A defence of the doctrine touching the spring and weight of the air propos'd by Mr. R. Boyle in his new physico-mechanical experiments, against the objections of Franciscus Linus ; wherewith the objector's funicular hypothesis is also examin'd, by the author of those experiments.

A DEFENCE Of Mr. R. BOYLE's EXPLICATIONS of his Phy∣sico-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 se∣veral Chapters of it employ'd to oppose the Ex∣plications I ventur'd to give of some of my new Experiments touching the Spring of the Air arrow_forward . 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 forborne provoking Language in his Objections, allowes me in answering them to comply with my Inclinations & Custom of exercising Civility, even where I most dissent in point of Judgement. Besides, the Author himselfe 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 parts 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 then 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 arrow_back Air arrow_forward : 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 arrow_back Air arrow_forward 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 arrow_back Air arrow_forward 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 then 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, ita 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 arrow_back Air arrow_forward depends upon his former Chap∣ter, wherein he thinks he has disprov'd the Weight of the arrow_back Air arrow_forward ; 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 tan∣tum digitorum (quo usi sumus in primo Argumento) non * 1.2 totus impleatur argento, ut prius, sed spatium aliquod inter digitum superiorem & argentum relinquatur in quo fit solus aër; videbimus substracto inferiore digito superiorem non solum deor∣sum trahi; ut prius, sed etiam argentum jam descendere, idque no∣tabiliter, quantum nimirum extendi potest exigua illa aëris particu∣la à tali pondere descendente. Unde si loco illius aëris ponatur aqua, aliusve liquor qui non tam facilè extenditur, descensus nullus erit.

Hinc, inquam, contra hanc sententiam formatur argumentum: nam si externus ille aër neque at velhos viginti digitos argenti à lapsu su∣stentare, 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 Answer 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 re∣pelli, quam eidem affigi, cum non minus sursum quam deorsum fiat hujusmodi dilatatio: He considers not, that though the endea∣vour of the included arrow_back Air arrow_forward to expand it selfe be at first every way alike, yet the expansion it selfe 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 arrow_back Air arrow_forward , 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 arrow_back Air arrow_forward there is the Weight of the whole Mercurial Cylinder to assist the Spring of the arrow_back Air arrow_forward , to sur∣mount the Weight of the Atmosphere that gravitates upon the restagnant Mercury. So that the arrow_back Air arrow_forward included and endeavouring to expand it selfe, finding no assistance to expand it self upward, and a considerable one to expand it selfe downward, it is very natural that it should expand it selfe that way whence it finds less resistance. As accordingly it will happen, till the Spring of the arrow_back Air arrow_forward 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 arrow_back Air arrow_forward 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 arrow_back Air arrow_forward , and then inverting it, open it under Water, you will perceive the included Inch of arrow_back Air arrow_forward not to dilate it selfe any thing near (for I need not here define the Proportion) halfe 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 halfe on∣ly of Quicksilver, and consequently the inward arrow_back Air arrow_forward is far less

assisted to dilate it self and surmount the pressure of the out∣ward arrow_back Air arrow_forward by the Cylinder of Water then by that of Mercury. And as for what our Author sayes, that if instead of arrow_back Air arrow_forward , 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 arrow_back Air arrow_forward 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 Quick-silver, its spring must be pro∣portionably weakned. And consequently that part of the Fin∣ger that is within the Tube will have much less pressure against it from the dilated arrow_back Air arrow_forward within, then the upper part of the same Finger will have from the unrarefi'd arrow_back Air arrow_forward 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 de∣clare 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 his 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 Autores quam maxime refugiunt, asserentes rarefactionem non aliter fieri, quam per cor∣puscula aut vacuitates: I wish he had more clearly express'd him∣self, since as his words are couch'd I cannot easily guess what he means, and much less easily discern how they make an Argu∣ment against his Adversaries. For, sure he thinks them not so absurd, as to imagine that the arrow_back Air arrow_forward can dilate it self, and thrust down the Mercury, without in some sense taking up more room then it did before: For the very word Dilatation, and the effect

they ascribe to the included arrow_back Air arrow_forward , clearly imply as much; so that I see not why he should say that they are so averse from granting the arrow_back Air arrow_forward to take up more Place then before, especially since he takes notice in the former Chapter, that we compare the Ex∣pansion of the arrow_back Air arrow_forward to that of compress'd Wooll; and since he here also annexes that we explicate Rarefaction either by Cor∣puscles or Vacuities. But this later Clause makes me suspect his meaning to be, that the Elaterists do not admit that the same arrow_back Air arrow_forward may adequately fil more of Place at one time then at another; which I believe to be as true as that the self-same lock of com∣press'd Wooll has no more Hairs in it, nor does adequately fill more Place with them, when it is permitted to expand it self, then whilest it remain'd compress'd. But against this way of Rarefaction our Author here has not any Objection, unless it be intimated in these words, Concipi non potest: Which if it be, I shall need only 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 Rarefa∣ction conceivable; and he acknowledges (as we shall see anon) that it is not clear; what the ablest of his Party (the modern Ple∣nists) are wont to object against the way of Rarefaction he dis∣likes, 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 apertus, sed longior, put a digitorum 40. Argentoque impleatur, eique * 1.4 digitus supernè applicetur ut prius, videbimus subtracto in∣feriore digito, argentum quidem descendere usque ad consuetam suam stationem; Digitum autem superiorem fortiter intra tubum trahi, eique firmissime, ut prius, adhaerere. Ex quo rursum evidenter con∣cluditur, argentum, in sua statione constitutum, non ibidem susten∣tari ab externo aëre, sed à funiculo quodam interno suspendi, cujus

superior éxtremitas, 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 suf∣ficient 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 then in the third Experiment (where some arrow_back air arrow_forward is included, 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 keep it off from the de∣serted Cavity of the Tube, save only 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 Quick silver, 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, then 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 in∣deed the principal thing in his Book. Sumatur (sayes he) tubus brevior digit is 29½ puta digitorum 20. non ta∣men * 1.5 clausus altero extremo, (ut hactenus) sed utrinque apertus: Eic Tubus, immerso ejus orificio Argento restagnanti, sup∣pes••oque digito, n••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 ar∣gento 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 ante aëre externo: nunquam profecto per eam explicabitur, quomodo digitus ille sic trahatur deorsum, tubo{que} tam vehementer adhareat; non enim à trudente 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 unanswerable 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 arrow_back Air arrow_forward which thrust up the Quicksilver cannot so strongly draw down the Finger. As if the arrow_back Air arrow_forward were not a fluid body, but a single and entire pillar of some solid mat∣ter. But to shorten our reply to his objections, the best way per∣haps 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 arrow_back Air arrow_forward ; 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 arrow_back Air arrow_forward : so that against those parts of the Finger that are contiguous to the arrow_back Air arrow_forward there is all the wonted pressure of the outward arrow_back Air arrow_forward ; where∣as 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, because the Mer∣curial Cylinder in this Experiment is suppos'd to be twenty Inches high; and if it were but a little more then thirty Inches high, (which is a third more) then the weight of the Quicksilver would take off not two thirds onely, but the whole pressure of the outward arrow_back Air arrow_forward , 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 Examiners third Argument, That the pressure of the out∣ward arrow_back Air arrow_forward is taken off from the body that remains in the upper part of the Tube, according to the weight of the liquor suspend∣ed in the Tube; and since in our Hypothesis the pressure of the outward arrow_back Air arrow_forward is able to keep thirty 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 arrow_back Air arrow_forward , equal to the weight of a Cylinder 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 perswaded of; yet as far as I and another person very well vers'd in these Experiments have pur∣posely tryed, 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 cavi∣ty of the Pipe. And if by pressing your Finger against the Ori∣fice 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 arrow_back Air arrow_forward being a fluid as well as a heavy body, it does not (as

grosser Weights would) press only against the upper part of the Finger, but pressing as much of the finger as is expos'd to it almost every where, and almost uniformly, as well as strongly, it does by its lateral pressure on every side thrust in the Pulp of the Fin∣ger into the hole where there is not any resistance at all, or at least near so much pressure against the Pulp as that of the ambi∣ent arrow_back Air arrow_forward against the parts of the Finger contiguous to it.

By this it may appear that we need not borrow the Objection our Author offers to lend us; namely, that in the Experiment under consideration the Quicksilver is press'd downward by the Spring of some arrow_back Air arrow_forward 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 notwithstanding what our Author Objects, that the arrow_back Air arrow_forward expanding it self wil thrust away the Finger upwards, since the contrary of that pretence we have lately manifested in the An∣swer to his Third Argument. And as for what he adds to con∣firm his Argumentation in these Words, Quod vel inde confirmatur, Quia cum praponderans ille aër succedat * 1.6 (uti asseritur) loco sublati inferioris digiti, id est, eodem modo nunc sustentet Argentum quo ante ab applicato digito inferiore sustenta∣batur; manifestum est, non debere, juxta hanc sententiam, magis deorsum trahi digitum superiorem post sublatā inferiorem quam ante. Cum it aque contrarium planè doceat experientia, satis liquet sententi∣am illam esse falsam. We must consider that the Tube being suppos'd perfectly 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 in∣deed keep up the Mercury in the Tube, and the pressure of the outward arrow_back Air arrow_forward 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 un∣dermost Finger. And therefore whereas the Atmospherical

Cylinder will not keep up a Cylinder of Quicksilver of above thir∣ty 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 under∣most Finger, the Pulp of the uppermost must have about the same Pressure against it where it is contiguous to the Mercury, as there is against the other part of the same Finger; after the removal of the undermost Finger, there is as much of the At∣mospherical 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 (sayes he) impugnatur: Quia ex eo sequeretur, Argentum vivum per similem Tubum è vasculo exsugi posse eâdem prorsus facilitate quâ ex eodem exsugeretur * 1.7 aqua: quod tamen experientiae repugnat, quâ docemur aquam in ••s sugentis facillime attrahi; quo tamen Argentum vivum ne toto quidem adhibito conatu perduci queat, imo vix ad Tubi medie∣tatem.

Sequelam autem sic ostendo: Quia cum in hac sententia nihil aliud agendum sit quam hoc, ut per Tubum sic ascendat subjectus Liquor, sive Aqua fuerit, sive Argentum, nisi ut sugendo sursum trahatur aër Tubo inclus s, quo sic attracto ascendit illico subjectus Liquor, protrusus nimirum ab externo aëre jam praeponderante (uti docet Pec∣quetius in Dissertatione Anatomica pag. 63.) manifestum est, ea∣dem planè facilitate exsugendum sic Argentum vivum qua exsu∣gitur Aqua: Quod quum Experientiae tam aperte repugnat, ne∣cesse est sententiam ex qua sequitur falsam 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 Au∣thors Third Argument, That when the Mercurial Cylinder that leans upon the restagnant Mercury has at the other end of it arrow_back Air arrow_forward , kept from any entercourse with the Atmosphere, that included arrow_back Air arrow_forward has so much of the Pressure of the external arrow_back Air arrow_forward taken off from it as counterpoises the Mercurial Cylinder. And the Fin∣ger that is expos'd to the whole Pressure of the ambient arrow_back Air arrow_forward in some of its Parts, and in others but to the much fainter Pres∣sure of the included arrow_back Air arrow_forward , endures an unusual 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 Respirati∣on the Pressure of the whole ambient arrow_back Air arrow_forward . Which Pressure, notwithstanding the Muscles design'd for the use of Respiration, are able without any considerable resistance to dilate the Thorax at pleasure; because, as fast as they open the Chest, and by di∣lating it weaken the Spring of that arrow_back Air arrow_forward which is then within the Body, the external arrow_back Air arrow_forward by flowing in, for want of finding the usual resistance there, keeps that within the Thorax in an Aequili∣brium of force with that without. These things premised, 'tis not difficult in our Hypothesis to give an Answer to the Exami∣ners Experiment. For we say when a Cylinder of Mercury is rais'd in the Tube to any considerable height, the Pressure of the arrow_back Air arrow_forward in the Thorax is lessen'd by the whole weight of that Mer∣curial 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 arrow_back Air arrow_forward against the weakned Pressure of the internal: But if in stead of Mercury, you substitute Water, so short a Cylinder

of that comparatively light Liquor takes off so little of the Pressure of the included arrow_back Air arrow_forward , that it comes into the Lungs with almost its usual Strength, and consequently with almost as much Force as the outward arrow_back Air arrow_forward presses with against the Thorax.

And on this occasion there occurrs 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 arrow_back Air arrow_forward , it would follow, as the Examiner sayes it should, that the Quicksilver would by the Pressure of the outward arrow_back Air arrow_forward be im∣pell'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 being so per∣tinent and considerable, we shall annex it in the same words wherein it is related by his Country-man and Acquaintance, the Learned and Candid Gassendus. Neque hoc verò solum, sed insuper vitreo Diabete Clysteréve ea qua * 1.8 par fuerit longitudine confecto, & post embolum ad orificium usque compulsum, immisso ad nor∣mam in subjectum Hydrargyrum deprehendit, ubi embolum sensim deinde educitur, consequi Hydrargyrum ascendere{que} ad eandem us{que} duorum pedum & digitorum trium cum semisse altitudinem. To which he immediately subjoynes a Circumstance very conside∣rable to the present Controversie in the following Clause. Ac ubi deinceps, adhibita licet non majore vi, Embolum altius educi∣tur, 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 Examiners Experiment, we may well explicate it in our Hypothesis, by saying, that agreeably to it it happens, that in a more forcible Respiration the Mercurial Cylinder is raised higher then in a more languid; because, in the former Case, the Chest being more dilated, the included arrow_back Air arrow_forward is also more expanded; whereby its debilitated Spring cannot as before enable the Mercurial Cylinder to counterpoise altoge∣ther

the Pressure of the ambient arrow_back Air arrow_forward . And that the Reason why the Quicksilver is not by Respiration rais'd as high as it is kept suspended in the Torricellian Experiment, is not, that the Pres∣sure of the outward arrow_back Air arrow_forward is unable to raise it so high, but because, as we have already declar'd, the free Dilatation of the Thorax is opposed by the Pressure of the ambient arrow_back Air arrow_forward ; which Pressure being against so great a Superficies, and being but imperfectly resisted by the debilitated Pressure of the arrow_back Air arrow_forward within the Tho∣rax, will be easily imagined to be very considerable by him who considers that in our Engine, the Pressure of the external arrow_back Air arrow_forward against the Sucker of less then 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 Quicksilver in a Glass Tube, though the Ele∣vation of the Quicksilver be according to our Author perfor∣med likewise by his Funiculus contracting it selfe 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 Authors four Arguments, to prove that in the Torricellian Experiment the Quicksilver can∣not be kept suspended by the counterpoise of the external arrow_back Air arrow_forward : 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 then 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 then in hot, because the arrow_back Air arrow_forward 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 Authors Consequence; it will be here sufficient to Reply, that the Observation on which he grounds it does not constantly hold, as his Objection supposes: which may appear by that part of our 18. Experi∣ment whence the matter of Fact is desum'd, as we shall have oc∣casion-to take further notice of when we shall come to the De∣fence of that Experiment. So that what has been hitherto Dis∣cours'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 suf ficit, Argentum (facto Experimento in loco a∣perto) * 1.10 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 ip∣sum aëris Elaterium, is very short, and does not require that we should dwell long upon it. For the proof he brings of his Asser∣tion being this, Cum tota vis hujus Elaterii pendeat à re∣futato jam aëris aequipondio cum digitis 29½ Argenti vivi, * 1.11 ita ut nec plus net minus faciat hoe elaterium in loco occluso quam fit-per illud aequipondium in loco aperto; manifestum est, cum jam oftensum sit fictitium planè esse hujusmodi aequipondium, 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 di∣stinct Reply to this. We shal rather desire the Reader to take no∣tice, that whereas our Author sayes that according to his Adver∣saries, Ncc plus nec minus faciat hoc Elaterium in loco occluso quam fit per illud Aequipondium in loco aperto; whatever others may have written, we for our part allow of this Opinion but in some Cases; for in others we have perform'd much more by the Spring of

the arrow_back Air arrow_forward , which we can within certain limits increase at pleasure, then can be perform'd by the bare weight, which for ought we know remains alwayes somewhat near the same. And of this advantage that the Spring of the arrow_back Air arrow_forward may have in point of force above the weight of it, we have formerly given an Instance in our 17. Experiment, (where, by compressing the arrow_back Air arrow_forward in the Receiver, we impell'd the Mercurial Cylinder higher then the station at which the Counterpoise of the arrow_back Air arrow_forward is wont to sustain it) and shall hereafter have occasion to give yet more conside∣rable proofs. To the lately recited words our Examiner sub∣joyns these; Adde, cum allata jam capite praecedente ex∣perimenta de adhaesione digiti, &c. eodem modo se habent in * 1.12 loco clauso ac in aperto, necessarium esse facta ex eis argumenta contra aquipondium, 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 already given an account in our Hypothesis) I see not how it requires any new and particular Answer. And whereas he sayes, that the Experiments he had mentioned concerning the adhesion of ones Finger, &c. eodem modo se habent in loco clauso ac in aperto; I could wish he had added what way he took to make the Tryals. For he gives no intimation that he did them any other wayes then in ordinary rooms. And in such there scarce ever wants a communication betwixt the inward and outward arrow_back Air arrow_forward , 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 operation 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 (sayes he) si secum ex∣penderent hi Authores, quanta sit difficultas explicandi hu∣jusmodi * 1.13 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 then any man that I know of has yet done,

how the same arrow_back Air arrow_forward can adequately fill more space at one time then at another, before he perswade me to change my opini∣on about the Spring of the arrow_back Air arrow_forward : Especially since he himself allowes that the arrow_back Air arrow_forward has a Spring, whereby it * 1.14 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 difficulty to make out the Spring of the arrow_back Air arrow_forward . 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 arrow_back Air arrow_forward are really perform'd by neither, but by a certain Funiculus, or extremely thin substance, provided in such cases by Nature, ne detur va∣cuum, which being exceedingly 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, ap∣pear 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 then this; which seems to be partly precarious, partly unintelligible, and partly insuffi∣cient, and besides needless: though it will not be so convenient to prove each of these apart, because divers of my Objections tend to prove the Doctrine, against which they are alledged, ob∣noxious to more then one of the imputed Imperfections.

First, then, the Arguments by which our Author endeavours to evince his Funiculus, are incompetent for that end. The Ar∣guments which he proposes in his sixth Chapter (where he un∣dertakes to make good his Assertion) I there find to be three.

The first he sets down in these words, Constat hoc primò ex jam dictis Capite praecedente: nequit enim argentum descen∣dens sic digitum deorsum trahere, tubo{que} affigere, nisi à tali * 1.15 Funiculo suspendatur, eum{que} suo pondere vehementer extendat, 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 de∣clare my selfe for, or against, a Vacuum; yet since I am now wri∣ting against the Funicular Hypothesis. it will much conduce to shew that it is not firmly grounded, if I examine what he here al∣ledges 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 Expe∣riments does act after so extraordinary a manner, as is requisite to the production of his Funiculus. For in the 47. Page, having in his Adversaries name demanded what need there is at the de∣scent 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 immediately subjoyns, (with what cogency I will not now examine:) At{que} hinc plane

confirmatur commune. illud per tot jam elapsa secula usurpalum in Scholis axi••••••a viz. Naturam à vacuo, abhorrere. And though he seem to make his Funiculus the immediate cause of the Phae∣nomena occurring in the Torricellian and our Experiments: 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; Namlicet (sayes he) immediata ratiocur aqua v. g. ex hydria hortulana superne clausa (quo exemplo. * 1.16 utuntun) non descendat, non sit metus vacui, sed ea quam modo dixi∣mus, nempe quod non detur sufficiens pondus ad solvendum illum nexum quo adhaer eat aqua clausae hydriae summitati; ad eam tamen rationem tandem necessario veniendumest. But, though as well our Author's Fumiculus, as the other scarce conceivable Hypo∣theses that learned men have devised, to account for the suspen∣sion of the Quicksilver otherwise then by the resistance of the external arrow_back Air arrow_forward , seem to have been excogitated onely to shun the necessity of admitting a Vacuum: yet I see not how our Exami∣ner cogently proves, either that there can be none in rerum na∣turâ, or that Defacto there is none produc'd in these Experi∣ments. For in his fifth Chapter (where he professedly under∣takes that task) he has but these two incompetent Arguments. The first is drawn from the attraction, as he supposes, of the Fin∣ger into the deserted cavity of the Tube in the Torricellian Expe∣riment: Quaequidem (sayes he) tam vehemens tractio & adhaesio, cum non nisi à reali aliquo corpore inter digitum * 1.17 & argentum constitutum queat provenire, manifestum est spatium illud vacuum non esse, sed verâ aliquâ substantiâ repletum. But to this Argument 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 replenish the deserted Cavity; without pressing this, I say, let us) consi∣der his other, which he draws from the Diaphaneity of the deser∣ted part of the Tube, which space (he sayes) were it empty, would appear like a little black Pillar, Eo quod nullaespecies visua∣les

ne{que} ab eo ne{que} per illud possunt ad oculum perventre. But (not to engage our selves in Optical Speculations and Controversies) if we grant him some what more then 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 Proposer of it does twice in this Chapter) That space verâ aliquâ substantiâ 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 Va∣cuities 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 united 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 may 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 sumes dri∣ven over by hear, 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 arrow_back Air arrow_forward .

To which I might adde, that the Torricellian Experiment being made in a dark night, or in a Room perfectly darken'd, if it suc∣ceed (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 bring∣ing 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 necessarily follow, that the deserted part of the Tube must be full: As in our 27. Experiment (though many of those gross Aerial Particles that appear'd necessary to convey a languid sound were drawn out of our Receiver at the first and second Exsuction; yet there re∣main'd so many of the like Corpuscles, that those that were wanting were not miss'd by the sense, though afterwards, when a far greater number was drawn out, they were) so there may be matter enough remaining to transmit the impulse 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 mentioned, 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 Vacuum.

But notwithstanding what we have now discours'd, as in our 17. Experiment we declin'd determining whether there be a Va∣cuum or no; so now what we have said to the Examiners Argu∣ment, has not been to declare our whole sense of the Contro∣versie, but onely to shew, that though his Hypothesis supposes there is no Vacuum, yet his Arguments do not sufficiently prove it: which may help to shew his Doctrine to be precarious; for otherwise the Cartesians, though Plenists, may plausibly enough (whether truly or no I now dispute not) decline the necessity of admitting a Vacuum in the deserted space of the Tube, by suppo∣sing 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 pres∣sure of the outward arrow_back Air arrow_forward to be the cause of the suspension of the

Quicksilver: for though the materia coelestis may readily fill the spaces the Mercury deserts; yet that within the Tube cannot binder so ponderous a liquor from subsiding as low as the restag∣nant Mercury; since all the parts of the Tube, as well the low∣ermost as the uppermost, being pervious to that subtile matter, it may with like facility succeed in whatever part of the Tube shall be for saken by the Quicksilver.

The Examiners second Argument in the same place is, That since the Mercurial Cylinder is not sustain'd by the outward arrow_back Air arrow_forward , 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 Mercu∣rial Cylinder, resting in its wonted station, does not gravitate: as may appear by applying the Finger to the immers'd or lower Orifice of the Tube. Whence he infers, that it must of neces∣sity 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 restag∣nant Mercury, (which circumstance must not be neglected, though our Author have omitted it) that so you may shut up no more Quicksilver then 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 apart, as if it endeavoured to thrust away your Finger from the Tube. But the reason of this is not hard to give in our Hypothesis; for according to that, the Mercurial Cylinder and the arrow_back Air arrow_forward counterpoising one another, the Finger su∣stains not any sensibly-differing pressure from the ambient arrow_back Air arrow_forward that presses against the Nail and sides of it, and from the included Quicksilver that presses against the Pulp. But if the Mercurial Cylinder should exceed the usual length, then the Finger would

feel some pressure from that surplusage of Quicksilver, which the arrow_back Air arrow_forward 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 removal 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 arrow_back Air arrow_forward 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 certain∣ly the Finger must feel much pain by being squeez'd betwixt two such pressures, as that of a Pillar of thirty Inches of Quick-silver on the one side, and an equivalent pressure from the At∣mospherical Pillar on the other, it may readily be represented, 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 bo∣dies as (unless Experience had otherwise instructed us) we should perhaps imagine. For, not to mention that having in∣quired 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 incumbent, 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 arrow_back Air arrow_forward that leans upon the restagnant Mercury. Which arrow_back Air arrow_forward by its own Spring again forcibly dilating it self to re∣cover its former extension, and (as is usual in Springs) hastily fly∣ing 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 be∣fore) of impetus or power, to force the Corpuscles of the arrow_back Air arrow_forward to a Sub-ingression; and this reciprocation of pressure betwixt the Quicksilver and the outward arrow_back Air arrow_forward decreasing by degrees, does at length wholly cease, when the Mercury has lost that superadded pressure, which it acquired by its falling from parts of the Tube higher then its due station. But this first way of explicating these Vibrations is not necessary in the free arrow_back Air arrow_forward : for if we consi∣der the ambient arrow_back Air arrow_forward onely as a weight, and remember what we have newly said of the impetus acquir'd by descent; this Phaeno∣menon may be easily enough explain'd, by taking notice of what happens in a Balance, when one of the equiponderant 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 paral∣lel enough, and both perpendicular to that part of the Pipe that connected them, (such a Syphon is describ'd in our 36. Experi∣ment, to find the proportion of the gravity of Mercury and Wa∣ter) 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 erecting again the Pipe, though the Quicksilver were forc'd to ascend a

little in that stopt leg; yet by reason my Finger kept the arrow_back Air arrow_forward from getting away, the Quicksilver was kept lower by a good deal in that stopt leg then in the other; but if by suddenly re∣moving my Finger I gave passage to the included and somewhat comprest arrow_back Air arrow_forward , the preponderant Quicksilver in the other leg would with the Mercury in this unstopt leg, make divers undu∣lations before that liquor did in both legs come to rest in an aequi∣librium. Of which the Reason may be easily deduc'd from what has been newly deliver'd; and yet in this case there is no pre∣tence to be made of a Funiculus of violently distended arrow_back Air arrow_forward 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 pro∣ved 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. Where∣fore 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 Cy∣linder of liquor exceed the weight of a Mercurial Cylinder of 29½. Inches; and will subside no longer then till it is come to equiponderate a Cylinder of Quicksilver of that height; where∣as, 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 di∣stant

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 Author (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 extenuated into a Funicu∣lus, that he will not allow any humane force to be able to pro∣duce one, by the divulsion of two flat Marbles, in case the con∣tact of their Surfaces were so exquisite as quite to exclude all arrow_back Air arrow_forward ; though in the same place his Ratiocination plainly enough teaches (which Experience however does) that adhering Mar∣bles, though with extraordinary difficulty, may be forcibly se∣ver'd, and according to him the superficial parts may be distend∣ed into a Funiculus, that prevents a Vacuum.

But now the Hypothesis of his Adversaries is not at all incum∣bred with this difficulty. For the weight of the outward arrow_back Air arrow_forward being that which keeps liquors suspended in Tubes sealed at the top; it matters not of what nature or texture the suspended li∣quor 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 then sa∣tisfactory, and not made out by any such parallel operations of Nature, as his Adversaries will not (and may not well do it) dis∣pute the truth of. Whereas the Weight and Spring of the arrow_back Air arrow_forward may be inferr'd from such unquestion'd Experiments as are not concern'd in our present Controversie. For the gravity of the arrow_back Air arrow_forward may be manifested by a pair of Scales, & the Spring of it discloses it self so clearly in wind-guns and other Instruments, that our Ad∣versary (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 * 1.19 primo aspectu videtur) sed eidem quo{que} firmiter adhaerere. Patet hoc (subjoyns he) experimento illo in primo argumento capit is tertii de tubo utrin{que} aperto. But what is to be answer'd to this proof may be easily gathered 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 adhae∣sionem impediente, inungatur, non minus tamen firmiter * 1.20 adhaerebit digitus quàm priùs; an Answer may be drawn from the same place; nor perhaps will his reasoning much satisfie those who consider that bodies by trusion may easily enough be made stick together, as much as in our case the Tube and Fin∣ger 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 Quicksilver is not contiguous to the Finger, but many Inches below. As for what he addes concerning the reason why Water, and Quicksilver as∣cend by suction, we have already taught what is to be answered to it, by ascribing that ascension to the pressure of the external arrow_back Air arrow_forward : without any need of having recourse to a Funiculus; or imagining with him in this place, That because nothing besides the Water or Quicksilver can in such cases succeed, the arrow_back Air arrow_forward , (which yet is not easie to be prov'd in reference to a thin Aethere∣al substance) therefore, Partes ipsius aëris (to use his ex∣pression) sic tubo inclusae (quae aliàs tam facile separantur) * 1.21 nunc tam fortiter sibi invicem agglutinentur, ut validissimum (uti videmus) conficiunt catenam, qua non solum aqua, sed ponderosum illud argentum sic in altum trahatur. Which way of wreathing a little rarefied arrow_back Air arrow_forward into so strong a rope, how probable it is, I will for a while leave the Reader to judge, and advance to our Au∣thor's second Notandum, which he thus proposes:

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 frigore perficitur, sed etiam compressione, uti innumera passim docent exem∣pla. And 'tis true and obvious, that the Condensation of bo∣dies, 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 ga∣thered from the three Examples he subjoyns, 'tis onely the arrow_back Air arrow_forward that is capable of being so extended as his Hypothesis requires Quicksilver and even Stones must be. And I know not how it will be proved, that even arrow_back Air arrow_forward may be thus extended so far, as in the Magdeburg Experiment, to fill a place more then two thou∣sand times as big as that it fill'd before. For that the same arrow_back Air arrow_forward in this and his two foregoing Instances does adequately fill more space at one time then 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 distended arrow_back Air arrow_forward that con∣tracting it self draws up the water with it. Which Explication how much less likely it is, then that the water is in such cases im∣pell'd up by the pressure of the Atmosphere, we shall anon (when we come to discuss his way of Rarefaction and Condensa∣tion) have occasion to examine. In the mean time let us consi∣der with him the Explication which, after having premis'd the two above recited Observations, he gives us of his Funiculus; Cum per primum Notandum argentum ita adhaereat tubi vertici, & per secundum, rarefactio fiat per meram * 1.23 corporis distensionem, ita rem se habere, ut argentum descendens à vertice tubi affixam ei relinquat superficiem suam extimam sive su∣premam, eam{que} eous{que} suo pondere extendat extenuetque, donec faci∣lius sit aliam superficiem similiter relinquere quam priorem illam ul∣terius extendere: Secundam igitur relinquit, eam{que} eodem modo de∣scendendo extendit, donec facilius sit tertiam adhuc separari quam il∣lam secundam extendere ulterius: & sic deinceps, donec tandem vi∣res amplius non habeat superficies sic separandi & extendendi; nempe

donec perveniat ad altitudinem digitorum duntaxat 29½, ubi quie∣scit, ut capite primo dictum est. Thus far our Examiners Expli∣cation: By which 'tis easie to discern, that he is fain to assigne his Funiculus a way of being produc'd strange and unparallell'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 Mer∣cury leaves any such thing as he speaks of behind it. For the sense perceives no such matter 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 descend∣ing 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 behind 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 Do∣ctrine) can be able to break it; that contrary to all other strings it may be str••••••••ed without being made more slender; and that it has other very odde properties, some of which we shall anon have occasion to mention. As for what our Author subjoynes in these words, Eodem ita{que} fere modo sepa∣rari videntur hae superficies ab argento descendente, & * 1.24 in tenuissimum quendam per descendens pondus extendi, quo per ca∣lorem in accensa candela separantur hujusmodi superficies à subjecta cera aut sevo, & in subtilissimam flammam extenuantur. Ubi not atu dignum, quemadmodum flamma illa plusquam millies sine dubio ma∣jus spatium occupat, quàm antea occupaverat pars illa cerae ex qua conficitur; ita prorsus & his existimandum Funiculum illum plus∣quam millies majus spatium occupare quàm prius occupaverat illa argenti particula ex qua sit exortus: Uti etiam sine dubio contingit, quando talis particula à subjecto igne in vaporem convertitur.

Though it be the onely Example whereby he endeavours to il∣lustrate 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, name∣ly, an actual Fire to sever and agitate the parts of the Candle; and besides that there is a manifest wasting of the Wax or Tal∣low 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 then a thousand times, but so much as twice more of genuine space then the Wax 'twas made of. For it may be said that the flame is little or nothing else then 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 another, and make up about the Wiek such a figure as is usual in the flame of Candles burning in the free arrow_back Air arrow_forward . Nor will it necessarily follow, that the space which the flame seems to take up should contain neither arrow_back Air arrow_forward nor Aether, nor any thing else, save the parts of that flame, because the eye cannot discern any other 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; whenas yet there are so many Aeri∣al and other invisible Corpuscles mingled with it, as if all those parts of smoke that make a great show in the arrow_back Air arrow_forward were collect∣ed and contiguous, they would not perhaps amount to the big∣ness of a Pins head: as may appear by the great quantity of steams 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 Quicksilver into vapour, by putting fire under it: for if such be the Rarefaction of Mercury, 'tis not at all like to make such a Funiculus as he talks of, since those Mercurial Fumes appear by divers Experiments, to be Mercury divided and thrown abroad into minute parts, whereby

though the body obtain more of Surface then 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 rarefaction. 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 surfaces 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 metall of Quicksil∣ver, 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 separable) should, when the Funiculus once layes hold on the superficial Corpuscles, presently emulate the nature of consi∣stent bodies, and be drawn up like Masses each of them of an in∣tire 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 continue fluid bodies.

It seems also very difficult to conceive how this extenuated substance should acquire so strong a spring inward as the Exami∣ner all along his book 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 Fu∣niculus, he seems plainly to intimate that it has its spring in∣ward, upon the same account that Lute-strings and Ropes for∣cibly stretch'd have theirs. But there is no small disparity be∣twixt

them: for whereas in strings there is requir'd either wrea∣thing, or some peculiar and artificial texture of the component parts; a rarefaction of arrow_back Air arrow_forward (were it granted) does not include or infer any such contrivance of parts as is requisite to make bodies Elastical. And if the Cartesian Notion of the cause of Springi∣ness be admitted, then our extenuated substance having no Pores to be pervaded by the materia subtilis (to which besides our Au∣thor also makes Glass impervious) will be destitute of Springi∣ness. And however, since Lute-strings, Ropes, &c. must, when they shrink inwards, either fill up or lessen their Pores, and in∣crease in thickness as they diminish in length; our Examiners Funiculus must differ very much from them, since it has no Pores to receive the shrinking parts, and contracts it self as to length, without increasing its thickness. Nor can it well be pre∣tended that this self-contraction 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 consequently devoid of knowledge; and there∣fore 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 then final causes, 'tis not easie to conceive how arrow_back Air arrow_forward by being expanded (in which case its force (like that of other rarify'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 polish'd Marble is extended into a Funiculus, that Funiculus does so strongly aspire to turn into Marble again. I might like∣wise 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 arrow_back Air arrow_forward does so much and so suddenly relax the tension of his Funiculus; since that being (according to him) a real and

Poreless body, 'tis not so obvious how the presence of another 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 alwayes 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 arrow_back Air arrow_forward . 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∣stretch'd strings. On which occasion we might adde, that 'tis somewhat 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 peculiarity in our Authors 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 arrow_back Air arrow_forward , 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 Adversary) examin'd.

BUt this is not all that renders the Examiners Hypothesis im∣probable: For, besides those already mentioned particulars, upon whose score it is very difficult to be understood; it necessa∣rily supposes such a Rarefaction and Condensation, as is, I con∣fess, to me, as well as to many other considering persons, unin∣telligible.

For the better discernment of the force of this Objection we must briefly premise, That a body is commonly said to be rare∣fi'd or dilated, (for I take the word in a larger sense then, I know, many others do, for a reason that will quickly appear) when it acquires greater dimensions then the same body had before; and to be condens'd, when it is reduc'd into less dimensions, that is, into a lesser space then it contain'd before: (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 onely reduced into less room then it had before it was squeezed, but into less then it had even before it was wetted.) And I must further premise, That Rarefaction (as also Condensation) being amongst the most obvious Phaenomena of Nature, there are three (and for ought we know but three) wayes 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 be∣tween them to fill up the deserted 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 Cartesians, that these new Intervals produced be∣twixt the Particles of the rarefied body are but dilated Pores, re∣plenished,

in like manner as those of the tumid Spunge are by the imbibed 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 onely obtain a greater space in Rarefaction, and a lesser in Condensation, but adequately and exactly fill it, and so when rarefied acquires larger dimensions without either lea∣ving any vacuities betwixt its component Corpuscles, or admit∣ting between them any new or extraneous 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 explai∣ned by it; since to explain a thing is to deduce it from something or other in Nature more known then it self.

He that would meet with full Discussions of this Aristotelean Rarefaction, may resort to the learned writings of Gassendus, Car∣tesius and Maignan, who have accused it of divers great absurdi∣ties: 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 arrow_back Air arrow_forward , 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 denyed, but that as the whole parcel of arrow_back Air arrow_forward , 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, Corpo∣re occupante locum verbi gratia duplo majorem, necesse est * 1.26

ut 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 arrow_back Air arrow_forward ) there must likewise be two hundred thousand parts of space commensurate each of them to one of the fore-mentioned hundredth parts of arrow_back Air arrow_forward ; and conse∣quently, when he affirms that that half Inch of arrow_back Air arrow_forward 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 Aeriall parts, he must give us leave to con∣clude, that each part of arrow_back Air arrow_forward does adequately fill two thou∣sand parts of space. Now that this should be resolutely taught to be not onely 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 additi∣on 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; & upon Bodies, as having necessary relation to a commensurate space. Nor do I see, if one portion of arrow_back Air arrow_forward 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 addi∣tion of any new substance; I see not (I say) why the matter con∣tained 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-replen shed spaces is presumed to be exactly filled with Body, and no space, nor consequently that which the unrarefied arrow_back Air arrow_forward replenished, can be more then adequately full. And since, according to our Adversary, not onely fluid bodies, as arrow_back Air arrow_forward 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

then it is, without either admitting any thing of Vacuity betwixt its parts, or being increased 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 with∣in, nor any subtile matter permitted to enter from without, it were not more intelligible to suppose that God had created a new matter to joyn with the arrow_back Air arrow_forward in filling up the Cavity, then that the self-same arrow_back Air arrow_forward 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 occasions. But I know that many of them will not likewise think it concei∣vable, that without his immediate interposition an accession 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 then 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 diffi∣dent and doubtful strain of so difficult a matter, but to excuse my self if I have not alwayes guessed aright at his meaning.

The things he alledges in favour of the Rarefaction he would perswade 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 wayes of explicating the rigorous Rarefaction he contends for.

His Objections against the Epicurean and Cartesian wayes of making out Rarefaction are some of them more plausible then most of those that are wont to be urged against them; yet not such as are not capable enough of Answers. But whilest 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 then 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 onely adde in general, That whereas the Examiners 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 itself; whereas those to which the other wayes 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 Authors Objections against the two wayes 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 itself, 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 wayes 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, then that he himself scarce acquiesces in either of them.

And, first, having told us how Rarefaction may be explain'd, in case we admit bodies to be divisible in infinitum, he does him∣self make such an Objection against the infinity of parts in a con∣tinuum, as he is fain to give so obscure an Answer to, that I con∣fess I do not understand it; and presume, that not onely the most part of unprejudiced Readers will as little acquiesce 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 endeavours to excuse its being so, because in that Hypothesis it can scarce be other∣wise.

Wherefore I shall onely adde 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 sub∣stance, must have some Particle of space commensurate to it; and if the whole body be rarefied, for instance, to twice its for∣mer 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 hitherto∣mentioned way of explicating Rarefaction is, That many learned men, amongst whom he names two, Aquinas and Suarez, have taught that the same corporeal thing may naturally be, and de facto often is, in the souls of Brutes really indivisible and virtu∣ally extended. But, though I pay those two Authors a just re∣spect for their great skill in Scholastical and Metaphysical lear∣ning; 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 St. Thomas and Suarez, who have some of them in express words denyed this to be naturally possi∣ble; and others have declared themselves of the same judgment by establishing principles, 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 dis∣pute 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 Juxia probabiliorem sententiam hujusmodi virtualis extensio rei corporea concedenda non est, ut pote soli rei spirituali propria.

But to conclude at length this tedious Enquiry into the Ari∣stotelean 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 wayes 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 in∣genuous as (at the close of his discourse of the two wayes) 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, its tamen aperte non suc∣cumbit. So that in this discourse of Rarefaction, to which our Author has so often in the fore-going 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 formerly made against it are weighty. For according to this Hypothesis (which one would think he prefers, since he makes use of it in the three or four last Chapters of his Book) Necessariò fatendum est (sayes he) unam eandem{que} partem poni in duplici * 1.28 loco adaequate: Cum enim indivisibilis sit, locum{que} occupet majorem quam prius, necesse est ut tota sit in quolibet puncto totius loci, sive ut per totum illud spatium virtualiter extendatur. So that when he in the very next page affirms, that by this virtual extension 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 under∣stand) to desire he would explain to me what this extensio virtu∣alis is, and how it will remove the Difficulties that I formerly charged upon the Aristotelean Rarefaction. For the easier consi∣deration of this matter, let us resume what we lately supposed, namely, that in the Magdeburgick Experiment the half Inch of undilated arrow_back Air arrow_forward consisted of a hundred Corpuscles; I demand how

the indivisibility of these Corpuscles will qualifie them to make out such a Rarefaction as the Author imagines. For what does their being indivisible do in this case, but make it the less intelli∣gible how they can fill above a hundred parts of space? 'Tis easie to fore-see he will answer, That they are virtually extend∣ed. But not here to question how their indivisibility makes them capable of being so; I demand, whether by an Atoms being vir∣tually extended, its corporeal substance do really (I mean ade∣quately) fill more space then 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 ex∣tension will not serve the turn, what we have formerly argued against the Peripatetick Rarefaction will evince; and our Adver∣sary seems to confess as much, by devising this virtual extension to avoid the inconveniences to which he saw his Doctrine of Ra∣refaction 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 then before: This is but a Verbal shift, that may perhaps amuse an unwary Reader, but it will scarce satisfie a considering one. For I demand how that which is not a substance can fill place; and how this improper and but Metaphorical Extension will salve the Phaenomena of Rarefa∣ction: as how the half Inch of arrow_back Air arrow_forward at the top of the fore-menti∣oned Globe shall without a corporeal extension fill the whole Globe of two thousand times its bigness when the water is suck'd out of it, and act at the lower part of the Globe. Which last Clause I therefore adde, because not onely our Au∣thor teaches (pag. 91. & 92.) that the whole Globe was filled with a certain thin substance, which by its contraction violently snatch'd up the water into which the neck of the Glass was im∣mers'd; but in a parallel case he makes it his grand Argument to prove, that there is no Vacuum in the deserted part of the Tube in the Torricellian Experiment, That the attra∣ction of the Finger cannot be performed but by some * 1.29 real body. Wherefore till the Examiner do intelligibly ex∣plain

how a virtual Extension, as it is opposed to a corporeal, can make an Atome fill twice, nay, two thousand times more space then it did before; I suppose this device of virtual Extension will appear to unbiass'd Naturalists but a very 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 speakes) 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 re∣member that he himself sayes 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 then 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, then that in ours things are explicated by the ordinary course of Nature, whereas in the other recourse must be had to mi∣racles.

But though our Authors 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 parts. 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 (sayes he) haec omnia inde accidere, quod pulvis ille sic accensus & in flammam conversus, * 1.31 longe majus spatium nunc occupet quàm prius. Unde fit, ut cum to∣tum cubiculum antea fuerit plenissimum, disrumpantur sic parietes, ne detur corporum penetratio. In the Magdeburgick Experiment 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 heterogeneous 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 sub∣stance, which, however it was produc'd or got thither, was a true and real body; and that after the admission of the water there remained in the same Globe, besides the water that came in, no more then 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 ninety nine half Inches of Matter, that now appear no more, traversed 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 Mat∣ter? For that 'tis annihilated I suppose 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 many hundred parts of Matter should be retir'd into that one part of space that contains the one half Inch of arrow_back Air arrow_forward , is little less incredible: For that space was suppos'd perfectly full of body before, and how a thing can be more then perfectly full, who can conceive? To dispatch: According to our Authors way of Condensation, two, or perhaps two thousand, bodles may be crouded into a space that is adequately fill'd by one of them apart. And if this be not Penetration of Dimen∣sions, I desire to be informed what is so; and till then I shall leave it to any unprepossess'd Naturalist to judge, whether an Hypothesis that needs suppose a thing so generally concluded to be impossible to Nature, be probable or not; and whether to tell us that the very same parcel of arrow_back Air arrow_forward , that is now without vio∣lence 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 hewly possess'd, be not to turn a Body into a Spirit, and, confounding their Noti∣ons, 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 admitting the Examiners Hypothesis: yet if any happier Contemplator shall prove so sharp-sighted, as to devise and clearly propose a way of making the Rarefaction and Condensa∣tion hither to 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 Hypo∣thesis preferrable to ours, since that would not prove it either ne∣cessary, or so much as sufficient, but onely answer some of the Ar∣guments that tend to prove 'tis not intelligible. And that we have other Arguments on our side then those that relate to Ra∣refaction 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 Experi∣ments, at the tops and feet of Hills.

THere remain then yet a couple of Considerations to be op∣pos'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 onely 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 arrow_back Air arrow_forward 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 Paschall, mentioned by the famous Pecquet, and out of him by our Author: namely, that the Torricellian * 1.32 Experiment 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 wherin 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 arrow_back Air arrow_forward incumbent upon the restagnant Mercury; and consequently the less weight of Cylindrical Mercury will that arrow_back Air arrow_forward be able to counter-poise 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 arrow_back Air arrow_forward (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 arrow_back Air arrow_forward , 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 resistance of the external Aire. Nor do I think his Answers to the Argu∣ment drawn from hence will keep them from thinking it co∣gent. For to an Objection upon which he takes notice that they lay so much stress, he replyes but two things; which nei∣ther singly nor together will near amount to a satisfactory An∣swer.

And, First, he questions the truth of the Observation it self; because having made tryal in a low Hill, the event did no wayes 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, then 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) then upon Monsieur Paschals. 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, partim aëre libero, & * 1.33 nunc quidem flante, nunc silente vento. Which circum∣stances sufficiently argue the Diligence wherewith 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 o∣ther 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 arrow_back Air arrow_forward , 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 then it does further from it. To all this I shall adde 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, bethought themselves of so making the Torricellian Experiment at the top of the Hill, as to leave a determinate quantity of arrow_back Air arrow_forward in the

[illustration]

Tube, before the mouth of it was open'd under the vessell'd Mer∣cury; and taking notice how low such a quantity of that arrow_back Air arrow_forward de∣pressed the Mercurial Cylinder, they likewise observ'd, that at the Mountains foot the included arrow_back Air arrow_forward was not able to depress the Quicksilver so much. Whence we inferre, that the Cylinder of arrow_back Air arrow_forward at the top of the Hill being shorter and lighter, did not so strongly press against the included arrow_back Air arrow_forward , as did the ambient arrow_back Air arrow_forward at the bottom of the Hill, where the Aereal 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 arrow_back Air arrow_forward , 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, where∣in we hoped to find a sensibly-differing Weight of the Atmo∣spere, in a far less height then that of an ordinary Hill. But in stead of a common Tube we made use of a kind of Weather-glass, that the included arrow_back Air arrow_forward 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 belon∣ging to the Weather-glass, that small changes in the Weight or resistance of the Atmosphere in opposit on of the included arrow_back Air arrow_forward might be the more discernable. The Instrument we made use of consisted only of a Glass with a broad Foot and a narrow Neck (A B) and a slender Glass-Pipe (C D) 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 (A B) 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 (I I) and outward (K K) arrow_back Air arrow_forward , save by the cavity of the Pipe (C D). Now we chose this Glass (A B) more then ordinarily capacious, that the effect of the dilatation of the included arrow_back Air arrow_forward (I I) might be the more conspicuous. Then con∣veying a convenient quantity of Water (H H) into this Glass,

we carried it to the Leads of the lofty Abby-Church at Westmin∣ster, and there blew in a little arrow_back Air arrow_forward to raise the Water to the upper part of the Pipe, that being above the Vessel (A B) we might more precisely mark the several stations of the Water then otherwise we could. Afterward having suffered the Glass to rest a pretty while upon the Lead, that the arrow_back Air arrow_forward (I I) within might be reduc'd to the same state, both as to coldness and as to pressure, with (K K) 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 below the mark (F) we had put: whereupon having order'd him to put a mark at this second sta∣tion 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 Ex∣periment to succeed quite so regularly as before; yet the Water alwayes manifestly fell lower at the foot of the Wall then it was at the top: which I see no cause to ascribe barely to the differing temperature of the arrow_back Air arrow_forward above and below, as to Heat and Cold, since according to the general estimate, the more elevated Region of the arrow_back Air arrow_forward is, caeteris paribus, colder then that below, which would rather check the greater expansion of the included arrow_back Air arrow_forward at the top of the Leads then 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 Gal∣lery of the same height with the Leads: but the upper part of the Pipe being casually broken off, we thought fit to order the mat∣ter so, that the surface (G) of the remaining Water in the Pipe should be about an Inch higher then 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 only it was fallen as low as the other Water, but that the outward arrow_back Air arrow_forward deprest it so far, as whilest 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 arrow_back Air arrow_forward was at the top, (whereas in that we imploy'd the included arrow_back Air arrow_forward 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 (A B) and the bore of the Pipe (C D) with some other variety of Circumstances) together with the event of the cu∣riosity we had (which seemed very successful) to try the Torri∣cellian 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 Quicksilver, in the formerly-mentioned Appendix to the Epistle we have been defending. And it shall suffice us in the mean time that the Try∣als already mentioned seem to make it evident enough that the Atmosphere gravitates more, caeteris paribus, neer the surface of the Earth, then in the more elevated parts of the arrow_back Air arrow_forward . 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 only add this at present, that once being desirous to observe what we could touching the pro∣portions of the subsidence of the Water to the height of its se∣veral stations from the ground, purposely carrying down the Vessel so as not considerably to heat it, from the Leads down

the staires to a little window that we guest to be almost half way to the bottom, we there perceived the water to have already sub∣sided about a Barley-Corns length, notwithstanding that pro∣bably in spight 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 Do∣ctrine.

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 Monsieur 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 be∣fore. This, I say, having thus happened, we have here an Expe∣riment to prove our Hypothesis, wherein recourse cannot be had to any forcibly and preternaturally distended Body, such as that is pretended to be which remaines in the deserted space of the Tube in the Torricellian Experiment.

The other thing which the Examiner alledges against our Argument from Monsieur Paschals 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 cau∣sante. But this solution will not serve the turn: For the cold∣ness of the ambient arrow_back Air arrow_forward (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 him∣self teaches us, that 'tis from the shrinking of the Fu∣niculus occasion'd by the cold that the Water in Ther∣mometers * 1.35 ascends in cold weather. And whereas the only proof he adds of so improbable an Explication is taken from our eighteenth Experiment, wherein we relate, that sometimes the Quicksilver did sensibly fall lower in colder then in far less cold weather: I answer, that this eighteenth Experiment will scarce make more for him then against him: For, as I there take notice that the Quicksilver descended in cold weather, so it some∣times descended likewise in hot weather, and rose in cold. And 'tis very strange, that in all the Observations made, in dif∣fering Countries and at differing times, it should still so happen that the Mercurial Cylinder should be shorter near the top of the Atmosphere then further from it; if the resistance of the outward arrow_back Air arrow_forward have nothing to do with the keeping it suspended. 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 arrow_back Air arrow_forward 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 permission given me) insert it in this place. And the rather, that as the Mountains have by the Trials made on them of the Torricellian Experiment, afforded us a noble proof of the weight of the arrow_back Air arrow_forward ; 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 arrow_back Air arrow_forward . 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 foot in length, and carrying it * 1.38 to the bottom of Hallifax Hill, the Water stood in the shank at thirteen Inches above the Water in the Vessel: Thence car∣rying 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 then it was at the bottom of the said Hill; which (as he rightly inferrs) proves the Elasticity of the arrow_back Air arrow_forward : for the internal arrow_back Air arrow_forward 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 then the Mountain- arrow_back Air arrow_forward 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 then 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 al quor as Water should fall so much; yet I see not any reason to distrust upon this ground either His Experiment or Ours (late∣ly mention'd to have been made at Westminster;) but rather to wonder the Water fell not more (if the Hill be considerably high:) for their suspicion seems grounded upon a mistake, as if because the Quick-silver in the Torricellian Experiment made without purposely leaving any arrow_back Air arrow_forward 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 fourteenth part of that space; whereas in the Torricellian Experiment, the upper and deserted space of the Tube has little or no arrow_back Air arrow_forward left in it, but the Correspondent part of the Weather-glass was furnish'd with arrow_back Air arrow_forward , whose pressure was little less then that of the Atmosphere at the bottom of the Hill;

and consequently must be much greater then the pressure of the same Atmosphere at the top of the Hill, where the Atmosphe∣rical Cylinder's gravity (upon whose account it presses) must be much diminish'd by its being made much shorter, and by its con∣sisting of an arrow_back Air arrow_forward 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 Experiments which the Ex∣aminer in the 11. and 12. Chapters reckons up as urg'd by his Adversaries; yet I 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 Magde∣burg Experiments, to be discours'd by those that are more con∣cerned to examine them, contenting my self to have sufficiently disproved the Funiculus which his Expositions suppose, and clea∣red the grounds of explicating such Experiments aright.

CHAP. V.

Two new Experiments touching the measure of the Force of the Spring of arrow_back Air arrow_forward 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 arrow_back Air arrow_forward has some Weight and Spring, but affirms that it is very insufficient to per∣form * 1.40 such great matters as the counterpoising of a Mercurial Cylinder of 29. Inches, as we teach that it may: We shall now endeavour to manifest by Experiments purposely made, that the Spring of the arrow_back Air arrow_forward is capable of doing far more then '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 Lamp was in such a manner crooked at the bot∣tom, 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 subdi∣vided into eight parts) by a straight list of paper, which contain∣ing those Divisions was carefully pasted all along it: then put∣ting 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 other; we took care, by frequently inclining the Tube, so that the arrow_back Air arrow_forward might freely passfrom one leg into the other by the sides of the Mercury, (we took (I say) care) that the arrow_back Air arrow_forward at last included in the short∣er Cylinder should be of the same laxity with the rest of the arrow_back Air arrow_forward about it. This done, we began to pour Quicksilver into the lon∣ger leg of the Siphon, which by its weight pressing up that in the shorter leg, did by degrees streighten the included arrow_back Air arrow_forward : and continuing this pouring in of Quicksilver till the arrow_back Air arrow_forward in the short∣er 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 ob∣served, not without delight and satisfaction, that the Quicksilver in that longer part of the Tube was 29. Inches higher then 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 that we teach, and Monsieur Paschall and our English friends Experiments prove, that the greater the weight is that leans upon the arrow_back Air arrow_forward , 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 wil appear to agree rarely-well with the Hy∣pothesis, that as according to it the arrow_back Air arrow_forward in that degree of density

and correspondent measure of resistance to which the weight of the incumbent Atmosphere had brought it, was able to counter-balance and resist the pressure of a Mercurial Cylinder of about 29. Inches, as we are taught by the Torricellian Experiment; so here the same arrow_back Air arrow_forward 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 equivalent to them.

We were hindered from prosecuting the tryal at that time by the casual breaking of the Tube. But because an accurate Ex∣periment of this nature would be of great importance to the Do∣ctrine of the Spring of the arrow_back Air arrow_forward , and has not yet been made (that I know) by any man; and because also it is more uneasie to be made then one would think, in regard of the difficulty as well of procuring crooked Tubes fit for the purpose, as of making a just estimate of the true place of the Protuberant Mercury's surface; I suppose it will not be unwelcome to the Reader, to be infor∣med that after some other tryals, one of which we made in a Tube whose longer leg was perpendicular, and the other, that contained the arrow_back Air arrow_forward , parallel to the Horizon, we at last procured a Tube of the Figure exprest in the Scheme; which Tube, though of a pretty bigness, was so long, that the * 1.41 Cylinder whereof the shorter leg of it consisted ad∣mitted a list of Paper, which had before been divided into 12. In∣ches 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

divisions in the shorter Tube, the several Observations that were thus successively made, and as they were made set down, afforded us the ensuing Table.

A Table of the Condensation of the arrow_back Air arrow_forward .

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 4/16	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 2/16	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	5¾	32 3/16	61 5/16	60 18/23
22	5½	34 15/16	64 1/16	63 6/11
21	5¼	37 15/16	67 1/16	66 4/7
20	5	41 9/16	70 11/16	70—
19	4 3/4	45—	74 2/16	73 11/19
18	4½	48 12/16	77 14/16	77⅔
17	4¼	53 11/16	82 12/16	82 4/17
16	4	58 2/16	87 14/16	87⅜
15	3¾	63 15/16	93 2/16	93⅕
14	3½	71 5/16	100 7/16	99 6/7
13	3¼	78 11/16	107 12/16	107 7/13
12	3	88 7/16	117 9/16	116 4/8

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

B. The height of the Mercurial Cylin∣der in the longer leg, that compress'd the arrow_back Air arrow_forward 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 arrow_back Air arrow_forward .

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 convenient∣ly make use of it in a Chamber, we were fain to use it on a pair of Stairs, which yet were very lightsom, the Tube being for preser∣vations

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 transfusion from the Vessel into the Pipe, and to receive the whole Quicksil∣ver 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 lon∣ger, 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 little, according to the direction of him that observed below, it being far easier to pour in more, then 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 conveni∣ent posture to reflect to the eye what we desired to discern.

6. That when the arrow_back Air arrow_forward was so compress'd, as to be crouded into less then a quarter of the space it possess'd before, we tryed 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 tryed likewise whether heat would notwithstanding so forcible a compressure dilate it, and approching the flame of a Candle to that part where the arrow_back Air arrow_forward was pent up, the heat had a more sensible operation then the cold had before; so that we scarce doubted but that the expansion of the arrow_back Air arrow_forward would notwithstanding the weight that opprest it have been made conspicuous, 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 parti∣culars do not so exactly answer to what our formerly intimated

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 tryal hath more clearly informed me, I shall not venture to determine whether or no the intimated Theory will hold universally and precisely, either in Condensation of arrow_back Air arrow_forward , or Rarefaction: all that I shall now urge being, That however, the tryal already made sufficiently proves the main thing for which I here alledge it; since by it 'tis evident, that as common arrow_back Air arrow_forward when reduc'd to half its wonted extent, obtained near about twice as forcible a Spring as it had before; so this thus-comprest arrow_back Air arrow_forward being further thrust into half this narrow room, obtained thereby a Spring a∣bout as strong again as that it last had, and consequently four times as strong as that of the common arrow_back Air arrow_forward . And there is no cause to doubt, that if we had been here furnisht with a greater quantity of Quicksilver and a very strong Tube, we might by a further compression of the included arrow_back Air arrow_forward have made it counter-balance the pressure of a far taller and heavier Cylinder of Mer∣cury. For no man perhaps yet knows how near to an infinite compression the arrow_back Air arrow_forward may be capable of, if the compressing force be competently increast. So that here our Adversary may plainly see that the Spring of the arrow_back Air arrow_forward , which he makes so light of, may not onely 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 resist∣ed by the imprisoned arrow_back Air arrow_forward , 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 Mercury in the Tube did notably ascend. Which considerable Phaenomenon 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 ren∣der this reason of it, That the pressure of the incumbent arrow_back Air arrow_forward be∣ing in part taken off by its expanding it self into the Suckers dila∣ted chest; the imprison'd arrow_back Air arrow_forward 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 com∣prest arrow_back Air arrow_forward on the one part, and the tall Mercurial Cylinder, toge∣ther with the contiguous dilated arrow_back Air arrow_forward , on the other part.

Now, if to what we have thus delivered concerning the com∣pression of arrow_back Air arrow_forward we adde some Observations concerning its spon∣taneous Expansion, it will the better appear how much the Phae∣nomena of these Mercurial Experiments depend upon the differ∣ing measures of strength to be met with in the Airs Spring, ac∣cording 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 tryals I had made about measuring the Ex∣pansion of the arrow_back Air arrow_forward to any certain Hypothesis, when that ingenious Gentleman Mr. Richard Townely was pleased to inform me, that having by the perusal of my Physico-Mechanical Experiments been satisfied that the Spring of the arrow_back Air arrow_forward 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 precise estimate how much arrow_back Air arrow_forward di∣lated of it self loses of its Elastical force, according to the mea∣sures 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 begin∣ning, which gives me a just Curiosity to see it perfected. But, because I neither know, nor (by reason of the great distance be∣twixt our places of residence) 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-accurate Table of the Decrement of the force of dila∣ted

arrow_back Air arrow_forward ; our present design invites us to present the Reader with that which follows, wherein I had the assistance of the same per∣son that I took notice of in the former Chapter, as having writ∣ten something about Rarefaction: whom I the rather make men∣tion of on this occasion, because when he first heard me speak of Mr. Townley's suppositions about the proportion wherein arrow_back Air arrow_forward loses of its Spring by Dilatation, he told me he had the year be∣fore (and not long after the publication of my Pneumatical Trea∣tise) made Observations to the same purpose, which he acknow∣ledged to agree well enough with Mr. Townley's Theory: And so did (as their Author was pleased to tell me) some Tryals made about the same time by that Noble Virtuoso and eminent Mathe∣matician 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 arrow_back Air arrow_forward .

A	B	C	D	E
1	00 0/0	Subttracted from 29¾ leaves	29¾	29¾
1 1/2	10⅝	19⅛	19⅚
2	15⅜	14⅜	14⅞
3	20 2/8	9 4/8	9 15/12
4	22⅝	7⅛	7 7/16
5	24⅛	5⅝	5 19/20
6	24⅞	4⅞	4 23/24
7	25 4/8	4 2/8	4¼
8	26 0/0	3 6/8	3 23/32
9	26⅜	3 1/8	3 11/36
10	26 6/8	3 0/0	2 39/40
12	27⅛	2⅝	2 23/48
14	27 4/8	2 2/8	2⅛
16	27 6/8	2 0/0	1 5••/64
18	27⅞	1⅞	1 47/72
20	28 ••/••	1 6/8	18 9/0
24	28 2/8	1 4/8	1 23/96
28	28⅜	1⅜	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 arrow_back Air arrow_forward .

B. The height of the Mercurial Cylinder, that together with the Spring of the included arrow_back Air arrow_forward counterbalanced the pressure of the Atmo∣sphere.

C. The pressure of the Atmosphere.

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

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

To make the Experiment of the debilitated force of expanded arrow_back Air arrow_forward the plainer, 'twill not be amiss to note some particulars, especially touching the manner of making the Tryal; which (for the reasons lately mention'd) we made on a lightsome pair of stairs, and with a Box also lin'd with Paper to receive the Mer∣cury that might be spilt. And in regard it would require a vast and in few places procurable quantity of Quicksilver, to employ vessels of such kind as are ordinary in the Torriccllian Experi∣ment, we made use of a Glass-Tube of about six foot long, for that being Hermetically sealed at one end, serv'd our turn as well as if we could have made the Experiment 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 greater 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 included 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 then an Inch of the slender Pipe left above the surface of the re∣stagnant Mercury, and consequently unfill'd therewith, the pro∣minent orifice was carefully clos'd with sealing Wax melted; after which the Pipe was let alone for a while, that the arrow_back Air arrow_forward 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 then an Inch of arrow_back Air arrow_forward , and in either case we were fain to rectifie the error by a small hole made (with an heated Pin) in the Wax, and afterwards clos'd up again.

Fifthly, Having thus included a just Inch of arrow_back Air arrow_forward , we listed

up the slender Pipe by degrees, till the arrow_back Air arrow_forward 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 Airs 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 29 ¾ Inches.

Seventhly, Our Observations made after this manner furnish'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 arrow_back Air arrow_forward when expanded to double its former dimensions, and what that force should have been precisely according to the Theory, but that the included Inch of arrow_back Air arrow_forward receiv'd some little accession during the Tryal; which this newly-mention'd diffe∣rence making us suspect, we found by replunging the Pipe into the Quicksilver, that the included arrow_back Air arrow_forward had gain'd about half an eighth, which we guest to have come from some little aerial bubbles in the Quicksilver, contain'd in the Pipe (so easie is it in such nice Ex∣periments to miss of exactness.) We try'd also with 12. Inches of arrow_back Air arrow_forward shut up to be dilated; but being then hindred by some unwelcome avocations to prosecure those Experiments, we shall elsewhere, out of other Notes and Tryals (God permitting) set down some other accurate Tables concerning this matter. By which possibly we may be assisted to resolve whether the At∣mosphere should be look'd upon (as it usually is) as a limited and bounded Portion of the arrow_back Air arrow_forward ; or whether we should in a stricter sense then we did before, use the Atmosphere and Aereal part of the World for almost equivalent terms; or else whether we should allow the word Atmosphere some other notion in relation to its Extent and Limits; (for as to its Spring and Weight, these Experiments do not question, but evince them.) But we are wil∣ling, as we said, to referre these matters to our Appendix, and

till then to retain our wonted manner of speaking of the arrow_back Air arrow_forward and Atmosphere. In the mean time (to return to our last-mention'd Experiments) besides that so little a variation may be in great part imputed to the difficulty of making Experiments of this na∣ture exactly, and perhaps a good part of it to something of ine∣quality in the Cavity of the Pipe, or even in the thickness of the Glass; besides this, I say, the proportion betwixt the several pressures of the included arrow_back Air arrow_forward undilated and expanded, especially when the Dilatation was great (for when the arrow_back Air arrow_forward 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 pro∣portion, I say, was sutable enough to what might be expected, to allow us to make this reflection upon the whole, That whe∣ther or no the intimated Theory will hold exactly, (for about that, as I said above, I dare determine nothing resolutely till I have further considered the matter) yet since the Inch of arrow_back Air arrow_forward when it was first included was shut up with no other pressure then that which it had from the weight of the incumbent arrow_back Air arrow_forward , and was no more comprest then the rest of the arrow_back Air arrow_forward we breathed and mo∣ved in; and since also this Inch of arrow_back Air arrow_forward , when expanded to twice its former dimensions, was able with the help of a Mercurial Cylinder of about 15. Inches to counterpoise the weight of the Atmosphere, which the weight of the external arrow_back Air arrow_forward gravitating upon the restagnant Mercury was able to impell up into the Pipe, and sustain above twenty eight Inches of Mercury when the inter∣nal arrow_back Air arrow_forward by its great expansion 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 arrow_back Air arrow_forward here below appears to be almost as strongly comprest by the weight of the incumbent arrow_back Air arrow_forward 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 decreement of whose force holds a

stricter proportion to its increase of dimension, then has been hitherto taken notice of.

I must not now stand to propose the several reflections that may be made upon the foregoing Observations touching the Compression and Expansion of arrow_back Air arrow_forward ; 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 maine things that induced the Learned Examiner to reject our Hypothe∣sis are, that Nature abhors a Vacuum, and that though the arrow_back Air arrow_forward have some Weight & Spring, yet these are insufficient to make out the known Phaenomena; for which we must therefore have recourse 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 arrow_back Air arrow_forward may suffice to perform greater things then what our Explication of the Torri∣cellian Experiments and those of our Engine obliges us to as∣cribe to it. Wherefore since besides the several difficulties that incumber the Hypothesis we oppose, and especially its being scarce, if at all, intelligible, we can adde 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 suppo∣ses such a rarefaction and condensation, as many famous Natu∣ralists rejected for its not being comprehensible, even when they knew of no other way (that was probable) of solving the Phaeno∣mena wont to be explicated by it.

The III. Part.

Wherein what is objected against Mr. Boyle's Explications 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 Examiner is pleas'd to object against some passages of our Physicho-Mechanical 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 recor∣ded 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 Ex∣plications, 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 incongruous 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, together 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 maintain, and take away our Authors imaginary Funiculus; it will not be re∣quisite for us on such occasions to examine his particular Asser∣tions 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 repetition. Wherefore presuming he will do so, we shall not stay to examine the first and second Corollaries, which in his 17. Chapter he an∣nexes to the manner of emptying our Receiver 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 arrow_back Air arrow_forward is rarefied, the more forcibly it is able to contract it self.

A defence of our 1. and 2. Experiments.

And to proceed now to his 18 Chapter, which he intitles De Experiment is Boyleanis, we shall find according to what we lately noted, that against the First Experiment he objects nothing save that, if one of the Fingers be applied to the Orifice of the Valve when the Pump is freed from arrow_back Air arrow_forward , the Experimenter shall feel to his pain that the Sucker is not thrust inward by the external arrow_back Air arrow_forward , but, as the Finger, drawn inward by the internal. But this Phae∣nomenon of the intrusion of the Finger into a Cavity, where it finds no resistance, having been formerly accounted for accor∣ding to our Hypothesis, we shall not need to repeat our Explication of it; though this mistaken Phaenomenon supplies our Adversary with divers of his following Animadversions, and indeed with a great part of his book. And accordingly his Objection against our Second Experiment being of the same nature with that a∣gainst the first, requires but the same Answer: For it will not al∣ter the case that he adds upon this Experiment, Hoc esse discri∣men

manifestum inter pressionem & suctionem, quod suctio efficiat hujusmodi adhaesionem, pressio autem minimè; since to say so is but to affirme, 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 onely sayes that Nullatenus satisfacit, ut legenti constabit; I would not do the Rea∣der the injury to suspect him of taking this proofless Assertion for a rational Confutation; especially since upon the review of that third Experiment I find nothing that agrees not with my Hypothesis, however it may disagree with the Examiners. 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 convenit: Cum enim per illam Emboli depressionem aër in cavitate brachii inclusus separetur ab eodem brachio, descendat{que} simul cum Embolo (uti de aqua simul cum argento vivo descendente capite decimo tertio vidimus) fit ut in tota illa depressione, novae semper ab aëre illo desoendente supersicies diripiantur simul & extendantur, ut ibidem de aqua est explicatum: cum ita{que} aeque facile diripiantur & extendantur hujusmodi superfi∣cies in fine depressionis ac initio, mirum non est quod eadem utrobi{que} sentiatur deprimendi 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 mention 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 arrow_back Air arrow_forward .

And in his third Corollary (which we lately desired the Reader to observe) speaking of the arrow_back Air arrow_forward in the Receiver (and the case is the same with the arrow_back Air arrow_forward in the Cylinder) he affirms more then once, Eo magis extendi ac rarefieri aërem relictum, quo plus inde exhauritur, majoremque proinde acquirere vim sese contrahendi. Whereas here he would have us believe, that the little internal arrow_back Air arrow_forward 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, re∣fist its depression, when the Sucker is yet near the top of the Cy∣linder, (and consequently when the included arrow_back Air arrow_forward is but a little dilated) as when the same Sucker being forced down to the low∣er part of the Cylinder, the same portion of remaining arrow_back Air arrow_forward must be exceedingly more distended.

The 4. Experiment.

In the Fourth Experiment, touching the swelling of a Bladder upon the removal of the ambient arrow_back Air arrow_forward ; and proportiona∣bly to that removal our Author objects nothing against the Ex∣plication we give of it by the Spring of the arrow_back Air arrow_forward included in the Bladder, and distending it according as the pressure of the ambi∣ent arrow_back Air arrow_forward is weakned. But he endeavours also to explicate it his way, to which he sayes this circumstance does excellently agree, that upon the regress of the external arrow_back Air arrow_forward into the Receiver, the tumid Bladder immediately shrinks, because (saith he) by such ingress of the external arrow_back Air arrow_forward , the arrow_back Air arrow_forward in the Receiver, which drew the sides of the Bladder outward from the middle of it, is re∣lax'd. Which Explication whether it be more natural then ours (that ascribes the shrinking of the Bladder to the pressure of the arrow_back Air arrow_forward that is let into the Receiver) let the Reader judge, who has considered what we have formerly objected against the Exa∣miners Funiculus, and the Relaxation of it upon the admission of arrow_back Air arrow_forward .

As for the reason likewise he adds, why a perforated Bladder does not also swell, namely, that by the hole, how little soever,

the included arrow_back Air arrow_forward is suck'd out by the rarefi'd ambient, we leave it to the impartial Reader to consider whether is the more genu∣ine Explication, either ours (against which he has nothing to ob∣ject) 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 superfi∣cies 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 arrow_back Air arrow_forward has Spring and Weight, as we deny his Funiculus to have any other then an imaginary existence; and whereas he acknow∣ledges that by the Instrument the arrow_back Air arrow_forward about the Bladder is ex∣hausted; to shew that there needs no more then that, and conse∣quently no Funiculus, to draw asunder the sides of the Bladder, we can confirm our Explication by the formerly mentioned Ex∣periment of the ingenious Paschall, who carrying a flaccid Foot-ball from the bottom to the top of a high Mountain, found it to swell proportionably as he ascended, and as the weight and pres∣sure of the ambient arrow_back Air arrow_forward 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 violently-rarefi'd arrow_back Air arrow_forward to draw asunder eve∣ry 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 onely ascribes the breaking of the Blad∣der

to the self-contraction of the rarefi'd arrow_back Air arrow_forward in the Receiver. 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 arrow_back Air arrow_forward , whereby its debilitated pressure became unable to resist the unweakned pressure of the outward arrow_back Air arrow_forward . But this Ex∣plication the Examiner confidently rejects in these words, At pro∣fecto non videtur credibile, mollissimum hunc aërem tam vehementer vitrum (tantae praesertim crassitudin is quantae ibidem dicitur) undi{que} sic comprimere ut illud perfring at: as if it were more credible that the little arrow_back Air arrow_forward within (which, according to him, is so much thinner then common arrow_back Air arrow_forward ) should be able to act more powerful∣ly upon the Glass then the arrow_back Air arrow_forward without, which himself confesses to be a heavy body, and which not onely reaches from the sur∣face of the Earth to the top of the highest Mountains, but which (as may not improbably be argued from what we have else∣where 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 be not a bounded port on of the arrow_back Air arrow_forward , * 1.42 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 exhaustio∣nem illam latera ejus vehementius introrsum sint attracta, quam ut ob figuram illam resistendo minus idoneam resistere potuerunt. Cum enim inclusus aër lateribus vitri firmissimè adhaereat, nihil aliud erit aërem illum sic exhaurire, quam satagere latera vitri introrsum fle∣ctere: By what we have already discoursed 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 rece∣dere: potest{que} vel inde solum satis refutari; quia si tanta sit pressura aeris sic per tubum illum in phialam descendent is, ut ipsam phialam perfringat, deberet profecto inclusam aquam, cui immergitur ille tu∣bus, valde quo{que} ante fractionem phialae commovere, bullulas{que} in ea∣dem excitaro, &c. ut constat, siquis, insufflando per illum tubulum, aquam vel mediocriter sic premat. At certum est aquam, antequam frangatur sit phiala, nec tantillum moveri: ut experienti constabit.

But, I do confess, I do for all this think our Explication more true, then well considered by our Author. For the putting of water into the Vial that was broken, was done (as is clearly inti∣mated in the beginning of our Narrative) upon a particular de∣sign (as indeed we tryed divers other things with our Engine, not so much with immediate reference to the Spring of the arrow_back Air arrow_forward , as to make use of such Tryals in some other of our Writings.) And accordingly in the second Tryal mentioned in the same Ex∣periment 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 blow∣ing in of the arrow_back Air arrow_forward 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 su∣perficies remaining as great as ever. And therefore we need not altogether deny what the Examiner sayes, that Licet clausus su∣perne fuisset tubulus ille, codem tamen modo fracta sine dubio, fuisset

phiala. For, since in such cases the arrow_back Air arrow_forward (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 arrow_back Air arrow_forward . But, how confidently soever our Author speaks, I thought fit to adde the word almost, because we observed in the 39. Ex∣periment, that such thin Vials (and thick ones will not break) are subject upon the withdrawing of the ambient arrow_back Air arrow_forward to retch a little, whereby the Spring of the arrow_back Air arrow_forward 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 communicates, and which leans upon it. And when the Vial does actually begin to break, then the pursuing pressure of the outward arrow_back Air arrow_forward upon the yielding arrow_back Air arrow_forward 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 Experi∣ment, 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 arrow_back Air arrow_forward at pleasure upon the restagnant Mercury, and consequently weak∣ning and increasing its pressure, we might make it more clearly appear then hither to had been done by Experiment, that the sus∣pension of the Mercurial Cylinder, and the height of it, depend∣ed upon the greater or lesser pressure of the arrow_back Air arrow_forward . But against our Explication of this Experiment (which has had the good for∣tune 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 observations 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 sus∣pended 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 arrow_back Air arrow_forward shut up in the Recei∣ver, he subjoyns onely this, Sed rectius sane infertur, Cylindrum illum nihil ibidem antea praestitisse. But whether this be not gra∣tis dictum we leave the Reader to collect from what we have for∣merly discourst in the second Part of this Defence of the Spring of the arrow_back Air arrow_forward ; especially from that Experiment; by which it ap∣pears, That Spring may sustain a far higher Cylinder of Quick-silver.

In the second Observation he mentions of ours, he summarily recites our Explication of the descent and ascent of the Mercury in the Tube, by the debilitated and strengthned Spring of the arrow_back Air arrow_forward . But without finding fault with our application of that principle to the Phaenomena, he sayes that he has sufficiently re∣futed the principle it self in the fourth Chapter, (which how well he has done we have already seen) and therefore explicates the matter thus; Dico igitur (sayes he) argentum per illam exhaustio∣nem sic in tubo descendere, quod deorsum traha••ur ab aëre qui incum∣bit argento restagnanti: siquidem incumbens ille aër jam per exhau∣stionem valde rarefactus & extensus, sese vehementer contrahit, & contrahendo conatur etiam subjectum sibi argentum restagnans è suo vasculo elevare, unde fit ut (argento illo restagnante minus jam gravi∣tante 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 one∣ly subioyn, 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 arrow_back Air arrow_forward into the Receiver, impell'd the Quicksilver to a considerably-greater height then '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 explicate this no∣table Phaenomenon) At{que} hinc etiam redditur ratio alterius quod ibi∣dem quo{que} notaîur, nempe quod per violentam intrusionem aëris ex∣ternt in Recipientem, ascenderit argentum notabiliter supra digitos 29½. Nam sicut per extractionem aëris argentum infra stationem de∣trahitur, sic etiam per intrusionem novi supra eandem elevabitur. For in this passage I see not how he himself does not rather re∣peat the matter of fact, then give any account how it is perform'd. And if it be alledged on his behalf, That according to his princi∣ples it may be said that, upon the pressure of the adventitious arrow_back Air arrow_forward 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 arrow_back Air arrow_forward 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 then the arrow_back Air arrow_forward forc'd into the Receiver. And therefore it remains that the additional arrow_back Air arrow_forward counterpoises the additional Mercury by its Spring. And if we consider withall, that there's no reason to doubt, (especially considering what we have formerly delivered upon tryal touching the power of comprest arrow_back Air arrow_forward to impell up Quicksil∣ver) but that, had we not been afraid of breaking our Vessel, we might by forcing more arrow_back Air arrow_forward into the Receiver have impell'd it up to the top of the Tube, and kept it there; we shall scarce de∣ny but that, supposing there could be no such Funiculus as our Examiner's in rerum natura, the pressure of the incumbent arrow_back Air arrow_forward

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 arrow_back Air arrow_forward in the Recei∣ver, the Quicksilver in the Tube may be made to rest at any height greater or lesser, provided it exceed 30. Inches, onely be∣cause its weight is just able to counterbalance the pressure of the contiguous arrow_back Air arrow_forward .

I know not whether I may not adde (to express an unwilling∣ness to omit what some may think proper to do my Adversary right) that it may be said for the Examiner, that he in the 11. page acknowledging with us a power in the arrow_back Air arrow_forward to recover its due extension if it be crouded into less room then its disposition requires; a man may from that principle solve the Phaenomena in question by saying, that the arrow_back Air arrow_forward in the Receiver being forcibly comprest by the intrusion of fresh arrow_back Air arrow_forward into the same vessel, does by its endeavour to recover its due expansion press upon the re∣stagnant 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 otherwise 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 at the cause why a Cylinder of Mercury did in Winter rise and fall in the Tube, sometimes 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 Hypo∣thesis of the Atmospherical Cylinder, and clearly shew that the

Quicksilver is not sustained by it: Nam (sayes he) si hic ab eo su∣stentatum fuisset, debuisset potius frigidiore tempore ascendere quam descendere, eo quod aër tunc multo densior esset & gravior. Ita{que} non sustentatur argentū ab aër is aequipondio, ut asseritur. And by the same Argument he concludes against the Mercury's being sustained by the Spring of the arrow_back Air arrow_forward . 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 Objecti∣on 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 arrow_back Air arrow_forward , and that a parcel of arrow_back Air arrow_forward may be made heavier by Condensation; yet that is in regard of the ambient arrow_back Air arrow_forward that retains its wonted laxity, in which the condensed arrow_back Air arrow_forward is weighed. But our Author has not yet proved, that in case the cold of the Winter should condense the whole incumbent Atmo∣sphere, it would then gravitate sensibly more upon the restag∣nant Quicksilver then before. As a Pound of Wooll will not sensibly vary its weight, though the hairs whereof it is com∣posed be made to lye sometimes in a looser, sometimes in a clo∣ser, 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, contracto hoc funiculo per frigus, aqua illa tempore frigido ascendat, descendat au∣tem 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 Phaeno∣menon

under consideration but as a Conjecture, 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 rejects our Explication, substi∣tutes no other then what may be gathered from these words, Ego certe non dubito quin dentur hujusmodi occultae causae, quibus funiculus ille subtilis, quo in tubo suspenditur argentum (ut dictum est capite decimo) modo producatur, modo abbrevietur, &c. sic{que} ar∣gentum nunc demittat, nunc elevet. For, since we have made it probable that the copious Fumes, sometimes suddenly ascending into the arrow_back Air arrow_forward , 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 Expe∣riment, may alter the density and gravity of the arrow_back Air arrow_forward that leans upon the restagnant Mercury; I suppose the Reader will think it more intelligible and probable, that alterations, other then those produced by heat and cold, may happen to the incumbent At∣mosphere, which freely communicates with the neighbouring arrow_back Air arrow_forward , and may thereby become sometimes more stufft, and some∣times more destitute of adventitious Exhalations; then 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 some∣times contracted, and sometimes stretch'd.

The 19. Experiment.

Upon this the Examiner has onely this short Animadversion, In decimo nono ostendit aquam eodem modo per exhaustionem Recipi∣ent is descendere, quo in praecedente descendere ostender at 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 them∣selves, which of the two is the more probable, either ours, that onely requires that the arrow_back Air arrow_forward 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 no∣ted) 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 arrow_back Air arrow_forward , 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 per∣ceive, 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 in∣tumescence of it might (at least in great part) proceed from that of the small parcels of arrow_back Air arrow_forward , which I thought to be usually har∣boured in the body of that liquor.

But whereas I ascribe the appearance of the Bubbles in the wa∣ter to this, that upon the exhaustion of some of the arrow_back Air arrow_forward incum∣bent on the water, the pressure of what remains is much de∣bilitated, whereby the little Particles of arrow_back Air arrow_forward lurking in the Water are allowed to expand themselves into bubbles; he re∣jects this Explication as manifestly false: Nam (sayes * 1.43 he) si it a sieret, deberent profecto hujusmodi bullulae non è fundo vasis sic ascendere, (uti tam in hoc quam in sequentibus experi∣ment is 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 Ob∣jection, yet see: For in the bottom of the next page he sayes, he will not deny but that Aerial Particles latitant in the other parts

of the water (he had before spoken of the bottom of it) may be extended into bubbles by his way of Rarefaction. And that we particularly mentioned the rising of bubbles, even from the bot∣tom of the water, was because that circumstance seem'd to de∣serve a peculiar 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 * 1.44 the following Experiments observ'd, that the ascending bubbles grew bigger the nearer they came to the top. Which agrees more clear∣ly with our Hypothesis, wherein their conspicu∣ous swelling as they ascend is attributed more to the lessening of the pressure of the incum∣bent arrow_back Air arrow_forward then 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 then ours) then with the Explication which the Examiner gives in these words, Re∣spondeo, aquam per illam aëris exhaustionem non sponte sic ascendere, sed sursum violenter trahi, ac elevari à rarefacto illo aëre sese contra∣hente. Quemadmodum enim aqua aliqualem patitur compressionem (ut experientiâ constat) ita & aliqualem quo{que} hic patitur, distensionem. At{que} hinc clarè patet, cur potius à fundo vasis quam à parte aquae su∣periore oriantur hujusmodi bullae. Cum enim vehemens illa suctio conetur 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 endeavour onely of the Funiculus to draw up the water from the bottom of the Vial, to which, that endeavour notwithstanding, it remains contiguous, should generate in some parts of the bottom of the Glass, and not in others, such a subtil 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 generation of subtil matter

comes to be effected. And I presume it will likewise be ex∣ected that he also declare, why both in our case and in the Tor∣ricellian 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 fuction he speaks of be great∣er upon the lower part of the liquor then the upper, to which alone nevertheless his Funiculus, 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 at the cause why two very flat and smooth Marbles stick so closely to∣gether, that by lifting up the uppermost you may take up also the lowermost, approves my way of examining that Conjecture. But whereas I say that the reason why, though the Marbles were kept together by the pressure of the ambient arrow_back Air arrow_forward , 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 arrow_back Air arrow_forward could not be sufficiently drawn out: yet he tells us with his wonted confidence, Certum esse, sententiam illam vel hoc solo Experimento satis refelli. But possibly he would have spoken less resolutely, if he had made all the tryals about the adhesion of Marbles that we relate our selves to have made in the short History we have publish'd of Flu∣idity and Firmness. For our Examiner speaks as if all that we ascribe to the arrow_back Air arrow_forward in such Experiments were to sustain the lower Marble with the weight perhaps of a few Ounces: Whereas in case the arrow_back Air arrow_forward be kept from getting in at all between the stones, it may (according to our Hypothesis) sustain a Weight either alto∣gether or well-nigh equal to that of a pillar of arrow_back Air arrow_forward as broad as the Basis of the lower Marble, and as long as the Atmosphere is

high, or to the weight of a pillar of Quicksilver of the same thick∣ness, and about 30. Inches long; these two pillars appearing by the Torricellian Experiment to counterpoise each other. And therefore since in the seventeenth Experiment, when we had ex∣hausted our Receiver as far as we could, there remain'd arrow_back Air arrow_forward enough to keep up in the Tube a Cylinder of about an Inch long of Quicksilver; and since the broader the contiguous Marbles are, the greater weight fastned to the lowermost may be sustain'd by the resistance of the arrow_back Air arrow_forward , (as is obvious to him that considers the Hypothesis, and as we have proved by Experiment in the forementioned Tract) it need be no wonder that the arrow_back Air arrow_forward re∣maining 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 Mer∣curial 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-informe 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 clog'd with a weight of above 430. Ounces.

As for the account the Examiner substitutes of our Phaenome∣non, I know not whether many Readers will acquiesce in it: For, not to insist upon the Objection which himself takes notice of, that according to him the distended arrow_back Air arrow_forward in the Receiver should draw asunder the adhering Marbles; his Explication supposes that there cannot naturally be a Vacuum, whence he infers that, Necesse er at ut lapis ille non aliter descenderet, quàm relinquendo post se tenuem hujusmodi substantiam, qualis ab argento 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 separated from Marble then from Quicksilver or any other kind of body; that Asser∣tion is precarious. And though I have tryed 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 then that of a Pillar of the Atmosphere that prest against the lowermost: Which is a considerable Cir∣cumstance, that much better agrees with our Explication then our Adversaries. And whereas he further sayes, Unde existimo planè, si perfectè complanata fuerint duo marmora sic conjuncta, it a ut nullus omnino aër inter utrum{que} mediaret, non posse ea ullis huma∣nis viribus ab invicem divelli: I hope I need not tell the Reader, that whether or no this agree with what he had immediately be∣fore taught of the separableness of a subtil substance even from Marble, so bold and improbable an Assertion requires the being countenanc'd with a much better proof then the onely one he subjoyns in these words, Uti etiam confirmat exemplum quod ibi∣dem adducit Author de lamina aenea, tabulae cuidam marmoreae ita adhaerente, ut à lacertoso juvene, de suis viribus gloriante, non potue∣rit per annulum centro ejus affixum inde elevari. For sure there is great odds betwixt the strength of a man unassisted by any En∣gine, and the ut most extent of Humane Power. And indeed according to our Hypothesis, and without having recourse to Na∣tures dreading of a Vacuum, the case is clear enough: For, sup∣posing 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 cohesion 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 exa∣mines together, he objects nothing peculiar, but contents him∣self 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 op∣pos'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 distend∣ed arrow_back Air arrow_forward in the exhausted Cylinder draws up the Sucker with the annexed weight, Eodem fere modo quo videmus in cucurbitulis dorso aegrotantis applicatis, in quibus, extincta jam flamma, rarefactus aër se contrahens carnem tam vehementer, uti videmus, elevat attrahit{que} intra cucurbitulam. But that Phaenomenon is easily enough expli∣cable in our Hypothesis, by saying, that upon the vanishing of that heat which strengthned the pressure of the included arrow_back Air arrow_forward , the Spring of it grows too weak to resist any longer the pressure of the ambient arrow_back Air arrow_forward ; which thereupon thrusts the flesh and neigh∣bouring bloud of the Patient into the Cupping-glass, almost af∣ter the same manner as we formerly taught the Pulp of the Fin∣ger to be thrust into the deserted Cavity of the Glass-Tube in the Torricellian Experiment.

The 34, 35, and 36. Experiments.

To these our Author saying nothing but this, In his tribus ni∣hil 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 arrow_back Air arrow_forward . And indeed though I do still look upon some of the things that I hesitantly propos'd about this difficult Phaenomenon but as meer Conjectures, and though he annexes his Explication of it; yet I see not but that it is coincident with ours, or not better then it. For, to what I had said of the Commotion of the parts of the arrow_back Air arrow_forward , he adds onely

in two or three several places their being violently distended; which how it improves the Explication of the Phaenomenon I do not readily see. And whereas he subjoyns, Existimo autem di∣cendum potius candorem illum esse lumen quoddam reflexum, quam innatum, eo quod (ut testatur Author) in tenebris non appareat, sed solum de die aut accensa candela: I presume the attentive Reader will easily discern that his Opinion is much-what the same that I propos'd and grounded on the same reason. But the chief diffi∣culty in this abstruse Phaenomenon, 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 Rea∣der that I seem to ascribe the sudden extinction of the included Animals to the excessive thinness of the arrow_back Air arrow_forward remaining in the Receiver, made by the recess of what was drawn out, unfit for Respiration; he adds resolutely enough, Verum impossibile vide∣tur, ut hujusmodi animalcula ob solum defectum crassioris aëris tam cito moriantur: but gives no other reason then that they dye so soon, which is no more then what he said in the newly-cited words, and besides is grounded upon something of mistake. For the Creatures he mentions were a Bee, a Flye, and a Caterpil∣lar, and those included too in a small Receiver, 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 sanguineous 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 En∣gine wherein he could carry arrow_back Air arrow_forward with him to the bottom of the Sea) how long he could endure, before he was accustomed to dive, without breathing or the use * 1.45 of a Spunge; 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 continue under water so long, either by a pe∣culiarly-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 then that when exactly measured amounts to. For, having purposely made tryal 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 Mi∣nutes in killing; whereas the other being immediately after de∣tain'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 tryal 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 in∣deed our Author either should have proved that 'tis not possible for the want of arrow_back Air arrow_forward 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, qui a per rarefactum illum aë∣rem sese contrahentem extractus sit eorum halitus: I see not that hereby, if he explicate the Phaenomenon otherwise then 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 arrow_back Air arrow_forward contained in the Lungs (supposing these Animalcula have any) must in great part pass thence into the Receiver, (for whether that be done by the Spring of the arrow_back Air arrow_forward it self, that was harboured in the

Lungs, or the traction on of the more rarefi'd arrow_back Air arrow_forward in the Receiver, is not material in our present case) the Examiner 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 Reader will think it had not been amiss that the Au∣thor had more intelligibly deduc'd these Tragick Symptoms from his Assumption, for the sake of those that are not Anato∣mists 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 arrow_back Air arrow_forward ; 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 consider'd his Animad∣version upon that, although this presumed distension of the water is not visible that we have observ'd, when cold water, that has been first freed from his interspers'd arrow_back Air arrow_forward , is put into the Recei∣ver, 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 preferred, 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 Gods assistance considered what the Exam ner 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 reputation; nor did I intend to use any more freedom of Speech in the an∣swering his Objections, then his resolute way of proposing divers of them made it on those occasions needful for the Caution of those Readers who are not acquainted with our differing wayes 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 exchange 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 Hypo∣thesis he would substitute in the room of ours (besides that it is partly precarious) supposes things which divers of the eminent∣est Wits of our Age (otherwise of differing Opinions) profess they cannot admit or so much as understand: whereas the Weight and Spring of the arrow_back Air arrow_forward are not denyed by our Author himself, and are demonstrable by Experiments that are not con∣troverted betwixt us. Which things I represent for the defence of what I think the Truth, and not to offend my learned Adversa∣ry, who shall have my free consent to be thought to have fail'd ra∣ther in the Choice then 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 emi∣nent

Persons he has nam'd among his Adversaries, I am induc'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 Adversaries, that had disputed against him with much more Subtilty then Reason, In mala causa non possunt aliter, at malam causam quis eos coegit ha∣bere? But this notwithstanding I am, as I was going to say, con∣tent my Adversary should be thought to have said for his Prin∣ciples 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, then 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 dis∣agree.

FINIS.

AN EXPLICATION OF RAREFACTION.

THe chief Arguments of the Author of a cer∣tain Treatise De corporum inseparabilitate, whereby he endeavours to invalidate the Hy∣pothesis of the Weight and Spring of the arrow_back Air arrow_forward , and to set up and establish instead thereof an unintelligible Hypothesis of Attraction, perfor∣med by I know not what strange imaginary Funiculus, are onely Five, two against the former, and three for the later. The first of which is, That the Weight and Spring of the arrow_back Air arrow_forward are not sufficient to perform the Effects ascribed to them: The second, that could they be performed by that Hypo∣thesis granted, yet the way of this strange Spring it self is not in∣telligibly explained or explicable by the Defenders of it. Now the former of these being little else but a bare Affirmati∣on, and the later bearing some shew of Demonstration, I shall endeavour to examine it as I find it set down in his 20, 21, 22, 23, and 24. Chapters, to which (especially the 23.) he very often in his Book refers the Reader for satisfaction, pretending there to evince that Rarefaction cannot be made out any otherwise

then by supposing a body to be in 2, 3, 4, 10, 100, 1000, 1000000 of places at the same instant, and adequately to fill all and every one of those places.

First therefore, we will examine his Negative, and next his Affirmative, Arguments for this strange Hypothesis.

His Negative I find in the 20. Chapter, where he endeavours to confute the two wayes of explicating the Rarefaction and Spring of the arrow_back Air arrow_forward , namely, that of the Vacuists and that of the Plenists.

Concerning the first of these we find him conclude it impos∣sible, first, because he had before proved that there can be no Vacuum, which being done by a Circle (viz. There is no Vacuum in the Tube because Nature abhors a Vacuum, and we see Na∣ture abhors a Vacuum because she will not suffer a Vacuum in the Tube above the Mercury, but to prevent it will continually spin the Quicksilver into supe ficies, and never diminish the body of it) will suffer me to pass to his next, which is, That this way is false, because in the Experiment of the Carps Bladder the arrow_back Air arrow_forward is rare∣fi'd a 1000. times bigger; nay, in respect of the body of Gold it has 1000000. times less matter in equal spaces. And this, sayes he, is a Phaenomenon that is impossible ever to be made out by interspers'd Vacuities. Now that the Vacuists cannot pre∣sently, by so bold an assertion as this, be made to forsake their Principles, he may perceive by these following Solutions which I shall give of all the Phaenomena he recites, flowing naturally from an Hypothesis that I shall for the present assume. Let us suppose then the Particles of Bodies, at least those of the arrow_back Air arrow_forward , to be of the form of a piece of Riband, that is, to be very long, slender, thin and flexible laminae, coyled or wound up together as a Cable, piece of Riband, Spring of a Watch, Hoop, or the like, are: we will suppose these to have all of them the same length, but some to have a stronger, others a weaker Spring: we will further suppose each of these so coyled up to have such an innate circular motion, as that thereby they may describe a Sphere equal in Diameter to their own, much after the manner that a Meridian turn'd about the Poles of a Globe will describe

by its revolution a Sphere of the same Diameter with its own in the arrow_back Air arrow_forward . By this Circular motion the parts of the laminae en∣deavouring to recede from the Centre or Axis of their motion, acquire a Springiness outward like that of a Watch-Spring, and would naturally flye abroad untill they were stretch'd out at length, but that being incompast with the like on every side, they cannot do it without the removal of them, as not having room sufficient for such a motion. And the faster this circular motion is, the more do the parts endeavour to recede from the Axis, and consequently the stronger is their Spring or endeavour out∣ward. These springy bodies thus shap'd and thus moved are sufficient to produce all the Phaenomena he names as impossible to be explicated. And, first, for the business of Expansion, it will very naturally be explained by it: As let us suppose for instance the Diameter of these small coyled Particles of the arrow_back Air arrow_forward (which being next the Earth are press'd upon by all those nume∣rous incumbent Particles that make up the Atmosphere, and are thereby so crouded that they can but very little untwist them∣selves; let us suppose, I say, the Diameter of these Particles) to be 1/1000000000000 of an Inch; and then to be much of the form of those represented in the 4. Figure by A B C D: and that these Particles, when a considerable quantity of the pressure of the ambient parts is taken away, will flye abroad into a Coyle or Zone ten times as big in Diameter as before; that is, they will now be 10/1000000000000 of an Inch in Diameter, and appear in the form of those in the Figure exprest by E F G H: these Zones whirl'd round as the former will describe a Sphere a 1000. times as big in bulk, and thereby fence that space from being entred by any of the like Zones: this it would do, supposing those Spheres did immediately alwayes touch each other; but because of their circular motion, whenever they meet they must necessa∣rily be beaten, and flye off from one another, and so require a yet greater space to perform their motion in. This suppos'd, there are no Phaenomena of Rarefaction (which is enough at pre∣sent to answer what he objects) but may be naturally and intelli∣gibly

made out. As first, for that of the swelling of a Carps Bladder, if we suppose some small parcels of the former com∣prest laminae to lye latitant within the folds of it, and being much coyled up together scarce to take any sensible room, this Blad∣der in the arrow_back Air arrow_forward will appear to contain very little or nothing within it; whereas when the pressure of the arrow_back Air arrow_forward is taken off in good part from the outsides of it, then those formerly latitant Parti∣cles disclose themselves by flying open into much bigger Zones, so as perhaps to be able to defend a thousand times bigger space from being entred into by their like or any other gross Parti∣cles, such as those of the Bladder. Now because the Pores of a Bladder are such as are not easily permeable by the Particles of arrow_back Air arrow_forward , therefore these lurking Particles so expanding themselves must necessarily plump out the sides of the Bladder, and so keep them turgid untill the pressure of the arrow_back Air arrow_forward that at first coyled them be re-admitted to do the same thing for them again.

Next, as for Rarefaction by heat, that will as naturally follow as the former from this Hypothesis. For the Atoms of fire flow∣ing in in great numbers, and passing through with a very rapid motion, must needs accelerate the motion of these Particles, from which acceleration their Spring or endeavour outward will be augmented, that is, those Zones will have a strong nitency to flye wider open, (for we know that the swifter any body is moved circularly, the more do the parts of it endeavour to re∣cede from the Centre of that motion) from whence if it has room will follow a Rarefaction. As for the conveyance of Light, that being according to Epicurus performed by the local motion of peculiar Atoms, their motions to and fro through this medium will be less impeded by the rarefi'd arrow_back Air arrow_forward then by the condens'd; as indeed upon Experiment we shall really find them.

As for his third Objection drawn from his supposed attractive virtue of the thus rarefi'd arrow_back Air arrow_forward , that is quickly answered, by de∣nying it to have any power at all of attraction; and by shewing (which is already done) that what effects he would have to be performed by the attraction of the included, is really done by the pressure of the ambient, arrow_back Air arrow_forward .

And, lastly, the Phaenomena of my Lord Bacons Experiment are sufficiently obvious and easie to be deduc'd.

So then, by granting Epicurus his Principles, that the Atoms or Particles of bodies have an innate motion; and granting our Supposition of the determinate motion and figure of the Aerial Particles, all the Phaenomena of Rarefaction and Condensation, of Light, Sound, Heat, &c. will naturally and necessarily follow: and the Authors Objections against this first way of Rarefaction will signifie very little.

As to the second way of Rarefaction, by the intrusion or inter∣vention of some subtil matter of Aether into the spaces deserted by the raresying Particles, which is that propos'd by the Asser∣tors of a Plenum, this also is by the Author condemned, and branded with Impossibility. And why? First, because 'tis (he sayes) impossible that the above-mentioned Phaenomena of the Carps Bladder can be explained by it. Secondly, because 'tis impossible to give a reason from it of the impetuous ascent of Water admitted into an exhausted Receiver. And, Thirdly, because 'tis impossible to explicate the Phaenomena of Gun-pow∣der. His Reasons to confirm which three Impossibilities, be∣cause drawn from a meer mistake, or ignorance of those Hypo∣theses which have been invented by the Assertors of that Opini∣on, I shall pass over, and content my self to explain a way how these Impossibilities may become Possibilities, if not Probabi∣lities.

And the way that I shall take, shall be that of the most acute Modern Philosopher Monsieur Des Cartes, published in his Phi∣losophical Works: Which is this, That the arrow_back Air arrow_forward is a Body con∣sisting of long, slender, flexible particles, agitated or whirl'd round by the rapid motion of the Globuli Coelestes, and the subtile Mat∣ter of his first Element, whereby they are each of them enabled to drive or force out of their Vortice all such other agitated par∣ticles. Now the swifter these Bodies are whirl'd round, the more do their flexible parts fly asunder and stretch themselves out; and the more forcibly do they resist the ingresse of any other so

agitated particles into their Vortice, and consequently the slower their motion is, the less will be their resistance. And because there is a vast number of these whirled particles lying one above another, and each particle having its peculiar gravi∣ty; it will necessarily follow that the undermost (which to maintain their Vortice must resist so great a pressure) must very much be hindred from expanding themselves so far as other∣wise they would, were there none of those incompassing agi∣tated Particles that lay in their way: and that those being by any means removed, or they themselves by a more rapid motion of the Particles of their Vehicles, the first and second Element, (which is according to that Hypothesis an effect of Heat) more swiftly and strongly whirled round, they presently begin to ex∣pand themselves, and maintain a bigger Vortice then before. Now to perform what I just now promised, I shall endeavour to give a possible, if not a probable, cause of the objected Phaeno∣mena. And, First, for that of the Carps Bladder, where the arrow_back Air arrow_forward is rarefi'd (sayes the Author) 1000. times, it will easily be ex∣plained by supposing the few Particles of the arrow_back Air arrow_forward , which (whilest they sustain the pressure of all the incumbent Atmosphere) in∣conspicuously luck within the Bladder, (each of them being able to maintain but a very small Vortice) to be by the subsiding Mercury in the Torricellian Experiment freed from the pressure of the arrow_back Air arrow_forward , and their motion continuing the same (by reason that the Transcursion of their Vehicles is not at all or very little hin∣dered either by the Glass or Bladder) their parts having room to expand themselves, will flye abroad to such Extensions as may perhaps make a Vortice 1000. times as big in bulk as what they were not able just before to exceed. Hence the Particles of the arrow_back Air arrow_forward (being so gross as not easily to pervade the Pores of the Bladder) must necessarily drive out the fides of the Bladder to its utmost extent, and serve to fill the Receiver in the Magde∣burgick Experiment. Now, whereas these Particles will by the same pressure of the arrow_back Air arrow_forward be reduc'd to the same state they were in at first, that is, to be thronged into a very little room, and

thereby be able to maintain a very small Vortice; the arrow_back Air arrow_forward let in in the Torrecellian Experiment reduces the arrow_back Air arrow_forward in the Bladder to its former inconspicuousness; as the admission of the Water in the Magdeburg Experiment does that Receiver full of rarefi'd arrow_back Air arrow_forward into the bigness of a Hazel Nut. Now the Water in this last-mention'd Experiment enters with a great impetuosity, because driven on with the whole pressure of the Atmosphere, and re∣sisted onely by the small force of the so-far-rarefi'd arrow_back Air arrow_forward .

As for the Authors Objection against this way of Rarefaction drawn from the Phaenomena of Gun powder, I shall endeavour to answer it by shewing them possibly explicable by a Cartesian Hypothesis. For supposing those Terrestrial parts of the Gun pow∣der to be first at rest, and afterwards agitated by the rapid moti∣on of his first Element, there will be sufficient difference of the former and later condition in respect of Extension; and suppo∣sing the particular constitution of Gun-powder (arising partly from the Specifick forms of the Particles of its ingredients; Nitre, Sulphure and Char-coal, and partly from their proportionate commistion) to be such as will readily yield to the motion of his Materia subtilis, so soon as an ingress is admitted to it by the fire∣ing of any particular parcel of it, the Expansion will be speedy enough.

So then let us suppose a Barrel of Gun-powder placed in some close room, to some grains of which we will suppose some actual fire to be applied, by which actual fire (the Texture of the Pow∣der being such) those grains are suddenly fired, that is, many Millions of parts, which before lay still and at rest, are by the action of the burning Coals shatter'd, as it were, and put into a posture ready to be agitated by the rapid motion of the Materia subtilis: into which posture they are no sooner put, then agita∣ted and whirled sufficiently by it; whence follows a vast Expan∣sion of that part of Gun-powder so fired. For each of its parts being thus whirl'd and hurried round, expell and beat off with great violence all the contiguous Particles, so as that each Particle takes up now 1000. times as much Elbow-room (if I

may so speak) as just before serv'd its turn, and consequently those that are outermost take every one their way directly from the parcel or Corn they had lain quiet in, being hurried away by the sudden Expansion of the Particles that lay next within them; so that whatever grain or parcel of Gun-powder they chance to meet with, before they have lost their motion, they presently shiver and put into such a motion as makes them fit to receive the action of the Materia subtilis. Which subtil Matter being every where present, and nothing slow in performing its office, imme∣diately agitates those also like the former; so that in a trice the Particles of the whole Barrel of Gun-powder are thus disorder∣ed, and by the motion the Materia subtilis must needs be hur∣ried away with so great an impetuosity on all sides, as not onely to break in pieces its slight wooden prison, and remove the lighter Particles of the ambient arrow_back Air arrow_forward , but huge Beams, nay, vast accumulated Masses of the most compacted Structures of Stone, and even shake the very Earth it self, or whatever else stands in its way, whose Texture is so close as not to give its Particles free passage through its Pores. This understood, I see not, first, what the Authors three Arguments brought to prove his Ob∣jection signifie, for there are no more Corpuscles in the room before the Gun-powder is fired then after, nor is there any more matter or substance before the sides of the room by yielding give place for the external fluid bodies to succeed, and the onely change is this, that the Globuli secundi Elementi (as he calls them) are expell'd out of the room, and the Materia primi Ele∣menti succeeds in the place of it. Nor do I see, secondly, what great reason he had for his grand Conclusion, Haec abundè demon∣strant, rarefactionem per hujusmodi corpuscula nullatenus posse ex∣plicari.

Having thus examined the Authors first Arguments, that Rarefaction cannot be made out by any other way then his; we shall find his other, which he brings to establish his own Hypothe∣sis, much of the same kind. As, First, that his way of Rarefacti∣on implies no Contradiction: For if the affirming a body to be

really and totally in this place, and at the same time to be really and wholly in another, that is, to be in this place, and not to be in this place, be not a Contradiction, I know not what is. Next, that some learned School-men have thought so; to which I an∣swer, more learned men have thought otherwise. And, lastly, that there are very plain Examples of the like nature to be found in other things; of which he onely brings one, viz. that of the Rota Aristotelica, which upon examination we shall find to make as little to the purpose as any of the other.

An Explication of the Rota Aristotelica.

THe great Problem of the Rota Aristotelica, by his explication of which he pretends not onely to solve all the difficulties concerning Local motion, quae Philosophorū ingenia hactenus valde exercuerant, but to give an instance for the confirmation of his unintelligible Hypothesis of Rarefaction, wherein there is extensio seu correspondentia ejusdem rei ad locum nunc majorem, nunc mino∣rem; we may upon examination find to be either a Paralogisme, or else nothing but what those Philosophers said whom he ac∣counts gravel'd with it. Of this Subject he begins in his 25. Chapter, where after he has set down a description of it, he makes an instance in a Cart-wheel; Rem ante oculos ponit rota ali∣cujus currus, ejus{que} umbo seu lignum illud crassum & rotundum cui infiguntur radii; siquidem dum progrediente curru ipsa rota circum∣ducta describit in subjecta terra orbitam sibi aequalem, umbo ille de∣scribit in subjecto aëre orbitam. (I suppose both here and before he means Lineam) se multo longiorem, utpote aequalem orbitae totius ro∣tae, licet ipse non nisi semel quo{que} fuerit circumvolutus. (As for what he sayes, that the Nave must be suppos'd to pass through the arrow_back Air arrow_forward , and not to touch a solid Plain, I do not yet understand the force of his Reason, nor why he sets it down, making no∣thing to his present purpose, unless it were because he did not

well understand the thing) In which, sayes he, the great difficul∣ty is to explain how the Nave should be so turned about its Axis, ut partes suas successivè applicet lineae duplo plures partes ha∣benti, id{que} motu perpetuo ac uniformi nè vel ad oculum instar inter∣rupto. Which how true, and what great occasion he had to won∣der at the solution of that Problem by the Example of a man standing still and another walking, we shall find by and by, when we come to explain the Problem: but first I shall examine his Hypoth sis and Explication. And First, he supposes Time to consist of a determinate number of Indivisibles, (that is, such as have neither prius nor posterius included in them) which he calls Instants. And next he supposes the praesentiam localem seu ubica∣tionem cujuslibet part is indivisibilis & virtualiter extensae esse quo{que} indivisibilem & virtualiter extensam: Which supposition so strangely exprest is no more then this, that the extension or space of his Indivisibles is also indivisible. But as for his Virtual Extension, I consess I understand as little what it is as I verily believe he did; and therefore I will proceed to his following sup∣position. His Third therefore is, That by how much more rare a body is, by so much the more are its Indivisibles virtually ex∣tended. Hence his Fourth is, That though these Indivisibles be really indivisible, yet they are virtually in quotvis partes divisibi∣les. Whence he deduces his Fifth Principle, That since these Indivisibles are really indivisible and virtually extended, they must necessarily be moved after the same manner that other indi∣visible and virtually-extended things are. His Instances are in the motions of an Angel and an indivisible piece of wood, which, he sayes, are both of the same kind. As for that of Angels, ha∣ving no immediate Revelation, and a Spirit and its actions not falling under sense, and not having any third way by which to be inform'd, I shall leave him there to enjoy his fancies. But as for that of his piece of wood, we shall find it sufficiently full of ab∣surdities and contradictions. And first, he calls it indivisible, but why I know not, for 'tis neither really nor yet mentally so: not mentally so by his fourth Principle, where he sayes that 'tis

virtualiter in quotvis partes divisibiles, by which word virtualiter he means the same thing with mentaliter, or nothing. Nor, se∣condly, is it really so: for then (according to the main business of his Book, as may be gathered from the first words of his Title-Page, Tractatus de Corporum Inseparabilitate) it would be impossible that any thing in the world should be divisible; for he making an inseparable continuity, and that bodies will rather be (I can't tell how) stretcht beyond their own dimension in in∣finitum, then part from one another; a body may as soon pass through the dimensions of any one Indivisible, as pass between two. Next, he grants in the strange stretching or rarefaction of these Indivisibles a temporary motion of the condens'd Dimen∣sion; whence there will follow that there must be distinct places or Ubi's, it must be terminus à quo, terminus ad quem, & me∣dium. And next, it were impossible to divide a line into two parts, supposing it consisted of an unequal number of Indivisibles; as if 101. Indivisibles of exceedingly-rarefi'd arrow_back Air should be ex∣tended in length an Inch, it were impossible to divide that Inch into two equal parts. I might run over many more, but it would be too tedious to be here recited. As for his indivisible parts of Time, those also must necessarily be in quotvis partes di∣visibiles; for else the same body or Indivisible must necessarily be in divers places at the same instant. But because he can swal∣low, nay confidently affirm, this and many other such like con∣tradictions and absurdities, I am not willing to mention them; and I think it would have made more for the Authors reputation if he had done so too. As for his last Chapter, where he applies these Principles to the Explication of the Rota Aristotelica, I have not here time to set down all the absurdities that any one that has but a smattering in the Mathematicks may observe: as, some∣times half an indivisible part of a Circumference may touch an indivisible of a Line; sometimes one may touch half, a quarter, a hundredth part, a whole one, two, ten, a hundred, &c. at the same instant; nay, an indivisible of a Circle may be all of it in a thousand places together, and the like. And this he brings as a

great Argument to establish his Hypothesis of Rarefaction, pre∣tending it to comprise many Aenigma's and very great difficul∣ties; whereas the thing is very plain and easie, and contains no such obscurities. For if, for example, we suppose a Wheel ABCD to be moved in a direct motion from AIC to KLM, eve∣ry point of it retaining the same position to that line that they had at the beginning of their motion, each of the points AEIGC will on a Plain, or in the Medium it pervades, pass through or describe a line equal to the line IL, and not onely all the points lying in the line AIC, but all and every point of the whole Area of the Circle; this must necessarily happen if the Diameter AIC be moved parallel to it self: But if whilest it be thus moved with an equal progression, it be likewise moved with an equal circulation, the case will be altered. For then, first, each point will by this compound motion describe on the Plain or Medium either a perfect Cyclorid, as when the Wheel makes one perfect revolution, whilest the whole is progressively moved from I to L; or some Piece, as when the Wheel has not perfected its revolu∣tion; or more then a whole one, as when the Circle has made more then one whole revolution whilest it is moved in its deter∣minate length. I shall here onely consider the first, as pertain∣ing more especially to my present purpose, and in regard the two later on occasion may be easily explicated by it. Next, each point of this Circle acquires from its compounded motion vari∣ous degrees of Celerity as to its progression, according to its va∣rious position to a point which is alwayes found in some part of the line drawn through the Centre of the circular motion per∣pendicular to the progressive. And it is found thus, as the Cir∣cumference to the Radius, so is the line of the progressive moti∣on to the distance of the point from the Centre. And this hap∣pens because the line of Progression is equal to the Circle descri∣bed on that distance as Radius; each point therefore of this smaller Circle, when it comes to touch the Perpendicular, must, as to its progressive motion, stand still: This point therefore will be the Centre of this compounded motion. Now because for

the explication of the Rota Aristotelica we need not consider any other then those Points which are transient through or cross the Perpendicular line, we shall onely examine them. Let then in our Example A be the Centre or immoveable point, the Cir∣cumference therefore ABCD will be equal to IL or AK by our Hypothesis. Now because the point I, which is the Centre of the Rotation, has onely one motion, viz. that of Lation, its ce∣lerity will be equal to the single celerity of the Lation; we will therefore put it to have one degree. C, because it is moved with two motions, both tending the same way, and each equal to the velocity of I, must needs have two degrees of velocity. The point F, because moved with two motions, both tending the same way, the one (viz. its Lation) being equal to that of I, and the other (because it is but half as far distant from the Centre of Rotation as C, and therefore is moved but with half the celerity of C, which was equal to that of I) but half as quick, we will put to have one degree and an half. By the like method we might find the velocity of all the points in the Perpendicular, viz. such as we have there marked some of them; but it would be too te∣dious, we needing not to consider more then the two points A and E. The point at E being moved forward by its progression with the same velocity that I, but by its rotation (which is but half as swift as that of the Circle ABCD, that is double the Circle EFGH) being moved the contrary way or backwards with half the velocity, loseth half of its progression forwards. The point in A being by its progression moved forwards equally swift with I, and by its rotation (the Circle ABCD being equal to the line IL) being carried backwards with equal velocity, must necessarily stand still as to its progression. Now having shewn that the point A (being by reason of its two equal opposite motions at rest) does onely touch a point of the line AK, and is not at all moved on it; and that the point E (being carried forward twice as fast by its progression as it is carried backward by its rotation, and thereby moved half as fast as the point I) does not onely touch the line EK, but whilest it touches it is moved on it with a

progressive motion half as swift as that of I: It will necessarily follow, that each point situate in E must necessarily describe a small line, which is a part of the whole EC. Now both the con∣tact of the former, and the contact and progression of the later, being performed by an infinite succession of points in the space of an infinite succession of Instants; I see not any one difficulty of this Problem but may satisfactorily be given an account of by it, without having recourse to the Hypothesis of the determinate number of indivisibles of space and time; which at best will one∣ly come to this, that In such a determinate moment or minute space of time, (which consists of an infinite consecution of Instants, and has prius and posterius in it; though yet he will call it an Instant, and have it to have the same proprieties with an Instant used in the common Philosophical sense) such a determinate minute Corpuscle (which, though it have extension in length, breadth and thick∣ness, yet will he not admit it to be divisible or have parts, no not though, according to his Hypothesis, the indivisible of one body may be rarefied to be as big in bulk as a million of the indivisibles of another, but will have it to be called and to be a real indivisible) will successively pass over such a determinate space or length (which yet he will not admit to be divisible, though according to his Principles it may equalize the length of millions of his other Indivisibles, nor admit a successive mo∣tion, but instantaneous, though that does necessarily put a bo∣dy into two, three, ten, a hundred, &c. places at once; but will have these also to be indivisible.) Haste makes me pass over the absurdities about the contact of a Circle and a Line, and to comprise in short all that great Explication he has given of this and other intricate (as he calls them) Problems, which is this, That the reason of the celerity of the moti∣on of some one of these indivisibles above another is, that it passes through a greater part of an indivisible in the same instant then the slower; that is in plain sense no more then this, One body is swifter then another because it is moved faster, From whence he draws several Corollaries, as that

Hence may be given a reason why an Eagle is swifter then a Tortoise, viz. because it moves faster. I should have sol∣ved several Objections which may be brought against the di∣visibility of Quantity in infinitum; but that as all the Scho∣lastick Writers are full of them, so it is a Subject which we are least able to dispute of, having very little information of the nature of Infinity from the Senses.

FINIS.

Notes

• * 1.1

  Pag. 20.
• * 1.2

  Pag. 16.
• * 1.3

  Pag. 17.
• * 1.4

  Pag. 15.
• * 1.5

  Pag. 12.
• * 1.6

  Pag. 14.
• * 1.7

  Pag. 8.
• * 1.8

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

  Pag. 19.
• * 1.10

  Pag. 19. 20.
• * 1.11

  Pag. 20.
• * 1.12

  Pag. 21.
• * 1.13

  Pag. 21.
• * 1.14

  Pag. 11.
• * 1.15

  Pag. 24.
• * 1.16

  Pag. 48.
• * 1.17

  Pag. 22.
• * 1.18

  Pag. 25.
• * 1.19

  Pag. 38.
• * 1.20

  Pag. 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 Tomo 1. pag. 211.
• * 1.34

  Pag 68.
• * 1.35

  Pag. 50.
• † 1.36

  Mr. Croon one of the learned Pro∣fessors of Gresham Colledge.
• * 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 Mountaine-Aire there seems to have act∣ed rather by its Weight then Elasticity.
• * 1.40

  Page 11.
• * 1.41

  See the 5. Figure.
• * 1.42

  See Part 2. C 5.
• * 1.43

  Sed contra manifestè.
• * 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. Hobbes.