredth part) of the whole space: According to what we have noted in the 17. Experiment, that a Room my appear full of the smoke of a Perfume, though if all the Corpuscles that compose that smoke were re-united, they would again make up but a small Pastil. To which purpose I remember I have taken Camphire, of which a little will fill a Room with its odour, and having in well-clos'd distillatory Glasses caught the Fumes driven over by heat, I thereby reduc'd them to re-conjoyn into true Camphire, whose bulk is very inconsiderable in comparison of the space it fills as to sense, when the odorous Corpuscles are scattered through the free Air.

To which I might adde, that the Torricellian Experiment being made in a dark night, or in a Room perfectly darkn'd, if it succeed (as there is little cause to suspect it will not) it may well be doubted whether our Authors Argument will there take place. For if he endeavour to prove that the place in question was full in the dark, because upon the letting in of the Day, or the bringing in of a Candle, the light appears within it; the Vacuists may reply according to their Hypothesis, That that light is a new one, flowing from the lucid body that darts its corporeal beams quite through the Glass and Space we dispute about, which for want of such Corpuscles were not just before visible.

And supposing light not to be made by a trajection of Atoms through Diaphanous bodies, but a propagation of the impulse of lucid bodies through them; yet it will not thence necessa∣rily follow, that the deserted part of the Tube must be full: As in our 27. Experiment (though many of those gross Aërial

Particles that appear'd necessary to convey a languid sound were drawn out of our Receiver at the first and second Exsuction; yet there remain'd so many of the like Corpuscles, that those that were wanting were not miss'd by the sense, though after∣wards, when a far greater number was drawn out, they were) so there may be matter enough remaining to transmit the im∣pulse of light; though betwixt the Particles of that matter there should be store of vacuities intercepted. Whereas our Author pretends to prove, not onely that there is no coacervate Vacuity in the space so often mention'd, but absolutely that there is none. For 'tis in this last sense, as well as the other, that the Schools and our Author, who defends their Opinion, deny a V••cuum.

But notwithstanding what we have now discours'd, as in our 17. Experiment we declin'd determining whether there be a Vacuum or no; so now what we have said to the Examiners Argument, has not been to declare our whole sense of the Con∣troversie, but onely to shew, that though his Hypothesis sup∣poses there is no Vacuum, yet his Arguments do not sufficiently prove it: which may help to shew his Doctrine to be precari∣ous; for otherwise the Cartesians, though Plenists, may plau∣sibly enough (whether truly or no I now dispute not) decline the necessity of admitting a Vacuum in the deserted space of the Tube, by supposing it fill'd with their second and first Element, whose Particles they imagine to be minute enough freely to pass in and out through the Pores of Glass. But then they must allow the pressure of the outward Air to be the cause of the suspension of the Quicksilver: for though the materia caelestis may readily fill the spaces the Mercury deserts; yet that within the Tube cannot hinder so ponderous a liquor from subsiding as low as the restagnant Mercury; since all the parts of the Tube, as well the lowermost as the uppermost, being pervious to that subtile matter, it may with like facility succeed in whatever part of the Tube shall be forsaken by the Quicksilver.

The Examiners second Argument in the same place is, That since the Mercurial Cylinder is not sustain'd by the outward Air it must necessarily be, that it be kept suspended by his

internal string. But since for the proof of this he is content to refer us to the third Chapter; our having already examin'd that, allows us to proceed to his third Argument, which is, That the Mercurial Cylinder, resting in its wonted station, does not gravitate: as may appear by applying the Finger to the im∣mers'd or lower Orifice of the Tube. Whence he infers, that it must of necessity be suspended from within the Tube. And indeed if you dexterously apply your Finger to the open end of the Tube, when you have almost, but not quite, lifted it out of the restagnant Mercury, (which circumstance must not be neglected, though our Author have omitted it) that so you may shut up no more Quicksilver than the Mercurial Cylinder is wont to consist of, you will find the Experiment to succeed well enough: (Which makes me somewhat wonder to find it affirm'd, that the learned Maignan denies it) not but that you will feel upon your Finger a gravitation or pressure of the Glass-Tube, and the contained Mercury as of one body; but that you will not feel any sensible pressure of the Mercury a∣part, as if it endeavoured to thrust away your Finger from the Tube. But the reason of this is not hard to give in our Hy∣pothesis; for according to that, the Mercurial Cylinder and the Air counterpoising one another, the Finger sustains not any sensibly-differing pressure from the ambient Air that presses a∣gainst the Nail and fides of it, and from the included Quick∣silver that presses against the Pulp. But if the Mercurial Cy∣linder should exceed the usual length, then the Finger would feel some pressure from that surplusage of Quicksilver, which the Air does not assist the Finger to sustain. So that this plea∣sant Phaenomenon may be as well solv'd in our Hypothesis, as in the Examiners: in which if we had time to clear an Objection, which we fore-see might be made, but might be answer'd too, we would demand why, when the Mercury included in the Tube is but of a due altitude, it should run out upon the re∣moval of the Finger that stops it beneath, in case it be sustain'd onely by the internal Funiculus, and do, according to his Doctrine, when the Funiculus sustains it, emulate a solid body,

if the pressure of the external Air has not (as our Author teaches it not to have) any thing to do in this matter.

And if some inquisitive person shall here object, That cer∣tainly the Finger must feel much pain by being squeez'd be∣twixt two such pressures, as that of a Pillar of thirty Inches of Quicksilver on the one side, and an equivalent pressure from the Atmospherical Pillar on the other, it may readily be re∣presented, that in fluid bodies (such as are those concern'd in our Difficulty) a solid body has no such sense of pressure from the ambient bodies as (unless Experience had otherwise in∣structed us) we should perhaps imagine. For, not to mention that having inquired of a famous Diver, whether he found himself sensibly compressed by the Water at the bottom of the Sea; he agreed with the generality of Divers in the Negative: I am inform'd that the learned Maignan did purposely try, that his hand being thrust three or four Palmes deep into Quicksilver, his fingers were not sensible, either of any weight from the in∣cumbent, or of any pressure from the ambient, Quicksilver. The reason of which (whether that inquisitive man have given it or no) is not necessary in our present Controversie to be lookt after.

To these three Arguments the Examiner addes not a fourth, unless he design to present it us in this concluding passage: Huc etiam faciunt insignes librationes quibus argentum subito descendens agitatur: Idem enim hic fit quod in aliis Pen∣dulis * 1.18 & ab alto demissis fieri solet. But of this Phaenomenon also tis easie to give an account in our Hypothesis by two several wayes; whereof the First (which is proper chiefly when the Experiment is made in a close place, as our Receiver) is, That the Quicksilver by its sudden descent acquires an impetus super∣added to the pressure it has upon the score of its wonted gra∣vity; whereby it for a while falls below its station, and thereby compresses the Air that leans upon the restagnant Mercury. Which Air by its own Spring again forcibly dilating it self to recover its former extension, and (as is usual in Springs) hastily flying open, expands it self beyond it, and thereby impells up

the Quicksilver somewhat above its wonted station, in its fall from whence it again acquires somewhat (though not so much as before) of impetus or power, to force the Corpuscles of the Air to a Sub-ingression; and this reciprocation of pressure betwixt the Quicksilver and the outward Air decreasing by degrees, does at length wholly cease, when the Mercury has lost that super∣added pressure, which it acquired by its falling from parts of the Tube higher than its due station. But this first way of Ex∣plicating these Vibrations is not necessary in the free Air: For if we consider the ambient Air onely as a weight, and remem∣ber what we have newly said of the impetus acquir'd by descent; this Phaenomenon may be easily enough explain'd, by taking no∣tice of what happens in a Balance, when one of the equiponde rant Scales chancing to be depress'd, they do not till after many Vibrations settle in aequilibrio.

And on this occasion I shall adde this Experiment: I took a Glass Pipe, whose two legs (very unequal in length) were par∣allel enough, and both perpendicular to that part of the Pipe that connected them; (such a Syphon is describ'd in our 36. Ex∣periment, to find the proportion of the gravity of Mercury and Water) into this Quicksilver was pour'd till 'twas some Inches high, and equally high in both legs: then the Pipe being inclin'd till the most part of the Quicksilver was fallen into one of the legs, I stopt the Orifice of the other leg with my Finger, and e∣recting again the Pipe, though the Quicksilver were forc'd to ascend a little in that stopt leg; yet by reason my Finger kept the Air from getting away, the Quicksilver was kept lower by a good deal in that stopt leg than in the other; but if by suddenly removing my Finger I gave passage to the included and some∣what comprest Air, the preponderant Quicksilver in the other leg would with the Mercury in this unstopt leg, make divers un∣dulations before that liquor did in both legs come to rest in an aequilibrium. Of which the Reason may be easily deduc'd from what has been newly deliver'd; and yet in this case there is no pretence to be made of a Funiculus of violently distended Air to effect the Vibrations of the Mercury.

CHAP. II Divers other Difficulties are objected against the Funicular Hypothesis

THirdly, But though our Examiner have not sufficiently proved his Hypothesis, yet perhaps it may be in its own nature so like to be true, as to deserve to be imbrac'd as such. Wherefore we will now take notice of some of those many things that to our apprehension render it very improbable.

And first, whereas our Author acknowledges that Quicksil∣ver, Water, Wine, and other Liquors, will, as well one as ano∣ther, descend in Tubes exactly sealed at the top, in case the Cylinder of liquor exceed the weight of a Mercurial Cylinder of 29½. Inches; and will subside no longer than till it is come to equiponderate a Cylinder of Quicksilver of that height; whereas, I say, the Examiner is by the ingenious Monsieur Paschall's, and other Experiments, induc'd to admit this; it cannot but seem strange that, whatever the liquor be, there should be just the same weight or strength to extend them into a Funiculus: though Water, for instance, and Quicksilver be near fourteen times as heavy one as the other, and be otherwise of very distant natures; and though divers other liquors, as Oyle and Water, be likewise of Textures very differing. And this may somewhat the more be wondred at, because our Au∣thor (in his Animadversions upon our 31. Experiment) is pleased to make so great a difference betwixt the disposition of bodies of various consistences, as fluid and firm, to be extenu∣ated into a Funiculus, that he will not allow any humane force to be able to produce one, by the divulsion of two flat Marbles, in case the contact of their Surfaces were so exquisite as quite to exclude all Air; though in the same place his Ratiocination plainly enough teaches (which Experience however does) that adhering Marbles, though with extraordinary difficulty, may be forcibly sever'd, and according to him the superficial parts may be distended into a Funiculus, that prevents a Vacuum.

But now the Hypothesis of his Adversaries is not at all in∣cumbred

with this difficulty. For the weight of the outward Air being that which keeps liquors suspended in Tubes sealed at the top; it matters not of what nature or texture the su∣spended liquor is, provided its weight be the same with that of a Mercurial Cylinder equiponderant to the Aerial one: As if there be a pound of Lead in one Scale, it will not destroy the aequilibrium, whether what be put in the other be Gold, or Quicksilver, or Wooll, or Feathers, provided its weight be just a pound.

In the next place we may take notice, That the account our Examiner gives us of his Funiculus in the tenth Chapter, (where he takes upon him to Explicate it) is much more strange than satisfactory, and not made out by any such parallel ope∣rations of Nature, as his Adversaries will not (and may not well do it) dispute the truth of. Whereas the weight and Spring of the Air may be inferr'd from such unquestion'd Ex∣periments as are nor concern'd in our present Controversie. For the gravity of the Air may be manifested by a pair of Scales, and the Spring of it discloses it self so clearly in wind guns and other Instruments, that our Adversary (as we have already had occasion to inculcate) does not deny it. But to consider his explication of his Funiculus, he would have us note two things: First, Argentum dum replet totum tubum, non mere tangere ejus summitatem (ut primo aspectu videtur) * 1.19 sed eidem quo{que} firmiter adhaerere. Patet hoc (subjoyns he) ex∣perimento illo in primo argumento capitis tertii de tubo utrin{que} aper∣to. But what is to be answer'd to this proof may be easily ga∣thered from what we have replyed to that Argument. And to what our Author addes to prove, That the adhesion of the Finger is to the subjacent Mercury, not to the Tube; namely, That Licet illud tubi orificium oleo, aliâve materiâ ad∣haesionem impediente, inungatur, non minus tamen fir∣miter * 1.20 adhaerebit digitus quàm priùs; an Answer may be drawn from the same place: nor perhaps will his reasoning much sa∣tisfie those who consider that bodies by trusion may easily e∣nough be made stick together, as much as in our case the Tube

and Finger do, notwithstanding one of them is anoynted with Oyle, and that this adhesion of the Finger to the Tube is to be met with in cases where the Surface of the included Quick-silver is not contiguous to the Finger, but many Inches below. As for what he addes concerning the reason why Water and Quicksilver ascend by suction, we have already taught what is to be answered to it, by ascribing that ascension to the pressure of the external Air: without any need of having recourse to a Fu∣niculus; or imagining with him in this place, That because nothing besides the Water or Quicksilver can insuch cases succeed the Air, (which yet is not easie to be prov'd in reference to a thin AEthe∣real substance) therefore, Partes ipsius aëris (to use his expression) sic tubo inclusae (quae aliàs tam facile * 1.21 separantur) nunc tam fortiter sibi invicem agglutinentur, ut va∣lidissimam (uti videmus) conficiunt catenam, qua non solum a∣qua, sed ponderosum illud argentum sic in altum trahatur. Which way of wreathing a little rarefied Air into so strong a rope, how probable it is, I will for a while leave the Reader to judge, and advance to our Author's second Notandum, which he thus pro∣poses: Rarefactionem sive extensionem corporis ad occupan∣dum majorem locum fieri non solo calore, sed etiam dis∣tensione * 1.22 seu vi divulsivâ: sicut è contra condensatio non solo fri∣gore perficitur, sedetiam compressione, uti innumeŕa passim docent exempla. And 'tis true and obvious, that the condensation of bodies, taking that word in a large sense, may be made as well by compression as cold. But I wish he had more clearly exprest what he means in this place by that Rarefaction, which he sayes is to be made by distension, or a vis divulsiva, whereof he tells us there are innumerable instances. For, as far as may be gathered from the three Examples he subjoyns, 'tis onely the Air that is capable of being so extended as his Hypothesis re∣quires Quicksilver and even Stones must be. And I know not how it will be proved, that even Air may be thus extended so far, as in the Magdeburg Experiment, to fill a place more than two thousand times as big as that it fill'd before. For that the

same Air in this and his two foregoing Instances does adequa∣tely fill more space at one time than another, he proves but by the rushing in of water into the evacuated Glass, and filling it within a little quite full, which he sayes, is done by the dis∣tended Air that contracting it self draws up the water with it. Which Explication how much less likely it is, than that the water is in such cases impell'd up by the pressure of the At∣mosphere, we shall anon (when we come to discuss his way of Rarefaction and condensation) have occasion to examine. In the mean time let us consider with him the Explication which, after having promis'd the two above recited Observations, he gives us of his Funiculus; Cum per primum Notandum argentum it a adhaereat tubi vertici, & per secundum, ra∣refactio * 1.23 fiat per meram corporis distensionem, it a rem se habere, ut argentum descendens à vertice tubi affixam eirelinquat superficiem suam extimam sive supremam, eam{que} eous{que} suo pondere extendat extenuetque, donec facilius sit aliam superficiem similiter relinquere quam priorem illam ulterius extendere: Secundam igitur relin∣quit, eam{que} eodem modo descendendo extendit, donec facilius sit tertiam adhuc separari quam illam secundam extendere ulterius: & sic deinceps, donec tandem vires amplius non habeat superficies sic separandi & extendendi; nempe donec perveniat ad altitudinem digitorum duntaxat 29½. ubi quiescit, ut capite primo dictum est. Thus far our Examiners Explication: By which 'tis easie to dis∣cern, that he is fain to assign his Funiculus a way of being pro∣duc'd strange and unparallel'd enough. For, not to repeat our Animadversions upon the first of the two Notandum's, on which the Explication is grounded, I must demand by what force, upon the bare separation of the Quicksilver and the top of the Tube, the new body he mentions comes to be produc'd; or at least how it appears that the Mercury leaves any such thing as he speaks of behind it. For the sense perceives no such mat∣ter at the top of the Tube, nor is it necessary to explicate the Phaenomena as we have formerly seen. It may also be marvell'd at, that the bare weight of the descending Mercury should be able to extend a Surface into a Body. And besides, it seems

precariously affirm'd, that there is such a successive leaving be∣hind of one Surface after another as is here imagin'd: Nor does it at all appear how, though some of the Quicksilver were turn'd into a thin subtile substance, yet that substance comes to be contriv'd into a Funiculus of so strange a nature, that scarce any weight (for ought appears by his Doctrine) can be able to break it; that contrary to all other strings it may be stretched with∣out being made more slender; and that it has other very odde pro∣perties, some of which we shall anon have occasion to mention. As for what our Author subjoyns in these words, Eodem ita{que} fere modo separari videntur hae superficies ab argento descendente, & in tenuissimum quendam funiculum * 1.24 per descendens pondus extendi, quo per calorem in accensa candela separantur hujusmodi superficies à subject a cera aut sevo, & in sub∣tilissimam flammam extenuantur. Vbinotatu dignum, quemad∣modum flamma illaplusquam millies sine dubio majus spatium occu∣pat, quam antea occupaverat pars illa cerae ex qua conficitur; ita prorsus & hic existimandum Funiculum illum plusquam millies majus spatium occupare quàm prius occupaverat illa argenti parti∣cula ex qua sit exortus: Vti etiam sine dubio contingit, quando talis particula à subjecto igne in vaporem convertitur. Though it be the onely Example whereby he endeavours to illustrate the generation of his Funiculus, yet (I presume) he scarce expects we should think it an apposite one. For besides that there here intervenes a conspicuous and powerful Agent, namely, an ac∣tual Fire to sever and agitate the parts of the Candle; and be∣sides that there is a manifest wasting of the Wax or Tallow turn'd into flame; besides these things, I say, we must not admit that the Fuel when turn'd into a flame does really fill (I say, not, with our Author) more than a thousand times, but so much as twice more of genuine space than the Wax 'twas made of. For it may be said that the flame is little or nothing else than an aggregate of those Corpuscles which before lay upon the upper superficies of the Candle, and by the violent heat were divided into minuter particles, vehemently agitated and brought from lying as it were upon a flat to beat off one ano∣ther,

and make up about the Wiek such a figure as is usual in the flame of Candles burning in the free Air. Nor will it neces∣sarily follow, that the space which the flame seems to take up should contain neither Air nor AEther, nor any thing else, save the parts of that flame, because the eye cannot discern any o∣ther body there: For even the smoke ascending from the snuff of a newly-extinguish'd Candle appears a dark pillar, which to the eye at some distance seems to consist of smoke; when as yet there are so many Aerial and other invisible Corpuscles mingled with it, as if all those parts of smoke that make a great show in the Air were collected and contiguous, they would not perhaps amount to the bigness of a Pins head, as may appear by the great quantity of streams that in Chymical Vessels are wont to go to the making up of one drop of Spirit. And therefore it does not ill fall out for our turn, that the Examiner, to inforce his former Example, alledges the turning of a particle of Quick∣silver into vapour, by putting fire under it: for if such be the Rarefaction of Mercury, 'tis not at all like to make such a Funi∣culus as he talks of, since those Mercurial Fumes appear by divers Experiments to be Mercury divided and thrown abroad into mi∣nute parts, whereby though the body obtain more of Surface than it had before, yet it really fills no more of true and genuine space, since if all the particular little spaces fill'd by these scatter'd Corpuscles were reduc'd into one, (as the Corpuscles themselves often are in Chymical Operations) they would amount but to one total space, equal to that of the whole Mercury before ra∣refaction. But these Objections against this Explication are not all that I have to say against our Adversaries Funiculus it self.

For I farther demand how the Funiculus comes by such hooks or graple-irons, or parts of the like shape, to take fast hold of all contiguous bodies, and even the smoothest, such as Glass, and the calm surface of Quicksilver, Water, Oyle, and other fluids: And how these slender and invisible hooks cannot onely in the tersest bodies find an innumerable company of ears or loops to take hold on, but hold so strongly that they are able not alone to lift up a tall Cylinder of that very ponderous me∣tal

of Quick-silver, but to draw inwards the sides of strong Glasses so forcibly, as to break them all to pieces. And 'tis also somewhat strange, that Water and other fluid bodies (whose parts are wont to be so easily separ∣able) should, when the Funiculus once layes hold on the superficial Corpuscles, presently emulate the nature of consis∣tent bodies, and be drawn up like Masses each of them of an intire piece; though even in the exhausted Receiver they appear by their undulation (when they are stir'd by Bubbles that pass freely through them) and many other signs to con∣tinue fluid bodies.

It seems also very difficult to conceive how this extenuated substance should require so strong a spring inward as the Ex∣aminer all along his books ascribes to it. Nor will it serve his turn to require of us in exchange an Explication of the Airs spring outward, since he acknowledges, as well as we, that it has such a spring. I know, that by calling this extenuated substance a Funiculus, he seems plainly to intimate that it has its spring inward, upon the same account that Lute-strings and Ropes forcibly stretch'd have theirs. But there is no small dis∣parity betwixt them: for whereas in strings there is requir'd either wreathing, or some peculiar and artificial texture of the component parts; a rarefaction of Air (were it granted) does not include or infer any such contrivance of parts as is re∣quisite to make bodies Elastical. And if the Cartesian Notion of the cause of Springiness be admitted, then our extenuated substance having no Pores to be pervaded by the materia sub∣tilis (to which besides our Author also makes Glass impervi∣ous) will be destitute of Springiness. And however, since Lute-strings, Ropes, &c. must, when they shrink inwards, either fill up or lessen their Pores, and increase in thickness as they diminish in length; our Examiners Funiculus must differ very much from them, since it has no Pores to receive the shrink∣ing parts, and contracts it self as to length, without increasing its thickness. Nor can it well be pretended that this self con∣traction is done ob fugam vacui, since though it should not be

made, a Vacuum would not ensue. And if it be said that it is made that the preternaturally stretch'd Body might restore it self to its natural dimensions: I answer, That I am not very forward to allow acting for ends to Bodies inanimate, and consequent∣ly devoid of knowledge; and therefore should gladly see some unquestionable Examples produc'd of Operations of that nature. And however to me, who in Physical enquiries of this nature look for efficient rather than final causes, 'tis not easie to conceive how Air by being expanded (in which case its force (like that of other rarefi'd Bodies) seems principally to tend outwards, as we see in fired Gun-powder, in AEolipiles, in warm'd Weather-glasses, &c.) should acquire so prodigious a force of moving contiguous Bodies inwards. Nor does it to me seem very probable, that, when for instance part of a po∣lish'd Marble is extended into a Funiculus, that Funiculus does so strongly aspire to turn into Marble again. I might likewise wish our Author had more clearly explicated, how it comes to pass (which he all along takes for granted) that the access of the outward Air does so much and so suddenly relax the ten∣sion of his Funiculus; since that being (according to him) a real and Poreless body, 'tis not so obvious how the presence of ano∣ther can so easily and to so strange a degree make it shrink. But I will rather observe, that 'tis very unlikely that the space which our Adversary would have replenish'd with his Funicular sub∣stance, should be full of little highly-stretcht strings, that lay fast hold of the surfaces of all contiguous Bodies, and always vio∣lently endeavour to pull them inwards. For we have related in our 26. Experiment, that a Pendulum being set a moving in our exhausted Receiver, did swing to and fro as freely, and with the string stretch'd as streight, as for ought we could perceive it would have done in the common Air. Nay, the Balance of a Watch did there move freely and nimbly to and fro; which 'tis hard to conceive those Bodies could do, if they were to break through a medium consisting of innumerable exceedingly-stret∣ched strings. On which occasion we might add, that 'tis some∣what strange that these strings, thus cut or broken by the passage

of these bodies through them, could so readily have their parts re-united, and without any more ado be made intire again. And we might also take notice of this as another strange pe∣culiarity in our Author's Funiculus, That in this case the two divided parts of each small string that is broken do not, like those of other broken strings, shrink and fly back from one ano∣ther; but (as we just now said) immediately redintegrate them∣selves: Whereas, when in the Torricellian Experiment the Tube and contain'd Mercury is suddenly lifted up out of the restagnant Quicksilver into the Air, the Funiculus does so strangely con∣tract it self, that it quite vanishes; insomuch that the ascending Mercury may rise to the very top of the Tube. These, I say, and divers other difficulties might on this occasion be insisted on; but that, supposing our selves to have mentioned enough of them for once, we think it now more seasonable to proceed to the remaining part of our Discourse.

CHAP. III. The Aristotelean Rarefaction (proposed by the Adver∣sary) examin'd.

BUt this is not all that renders the Examiner's Hypothesis im∣probable: For, besides those already mentioned particulars, upon whose score it is very difficult to be understood; it neces∣sarily supposes such a Rarefaction and Condensation, as is, I confess, to me, as well as to many other considering persons, unintelligible.

For the better discernment of the force of this Objection we must briefly premise, That a Body is commonly said to be rarefi'd or dilated, (for I take the word in a larger sense than, I know, many others do, for a reason that will quickly ap∣pear) when it acquires greater dimensions than the same Bo∣dy had before; and to be condens'd, when it is reduc'd into less dimensions, that is, into a lesser space than it contain'd be∣fore: (as when a dry Spunge being first dipp'd in water swells to a far greater bulk, and then being strongly squeez'd and held compressed, is not only reduced into less room than it had

before it was squeézed, but into less than it had even before it was wetted.) And I must further premise, That Rarefaction (as also Condensation) being amongst the most obvious Phae∣nomena of Nature, there are three (and for ought we know but three) ways of explicating it: For, either we must say with the Atomists and Vacuists, that the Corpuscles whereof the rarefied Body consists do so depart from each other, that no other substance comes in between them to fill up the de∣serted spaces that come to be left betwixt the incontiguous Corpuscles; or else we must say with divers of the ancient Philosophers, and many of the Moderns, especially the Car∣tesians, that these new Intervals produced betwixt the Parti∣cles of the raresied Body are but dilated Pores, replenished, in like manner as those of the tumid Spunge are by the imbi∣bed water, by some subtile AEthereal substance, that insinu∣ates it self betwixt the disjoyned Particles: Or, lastly, we must imagine with Aristotle and most of his followers, that the self-same Body does not only obtain a greater space in Ra∣refaction, and a lesser in Condensation, but adequately and exactly fill it, and so when rarefied acquires larger dimensions without either leaving any vacuities betwixt its component Corpuscles, or admitting between them any new or extrane∣ous substance whatsoever.

Now 'tis to this last (and, as some call it, rigorous) way of Ra∣refaction that our Adversary has recourse in his Hypothesis: Though this, I confess, appear to me so difficult to be concei∣ved, that I make a doubt whether any Phaenomenon can be explained by it; since to explain a thing is to deduce it from something or other in Nature more known than it self.

He that would meet with full Discussions of this Aristotelean Rarefaction, may resort to the learned writings of Gassendus, Cartesius and Maignan, who have accused it of divers great ab∣surdities: But for my part, I shall at present content my self to make use to my purpose of two or three passages that I meet with (though not together) in our Author himself.

Let us then suppose, that in the Magdeburg Experiment he

so often (though I think causlesly enough) urges to prove his Hypothesis; let us (I say) for easier considerations sake suppose, that the undilated Air, which (as he tells us) possessed about half an inch of space, consisted of a hundred Cor∣puscles, * 1.25 or (if that name be in this case disliked) a hundred parts; (for it matters not what number we pitch upon) and 'twill not be denied, but that as the whole parcel of Air, or the Aggre∣gate of this hundred Corpuscles, is adequate to the whole space it fills, so each of the hundred parts, that make it up, is likewise adequately commensurate to its peculiar space, which we here suppose to be a hundredth part of the whole space. This premi∣sed, our Author having elsewhere this passage, Corpore occupante locum verbi gratia duplo majorem, necesse est ut * 1.26 quaelibet ejus pars locum quo{que} duplo majorem occupet; prompts us to subjoyn, that in the whole capacity of the Globe (which according to him was two thousand times as great as the room possessed by the unexpanded Air) there must likewise be two hundred thousand parts of space commensurate each of them to one of the fore-mentioned hundredth parts of Air; and conse∣quently, when he affirms that that half Inch of Air possessed the whole cavity of the Globe, if we will not admit (as he does not) either Vacuities or some intervening subtile substance in the Interval of the Aërial parts, he must give us leave to conclude, that each part of Air does adequately fill two thousand parts of space. Now that this should be resolutely taught to be not only naturally possible, (for we dispute not here of what the Divine Omnipotence can do) but to be really and regularly done in this Magdeburg Experiment, will questionless appear very absurd to the Cartesians and those other Philosophers, who take Extension to be but notionally different from Body, and consequently impossible to be acquir'd or lost without the ad∣dition or detraction of Matter; and will, I doubt not, appear strange to those other Readers, who consider how generally Naturalists have looked upon Extension as inseparable, and as immediately flowing from matter; and upon Bodies, as having necessary relation to a commensurate space. Nor do I see, if one

portion of Air may so easily be brought exactly to fill up a space two thousand times as big as that which it did but fill before without the addition of any new substance; I see not (I say) why the matter contained in every of these two thousand parts of space may not be further brought to fill two thousand more, and so onwards, since each of these newly-replenished spaces is presumed to be exactly filled with Body, and no Space, nor consequently that which the unrarefied Air replenished, can be more than adequately full. And since, according to our Ad∣versary, not only fluid Bodies, as Air and Quicksilver, but even solid and hard ones, as Marble, are capable of such a Distension as we speak of, why may not the World be made I know not how many thousand times bigger than it is, without either ad∣mitting any thing of Vacuity betwixt its parts, or being increa∣sed with the addition of one Atome of new matter? Which to me is so difficult to conceive, that I have sometimes doubted, whether in case it could be proved, that in the exhausted Globe we speak of there were no Vacuities within, nor any subtile matter permitted to enter from without, it were not more intelligible to suppose that God had created a new mat∣ter to joyn with the Air in filling up the Cavity, than that the self-same Air should adequately fill two thousand spaces, whereof one was exactly commensurate to it even when it was uncompressed. For divers eminent Naturalists, both ancient and modern, believing upon a Physical account the Souls of men to be created and infused, will admit it as intelligible that God does frequently create substances on certain emergent occa∣sions. But I know that many of them will not likewise think it conceivable, that without his immediate interposition an ac∣cession of new, real Dimensions should be had without either vacuities or accession of matter.

And indeed when I considered these difficulties and others, that attend the Rarefaction our Examiner throughout his whole Book supposes, and when I found that ever and anon he remits us to what he teaches concerning Rarefaction; I could not but with some greediness resort to the Chapters he addressed me to.

But when I had perused them, I found the Difficulties remained such still, and that 'twas very hard even for a witty man to make more of a subject than the nature of it does bear. Which I say, that by professing my self unsatisfied with what he writes, I may not be thought to find fault with a man for not doing what per∣haps is not to be done, and for not making such abstruse Notions plain, as are scarcely (if at all) so much as intelligible. And in∣deed as he has handled this subject modestly enough, so in some places his Expressions are to me somewhat dark; which I men∣tion, not to impute it as a Crime in him, that he wrote in a diffident and doubtfull strain of so difficult a matter, but to excuse my self if I have not always guessed aright at his meaning.

The things he alledges in favour of the Rarefaction he would persuade are two: The one, That the Phaenomena of Rarefaction cannot be explicated either by Vacuities or the subingression of an AEthereal substance; and the other, That there are two ways of explicating the rigorous Rarefaction he contends for.

His Objections against the Epicurean and Cartesian ways of making out Rarefaction are some of them more plausible than most of those that are wont to be urged against them; yet not such as are not capable enough of Answers. But whilst some of the passages appeared easie to be replyed to by the Favou∣rers of the Hypothesis they oppose, before I had fully examined the rest, chancing to mention these Chapters to an ingenious Man, hereafter to be further mentioned in this Treatise; he told me he had so far considered them more than the rest of the book, that he had thought upon some Hypotheses, whereby the Phaenomena of Rarefaction might be made out either according to the Vacuists, or according to the Cartesians, adding, that he had also examined the Instance our Adversary pretends to be af∣forded him of his Rarefaction by what happens in the Rota Ari∣stotelica. Wherefore being sufficiently distressed by Avocations of several sorts, and being willing to reserve the Declaration of my own thoughts concerning the manner of Rarefaction and Condensation for another Treatise, I shall refer the Reader to

the ingenious Conjectures about this Subject, which the Writer of them intends to annex to the present Discourse; and only add in general, That whereas the Examiner's Argument on this occasion is, That his way of Rarefaction must be admitted, be∣cause neither of the other two can be well made out, his Adver∣saries may with the same reason, argue that one of theirs is to be allowed, since his is incumbred with such manifest difficulties. And they may enforce what they say by representing, that the inconveniences that attend his Hypothesis about Rarefaction are insuperable, arising from the unintelligible nature of the thing it self; whereas those to which the other ways are obnoxious, may seem to spring but from mens not having yet discovered what kind of Figures and Motions of the small Particles may best qualifie them to make the Body that consists of them ca∣pable of a competent expansion.

After our Author's Objections against the two ways of Rare∣faction proposed, the one by the Vacuists, and the other by the Cartesians and others, that admit the solidest Bodies, and even Glass it self, to be pervious to an AEthereal or subtile matter; he attempts to explicate the manner by which that rigorous Ra∣refaction he teaches is perform'd: and having premised, that the Explication of the way how each part of the rarefy'd Body becomes extended, depends upon the quality of the parts into which the Body is ultimately resolv'd; and having truly ob∣serv'd, that they must necessarily be either really indivisible, or still endlesly divisible; he endeavours to explicate the Aristo∣telean Rarefaction according to those two Hypotheses. But, though he thus propose two ways of making out his Rarefacti∣on; yet besides that they are irreconcilable, he speaks of them so darkly and doubtfully, that it seems less easie to discern which of the two he would be content to stick to, than that he himself scarce acquiesces in either of them.

And, first, having told us how Rarefaction may be ex∣plain'd, in case we admit Bodies to be divisible in infinitum, he does himself make such an Objection against the infinity of parts in a continuum, as he is fain to give so obscure an Answer to,

that I confess I do not understand it; and presume, that not only the most part of unprejudiced Readers will as little ac∣quiesce in the Answer as I do; but even the Author himself will not marvel at my confession, since in the same place he acknowledges the Answer to be somewhat obscure, and endea∣vours to excuse its being so, because in that Hypothesis it can scarce be otherwise.

Wherefore I shall only add on this occasion, that 'tis not clear to me, that even such a divisibility of a continuum as is here supposed would make out the Rarefaction he contends for. For, let the integrant parts of a continuum be more or less finite or infinite in number, yet still each part, being a corporeal substance, must have some Particle of space com∣mensurate to it; and if the whole Body be rarefied, for in∣stance, to twice its former bigness, then will each part be likewise extended to double its former dimensions, and fill both the place it took up before, and another equal to it, and so two places.

The second Argument alledged to recommend the hither∣to-mentioned way of explicating Rarefaction is, That many learned Men, amongst whom he names two, Aquinas and Sua∣rez, have taught that the same corporeal thing may naturally be, and de facto often is, in the souls of Brutes really indivisi∣ble and virtually extended. But, though I pay those two Au∣thors a just respect for their great skill in Scholastical and Me∣taphysical learning; yet the Examiner cannot ignore, that I could make a long Catalogue of Writers, both ancient and modern, at least as well vers'd in natural Philosophy as Saint Thomas and Suarez, who have some of them in express words denied this to be naturally possible; and others have decla∣red themselves of the same judgment by establishing princi∣ples, with which this Conceit of the virtual extension of the indivisible Corpuscles is absolutely inconsistent. And though no Author had hitherto opposed it, yet I, that dispute not what this or that man thought, but what'tis rational to think, should nevertheless not scruple to reject it now; and should

not doubt to find store of the best Naturalists of the same opini∣on with me, and perhaps among them the Examiner himself, who (however this acknowledgment may agree with the three following Chapters of his book) tells us, (pag. 160.) that Juxta probabiliorem sententiam hujusmodi virtualis extensio rei corporeae concedenda non est, utpote soli rei spirituali propria.

But to conclude at length this tedious Enquiry into the Aristo∣telean way of Rarefaction, (which is of so obscure a nature that it can scarce be either proposed or examined in few words) I will not take upon me resolutely to affirm which of the two ways of explicating it (by Atomes or by Parts infinitely divisible) our Author declares himself for. But which of them soever it be, I think I have shown that he has not intelligibly made it out: And I make the less scruple to do so, because he himself is so inge∣nuous as (at the close of his discourse of the two ways) to speak thus of the Opinion he prefers; Praestat communi & receptae hactenus in Scholis sententiae insistere, quae li∣cet * 1.27 difficultates quidem non clarè solvat, iis tamen aperte non suc∣cumbit. So that in this discourse of Rarefaction, to which our Author has so often in the foregoing part of the Book referred us, as that which should make good what there seemed the most improbable; he has but instead of a probable Hypothesis need∣lesly rejected, substituted a Doctrine which himself dares not pre∣tend capable of being well freed from the difficulties with which it may be charged; though I doubt not but other Readers, espe∣cially Naturalists, will think he has been very civil to this obscure Doctrine, in saying that Difficultatibus non aperte succumbit.

As for the other way of explicating Rarefaction, namely, by supposing that a body is made up of parts indivisible; he will not I presume, deny, but that the Objections we former∣ly made against it are weighty. For according to this Hypothe∣sis (which one would think he prefers, since he makes use of it in the three or four last Chapters of his Book) Necessa∣riò fatendum est (says he) unam eandem{que} partem poni * 1.28 in duplici loco adaequate: Cum enim indivisibilis sit, locum{que} occupet majorem quam prius, necesse est ut tota sit in quolibet puna∣to

totius lici, sive ut per totum illud spatium virtualiter extenda∣tur. So that when hein the very next Page affirms, that by this virtual extention of the parts, the Difficulties that have for so many Ages troubled Philosophers may be easily solved, he must give me leave (who love to speak intelligibly, and not to admit what I cannot understand) to desire he would explain to me what this extensto virtualis is, and how it will remove the Difficulties that I formerly charged upon the Aristotelean Rarefaction. For the easier consideration of this matter, let us resume what we lately supposed, namely, that in the Mag∣deburgick Experiment the half Inch of undilated Air consisted of a hundred Corpuscles; I demand how the indivisibility of these Corpuscles will qualifie them to make out such a Rare∣faction as the Author imagines. For what does their being in∣divisible do in this case, but make it the less intelligible how they can fill above a hundred parts of space? 'Tis easie to fore∣see he will answer, That they are virtually extended. But not here to question how their indivisibility makes them capable of being so; I demand, whether by an Atoms being virtually ex∣tended, its corporeal substance do really (I mean adequately) fill more space than it did before, or whether it do not: (for one of the two is necessary.) If it do, then 'tis a true and real, and not barely a virtual extension. And that such an exten∣sion will not serve the turn, what we have formerly argued against the Peripatetick Rarefaction will evince; and our Ad∣versary seems to consess as much, by devising this virtual ex∣tension to avoid the inconveniences to which he saw his Doc∣trine of Rarefaction would otherwise plainly appear expos'd. But if it be said, That when an Atome is virtually extended, its corporeal substance fills no more space than before: This is but a Verbal shift, that may perhaps amuse an unwary Rea∣der, but it will scarce satisfie a considering one. For I de∣mand how that which is not a substance can fill place; and how this improper and but Metaphorical Extension will salve the Phaenomena of Rarefaction: as how the half Inch of Air at the top of the fore-mentioned Globe shall without a corporeal

extension fill the whole Globe of two thousand times its big∣ness when the water is suck'd out of it, and act at the lower part of the Globe. Which last Clause I therefore add, because not only our Author teaches (pag. 91. and 92.) that the whole Globe was filled with a certain thin substance, which by its con∣traction violently snatch'd up the water into which the neck of the Glass was immers'd; but in a parallel case he makes it his grand Argument to prove, that there is no Vacuum in the de∣serted part of the Tube in the Torricellian Experiment, That the attraction of the Finger cannot be perform∣ed * 1.29 but by some real Body. Wherefore till the Examiner do in∣telligibly explain how a virtual Extension, as it is opposed to a corporeal, can make an Atome fill twice, nay, two thousand times more space than it did before; I suppose this device of virtual extension will appear to unbiass'd Naturalists but a ve∣ry unsatisfactory evasion.

Two Arguments indeed there are which our Adversary offers as proofs of what he teaches. The first is, That they commonly teach in the Schools, that at least divinitus (as he speaks) such a thing as is pleaded for may be done, and that consequently it is not repugnant to the nature of a body. But, though they that either know me, or have read what I have written about mat∣ters Theological, will, I hope, readily believe, that none is more willing to acknowledge and venerate Divine Omnipotence; yet in some famous Schools they teach, that it is contrary to the na∣ture of the thing. And that men who think so, and consequently look not upon it as an object of Divine Omnipotence, may (whatever he here say) without impiety be of a differing mind from him about the possibility of such a Rarefaction as he would here have, our Author may perchance think fit to grant, if he remember that he himself says a few Pages after, Cum tempus sit Ens essentialiter successivum, it a ut ne divini∣tus * 1.30 quidem possint duae ejus partes simul existere, &c. But, not now to dispute of a power that I am more willing to adore than question, I say, that our Controversie is not what God can do, but about what can be done by Natural Agents, not

elevated above the sphere of Nature. For though God can both create and annihilate, yet Nature can do neither: and in the judgment of true Philosophers I suppose our Hypothesis would need no other advantage to make it be preferred before our Adversaries, than that in ours things are explicated by the ordinary course of Nature, whereas in the other recourse must be had to miracles.

But though our Author's way of explicating Rarefaction be thus improbable, yet I must not here omit to take notice, that his Funiculus supposes a Condensation that to me appears incum∣bred with no less manifest difficulties. For, since he teaches that a body may be condens'd without either having any vacuities for the comprest parts to retire into, or having Pores filled with any subtile and yielding matter that may be squeez'd out of them; it will follow, that the parts of the Body to be condens'd do im∣mediately touch each other: which supposed, I demand how Bodies that are already contiguous can be brought to farther Approximations without penetrating each other, at least in some of their part. So that I see not how the Examiners Conden∣sation can be perform'd without penetration of dimensions. A thing that Philosophers of all Ages have looked upon as by no means to be admitted in Nature. And our Author himself speaks somewhere at the same rate, where to the Question, Why the walls that inclose fired Gun-powder must be blown asunder? Respondeo (says he) haec omnia inde acci∣dere, quod pulvis ille sic accensus & in flammam con∣versus, * 1.31 longe majus spatium nunc occupet quàm prius. Vnde fit, ut cum totum cubiculum antea fuerit plenissimum, disrumpantur sic parietes, ne detur corporum penetratio. In the Magdeburgick Ex∣periment he tells us (as we have heard already) that the whole capacity of the Globe is filled with an extremely-thin body. But not now to examine how properly he calls that a rare body, which according to him intercepts neither Pores nor any hete∣rogeneous substance, the greater or lesser absence of which makes men call a Body more or less dense; not to insist on this, I say, let us consider, that before the admission of water into

the exhausted Globe there was, according to him, two thousand half Inches of a substance, which, however it was produc'd or got thither, was a true and real Body; and that after the ad∣mission of the water there remained in the same Globe, besides the water that came in, no more than one half Inch of body. Since then our Author does not pretend (which if he did, might be easily disproved) that the one thousand nine hundred nine∣ty nine half Inches of Matter, that now appear no more, tra∣versed the body of Water; since he will not allow that it gets away through the Pores of the Glass, I demand, what becomes of so great a quantity of Matter? For that 'tis annihilated I sup∣pose he is too rational a man to pretend, (nor, if he should, would it be at all believ'd) and to say, that a thousand and so ma∣ny hundred parts of Matter should be retir'd into that one part of space that contains the one half Inch of Air, is little less incre∣dible: For that space was suppos'd perfectly full of body before, and how a thing can be more than perfectly full, who can con∣ceive? To dispatch: According to our Author's way of Con∣densation, two, or perhaps two thousand, Bodies may be croud∣ed into a space that is adequately fill'd by one of them apart. And if this be not penetration of Dimensions, I desire to be in∣formed what is so; and till then I shall leave it to any unpre∣possess'd Naturalist to judge, whether an Hypothesis that needs suppose a thing so generally concluded to be impossible to Na∣ture, be probable or not; and whether to tell us that the very same parcel of Air, that is now without violence contain'd in half an Inch of space, shall by and by fill two thousand times as much room, and presently after shrink again into the two thousandth part of the space it newly possess'd, be not to turn a Body into a Spirit, and, confounding their Notions, attribute to the former the discriminating and least easily conceivable properties of the later. And this Argument is, I confess, with me of that weight, that this alone would keep me from ad∣mitting the Examiners Hypothesis: Yet if any happier Con∣templator shall prove so sharp-sighted, as to devise and clear∣ly propose a way of making the Rarefaction and Condensa∣tion

hitherto argued against, intelligible to me, he is not like to find me obstinate. Nor indeed is there sufficient cause why his succeeding in that attempt should make our Adversaries Hypothesis preferrable to ours, since that would not prove it either necessary, or so much as sufficient, but only answer some of the Arguments that tend to prove 'its not intelligible. And that we have other Arguments on our side than those that re∣late to Rarefaction and Condensation, may appear partly by what has been discours'd already, and partly by what we have now to subjoyn.

CHAP. IV. A Consideration (pertinent to the present Controversie) of what happens in trying the Torricellian and other Experiments, at the tops and feet of Hills.

THere remain then yet a couple of Considerations to be oppos'd against the Examiners Hypothesis, which, though the past Discourse may make them be look'd upon as needless, we must not pretermit, because they contain such Arguments as may not only be imployed against our Adversaries Doctrine, but will very much tend to the confirmation of ours.

I consider then further, that the Hypothesis I am opposing, be∣ing but a kind of Inversion of ours, and supposing the spring or motion of Restitution in the Air to tend inwards, as according to us it tends outwards; it cannot be, that if the supposition it self were (what I think I have prov'd it is not) true, many of the Phae∣nomena would be plausibly enough explicable by it: the same motions in an intermediate body being in many cases producible alike, whether we suppose it to be thrust or drawn; provided both the endeavours tend the same way. But then we may be satisfied whether the effect be to be ascribed to Pulsion or to Traction, (as they commonly speak, though indeed the later seems reducible to the former) if we can find out an Experi∣ment wherein there is reason such an effect should follow, in case Pulsion be the cause inquired after, and not in case it be Tracti∣on. And such an Experimentum Crucis (to speak with our Illu∣strious

Verulam) is afforded us by that noble Observation of Mon∣sieur Paschal, mentioned by the famous Pecquet, and out of him by our Author: namely, that the Torricellian Ex∣periment * 1.32 being made at the foot and in divers places of a very high Mountain, (of the altitude of five hundred fathom or three thousand foot) he found, that after he had ascended a hundred and fifty Fathom, the Quicksilver was fallen two Inches and a quarter below its station at the Mountains foot; and that at the very top of the Hill it had descended above three Inches below the same wonted station. Whence it appears that the Quicksilver being carried up towards the top of the Atmosphere, falls down the lower, the higher the place is wherein the observation is made: of which the reason is plain in our Hypothesis, namely, that the nearer we come to the top of the Atmosphere, the shorter and lighter is the Cylinder of Air incumbent upon the restagnant Mercury; and consequently the less weight of Cylindrical Mercury will that Air be able to counterpoise and keep suspen∣ded. And since this notable Phaenomenon does thus clearly fol∣low upon ours, and not upon our Adversaries Hypothesis; this Experiment seems to determine the controversie betwixt them: because in this case the Examiner cannot pretend, as he does in the seventeenth and divers other of our Experiments, that the descent of the Quicksilver in the Tube is caus'd, not by the diminution of the external Airs pressure, but from the preternatural Rarefaction or Distension of that external Air (in the Receiver) when by seeking to restore it self, it endea∣vours to draw up the restagnant Mercury: For in our present case there appears no such forcible Dilatation of that Air, as in ma∣ny of the Phaenomena of our Engine he is pleas'd to imagine.

It need therefore be no great wonder, if his Adversaries do, as he observes, make a great account of this Experiment, to prove that the Mercury is kept up in the Tube by the resi∣stance of the external Air. Nor do I think his Answers to the Argument drawn from hence will keep them from think∣ing it cogent. For to an Objection upon which he takes no∣tice that they lay so much stress, he replies but two things;

which neither singly nor together will near amount to a satis∣factory Answer.

And, First, he questions the truth of the Observation it self; because having made trial in a low Hill, the event did no ways answer his expectation. But though, in stead of disapproving, I am willing to commend his Curiosity, to make the Experi∣ment himself, and especially since 'twas both new and impor∣tant; and though also I like his Modesty, in rather suspecting some mistake in the manner of the Observation, than that the Experimenters did not sincerely deliver it: yet, since there must be an Error somewhere, I must rather charge it upon the Exa∣miners observation (I say his Observation, not his want of sin∣cerity) than upon Monsieur Paschal's. For besides the com∣mendations that the learned Gassendus, who relates the Experi∣ment, gives to that ingenious Gentleman (Monsieur Paschal) by whose direction he supposes it to have been try'd: the same Gas∣sendus relates, that the like Observation was five times repeated, partim intra sacellum, partimaëre * 1.33 libero, & nunc quidem flante, nunc silente vento. Which circumstances sufficiently argue the Diligence where with the Experiment was try'd in Auvergne. Especially since I can con∣firm these Observations by two more made on distant Hills in England: the one of which I procur'd from that known Virtuoso Mr. J. Ball, whom I desir'd to make the Experiment at a Moun∣tain in Devonshire, on the side whereof he dwelt; and the other made in Lancashire by that ingenious Gentleman Mr. Rich. Townley. Both which Observations, since I have mention'd them at large in the Appendix to the Physico Mechanical Treatise, shall not now repeat; contenting my self to observe to our pre∣sent purpose, that however the proportion of the Descent of the Quicksilver may vary, according to the differing consistence and other accidents of the neighbouring Air, in the particular places and times of the Experiments being made, yet all Ob∣servations agree in this, That nearer the top of the Atmosphere the Quicksilver falls lower than it does further from it. To all this I shall add two things that will very much confirm our

Hypothesis. The one is, that the freshly-nam'd Mr. Townley, and divers ingenious Persons that assisted at the Tryal, be∣thought themselves of so making the Torricellian Experiment at the top of the Hill, as to leave a determinate quantity of Air in the Tube, before the mouth of it was open'd under the vessell'd Mercury; and taking notice how low such a quantity of that Air depressed the Mercurial Cylinder, they likewise observ'd, that at the Mountains foot the included Air was not able to depress the Quicksilver so much. Whence we inferre, that the Cylinder of Air at the top of the Hill being shorter and lighter, did not so strongly press against the included Air, as did the ambient Air at the bottom of the Hill, where the A∣ëreal Cylinder was longer and heavier.

But because that though Experiments made in very elevated places are noble ones, and of great importance in the Contro∣versies about the Air, yet there are but very few of those that are qualified to make Experiments of that Nature, who have the opportunity of making them upon high Mountains; we did with the assistance of an ingenious man attempt a Tryal, wherein we hoped to find a sensibly-differing Weight of the Atmosphere, in a far less height than that of an ordinary Hill. But in stead of a common Tube we made use of a kind of Weather-glass, that the included Air might help to make the event notable, for a reason to be mentioned ere long; and in stead of Quicksilver we employ'd common Water in the Pipe belonging to the Weather-glass, that small changes in the Weight or resistance of the Atmosphere in opposition of the in∣cluded Air might be the more discernable. The Instrument we made use of consisted onely of a Glass with a broad Foot and a narrow Neck (AB) and a slender Glass-Pipe (CD) open at both ends: which Pipe was so placed, that the bottom of it did almost, but not quite, reach to the bottom of the bigger Glass (AB) within whose Neck (A) it was fastned with a close cement, that both kept the Pipe in its place, and hindred all communication betwixt the inward (II) and ou••ward (KK) Air, save by the cavity of the Pipe (CD). Now we chose

this Glass (AB) more than ordinary capacious, that the effect of the dilatation of the included Air (II) might be the more conspicuous. Then conveying a convenient quantity of Water (HH) into this Glass, we carried it to the Leads of the lofty Abby-Church at Westminster, and there blew in a little Air to raise the Water to the upper part of the Pipe, that being above the Vessel (AB) we might more precisely mark the several stations of the Water than otherwise we could. Afterward having suffered the Glass to rest a pretty while upon the Lead, that the Air (II) within might be reduc'd to the same state, both as to coldness and as to pressure, with (KK) that without, having marked the station of the Water (F), we gently let down the Vessel by a long string to the foot of the Wall, where one attended to receive it; who having suffer'd it to rest upon the ground, cry'd to us that it was subsided about an Inch be∣low the mark (F) we had put: whereupon having order'd him to put a mark at his second station of it (E), we drew up the Vessel again; and suffering it to rest a while, we observ'd the Water to be re-ascended to or near the first mark (F), which was indeed about an Inch above (E) the other. And this we did that Evening a second time with almost a like success: though two or three dayes after, the wind blowing strongly upon the Leads, we found not the Experiment to succeed quite so regularly as before; yet the Water alwayes manifestly fell lower at the foot of the Wall than it was at the top: which I see no cause to ascribe barely to the differing temperature of the Air above and below, as to Heat and Cold, since according to the general estimate, the more elevated Region of the Air is, caeteris paribus, colder than that below, which would rather check the greater expansion of the included Air at the top of the Leads than promote it. But the better to avoid mistakes and prevent Objections, we thought fit to try the Experiment within the Church, and got into a Galery of the same height with the Leads: but the upper part of the Pipe being casually broken off, we thought fit to order the matter so, that the surface (G) of the remaining Water in the Pipe should be about

[illustration]

an Inch higher than the surface of the Water in the Vessel. And then my above-mentioned Correspondent letting down the Glass, almost as soon as it was setled upon the pavement, kneeling down to see how far it was subsided, I found that not onely it was fallen as low as the other Water, but that the outward Air deprest it so far, as whilst I was looking on, to break in beneath the bottom of the Pipe, and ascend through the Water in bubbles; after which the Glass being drawn up again, my Correspondent affirm'd, that the Water was very manifestly re-ascended. But because by the unlucky breaking of a Glass, we were hindred to observe, as we designed, what would happen as well in a Weather-glass, so contriv'd that the weight or pressure of the Atmosphere should make no change in it, as in another whose included Air was at the top, (where∣as in that we imploy'd the included Air was in the lower part,) and because there happened in our Tryals a Circumstance or two that seem'd not so devoid of difficulties, but that we think it may require further examination, we design to set down a more particular account of this Experiment, (as how it succeeds with Quicksilver instead of Water, together with the capacity of the Vessel (AB) and the bore of the Pipe (CD) with some other variety of Circumstances) together with the event of the curiosity we had (which seemed very successfull) to try the Torricellian Experiment upon the above-mentioned Leads, and then let down the Tube together with the restagnant Mercury to the ground, to observe the increasing altitude of the Quick∣silver, in the formerly-mentioned Appendix to the Epistle we have been defending. And it shall suffice us in the mean time that the Tryals already mentioned seem to make it evident enough that the Atmosphere gravitates more, caeteris paribus, near the surface of the Earth, than in the more elevated parts of the Air. For the Leads on which we made our Tryals were found by measure to be in perpendicular height but threescore and fifteen Foot from the ground. To which we shall onely add this at present, that once being desirous to observe what we could touching the proportions of the subsidence of the Water to the

height of its several stations from the ground, purposely car∣rying down the Vessel so as not considerably to heat it, from the Leads down the stairs to a little window that we guest to be almost half way to the bottom, we there perceived the water to have already subsided about a Barly-Corns length, notwithstanding that probably in spite of our care, the Vessel were a little warmed by the heat of his body that carried it, since by that time we were come to the foot of the Wall, the Water stood almost at the highest mark; but after the Vessel was suffered to rest a while, it relapsed by degrees to the lowest. And thus much for the first of the things I had to represent in favour of our Doctrine.

The other Particular I shall mention for confirmation of our Hypothesis, is that Experiment (which, though it be needless, seems yet more cogent and proper to prevent Evasions) made by the same Mousieur Paschal, of carrying a weakly-blown Foot-ball from the bottom to the top of an high Mountain. For that Foot-ball swell'd more and more, the higher it was carried, so that it appeared as if it were full blown at the top of the Mountain, and gradually growing lank again, as it was carried downwards; so that at the foot of the Hill it was flaccid as before. This, I say, having thus happened, we have here an Experiment to prove our Hypothesis, wherein recourse cannot be had to any forcibly and preternaturally distended Body, such as that is pretended to be which remains in the de∣serted space of the Tube in the Torricellian Experiment.

The other thing which the Examiner alledges against our Argument from Monsieur Paschal's Tryals, is, that supposing it to be true, yet it cannot thence be inferr'd, that the subsidence of the Mercury at the top of the Hill proceeded from the At∣mospherical Cylinder's being there lighter and less able to sustain the Quicksilver. Sed dici potest (sayes he) ideo sic in vertice Montis magis descendisse, quod ibidem esset * 1.34 Aura frigidior, aut ex alio Temperamento hujusmodi descensum causante. But this solution will not serve the turn: For the cold∣nes, of the ambient Air (which yet the Experimenters take not

notice of) would rather contract the rarefied substance within the Tube, and so draw up the Mercury higher, as our Author himself teaches us, that 'tis from the shrinking of the Funiculus occasion'd by the cold that the Water in Thermometers ascends in cold weather. And whereas the onely * 1.35 proof he addes of so improbable an Explication is taken from our eighteenth Experiment, wherein we relate, that sometimes the Quicksilver did sensibly fall lower in colder than in far less cold weather: I answer, that this eighteenth Experiment will scarce make more for him than against him: For, as I there take notice that the Quicksilver descended in cold weather, so it sometimes descended likewise in hot weather, and rose in cold. And 'tis very strange, that in all the Observations made, in differing Countries and at diffe ing times, it should still so happen that the Mercurial Cylinder should be shorter near the top of the Atmosphere than further from it; if the resistance of the outward Air have nothing to do with the keeping it sus∣pended. And 'tis yet more strange, that the foot-ball should in like manner grow turgid and flaccid, according as it is carried into places where it has a shorter or longer Pillar of Air incumbent on it.

I was going to proceed to what remains of this second Part of our Treatise, But that since I begun this Chapter casually meeting with an Experiment lately sent in a Letter to a very Ingenious * 1.36 Acquaintance of his and mine by a very Industrious Physician * 1.37 (who is said to have had the curiosity to try over again many of the Experiments of our Engine) and finding it very proper to confirm our newly related Experiment made at Westminster, and to be of such a nature as we have not in this part of England the opportunity to try the like, for want of Hills high enough, I shall (according to the per∣mission given me) insert it in this place. And the rather, that as the Mountains have by the Tryals made on them of the Torricellian Experiment, afforded us a noble proof of the weight of the Air; so they may afford us one of its Spring:

wherein I hope the Phaenomenon of the Waters descent will not be ascribed to any attraction made of the Water by the violently∣distended outward Air. And because the Experiment was not made by us, but by another, we will set it down in his words, which are these: This fifteenth of October 1661. we took a Weather glass A B, of about two * 1.38 foot in length, and carrying it to the bottom of Hallifax Hill, the Water stood in the shank at thirteen Inches above the Water in the Vessel: Thence carrying it thus fill'd, with the whole frame, immediately to the top of the said Hill, the Water fell down to the point D, viz. an Inch and a quarter lower than it was at the bottom of the said Hill; which (as he rightly inferrs) proves the Elasticity of the Air: for the internal Air A C, which was of the same power and extension with the exter∣nal at the bottom of the Hill, did manifest a greater Elasticity than the Mountain-Air there * 1.39, and so extended it self further by C D.

The like Experiment, I hear, the same Ingenious Doctor has very lately repea∣ted, and found the descent of the Wa∣ter to be greater than before. And though some Virtuosi have thought it strange, that in an Hill far inferi∣our to the Alps and Appennines, so short a Cylinder of so light a liquor as Water should fall so much; yet I see not any rea∣son to distrust upon this ground either His Experiment or Ours (lately mention'd to have been made at Westminster;) but ra∣ther to wonder the Water fell not more (if the Hill be consider∣ably high:) for their suspicion seems grounded upon a mistake, as if because the Quicksilver in the Torricellian Experiment made without purposely leaving any Air in the Tube, would not, at the top of the mention'd Hill, have subsided above an Inch, if so much, the Water, that is near fourteen times lighter, should not fall above a sourteenth part of that space; whereas in the Torricellian Experiment, the upper and deserted space of the Tube has little or no Air left in it, but the Correspondent part of the Weather-glass was furnish'd with Air, whose

pressure was little less than that of the Atmosphere at the bottom of the Hill; and consequently must be much greater than the pressure of the Atmosphere at the top of the Hill, where the Atmospherical Cylinder's gravity (upon whose account it presses) must be much diminish'd by its being made much shorter, and by its consisting of an Air less comprest. And thus much for the first of the two Considerations wherewith I promised to conclude this second part of the present Tract. Onely before I proceed I must in a word desire the Reader to take notice, that though I have here singled out but one of the nine Ex∣periments which the Examiner in the 11. and 12. Chapters reckons up as urg'd by his Adversaries; yet do not thereby declare my acquiescing in his Explications of those Phaenomena, but onely leave both them and some other things he delivers about Siphons and the Magdeburg Experiments, to be discours'd by those that are more concerned to examine them, content∣ing my self to have sufficiently disproved the Funiculus which his Expositions suppose, and cleared the grounds of explicat∣ing such Experiments aright.

CHAP. V. Two new Experiments touching the measure of the Force of the Spring of Air compress'd and dilated.

THE other thing that I would have considered touching our Adversaries Hypothesis is, That it is needless. For whereas he denies not that the Air has some Weight and Spring, but affirms that it is very insufficient to perform * 1.40 such great matters as the counterpoising of a Mercurial Cy∣linder of 29. Inches, as we teach that it may: We shall now endeavour to manifest by Experiments purposely made, that the Spring of the Air is capable of doing far more than 'tis necessary for us to ascribe to it, to salve the Phaenomena of the Torricellian Experiment.

We took then a long Glass-Tube, which by a dexterous hand and the help of a Lamp was in such a manner crooked at the bottom, that the part turned up was almost parallel to the rest

of the Tube, and the Orifice of this shorter leg of the Siphon (if I may so call the whole Instrument) being Hermetically seal'd, the length of it was divided into Inches, (each of which was subdivided into eight parts) by a streight list of paper, which containing those Divisions was carefully pasted all along it: then putting in as much Quicksilver as served to fill the Arch or bended part of the Siphon, that the Mercury standing in a level might reach in the one leg to the bottom of the divided paper, and just to the same height or Horizontal line in the o∣ther; we took care, by frequently inclining the Tube, so that the Air might freely pass from one leg into the other by the sides of the Mercury, (we took (I say) care) that the Air at last included in the shorter Cylinder should be of the same laxity with the rest of the Air about it. This done, we began to pour Quicksilver into the longer leg of the Siphon, which by its weight pressing up that in the shorter leg, did by degrees streighten the included Air: and continuing this pouring in of Quicksilver till the Air in the shorter leg was by condensation reduced to take up but half the space it possess'd (I say, possess'd, not fill'd) before; we cast our eyes upon the longer leg of the Glass, on which was likewise pasted a list of paper carefully divided into Inches and parts, and we observed, not without delight and satisfaction, that the Quicksilver in that longer part of the Tube was 29. Inches higher than the other. Now that this Observation does both very well agree with and confirm our Hypothesis, will be easily discerned by him that takes notice what we teach, and Monsieur Paschal and our English friends Experiments prove, that the greater the weight is that leans up∣on the Air, the more forcible is its endeavour of Dilatation, and consequently its power of resistance, (as other Springs are stronger when bent by greater weights.) For this being considered, it will appear to agree rarely-well with the Hypothesis, that as according to it the Air in that degree of density and correspon∣dent measure of resistance to which the weight of the incum∣bent Atmosphere had brought it, was able to counterbalance and resist the pressure of a Mercurial Cylinder of about 29.

Inches, as we are taught by the Torricellian Experiment; so here the same Air being brought to a degree of density about twice as great as that it had before, obtains a Spring twice as strong as formerly. As may appear by its being able to sustain or resist a Cylinder of 29 Inches in the longer Tube, together with the weight of the Atmospherical Cylinder, that lean'd upon those 29 Inches of Mercury; and, as we just now inferr'd from the Torricellian Experiment, was equiva∣lent to them.

We were hindered from prosecuting the trial at that time by the casual breaking of the Tube. But because an accurate Experiment of this nature would be of great importance to the Doctrine of the Spring of the Air, and has not yet been made (that I know) by any man; and because also it is more uneasie to be made than one would think, in regard of the difficulty as well of procuring crooked Tubes fit for the pur∣pose, as of making a just estimate of the true place of the Pro∣tuberant Mercury's surface; I suppose it will not be unwelcome to the Reader, to be informed that after some other trials, one of which we made in a Tube whose longer leg was per∣pendicular, and the other, that contained the Air, parallel to the Horizon, we at last procured a Tube of the Fi∣gure exprest in the Scheme; which Tube, though * 1.41 of a pretty bigness, was so long, that the Cylinder whereof the shorter leg of it consisted admitted a list of Pa∣per, which had before been divided into 12 Inches and their quarters, and the longer leg admitted another list of Paper of divers foot in length, and divided after the same manner: then Quicksilver being poured in to fill up the bended part of the Glass, that the surface of it in either leg might rest in the same Horizontal line, as we lately taught, there was more and more Quicksilver poured into the longer Tube; and notice being watchfully taken how far the Mercury was risen in that longer Tube, when it appeared to have ascended to any of the divi∣sions in the shorter Tube, the several Observations that were thus successively made, and as they were made set down, af∣forded us the ensuing Table.

A Table of the Condensation of the Air

A	A	B	C	D	E
48	12	00	Added to 29⅛ makes	29 2/16	29 2/16
46	11½	01 7/16	30 9/16	30 6/16
44	11	02 13/16	31 15/16	31 12/16
42	10½	04 6/16	33 8/16	33 1/7
40	10	06 3/16	35 5/16	35--
38	9½	07 14/16	37--	36 15/19
36	9	10 2/16	39 5/16	38⅞
34	8½	12 8/16	41 10/16	41 2/17
32	8	15 1/16	44 3/16	43 11/16
30	7½	17 15/16	47 1/16	46⅗
28	7	21 3/16	50 5/16	50--
26	6½	25 3/16	54 5/16	53 10/13
24	6	29 11/16	58 13/16	58 2/8
23	5 ¾	32 3/16	61 5/16	60 18/23
22	5½	34 15/16	64 1/16	63 6/11
21	5 ¼	37 15/16	67 1/16	66 4/7
20	5	41 9/16	70 11/16	70--
19	4 ¾	45--	74 2/16	73 11/19
18	4½	48 12/16	77 14/16	77 ⅔
17	4 ¼	53 11/16	82 12/16	82 4/17
16	4	58 2/16	87 14/16	87 ⅜
15	3 ¾	63 15/16	93 1/16	93 ⅕
14	3 ½	71 5/16	100 7/16	99 6/7
13	3 ¼	78 11/16	107 13/16	107 7/13
12	3	88 7/16	117 9/16	116 4/8

AA. The number of equal spaces in the shorter leg, that contained the same parcel of Air diversly extended.

B. The height of the Mercurial Cylin∣der in the longer leg, that compress'd the Air into those dimensions.

C. The height of a Mercurial Cylinder that counterbalanc'd the pressure of the Atmosphere.

D. The Aggregate of the two last Co∣lumns B and C, exhibiting the pressure sustained by the included Air.

E. What that pressure should be accor∣ding to the Hypothesis, that supposes the pressures and expansions to be in reciprocal proportion.

For the better understanding of this Experiment it may not be amiss to take notice of the following particulars:

1. That the Tube being so tall that we could not conveni∣ently make use of it in a Chamber, we were fain to use it on a pair of Stairs, which yet were very lightsome, the Tube be∣ing for preservations sake by strings so suspended, that it did scarce touch the Box presently to be mentioned.

2. The lower and crooked part of the Pipe was placed in a square wooden Box, of a good largness and depth, to prevent

the loss of the Quicksilver that might fall aside in the transfu∣sion from the Vessel into the Pipe, and to receive the whole Quicksilver in case the Tube should break.

3. That we were two to make the Observation together, the one to take notice at the bottom how the Quicksilver rose in the shorter Cylinder, and the other to pour in at the top of the longer, it being very hard and troublesome for one man alone to do both accurately.

4. That the Quicksilver was poured in but by little and lit∣tle, according to the direction of him that observed below, it being, far easier to pour in more, than to take out any in case too much at once had been poured in.

5. That at the beginning of the Operation, that we might the more truly discern where the Quicksilver rested from time to time, we made use of a small Looking-glass, held in a convenient posture to reflect to the eye what we desired to discern.

6. That when the Air was so compress'd, as to be crouded into less than a quarter of the space it possess'd before, we try∣ed whether the cold of a Linen Cloth dipp'd in Water would then condense it. And it sometimes seemed a little to shrink, but not so manifestly as that we dare build any thing upon it. We then tried likewise whether heat would notwithstanding so forcible a compressure dilate it, and approaching the flame of a Candle to that part where the Air was pent up, the heat had a more sensible operation than the cold had before; so that we scarce doubted but that the expansion of the Air would, notwithstanding the weight that opprest it, have been made con∣spicuous, if the fear of unseasonably breaking the Glass had not kept us from increasing the heat.

Now although we deny not but that in our Table some par∣ticulars do not so exactly answer to what our formerly-intima∣ted Hypothesis might perchance invite the Reader to expect; yet the Variations are not so considerable, but that they may probably enough be ascribed to some such want of exactness as in such nice Experiments is scarce avoidable. But for all

that, till further trial hath more clearly informed me, I shall not venture to determine whether or no the intimated Theo∣ry will hold universally and precisely, either in Condensation of Air, or Rarefaction: All that I shall now urge being, That however, the trial already made sufficiently proves the main thing for which I here alledge it; since by it 'tis evident, that as common Air when reduc'd to half its wonted extent, obtain∣ed near about twice as forcible a Spring as it had before; so this thus comprest Air being further thrust into half this nar∣row room, obtained thereby a Spring about as strong again as that it last had, and consequently four times as strong as that of the common Air. And there is no cause to doubt, that if we had been here furnisht with a greater quantity of Quick∣silver and a very strong Tube, we might by a further compres∣sion of the included Air have made it counterbalance the pres∣sure of a far taller and heavier Cylinder of Mercury. For no man perhaps yet knows how near to an infinite compression the Air may be capable of, if the compressing force be com∣petently increas'd. So that here our Adversary may plainly see that the Spring of the Air, which he makes so light of, may not only be able to resist the weight of 29 Inches, but in some cases of above an hundred Inches of Quicksilver, and that without the assistance of his Funiculus, which in our present case has nothing to do. And to let you see that we did not (a little above) inconsiderately mention the weight of the in∣cumbent Atmospherical Cylinder as a part of the weight re∣sisted by the imprisoned Air, we will here annex, that we took care, when the Mercurial Cylinder in the longer leg of the Pipe was about an hundred Inches high, to cause one to suck at the open Orifice; whereupon (as we expected) the Mercu∣ry in the Tube did notably ascend. Which considerable Phae∣nomenon cannot be ascribed to our Examiners Funiculus, since by his own confession that cannot pull up the Mercury, if the Mercurial Cylinder be above 29 or 30 Inches of Mercury. And therefore we shall render this reason of it, That the pressure of the incumbent Air being in part taken off by its expanding it¦self

into the Suckers dilated Chest; the' imprison'd Air was thereby enabled to dilate it self manifestly, and repel the Mercury that comprest it, till there was an equality of force betwixt the strong Spring of that comprest Air on the one part, and the tall Mercurial Cylinder, together with the contigu∣ous dilated Air, on the other part.

Now, if to what we have thus delivered concerning the com∣pression of Air we add some Observations concerning its spon∣taneous Expansion, it will the better appear how much the Phaenomena of these Mercurial Experiments depend upon the differing measures of strength to be met with in the Air's Spring, according to its various degrees of compression and Laxity. But, before I enter upon this subject, I shall readily acknowledge that I had not reduc'd the trials I had made about measuring the Expansion of the Air to any certain Hypothesis, when that ingenious Gentleman Mr. Richard Townley was plea∣sed to inform me, that having by the perusal of my Physico-Mechanical Experiments been satisfied that the Spring of the Air was the cause of it, he had endeavoured (and I wish in such attempts other ingenious men would follow his example) to supply what I had omitted concerning the reducing to a pre∣cise estimate how much Air dilated of it self loses of its Elasti∣cal force, according to the measures of its Dilatation. He added, that he had begun to set down what occurred to him to this purpose in a short Discourse, whereof he afterwards did me the favour to shew me the beginning, which gives me a just Curiosity to see it perfected. But, because I neither know, nor (by reason of the great distance betwixt our places of re∣sidence) have at present the opportunity to enquire, whether he will think fit to annex his Discourse to our Appendix, or to publish it by it self, or at all; and because he hath not yet, for ought I know, met with fit Glasses to make an any-thing-ac∣curate Table of the Decrement of the force of dilated Air; our present design invites us to present the Reader with that which follows, wherein I had the assistance of the same person that I took notice of in the former Chapter, as having writ∣ten

something about Rarefaction: whom I the rather make mention of on this occasion, because when he first heard me speak of Mr. Townley's suppositions about the proportion where∣in Air loses of its Spring by Dilatation, he told me he had the year before (and not long after the publication of my Pneuma∣tical Treatise) made Observations to the same purpose, which he acknowledged to agree well enough with Mr. Townley's Theory: And so did (as their Author was pleased to tell me) some Trials made about the same time by that Noble Virtuoso and eminent Mathematician the Lord Brouncker, from whose further Enquiries into this matter, if his occasions will allow him to make them, the Curious may well hope for something very accurate.

A Table of the Rarefaction of the Air.

A	B	C	D	E
1	00 0/0	Subtracted from 29¾ leaves.	29¾	29¾
1 ½	10 ⅝	19 ⅛	19 ⅚
2	15 ⅜	14 ⅜	14 ⅞
3	20 2/8	9 4/8	9 15/12
4	22 ⅝	7 ⅛	7 7/16
5	24 ⅛	5 ⅝	5 19/20
6	24 ⅞	4 ⅞	4 23/24
7	25 4/8	4 2/8	4 ¼
8	26 0/0	3 6/8	3 23/32
9	26 ⅜	3 ⅜	3 11/36
10	26 6/8	3 0/0	2 39/40
12	27 ⅛	2 ⅝	2 23/48
14	27 4/8	2 2/8	2 ⅛
16	27 6/8	2 0/0	1 55/64
18	27 ⅞	1 ⅞	1 47/72
20	28••	1 6/8	1 9/80
24	28 2/8	1 4/8	1 23/96
28	28 ⅜	1 ⅜	1 1/16
32	28 4/8	1 2/8	0 119/128

A. The number of equal spaces at the top of the Tube, that contained the same parcel of Air.

B. The height of the Mercurial Cylinder, that together with the Spring of the included Air counterbalanced the pressure of the At∣mosphere.

C. The pressure of the Atmosphere.

D. The Complement of B to C, exhibiting the pressure sustained by the included Air.

E. What that pressure should be according to the Hypothesis.

To make the Experiment of the debilitated force of expan∣ded Air the plainer, 'twill not be amiss to note some particu∣lars,

especially touching the manner of making the Trial; which (for the reasons lately mention'd) we made on a light∣some pair of Stairs, and with a Box also lin'd with Paper to receive the Mercury that might be spilt. And in regard it would require a vast and in few places procurable quantity of Quick∣silver, to imploy vessels of such kind as are ordinary in the Tor∣ricellian Experiment, we made use of a Glass-Tube of about six foot long, for that being Hermetically sealed at one end, serv'd out turn as well as if we could have made the Experi∣ment in a Tub or Pond of seventy Inches deep.

Secondly, We also provided a slender Glass-Pipe of about the bigness of a Swans Quill, and open at both ends: All along which was pasted a narrow list of Paper divided into Inches and half quarters.

Thirdly, This slender Pipe being thrust down into the grea∣ter Tube almost fill'd with Quicksilver, the Glass helpt to make it swell to the top of the Tube, and the Quicksilver getting in at the lower orifice of the Pipe, fill'd it up till the Mercury in∣cluded in that was near about a level with the surface of the surrounding Mercury in the Tube.

Fourthly, there being, as near as we could guess, little more than an Inch of the slender Pipe left above the surface of the re∣stagnant Mercury, and consequently unfill'd therewith, the prominent orifice was carefully clos'd with sealing Wax melted; after which the Pipe was let alone for a while, that the Air di∣lated a little by the heat of the Wax, might upon refrigeration be reduc'd to its wonted density. And then we observ'd by the help of the above-mentioned list of Paper, whether we had not included somewhat more or somewhat less than an Inch of Air, and in either case we were fain to rectifie the error by a small hole made (with a heated Pin) in the Wax, and af∣terwards clos'd up again.

Fifthly, Having thus included a just Inch of Air, we lifted up the slender Pipe by degrees, till the Air was dilated to an Inch, an Inch and an half, two Inches, &c. and observed in Inches and Eighths, the length of the Mercurial Cylinder,

which at each degree of the Air's expansion was impell'd above the surface of the restagnant Mercury in the Tube.

Sixthly, The Observations being ended, we presently made the Torricellian Experiment with the above-mention'd great Tube of six foot long, that we might know the height of the Mercurial Cylinder, for that particular day and hour; which height we found to be 29¾ Inches.

Seventhly, Our Observations made after this manner fur∣nish'd us with the preceding Table, in which there would not probably have been found the difference here set down betwixt the force of the Air when expanded to double its former dimen∣sions, and what that force should have been precisely accord∣ing to the Theory, but that the included Inch of Air receiv'd some little accession during the Trial; which this newly-men∣tion'd difference making us suspect, we found by replunging the Pipe into the Quicksilver, that the included Air had gain'd about half an eighth, which we guest to have come from some little Aëreal bubbles in the Quicksilver, contain'd in the Pipe (so easie is it in such nice Experiments to miss of exactness.) We try'd also with 12 Inches of Air shut up to be dilated; but being then hindred by some unwelcome avocations to prose∣cute those Experiments, we shall elsewhere, out of other Notes and Trials (God permitting) set down some other accurate Ta∣bles concerning this matter. By which possibly we may be assisted to resolve whether the Atmosphere should be look'd upon (as it usually is) as a limited and bounded Portion of the Air; or whether we should in a stricter sense than we did before, use the Atmosphere and Aëreal part of the World for almost equi∣valent terms; or else whether we should allow the word At∣mosphere some other notion in relation to its Extent and Li∣mits; (for as to its Spring and Weight, these Experiments do not question, but evince them.) But we are willing, as we said, to refer these matters to our Appendix, and till then to retain our wonted manner of speaking of the Air and Atmo∣sphere. In the mean time (to return to our last-mention'd Ex∣periments) besides that so little a variation may be in great

part imputed to the difficulty of making Experiments of this nature exactly, and perhaps a good part of it to something of inequality in the cavity of the Pipe, or even in the thickness of the Glass; besides this, I say, the proportion betwixt the seve∣ral pressures of the included Air undilated and expanded, especi∣ally when the Dilatation was great (for when the Air swell'd but to four times its first extent, the Mercurial Cylinder, though of near 23 Inches, differ'd not a quarter of an Inch from what it should have been according to Mathematical exactness) the proportion, I say, was sutable enough to what might be expected, to allow us to make this reflexion upon the whole, That whether or no the intimated Theory will hold exactly, (for about that, as I said above, I dare determine nothing reso∣lutely till I have further considered the matter) yet since the Inch of Air when it was first included was shut up with no other pressure than that which it had from the weight of the incumbent Air, and was no more comprest than the rest of the Air we breathed and moved in; and since also this Inch of Air, when expanded to twice its former dimensions, was able with the help of a Mercurial Cylinder of about 15 Inches to coun∣terpoise the weight of the Atmosphere, which the weight of the external Air gravitating upon the restagnant Mercury was able to impell up into the Pipe, and sustain above twenty eight Inches of Mercury when the internal Air by its great expan∣sion had its Spring too far debilitated to make any considerable (I say considerable, for it was not yet so dilated as not to make some) resistance: Since, I say, these things are so, the free Air here below appears to be almost as strongly comprest by the weight of the incumbent Air as it would be by the Weight of a Mercurial Cylinder of twenty eight or thirty Inches; and consequently is not in such a state of laxity and freedom as men are wont to imagine; and acts like some mechanical Agent, the decrement of whose force holds a stricter pro∣portion to its increase of dimension, than has been hitherto taken notice of.

I must not now stand to propose the several reflexions that may be made upon the foregoing Observations touching the Compression and Expansion of Air; partly because we could scarce avoid making the Historical part somewhat prolix; and partly because I suppose we have already said enough to shew what was intended, namely, that to solve the Phaenomena there is not of our Adversaries Hypothesis any need: the evincing of which will appear to be of no small moment in our present Controversie, to him that considers, that the two main things that induced the Learned Examiner to reject our Hypothesis are, that Nature abhors a Vacuum, and that though the Air have some Weight and Spring, yet these are insufficient to make out the known Phaenomena; for which we must therefore have re∣course to his Funiculus. Now as we have formerly seen, that he has not so satisfactorily disproved as resolutely rejected a Vacuum, so we have now manifested that the Spring of the Air may suffice to perform greater things than what our Expli∣cation of the Torricellian Experiments and those of our Engine obliges us to ascribe to it. Wherefore since besides the seve∣ral difficulties that incumber the Hypothesis we oppose, and especially its being scarce, if at all, intelligible, we can add that it is unnecessary; we dare expect that such Readers as are not byass'd by their reverence for Aristotle or the Peripatetick Schools, will hardly reject an Hypothesis which, besides that it is very intelligible, is now prov'd to be sufficient, only to imbrace a Doctrine that supposes such a rarefaction and conden∣sation, as many famous Naturalists rejected for its not being comprehensible, even when they knew of no other way (that was probable) of solving the Phaenomena wont to be expli∣cated by it.

The III. Part. Wherein what is objected against Mr. Boyle's Expli∣cations of particular Experiments, is answered.

AND now we are come to the third and last Part of our Defence; wherein we are to consider what our Exami∣ner is pleas'd to object against some passages of our Physico-Me∣chanical Treatise. But though this may seem the only part wherein I am particularly concern'd; yet perhaps we shall find it, if not the shortest, at least the easiest, part of our Task. Partly, because our Author takes no exceptions at the Experiments themselves, as we have recorded them (which from an Adversary, who in some places speaks of them as an Eye-witness, is no contemptible testimony that the matters of fact have been rightly delivered:) and partly, because there are divers Experiments which, together with their Explications, the Examiner has thought fit to leave untoucht, and thereby allows us to do so too: and partly also, because that (as to divers of those Experiments upon which he animadverts) he does not pretend to shew that our Explications are ill deduc'd or incon∣gruous to our Principles; but only that the Phaenomena may be explain'd either better or as well by his Hypothesis, where∣of he supposes himself to have demonstrated the truth, toge∣ther with the erroneousness of ours, in the other parts of his Book, especially the third, fourth and fifth Chapters. So that after what we have said to vindicate the Hypothesis we main∣tain, and take away our Author's imaginary Funiculus; it will not be requisite for us on such occasions to examine his particu∣lar Assertions and Explications. Which Advertisement we hope the Reader will be pleased to bear in mind, and thereby save himself and us the trouble of a great deal of unnecessary re∣petition. Wherefore presuming he will do so, we shall not stay to examine the first and second Corollaries, which in his

17 Chapter he annexes to the manner of emptying our Recei∣ver by our Pump. Neither should we say any thing as to his third and last Corollary, but that we think fit to desire the Reader to take notice, that according to what he teaches in that place, the more the Air is rarefied, the more forcibly it is able to con∣tract it self.

A defence of our 1. and 2. Experiments.

And to proceed now to his 18 Chapter, which he intitles De Experimentis Boylianis, we shall find according to what we lately noted, that against the first Experiment he objects no∣thing save that, if one of the Fingers be applied to the Orifice of the Valve when the Pump is freed from Air, the Experi∣menter shall feel to his pain that the Sucker is not thrust in∣ward by the external Air, but, as the Finger, drawn inward by the internal. But this Phaenomenon of the intrusion of the Finger into a Cavity, where it finds no resistance, having been formerly accounted for according to our Hypothesis, we shall not need to repeat our Explication of it; though this mista∣ken Phaenomenon supplies our Adversary with divers of his fol∣lowing Animadversions, and indeed with a great part of his Book. And accordingly his Objection against our Second Ex∣periment being of the same nature with that against the first, re∣quires but the same Answer: For it will not alter the case that he adds upon this Experiment, Hoc esse discrimen manifestum inter pressionem & suctionem, quod suctio efficiat hujusmodi ad∣haesionem, pressio autem minimè; since to say so is but to affirm, not to prove.

The 3. Experiment.

What our Author would except against the 3. Experiment he ought to have more intelligibly exprest: For whereas of a Dis∣course wherein I deliver several particulars, he only says that Nullatenus satisfacit, ut legenti constabit; I would not do the Reader the injury to suspect him of taking this proofless Asser∣tion for a rational Confutation; especially since upon the re∣view

of that third Experiment I find nothing that agrees not with my Hypothesis, however it may disagree with the Exa∣miners. But, to consider the Explication he substitutes in the room of our Doctrine, which he rejects, he gives it us in these words; Hoc quo{que} Experimentum principiis nostris optimè conve∣nit: Cum enim per illam Emboli depressionem aër in cavitate brachii inclusus separetur ab eodem brachio, descendat{que} simul cum Embo∣lo (uti de aqua simul cum argento vivo descendente capite decimo tertio vidimus) fit ut in tota illa depressione, novae semper ab aëre illo descendente superficies deripiantur simul & extendantur, ut ibidem de aqua est explicatum: cum ita{que} aeque facile diripian∣tur & extendantur hujusmodi superficies in fine depressionis ac initio, mirum non est quod eadem utrobi{que} sentiatur deprimen∣di difficultas.

By which though he seems to intend an Opposition to that part of the third Experiment which I oppos'd not against his Opinion, but that of some learned Vacuists: Yet (not to men∣tion that he seems to have somewhat mistaken my sense) he offers nothing at all to invalidate my inference against them; but instead of that proposes a defence of his own Opinion, which supposes the truth of his disproved Hypothesis, and is either unsatisfactory even according to that, or else disagrees with what himself hath taught us but a little before. For 'tis evident that the more the Sucker is depress'd, the more the Cylinder is exhausted of Air. And in his third Corollary (which we lately desired the Reader to observe) speaking of the Air in the Receiver (and the case is the same with the Air in the Cylinder) he affirms more than once, Eo magis extendi ac rarefi∣eri aërem relictum, quo plus inde exhauritur, majoremque proinde acquirere vim sese contrahendi. Whereas here he would have us believe, that the little internal Air that was in the Cavity of the shank of the Stop-cock, does as strongly retract the Sucker, or, which in our case is all one, resist its depression, when the Sucker is yet near the top of the Cylinder, (and con∣sequently when the included Air is but a little dilated) as when the same Sucker being forced down to the lower part of the

Cylinder, the same portion of remaining Air must be exceed∣ingly more distended.

The 4. Experiment.

In the Fourth Experiment, touching the swelling of a Blad∣der upon the removal of the ambient Air; and proportionably to that removal: Our Author objects nothing against the Ex∣plication we give of it by the Spring of the Air included in the Bladder, and distending it according as the pressure of the ambient Air is weakned. But he endeavours also to explicate it his way, to which he says this circumstance does excellent∣ly agree, that upon the regress of the external Air into the Receiver, the tumid Bladder immediately shrinks, because (saith he) by such ingress of the external Air, the Air in the Receiver, which drew the sides of the Bladder outward from the middle of it, is relax'd. Which Explication whether it be more natural than ours (that ascribes the shrinking of the Bladder to the pressure of the Air that is let into the Receiver) let the Reader judge, who has considered what we have for∣merly objected against the Examiners Funiculus, and the Re∣laxation of it upon the admission of Air.

As for the reason likewise he adds, why a perforated Blad∣der does not also swell, namely, that by the hole, how little soever, the included Air is suck'd out by the rarefi'd ambient, we leave it to the impartial Reader to consider whether is the more genuine Explication, either ours (against which he has nothing to object) or his, which to make clearly out he ought (according to what we formerly noted disputing against his Funiculus) to shew us what kind of strings they are; which though, according to him, strongly fastned to the inside of the Receiver and the superficies of the Bladder, must draw just as forcibly one as another, how long soever they be without the Bladder in comparison of those that within the Bladder draw so as to hinder the diduction of its sides. For Experience shews, that in a perforated Bladder the wrinkles continue as if there were no drawing at all.

And though he could describe how such a string may be con∣text, yet our Explication will have this advantage in point of probability above his, That whereas he denies not that the Air has Spring and Weight, as we deny his Funiculus to have any other than an imaginary existence; and whereas he acknow∣ledges that by the Instrument the Air about the Bladder is exhausted; to shew that there needs no more than that, and consequently no Funiculus, to draw asunder the sides of the Bladder, we can confirm our Explication by the formerly∣mentioned Experiment of the ingenious Paschal, who carry∣ing a flaccid Foot-ball from the bottom to the top of an high Mountain, found it to swell proportionably as he ascended, and as the weight and pressure of the ambient Air decreased, and likewise to shrink again as he descended. And yet in this case there is no recourse to be had to a Funiculus of vio∣lently-rarefi'd Air to draw asunder every way the sides of the Foot-ball. But however the Examiner will be able to defend his Explication, it may suffice us that he has objected nothing against ours.

The 5. Experiment.

Against the cause we assign of the fifth Experiment he like∣wise objects nothing, but only ascribes the breaking of the Bladder to the self-contraction of the rarefi'd Air in the Recei∣ver. And therefore referring the Reader to what we have newly said about the last Experiment, we will with our Author pass over the sixth and seventh, to which he has no quarrel, and proceed to the eighth.

The 8. Experiment.

This is that wherein we mention our having broke a Glass∣Receiver, which was not globular, by the exhaustion of most of the inward Air, whereby its debilitated pressure became un∣able to resist the unweakned pressure of the outward Air. But this Explication the Examiner confidently rejects in these words, At profect non videtur credibile, mollissimum hunc aërem tam ve∣hementer

vitrum (tantae praesertim crassitudinis quantae ibidem dicitur) undi{que} sic comprimere ut illud perfringat: as if it were more credible that the little Air within (which, according to him, is so much thinner than common Air) should be able to act more powerfully upon the Glass than the Air without, which himself confesses to be a heavy body, and which not only reaches from the surface of the Earth to the top of the highest Mountains, but which (as may not improbably be argued from what we have elsewhere delivered) may, for ought we know to the contrary, be heaped upon the Receiver to the height of some hundreds of Miles, nay, to I know not how many thousands, in case the Atmosphere * 1.42 be not a bounded portion of the Air, but reach as high as It.

As for the Explication he substitutes in these words, Verius ita{que} respondetur, ideo sic fractum esse illud vitrum, quia per ex∣haustionem illam later a ejus vehementiùs introrsum sint attracta, quam ut (ob figuram illam resistendo minus idoneam) resistere po∣tuerint. Cum enim inclusus aër lateribus vitri firmissimè adhae∣reat, nihil aliud erit aërem illum sic exhaurire, quam satagere la∣tera vitri introrsum flectere: By what we have already discour∣sed about the Funiculus, the Reader may easily discern what is to be answered. Nor does our Author here shew us any way by which his imaginary strings should take such fast hold of the sides of the Glass, as to be able to draw them together notwithstanding the resistance they find from the close texture of the Body to be broken.

The 9. Experiment.

Our Explication of the ninth Experiment he handles very se∣verely: for having briefly recited it, he proposes his Objection against it thus, Sed profecto nimis longè videtur hoc à veritate recedere: potest{que} vel inde solum satis refutari; quia si tanta sit pressura aëris sic per tubum illum in phialam descendentis, ut ip∣sam phialam perfringat, deberet profecto inclusam aquam, cui im∣mergitur

ille tubus, valde quo{que} ante fractionem phialae commo∣vere, bullulas{que} in eadem excitare, &c. ut constat, siquis, insuf∣flando per illum tubulum, aquam vel mediocriter sic premat. At certum est aquam, antequam frangatur sic phiala, nec tantillum moveri: ut experienti constabit.

But, I do confess, I do for all this think our Explication more true, than well considered by our Author. For the putting of water into the Vial that was broken, was done (as is clearly intimated in the beginning of our Narrative) upon a particular design (as indeed we tryed divers other things with our Engine, not so much with immediate reference to the Spring of the Air, as to make use of such Tryals in some other of our Writings.) And accordingly in the second Tryal mentioned in the same Experiment the water was omitted. But, notwithstanding this water, the sides of the Glass being exposed to the pressure of the Atmosphere, had that whole pressure against them before the exhaustion of the Receiver; so that there needed no such blowing in of the Air afresh as our Author imagines, to effect the breaking of the Vial, it being sufficient for that purpose, that the pressure against the convex superficies of it was taken off by the exhaustion of the Receiver, the pressure against the concave superficies remaining as great as ever. And therefore we need not altogether deny what the Examiner sayes that Licet clausus superne fuisset tubulus ille, eodem tamen modo fract a sine dubio fuisset phiala. For, since in such cases the Air (as we have often taught) is shut up with the whole pressure of the Atmosphere upon it, it may almost as easily break the Glass as if it were unstopt. And accordingly we mention in the 36. Experiment the breaking of a thin Glass Hermetically seal'd upon the recess of the ambient Air. But, how confidently soever our Author speaks, I thought fit to adde the word al∣most, because we observed in the 39 Experiment, that such thin Vials (and thick ones will not break) are subject upon the withdrawing of the ambient, Air to retch a little, whereby the Spring of the Air within the Vial might in some cases (I say, in some) be so far weakned as not to be able to break it, unless

assisted by the pressure of the Atmosphere wherewith it com∣municates, and which leans upon it. And when the Vial does actually begin to break, then the pursuing pressure of the out∣ward Air upon the yielding Air within the Vial may help to throw the parts of the Glass more forcibly asunder.

All the Experiments from the 9. to the 17. exclusively our Examiner leaving uncensured, we may with him advance to the consideration of the 17.

The 17 Experiment defended.

In this we relate how, when we made the Torricellian Ex∣periment, we shut up the restagnant Mercury together with the Tube and the suspended Mercurial Cylinder (of about 29. Inches) in our Receiver, that by drawing off and letting in the Air at pleasure upon the restagnant Mercury, and consequently weakning and increasing its pressure, we might make it more clearly appear than hitherto had been done by Experiment, that the suspension of the Mercurial Cylinder, and the height of it, depended upon the greater or lesser pressure of the Air. But against our Explication of this Experiment (which has had the good fortune to convince and satisfie many ingenious men) the Examiner objects nothing in particular, contenting himself to have recourse here also to his Funiculus. Yet two obser∣vations of ours he is pleased to take notice of.

The first is, that though the Quicksilver were exactly shut up into our Receiver after the manner newly declared, yet the suspended Quicksilver did not descend: whence having said that I argue, that it is now sustained not by the Counterpoise of the Atmosphere, but by the Spring of the Air shut up in the Receiver, he subjoyns onely this, Sed rectius sane infertur, Cylindrum illum nihil ibidem antea praestitisse. But whether this be not gratis dictum we leave the Reader to collect from what we have formerly discourst in the second Part of this De∣fence of the Spring of the Air; especially from that Experi∣ment; by which it appears, that Spring may sustain a far higher Cylinder of Quicksilver.

In the second Observation he mentions of ours, he summari∣ly recites our Explication of the descent and ascent of the Mercury in the Tube, by the debilitated and strengthned Spring of the Air. But without finding fault with our application of that principle to the Phaenomena, he sayes that he has sufficiently refuted the principle it self in the fourth Chapter, (which how well he has done we have already seen) and therefore expli∣cates the matter thus; Dico igitur (sayes he) argentum per illam exhaustionem sic in tubo descendere, quod deorsum trahatur ab aëre qui incumbit argento restagnanti: siquidem incumbens ille aër jam per exhaustionem valde rarefact us & extensus, sese vehe∣menter contrahit, & contrahendo conatur etiam subjectum sibi argentum restagnans è suo vasculo elevare, unde fit ut (argento illo restagnante minus. jam gravitante in fundum sui vasculi) argentum quod est in tubo descendat; ut per se patet. Adeo{que} mirum non est, quod, ingrediente postea aëre externo, rursum argentum ascendat, cum per illum ingressum vis illa sic elevans argentum restagnans debilitetur. But this Explication supposing such a Funiculus as we have already shewn to be but fictitious, the Reader will easily gather what is to be judged of it from what has been already delivered. Wherefore I shall onely subjoyn, that by this Explication, were it admitted, there is onely an account given of that part of our seventeenth Experi∣ment which relates to the descent of the Mercury below its wonted height, and its re-ascent to it. But as for our having by the forcing in some more Air into the Receiver, impell'd the Quicksilver to a considerably-greater height than 'tis wont to be sustain'd at in the Torricellian Experiment, I confess I understand not how the Examiner gives an account of it in the following words, (which are immediately annex'd to those we last recited of his, and which are all that he employes to ex∣plicate this notable Phaenomenon) At{que} hinc etiam redditur ra∣tio alterius quod ibidem quo{que} notatur, nempe quod per violentam intrusionem aëris externi in Recipientem, ascenderit argentum notabiliter supra digitos 29½. Nam sicut per extractionem aëris argentum infra stationem detrahitur, sic etiam per intrusionem

novi supra eandem elevabitur. For in this passage I see not how he himself does not rather repeat the matter of fact, than give any account how it is perform'd. And if it be alledged on his behalf, That according to his principles it may be said that, upon the pressure of adventitious Air upon the restagnant Mercury, the Funiculus in the Tube, that was not able before to draw it up above 29½ Inches, is now enabled to draw it up higher; I demand upon what account this new Air does thus press against the restagnant Mercury, and impell up and sustain that in the Tube. It will not be said that 'tis by its weight; for as much Mercury as may be thus impell'd up above the usual station will weigh a great many times more than the Air forc'd into the Receiver. And therefore it remains that the additional Air counterpoises the additional Mercury by its Spring. And if we consider withall, that there's no reason to doubt, (especi∣ally considering what we have formerly delivered upon tryal touching the power of comprest Air to impell up Quicksilver) but that, had we not been afraid of breaking our Vessel we might by forcing more Air into the Receiver have impell'd it up to the top of the Tube, and kept it there; we shall scarce deny but that, supposing there could be no such Funiculus as our Examiner's in rerum natura, the pressure of the incumbent Air alone might suffice to keep a correspondent Cylinder of Mercury suspended: and that without any attraction of the restagnant Mercury by a Funiculus of violently-distended Air in the Receiver, the Quicksilver in the Tube may be made to rest at any height greater or lesser, provided it exceed 30 Inches, onely because its weight is just able to counterbalance the pressure of the contiguous Air.

I know not whether I may not adde (to express an unwil∣lingness to omit what some may think proper to do my Adver∣sary right) that it may be said for the Examiner, that he in the 11 page acknowledging with us a power in the Air to recover its due extension if it be crouded into less room than its dispo∣sition requires; a man may from that principle solve the Phae∣nomena in question by saying, that the Air in the Receiver

being forcibly comprest by the intrusion of fresh Air into the same vessel, does by its endeavour to recover its due expansion press upon the restagnant Mercury, and force up some of it into the Tube. But this Explication, though it agree with what the Author teaches in a place very distant from his Notes upon our 17 Experiment, now under debate; yet still 'tis not clear to me how, by what he sayes in these Notes, the Phaenomenon is accounted for as the word Hinc imports it to be. But other∣wise I need not quarrel with the Explication, since without recurring to the Funiculus for the sustaining of the additional Mercury, the solution of the Phaenomenon is given upon the same principle that I employ.

The 18 Experiment.

Our Examiner in his Animadversion upon the 18 Experi∣ment, having recited my Conjecture as the cause why a Cy∣linder of Mercury did in Winter rise and fall in the Tube, some∣times as Water is wont to do in a Weather-glass, according to the laws of heat and cold, and sometimes quite contrary thereunto; adds, that this Experiment does strongly enough overthrow our Hypothesis of the Atmospherical Cylinder, and clearly shew that the Quicksilver is not sustained by it: Nam (sayes he) si hic ab eo sustentatum fuisset, debuisset potius frigi∣diore tempore ascendere quam descendere, eo quod aër tunc multo densior esset & gravior. Ita{que} non sustentatur argentum ab aëris aequipondio, ut asseritur. And by the same Argument he con∣cludes against the Mercury's being sustained by the Spring of the Air. But in his Animadversions upon this Experiment he seems to have been too forward to reprehend; for he neither well confutes my Conjecture, nor substitutes so much as a plausible one in the stead of it. And as to his Objection I answer,

First, That it doth not conclude: because that as sometimes the Quicksilver in the Tube did rise in warmer, and fall in colder, weather; so at other times it did rather emulate the ascent and descent of water in a Weather-glass.

Secondly, Though it be true, that Cold is wont to condense this or that parcel of Air, and that a parcel of Air may be made heavier by Condensation; yet that is in regard of the ambient Air that retains its wonted laxity, in which the con∣densed Air is weighed. But our Author has not yet proved, that in case the cold of the Winter should condense the whole incumbent Atmosphere, it would then gravitate sensibly more upon the restagnant Quicksilver than before. As a Pound of Wooll will not sensibly vary its weight, though the hairs whereof it is composed be made to lie sometimes in a looser, sometimes in a closer, order.

And, thirdly, this Objection does as little agree with his Doctrine as with my Conjecture: For in the 50. page, where he gives us an account according to his principles of the rising and falling of water in a Weather-glass, and compares it with the suspension of Quicksilver, he tells us, Hinc fit quod, con∣tracto hoc funiculo per frigus, aqua illa tempore frigido ascendat, descendat autem tempore calido, eo quod per calorem funiculus ille dilatetur. So that, according to the Examiner himself, the Quicksilver ought to have ascended in colder, and descended in warmer, weather. Now, although I proposed my thoughts of the difficult Phaenomenon under consideration but as a Con∣jecture, and therefore shall be ready to alter them, either upon further discovery, or better information; yet I see not why it should be post-posed to the Examiner's, who, though he re∣jects our Explication, substitutes no other than what may be gathered from these words, Ego certe non dubito quin dentur hu∣jusmodi occultae causae, quibus funiculus ille subtilis, quo in tubo suspen∣ditur argentum (ut dictum est capite decimo) modo producatur, modo abbrevietur, &c. sic{que} argentum nunc demittat, nunc elevet. For, since we have made it probable that the copious Fumes some∣times suddenly ascending into the Air, and rolling up and down in it, sometimes sensibly altering (if good Authors may be credited) the refraction of it, and since some other causes, mentioned in our eighteenth Experiment, may alter the density and gravity of the Air that leans upon the restagnant Mercury; I

suppose the Reader will think it more intelligible, and pro∣bable that alterations, other than those produced by heat and cold may happen to the incumbent Atmosphere, which freely communicates with the neighbouring Air, and may thereby become sometimes more stufft, and sometimes more destitute of adventitious Exhalations; than that such changes should happen to a Funiculus included in Glass, which according to our Author is impervious to the subtilest steams that are, and concerning which he offers not so much as a Conjecture upon what other account it can happen to be sometimes contracted, and sometimes stretch'd.

The 19 Experiment.

Upon this the Examiner has onely this short Animadver∣sion, In decimo nono ostendit aquam eodem modo per exhaustio∣nem Recipientis descendere, quo in praecedente descendere osten∣derat argentum vivum; cujus cum eadem sit ratio, non est cur amplius ei insistamus. In which words since he offers nothing new or peculiar to shew any incongruity in our Explication to our principles, which agree very well with the new Phaenomena of the Experiment; we are content to leave the Reader to judge of the Hypotheses themselves, which of the two is the more probable, either ours, that onely requires that the Air in the Receiver should equally resist a Cylinder of Water and of Quicksilver, when their weight is but the same, though their altitudes be not; or the Examiner's, which exacts that (according to what we formerly elsewhere noted) Bodies of such differing nature and texture as Quicksilver and Water should need but just the same weight or strength to rarefie them into a Funiculus.

The 20 Experiment.

In his Examen of this Experiment our Author makes me in∣fer from the Phaenomena he repeats, that not onely the Air, but the Water also has a Spring. But though I suspect not that he does wilfully mistake my sense, yet by what I write in this and the following Experiments the Reader may well enough

perceive, that I spoke but very doubtfully of a Spring in the water; nay, and that I did in the 154 page expresly teach, That the intumescence of it might (at least in great part) pro∣ceed from that of the small parcels of Air, which I thought to be usually harboured in the body of that liquor.

But whereas I ascribe the appearance of the Bubbles in the water to this, that upon the exhaustion of some of the Air in∣cumbent on the water, the pressure of what remains is much debilitated, whereby the little Particles of Air lurking in the Water are allowed to expand themselves into bubbles; he rejects this Explication as manifestly false: Nam * 1.43 (sayes he) si ita fieret, deberent profecto hujusmodi bullulae non è fundo vasis sic ascendere, (uti tam in hoc quam in sequentibus experimentis in quibus de istis bullis agitur semper asseritur) sed è superiore parte aquae, ubi minus premuntur, ut per se est manifestum. But why he should be here so peremptory I confess I do not, for all this Objection, yet see: For in the bottom of the next page he sayes, he will not deny but that Aërial Particles latitant in the other parts of the water (he had before spoken of the bottom of it) may be extended into bub∣bles by his way of Rarefaction. And that we particularly mentioned the rising of bubbles, even from the bottom of the water, was because that circumstance seem'd to deserve a pe∣culiar note; and not (as he seems to imagine) as if the bubbles did not also rise from the superior parts of the liquor, since we did take notice of it about the middle of the 149 page. And we often in this and the follow∣ing * 1.44 Experiments observ'd, that the ascending bubbles grew bigger the nearer they came to the top. Which agrees more clearly with our Hypothesis wherein their conspicuous swelling as they ascend is attributed more to the lessen∣ing of the pressure of the incumbent Air than to the decrement of the weight of the incumbent water, (since when the surface of this liquor is lean'd upon by the Atmosphere, the ascending bubbles scarce sensibly increase

in Vessels no deeper than ours) then with the Explication which the Examiner gives in these words, Respondeo, aquam per illant aëris exhaustionem non sponte sic ascendere, sed sursum violenter trahi, ac elevari à rare facto illo aëre sese contrahente. Quemadmo∣dum enim aqua aliqualem patitur compressionem (ut experientiâ constat) it a & aliqualem quo{que} hic patitur distentionem. At{que} hinc clarè patet, cur potius à fundo vasts quam à parte aquae superi∣ore oriantur hujusmodi bullae. Cum enim vehemens illa suctio co∣netur aquam à fundo phialae elevare, nascitur ibidem subtilis quae∣dam materia quae in bullas conversa sic ascendit, uti capite decimo quinto in quarto Experimento dictum est. For, whatever he may think, it does not hence so clearly appear how the endea∣vour only of the Funiculus to draw up the Water from the bottom of the Vial, to which, that endeavour notwithstand∣ing, it remains contiguous, should generate in some parts of the bottom of the Glass, and not in others, such a subtile matter as he tells us of. And I suppose the Reader will, as well as I, wish he had more intelligibly declared how this strange gene∣ration of subtile matter comes to be effected. And I presume it will likewise be expected that he also declare, why both in our case and in the Torricellian Experiment the bubbles grow so much larger by being nearer the top of the liquor; if, as he rejects our Explication of this Circumstance, the effect of the suction he speaks of be greater upon the lower part of the liquor than the upper, to which alone nevertheless his Funi∣culus, that is said so to draw the liquor, is contiguous.

Our Author making no particular Objection against the 10 following Experiments, we also shall pass them by, and fall with him upon the consideration of the 31 Experiment.

The 31 Experiment.

Upon this our Author having recited our Conjecture as the cause why two very flat and smooth Marbles stick so closely together, that by lifting up the uppermost you may take up also the lowermost, approves my way of examining that Con∣jecture. But whereas I say that the reason why, though the Mar∣bles

were kept together by the pressure of the ambient Air, yet they did not fall asunder in our exhausted Receiver, no not though a weight of 4 Ounces were hung at the lower stone, might be, that by reason of some small leak in the Receiver the Air could not be sufficiently drawn out: yet he tells us with his wonted confidence, Certum esse, sententiam illam vel hoc so∣lo Experimento satis refelli. But possibly he would have spoken less resolutely, if he had made all the trials about the adhesion of Maibles that we relate our selves to have made in the short History we have publish'd of Fluidity and Firmness. For our Examiner speaks as if all that we ascribe to the Air in such Ex∣periments were to sustain the lower Marble with the weight perhaps of a few Ounces: Whereas in case the Air be kept from getting in at all between the stones, it may (according to our Hypothesis) sustain a Weight either altogether or well-nigh equal to that of a pillar of Air as broad as the Basis of thelow∣er Marble, and as long as the Atmosphere is high, or to the weight of a pillar of Quicksilver of the same thickness, and about 30 Inches long; these two pillars appearing by the Tor∣ricellian Experiment to counterpoise each other. And therefore since in the seventeenth Experiment, when we had exhausted our Receiver as far as we could, there remain'd Air enough to keep up in the Tube a Cylinder of about an Inch long of Quick∣silver; and since the broader the contiguous Marbles are, the greater weight fastned to the lowermost may be sustain'd by the resistance of the Air, (as is obvious to him that considers the Hy∣pothesis, and as we have proved by Experiment in the foremen∣tioned Tract) it need be no wonder that the Air remaining in the Receiver should be able to support the lowermost Marble, whose Diameter was near two Inches, and a weight of four Ounces, those two Weights being inferior to that of a Mercurial Cylinder of that Diameter and an Inch in length. And though it were not, yet we are not sure that the Receiver was as well emptied when we made the 31 Experiment, as when we made the 17. And (if my Memory does not much mis∣inform me) 'twas with the same pair of Marbles that in the

presence of an illustrious Assembly of Virtuosi (who were Spectators of the Experiment) the uppermost Marble drew up the lowermost, though that were clogg'd with a weight of a∣bove 430 Ounces.

As for the account the Examiner substitutes of our Phaeno∣menon, I know not whether many Readers will acquiesce in it: For, not to insist upon the Objection which himself takes no∣tice of, that according to him the distended Air in the Recei∣ver should draw asunder the adhering Marbles; his Explication supposes that there cannot naturally be a Vacuum, whence he infers that, Necesse erat ut lapis ille non aliter descenderet, quàm relinquendo post se tenuem bujusmodi substantiam, qualis ab argen∣to vivo aut aquâ sic descendentibus relinqui solet. But whereas he adds, that the cause of the obstinate adhesion we meet with in our case is, that such a substance is far more difficult to be se∣parated from Marble than from Qucksilver or any other kind of Body; that Assertion is precarious. And though I have tried Experiments of this nature with stones of several sizes, perhaps an hundred times, yet I never could find that by their cohesion they would sustain a weight greater than that of a Pillar of the Atmosphere that prest against the lowermost: Which is a considerable Circumstance, that much better agrees with our Explication than our Adversaries. And whereas he further says, Vnde existimo planè, si perfectè complan at a fuerint duo marmora sic conjunct a, it a ut nullus omnino aër inter utrum{que} mediaret, non posse ea ullis humanis viribus ab invicem divelli: I hope I need not tell the Reader, that whether or no this a∣gree with what he had immediately before taught of the sepa∣rableness of a subtile substance even from Marble, so bold and improbable an Assertion requires the being countenanc'd with a much better proof than the only one he subjoyns in these words, Vti etiam confirmat exemplum quod ibidem adducit Au∣thor de lamina aenea, tabulae cuidam marmoreae it a adhaerente, ut à lacertoso juvene, de suis viribus gloriante, non potuerit per an∣nulum centro ejus affixum inde elevari. For sure there is great odds betwixt the strength of a man unassisted by any En∣gine,

and the utmost extent of Humane Power. And indeed accor ing to our Hypothesis, and without having recourse to Natures dreading of a Vacuum, the case is clear enough: For, supposing the Plate to be of any considerable breadth, the Pillar of the Atmosphere that lean'd upon it, and must at the instant of its deserting the superficies of the Table all at once be lifted up with it, may well exceed the force of a single man, especially in an inconvenient posture; since by the co∣hesion of a pair of Marbles of about three Inches Diameter, I did with my own hands take up above a thousand and three hundred Ounces.

The 32 and 33 Experiments.

Against our Explication of these two, which our Author examines together, he objects nothing peculiar, but contents himself to explicate them by his Funiculus: Wherefore neither shall we need to frame any peculiar defence for it, especially if the Reader will be pleased to refer hither as much of what we oppos'd to his Animadversion on the third Experiment as is justly applicable to our present Controversie. Our Author indeed endeavours to prove his Explication by saying, that the distended Air in the exhausted Cylinder draws up the Sucker with the annexed weight, Eodem fere modo quo videmus in cu∣eurbitulis dorso aegrotantis applicatis, in quibus, extincta jam flamma, rarefact us aër se contrahens carnem tam vehementer, uti videmus, elevat attrahit{que} intra cucurbitulam. But that Phae∣nomenon is easily enough explicable in our Hypothesis, by say∣ing, that upon the vanishing of that heat which strengthned the pressure of the included Air, the Spring of it grows too weak to resist any longer the pressure of the ambient Air; which thereupon thrusts the flesh and neighbouring blood of the Pa∣tient into the Cupping-glass, almost after the same manner as we formerly taught the Pulp of the Finger to be thrust into the deserted Cavity of the Glass-Tube in the Torricellian Ex∣periment.

The 34, 35 and 36 Experiments.

To these our Author saying nothing but this, In his tribus nihil peculiariter occurrit hic explicandum, cujus ratio ex jam dictis non facile pateat; we also may be allow'd to pretermit them, and pass on to

The 37 Experiment.

Of the appearance of Light or Whiteness, mentioned in this Experiment, the Examiner confesses that we have assigned a cause probable enough, by referring it to the vehement and sud∣den commotion of the included Air. And indeed though I do still look upon some of the things that I hesitantly pro∣pos'd about this difficult Phaenomenon but as mere Conjectures, and though he annexes his Explication of it; yet I see not but that it is coincident with ours, or not better than it. For, to what I had said of the Commotion of the parts of the Air, he adds only in two or three several places their being violent∣ly distended; which how it improves the Explication of the Phaenomenon I do not readily see. And whereas he subjoyns, Existimo autem dicendum potius candorem illum esse lumen quod∣dam reflexum, quam innatum, eo quòd (ut testatur Author) in tenebris non appareat, sed solum de die aut accensa candela: I presume the attentive Reader will easily discern that his Opi∣nion is much-what the same that I propos'd and grounded on the same reason. But the chief difficulty in this abstruse Phae∣nomenon, namely why we meet with it but sometimes, our Examiner's Explication leaves untouch'd.

The 38 and 39 Experiments.

Against these our Author makes no peculiar Objections.

The 40 and 41 Experiments.

But in his Animadversions upon these, having told the Reader that I seem to ascribe the sudden extinction of the in∣cluded Animals to the excessive thinness of the Air remaining

in the Receiver, made by the recess of what was drawn out, unfit for Respiration; he adds resolutely enough, Verum im∣possible videtur, ut hujusmodi animalcula ob solum defectum cras∣sioris aëris tam cito moriantur: But gives no other reason than that they dye so soon, which is no more than what he said in the newly-cited words, and besides is grounded upon some∣thing of mistake. For the Creatures he mentions were a Bee, a Fly, and a Caterpillar, and those included too in a small Re∣ceiver, which could be suddenly exhausted: and these indeed became moveless within a minute of an hour; but that minute was not (as the word is often us'd to signifie in English) a Moment, but the Sixtieth part of an Hour. And though these Insects did in so short a time grow moveless, yet they were not so soon kill'd; as appears by the Narrative. The sangui∣neous Animals that did indeed dye, were kill'd more slowly. And I remember that having purposely enquir'd of a man (us'd to go under water by the help of an Engine wherein he could carry Air with him to the bottom of the Sea) how long he could endure, before he was accustomed to dive, without breathing or the use of a Spunge; * 1.45 he told me, that at first he could hold out about two or three Minutes at a time: Which made me think that Divers become able to con∣tinue under Water so long, either by a pecu∣liarly-convenient Constitution of body, or by a gradual exer∣cise. And I am apt to think that he did, as men are wont to do, when he said two or three Minutes, mean what is indeed a much shorter time than that when exactly measured amounts to. For, having purposely made trial upon a couple of Moles that were brought me together alive, one of them included in a small, though not very small, Receiver was between two and three Minutes in killing; whereas the other being immediately after detain'd under Water did not there continue full a Minute and a quarter, before it finally ceas'd from giving any sign at all of life. By which trial it may appear, that 'tis not impossible that the want of Respiration should dispatch an Animal in as little

time as is mentioned in the Experiment I am now defending. And indeed our Author either should have proved that 'tis not possible for the want of Air to destroy Animals so soon, or should have given us some better account of the Phaenomenon. For whereas he teaches us, that according to his Doctrine the little Animals above mentioned were so soon kill'd, quia per ra∣refactumillum aërem sese contrahentem extractus sit corum halitus: I see not that hereby, if he explicate the Phaenomenon other∣wise than we, he explains it better; for he seems to speak as if he thought this halitus to be some peculiar part of the Animal in which his life resides. And besides he seems not to consider, that whereas, according to me as well as according to him, the Air contained in the Lungs (supposing these Animalcula have any) must in great part pass thence into the Receiver, (for whe∣ther that be done by the Spring of the Air it self, that was har∣boured in the Lungs, or the traction of the more rarefi'd Air in the Receiver, is not material in our present case) the Exami∣ner must, as well as I, render a reason why the extenuation or recess of the halitus should cause the hasty death of the included Animals; and condemning my Conjecture he ought to have substituted another reason: and though he subjoyns these words, and concludes with them, At{que} hinc quo{que} ortae sunt vehementes illae convulsiones, quas ante mortem passas esse aviculas quasdam memorat ibidem Author; yet I doubt not but the Rea∣der will think it had not been amiss that the Author had more intelligibly reduc'd these Tragick Symptoms from his As∣sumption, for the sake of those that are not Anatomists and Physicians enough to discern how his Funiculus could produce these effects.

For my part, as in the 41 Experiment I tender'd my thoughts concerning Respiration but doubtingly, so I am yet unwilling to determine resolvedly in a matter of that difficulty.

The 42 and 43 Experiments.

In his Examen of these two last of our Physico-Mechanical Experiments, the Author contents himself to endeavour to ex∣plicate

the Phaenomena recited in them by the contraction of the rarefi'd Air; which, according to him, endeavours to draw up the subjacent water out of the Vial, whereby it vehemently distends the parts of that water, as he taught in the like case upon the 20 Experiment. But since we have already consi∣der'd his Animadversion upon that, although this presumed di∣stension of the water is not visible that we have observ'd, when cold water, that has been first freed from his interspers'd Air, is put into the Receiver, notwithstanding that the Funiculus should in that case also distend it; we are so afraid of tiring out the Readers patience by the frequent repetition of the same things, that we will leave it to him to judge which of the two Explications, the Examiner's or ours, is to be prefer∣red, without troubling him and our selves with defence of Accounts against which our Adversary does not here make any peculiar Objections.

And thus have we by God's assistance considered what the Examiner hath been pleased to oppose either against our parti∣cular Explications, or against the Hypotheses that divers of them suppose: Wherein I have been the more particular and prolix, because I would willingly excuse my self and others from the trouble of any more Disputes of this kind. I hope there is not in my Answers any thing of Asperity to be met with; for I have no quarrel to the Person of the Author, or his just repu∣tation; nor did I intend to use any more freedom of Speech in the answering his Objections, than his resolute way of pro∣posing divers of them made it on those occasions needfull for the Caution of those Readers who are not acquainted with our differing ways of writing, and perhaps have not observed that some men are wont to consider as much what they propose but with a Perhaps, or some such expression of diffidence, as others do what they deliver far more resolutely. And though being very far from being wedded to my Opinions, I am still ready to ex∣change them for better, if they shall be duly made out to me, (which I think it possible enough they may hereafter be;) yet peradventure the Reader will think with me, that the Examiner

has not given me cause to renounce any of them, since the Objections he has propos'd against me have been sufficiently answered, and since the Hypothesis he would substitute in the room of ours (besides that it is partly precarious) supposes things which divers of the eminentest Wits of our Age (other∣wise of differing Opinions) profess they cannot admit or so much as understand: Whereas the Weight and Spring of the Air are not denied by our Author himself, and are demonstra∣ble by Experiments that are not controverted betwixt us. Which things I represent for the defence of what I think the Truth, and not to offend my learned Adversary, who shall have my free consent to be thought to have fail'd rather in the Choice than in the Management of the Controversie. Though since this passes for his first Book, and since conse∣quently he is not like to have been provoked, or engaged in point of Reputation, to challenge me or any of those far more eminent Persons he has nam'd among his Adversaries, I am in∣duc'd by the severity wherewith I have known eminent Virtuosi speak of his Attempts, and particularly of his Funiculus, to fear that some of those he has needlesly oppos'd, will be apt to apply to him that of St. Austin against some of his Adversa∣ries, that had disputed against him with much more Subtilty than Reason, In mala causa non possunt aliter, at malam causam quis eos coegit habere? But this notwithstanding I am, as I was going to say, content my Adversary should be thought to have said for his Principles as much as the Subject will bear; nor would I have it made his Disparagement, that I have declared that his whole Book has not made me depart from any of my Opinions or Explications, since his Hypothesis and mine being inconsistent, it may be looked upon as a sign rather that each of us have, than that either of us have not, reason'd closely to his own Principles, that the things we infer from our contrary Suppositions do so generally disagree.

FINIS.

Notes

• * 1.1

  Page. 20.
• * 1.2

  Page 16.
• * 1.3

  Pag. 17.
• * 1.4

  Pag. 15.
• * 1.5

  Page 12.
• * 1.6

  Page 14.
• * 1.7

  Pag. 18.
• * 1.8

  Gass Phys. Sect. 1. Lib. 2. Pag. 204. De nupero Inanis Ex∣perimento.
• * 1.9

  Pag. 19.
• * 1.10

  Pag. 19.
• * 1.11

  Pag. 20.
• * 1.12

  Pag. 21.
• * 1.13

  Pag. 21.
• * 1.14

  Pag. 11.
• * 1.15

  Page 24.
• * 1.16

  Pag. 48.
• * 1.17

  Page. 22.
• * 1.18

  Page 25.
• * 1.19

  Pag. 38.
• * 1.20

  Page. 38.
• * 1.21

  Pag. 40.
• * 1.22

  Pag. 40, 41.
• * 1.23

  Pag. 41.
• * 1.24

  Pag. 43, 44.
• * 1.25

  Pag. 42.
• * 1.26

  Pag. 160.
• * 1.27

  Pag 169.
• * 1.28

  Pag. 163.
• * 1.29

  Chap. 5.
• * 1.30

  Pag. 175.
• * 1.31

  Pag. 159.
• * 1.32

  Pag. 66.
• * 1.33

  Gassendus To∣mo. 1. pag. 211.
• * 1.34

  Page 63.
• * 1.35

  Pag. 50.
• * 1.36

  Mr. Croon one of the learned Pro∣fessors of Gresham College.
• * 1.37

  Dr. Hen. Power.
• * 1.38

  See the second Figure.
• * 1.39

  Probably these or the like words, did manifest Pressure, are here omitted, for the Mountain-Air there seems to have acted rather by its Weight than Elas∣ticity.
• * 1.40

  Pag. 11.
• * 1.41

  See the 5. Figure.
• * 1.42

  See Part 2. C. 5.
• * 1.43

  Sed contra manifeste.
• * 1.44

  See also in the 43 Experim. these pas∣sages, — And this Ef∣fervescence was so great in the upper part of the water, &c. As also, — The Efferve∣scence was confin'd to the upper part of the water, unless, &c.
• * 1.45

  See more concer∣ning this Obje∣ction in the An∣swer to it as 'tis propos'd by Mr. Hobbs.