New experiments physico-mechanical, touching the air

AN EXAMEN Of the greatest Part of Mr. HOBBS's DIALOGUS PHYSICUS De Natura Aeris.

CHAP. I. The Occasion and Scope of the present Treatise.

MEeting the other day with a Treatise then newly publisht by Mr. Hobbs, and intituled Dialogus Physicus De Natura Aeris; The Name of the Au∣thor, the Subject of the Book, and the Information I had a good while before received from his Friends that he was writing against me, invited me to peruse it as a Discourse wherein I might probably find my self concern'd: nor was I deceived in my Expectation. For having cursorily pass'd through it, I readily found, that though I be not expresly nam'd there, and though some things in the Title-page, and some others in the Book it self, seem to make the chief Design of it to be the Disparagement of the Society that is wont to meet at Gresham College; yet the Arguments are for the most part levelled at some Writings of mine, pu∣blished some of them the year before, and some of them this last Spring; As the Experiments, whose Explications he is

pleased to censure, do all along declare. I confesse I was somewhat surpriz'd to find that Mr. Hobbs, whom if my Books have at all mentioned, it has been with respect, should fall upon a person that had not provoked him, whilst such Mathematicians as Dr. Wallis, Dr. Ward, Tacquet, and Mo∣ranus (Men much too famous to be despicable Adversaries) having a good while since professedly and unchalleng'd writ∣ten against him, he hath yet, the whole Discourses of some, and so great a part of the Objections of the others, to reply to. And it somewhat added to my wonder, that a Writer of Politicks should causelesly and needlesly, for ought I can learn, fall upon a Society, whereof, besides many other Per∣sons of Quality and men of Parts, his own great Patron, and my highly Honour'd and Learned Friend, The Earl of Devon∣shire himself, is an Illustrious Member. And as for me, I shall not scruple to confess, that I could have been well enough contented Mr. Hobbs had spared this Dialogue, partly be∣cause I have a natural Indispos'dness to Contention, partly because I am at present distracted by store of other Employ∣ments both of a Publick and a Private nature, (and particu∣larly by the publishing of three or four Books of differing Subjects, and Printed in several places) partly because Mr. Hobbs's Objections are of such a Nature, that perhaps my Re∣plies, though as short as (my Design mention'd in the Pre∣face considered) I can conveniently make them, will amount to a longer Discourse than most Readers will think the Ob∣jections needed; and partly too, because Mr. Hobbs is pleas'd to write of divers Worthy and Learned-Men in so depreci∣ating, and of himself in so differing, a way, that I fear I shall find it somewhat uneasie to retain (under such Provocations to decline it) the Civility I am wont, and am desirous to write with; and that I must almost despair of dissenting with∣out an absolute Rupture from a Person, whose way of Dis∣coursing is such, that though I shall not give it any Epithete, yet I confess it leaves me but little hope that I can oppose him without angering him.

But however, because if I can (as I intend to do) so far comply with my Inclinations and my Custom, as to wave personal and extrinsick Matters, and restrain my self to the Examen of the Argumentative part of his Discourse; My Re∣ply will not need to be prolix; and because he has vouch∣safed rather to single out a young Writer, whose Books (at least of Matters Philosophical) do but begin to appear in the World, than to defend himself against those Illustrious Ene∣mies, upon whom he might expect to gain much more Ho∣nour; and because Mr. Hobbs's Name may with some Rea∣ders give his Arguments an Efficacy which their own Nature could not confer on them; I must resolve to submit to what he and my Concern for the Truths he rejects impose upon me. But to shorten as much as I can a Work to Which I can allow but very little time, it will be expedient before I de∣scend to the Examination of Particulars, to premise three or four Advertisements touching the Occasion and the Nature of the Controversie, that I might not be reduc'd to a fre∣quent and unwelcome Inculcation of the same things.

CHAP. II. Of some mistakes of Mr. Hobbs touching matters of fact, and the Author's Doctrine.

ANd first, whereas Mr. Hobbs is pleas'd to write as if the Explications and Experiments to be met with in the Physico-Mechanical Treatise he censures, were those of the whole Society at Gresham College; I must do them that Right to declare, that this way of Proceeding is manifestly grounded upon a Mistake. I will not affirm that the Mistake was wilsull, that Mr Hobbs might give himself a pretence to Quarrel with them, (who have hitherto suspended the Declar∣ing themselves as a Society) in the controverted Points. But there are some that think Mr. Hobbs might very easily have avoided this mistake: since the Book he censures was publish∣ed (and perhaps taken notice of by most of the Virtuosi here)

some Months before the Society was begun. And the Experi∣ments themselves had been long before the Book came sorth, not onely seen and discoursed of by divers Learned Men and Illustrious Persons, but had the Honour to have our great Monarch of the Virtuost, as well as of Great Britain, for a Spectator. And though possibly divers of the Learned Mem∣bers of our Assembly may have no unfavourable opinion of what I have delivered in that Book; yet the Assembly, as such, has been so far from Adopting or Owning my Opinions as theirs, that it has with Approbation been propos'd among them, to repeat the Experiments, and take a review of the Explications, that upon a strict Examen of the several Opi∣nions, and the Objections that could be brought in against them, they might see what Judgement will be fit to be past on them. And although there be very few Philosophers whose Parts may make their Judgement more formidable to me; yet to comply with their Design, whatsoever the event might be, I presented them the Engine it self, I had made use of and describ'd in my Book; chusing rather to undergo their Censures, than want their Instructions. By which it may ap∣pear, upon how little ground Mr. Hobbs has thought fit to impute to the Society those Opinions which (how Erroneous soever he is pleas'd to think them,) I must own to be mine. And this Justice I the rather do It, because 'tis all that I am to do in this Treatise on their Behalf, not onely for the Rea∣sons above intimated, but because the Vindication of such an Assembly against Mr. Hobbs deserves a better Pen than mine, though it doth not need it.

Secondly, undertaking then the Defence of my own Cause, without Interessing them in my Quarrel, I must next admon∣ish the Reader, that whereas Mr. Hobbs writes, as if the new Experiments were devised or at least employ'd, to prove a Vacuum; he is in this likewise mistaken. For neither has the Society declared either for or against a Vacuum, nor have I: Nay I have not only forborn to profess my self a Vacuist, or a

Plenist, but I have in a fit place of my Epistle expressly said, that I reserv'd the declaring of my own Opinion touching that Point to another Discourse (which as yet is not published.) Wherefore Mr. Hobbs either injures or mistakes those, whom he will needs make his Adversaries, when he represents the new Experiments as Demonstrations alledg'd by profess'd Vacuists to disprove the Fulness of the World. And though I shall be oblig'd in the following Discourse to reject Mr. Hob∣bs's Supposition of a Plenum; yet I intend not thereby to de∣clare whether or no I do absolutely allow a Vacuum. But that which I drive at, and which alone my present Work ex∣acts, is to shew that I may reasonably oppose the Hypothesis of a Plenum, as it is stated by Mr. Hobbs: and consequently, unless he had better prov'd it, I may very well refuse to let Him take it for demonstrated. But I intend not to question whether or no other Plenists may not have better Arguments than his Principles have suggested to him: nor to deny but that the Cartesians, may without granting a Vacuum, give a more plausible Account (whether true or no) of divers of the Phaenomena of our Engine, if they will add, as some of them of late have done the Spring of the Air to their Hypothe∣sis, That the Celestial Matter of which the Air does in great part consist, is subtile enough freely to pass through the Pores of the closest Bodies, and even Glass it self.

As for the Assertion Non dari vacuum, though, as I said, I need not in this place declare my self either for or against it, yet I confess I do not find that Mr. Hobbs, though all along this Discourse he argues from this Principle against those he thinks Vacuists, has demonstrated it. For in his Book De Corpore (though a main part of it depend * 1.1 upon the Plenitude of the World) He has that I remember, but one positive Argument (indeed he thinks that unanswerable) to evince it. And that is drawn from this Experiment: That if a Gardeners Watering-Pot be fill'd with Water, the hole at the top being stopt, the Water will not flow out at any of

the holes in the bottom: But if the finger be removed to let in the Air above, it will run out at them all; and, as soon as the finger is applied to it again, the Water will suddenly and total∣lay be stayed again srom running out. The cause whereof (sub∣joyns he) seems to be no other but this, that the Water cannot by its natural endeavour to descend drive down the Air below it, because there is no place for it to go into; unlesse either by thrusting away the next contiguous Air it proceed by continual endeavour to the hole at the top, where it may enter and succeed in the place of the Water that floweth out; or else by resisting the endeavour of the Water downwards penetrate the same, and pass up through it.

But this Experiment, as an obvious one, and without dreaming that Mr. Hobbs had laid such stress upon it, I have incidentally answer'd in what I say in two or three passages on the thirty third Experiment of my Epistle. But after found that it had been more fully answer'd (but upon Grounds some of which I do not need) by my Learned Friend Dr. Ward, with whom I thus take Mr. Hobbs his Argument to pieces. The Cause, according to Mr. Hobbs, of the Suspension of the Water in the Vessel is, that the Water cannot thrust away the Air. 2. And it cannot thrust that away unless Air succeed in its place. 3. But Air cannot succeed in its place, unless either by getting in at the upper Orifice, or at the Holes that perforate the bottom. By which view of the Argument it appears that the main force of it lies in the second Propositi∣on; but neither doth he demonstrate that (which omission might excuse us from any further Answer) nor indeed do I think it true. For if the Watering Pot were tall enough, what Reason is there, why the Water should not run out at the Holes of it? as Monsieur Paschall's Experiment mentioned in my Epistle manifests; That though in a Glass-Tube Hermeti∣cally sealed at one end, and several times as long as a Water∣ing-Pot, the Water will not fall down; yet it will, if the Tube exceed two or three and thirty foot, or thereabouts.

And indeed the Suspension or Descent of the Water depends upon the Proportion betwixt the weight of the Aqueous Pil∣lar that tends downwards, and the Resistance or Pressure of the Air that can come to bear against it. For as on the one side, when the height of that Pillar is so increas'd, as that it can outweigh the Atmospherical Cylinder that opposes its Des∣cent, 'twill flow out till those two Cylinders come to an AEquilibrium: so on the other side if instead of increasing the length of the Cylinder of the Water, you lessen the pressure and resistance of the Air, the Water will likewise descend, though the Pillar be very short, as I have shown in the nine∣teenth Experiment; where by withdrawing some of the Air, in the Receiver, and thereby weakning its Spring, the Water in a Tube Hermetically seal'd at one end of but about four foot long subsided about three foot, though That the space relinquish'd by the Water was not full of Air, as Mr. Hobbs his Argumentation requires it should be, may be prov'd by what is there added, That by letting in the outward Air when the Water was sunk so low it was immediately impell'd up again to the higher parts of the Tube.

And indeed (as I elsewhere discourse) it seems * 1.2 to me a difficult matter for those that reject, as Mr. Hobbs justly does, that Conceit of Natures Abhorring a Vacuum, and making it, as it were, her business to hinder it, to prove there can be no Vacuum at all by any particular Experiment. For if the Fulness of the World be not made necessary either by the Nature of Body in general, or by the Design of the Author of the Universe, it can scarce be easie to prove by a particular Experiment, that no Humane Force or Art can contrive a way of overcoming at least for some time, and as to some space, either the Gravity of fluid Bodies or whatever other Quality of the Air or Water it is by which the Contiguity of the neighbouring Parts of the World is wont to be maintain'd. As we see the Water that will not descendeven in a Tube of thirty foot, (and thereby has made

men think it will never descend whilst the Air is not permitted to succeed it,) may by our Engine be brought to subside in a Tube of about a foot long. And I shall here add this out of my (yet unpublisht) Dialogues of Flame and Heat: That whilst onely particular Experiments are brought to assert the Impossibility of a Vacuum, perhaps the Vacuists will have the Advantage on their side. For a thousand Experiments are not of that force to prove universally that a thing cannot be ef∣fected, as one that shews it may be, is to prove the contrary. And the Vacuists have as well as the Plenists store of Experi∣ments on their side that seem to favour their Hypothesis, accord∣ing to which, were it true, I see not why they may not solve the Objections drawn from either the ascension of Liquors upon Suction, or the non-descension of Liquors in Watering-Pots clos'd at the top, or from any of the like Experiments I have yet met with, in case the Weight and Spring of the Air be taken in to solve the Phaenomena. And the Vacuists will have this Advantage, that if Mr. Hobbs shall say that it it as lawfull for him to assume a Plenum as for others to assume a Vacuum; not onely it may be answer'd, 'tis also as lawfull for them to assume the contrary; and he but Barely Assuming, not Proving a Plenum, his Doctrine will still remain question∣able. But I think I could say more in favour of the Vacuists Experiments; namely, That whereas in some Phaenomena of the Torrecellian Experiment, and in many of those of our En∣gine, Mr. Hobbs proves the space deserted by the Quicksilver or the Air to have no Vacuity, because according to his Sup∣position the World is full; and not by any sensible Phaenom∣ena that prove the Space in Question to be perfectly full:) For no less Fulness is requisite to the truth of his Hypothesis:) The Vacuists on the other side need not go about to prove that those Spaces are not full by their Hypothesis. But they prove it by this, that it appears by sensible Phaenomena, that the Quicksilver deserts the upper part of the Tube; and that much Air is pump'd out of our Receiver. (The first of which is e∣vident

to the Eye; and so is the other too, when the Pump is kept under Water.) But it does not appear by the like Phae∣nomena, that the Air (as Mr. Hobbs would have it in is Ele∣ments) does Succeed to fill, I say, perfectly to fill the deserted space; which also they will confirm from hence, that in the Torrecellian Experiment by inclining the Tube the relin∣quish'd space may be again readily fill'd with Mercury; and if our exhausted Receiver be plung'd under Water, that Li∣quor, when access is given it to the Cavity, violently rushes into it, and almost fills it up.

From all which it seems probably deducible, That 'tis a very hard thing, by. Mr Hobbs's way of managing the Con∣troversie, to prove that there can be no Vacuum, But as for the Cartesian's more subtile and plausible way of asserting a Plenum, it concerns me not here to Dispute against it, or De∣clare for it.

I will add this, and but this, on the occasion of Mr. Hobbs's Building a great part of his Philosophy upon no surer a ground, That we may hence learn how little Reason there is to blame me as he is pleas'd to do, for making elaborate Experiments; and that though (as I have elsewhere purposely and amply dis∣cours'd) obvious Experiments are by no means to be despis'd; yet 'tis not safe in all Cases to content ones self with such: Espe∣cially when there is Reason to suspect that the Phaenomenon they exhibit may proceed from more Causes than one, and to expect that a more Artificial Trial may determine which of them is the true.

Thirdly, whereas Mr. Hobbs is pleas'd to find much sault with the Society, and me, for not assigning the Case of Springs in general; that Omission seeming to him very unworthy of Philosophers: I answer, that the Society having hitherto, for weighty Reasons, forborn to determine the particular Causes of Things, there was no Reason they should alter their Method, for Experiments that were not made or published by Them or by their Order And as for me, the Title of my

Book promises some Experiments touching the Spring of the Air and its Effects, not Speculations of the Causes of Springs in general. My avow'd Intention was candidly to communi∣cate with the Curious some Experiments which I thought their Novelty would render acceptable to them, wherein I have the good luck not to have been mistaken; nor can I be justly censur'd for not performing what I did not undertake, nor was oblig'd to. And perhaps Mr. Hobbs would more prejudice the Commonwealth of Learning by his severity, than he has yet Advantag'd it by any other way, if he could obtain, that none should publish an Experiment or Observation that can∣not by deduction from the First and Catholick Principles of Philosophy assign the true Cause of it. But when I take upon me to write, as Mr. Hobbs has done, Elements of Philosophy, then perhaps I shall be able to give an Account of Springs, not much more unsatisfactory than others think his. For though he referre us to his Explication given of the Motion of Restitution in his Book De Corpore; yet in the 22 Chap∣ter and 30. Section, which professedly contains his Theory of it, after having premis'd, (what rightly interpreted may be true enough,) that the Cause of the Restitution proceeds not from the taking away the force by which they were com∣pressed or extended the (removing of Impediments not having the Efficacy of a Cause) that which follows to the end of the Se∣ction is onely this: The Cause therefore of their Restitution is some Motion either of the Parts of the Ambient, or of the Parts of the Body compress'd or extended. But the Parts of the Am∣bient have no endeavour which contributes to their Compression or Extention, nor to the setting them at Liberty or Restitution. It remains therefore, that from the time of their Compression or Extension, there be left some endeavour (or Motion) by which the Impediment being remov'd, every Part resumes its former place; that is to say, the Whole restores it self. Now this not∣withstanding, I am so dull, or so wary, that though I had met with this passage, and all the Praises the Author in his

Dialogue gives it, yet I should have made some scruple to undertake the assigning the true Cause of Springs in general. For first, the Learned Gassendus, and the Epicureans both Ancient and Modern, together with divers other Naturalists, do not admit what Mr. Hobbs supposes a few lines before, that That which is at rest cannot be mov'd but by a moved and con∣tiguous Movent. For they think Motion, or at least conatus ad motum, an unlooseable Property, congenit to Matter. And, by the way, whatever exceptions I have to this Opinion, yet I am not satisfied with that Principle of Mr. Hobbs, though it be the Fundamental one of his Philosophy; unless it be more warily propos'd. For to assert universally and without exception, as he does in his Elements, that nothing can be mo¦ved but by a Body contiguous and moved; I do not take to be true, nor consistent with his other Assumptions. This I elswhere (in a Discourse against another than Mr. Hobbs, about the Christian Religion) prove more at large: But now it will suffice to represent that Mr. Hobbs not onely admitting, but making use in his Philosophy of the Creation of the World, either he must allow that Motion is Natural to some, if not all Parts of Matter; or that God put them into a Motion not in∣cluded in their Nature. From which it will necessarily follow, that at least some Bodies may have Motion though it be not given them by any Body contiguous and moved, as an atten∣tive considerer m••y easily discern. But to return to the Cause of Springs. Secondly, whereas Mr. Hobbs assumes that the Parts of the Ambient have no endeavour which contributes to their Compression or Extention, nor to the setting of them at Liberty or Restitution: He says this indeed, But does not go about to prove it. And I should the less have made this precarious Assertion, because that after the celebrated Des Cartes himself, the Cartesian Philosophers generally as∣cribed the Motion of Restitution to the passage of a subtile Ethereal Substance (and an AEther Mr. Hobbs also admits) through the Pores of the Springy Body, which striving to

obtain its wonted Freedom of passage, restores them to the shape and bigness from which they were forced. Nay, I shall have occasion to shew anon that Mr. Hobbs himself, whatever he say in this place, does elsewhere ascribe a Motion of their own to multitudes of Terrestrial Corpuscles. And I might add, that elsewhere he speaks of the re-kindling of the Fire taken out of the Receiver after this manner.

Quanquam vis illius motus in Recipiente (ut loquimini) * 1.3 evacuato diminuta sit, oppressa ab Aëris intus commoti consisten∣tia, non tamen extinguitur; & propterealevata oppressione, satis habebit virium ad excitandum phantasiam lucis quanquan debili∣orem. But I shall rather subjoyn, That yet, Thirdly, I do not think it improbable what the Learned Gassendus had taught, and what Mr. Hobbs here teaches, that the Restitu∣tion of bent Springs may proceed from a certain Endeavour or Motion in their internal Parts (left from the time of their Compression or Extension) which when the Impediment is remov'd, makes every Part resume its former place, and there∣by makes the Whole restore it self. But this notwithstanding, I fear'd others might be as Inquisitive as my self, and might expect from him that would undertake to settle a general The∣ory of the Motion of Restitution, the clear and distinct Ex∣plication of several Phaenomena that I had met with, which are not touch'd, nor perhaps were, some of them, thought upon, by Mr. Hobbs. As first, why such a de••••rminate Temper of Iron and Steel is requisite to make it Elastical; so that if after having been hardned and gradually heated it be sudden∣ly cool'd at an inconvenient point of time, it will be brittle, and fit to make Gravers and other rigid Tools, not Springs. Next, why Bows and other Elastical Bodies, if they be kept too long bent, lose in process of time almost all their Elastical Power, and continue crooked. Thirdly why not onely divers solid Bodies as well as Lead and Gold, which before tryal, one would think as likely as many Springy ones to have their Parts put into a due Motion by the force that bends them,

should be devoid of an Elastical Power. Fourthly, what kind of Motion, and what kind of Texture it is, by virtue where∣of, the Parts of a Body being for a very short time put into Motion, do some Months, perhaps some Years, retain in great part a smart Motion, without in so long a time commu∣nicating it to the Ambient Bodies, to some or other of which multitudes of them are perpetually contiguous, and thereby losing it themselves. Why upon such a bare and inartificial change made in the Texture of a Body as is scarce at all dis∣cernable to the Eye, it should acquire a strong Spring that it had not before (as I have try'd upon Silver and Copper, which though flexible before they were hammer'd, yet being beaten into thin Plates obtain'd a notable Spring:) And why (which may seem more strange, upon another light change of Texture) the acquired Spring may presently be lost again; as I have try'd in Silver, that Chymists teach us loses nothing in the fire, which having by being hammer'd acquir'd a strong Spring, we have presently made flexible again as before, by only heating it red-hot, without so much as melting it; which argues that in Springs, Texture is as well to be considered as Motion. To these I might add other Particulars that I had either made or observ'd (and mention in another Treatise) concerning Springs; all which Phaenomena perhaps every one that has read what we have lately recited out of Mr. Hobbs, will not presently be able satisfactorily to explicate. So that I hope the equitable Reader will not think it a fault that (con∣tenting my self to propose the two Explications of Springs, I saw most lik'd among the Curious; to which I should have added Mr. Hobbs's, if I had found it as much esteemed) I de∣clin'd engaging my self in Controversies about the Origine of Motion, and such other high Speculations, as had my Abilities enabled me, neither my Design exacted, nor my leasure per∣mitted that I should prosecute. And though Mr. Hobbs be pleased to speak thus of his Notion concerning the Restitution of Bodies; Sine qua Hypothest quantuscunque labor, ars, sumptus,

ad rerum naturalium invisibiles causas invenien∣das adhibetur frustra erit: Yet whether that * 1.4 bold Assertion should passe for an Argument, for an Hyper∣bole, or for a Complement to himself, I am content to let the Reader judge.

Fourthly, Mr Hobbs in divers passages wherein he disputes against me, seems to have misapprehended my Notion of the Air. For when I say, that the Air has Gravity and an Elastical Power, or that the Air is, in great part, pump'd out of the Receiver, 'tis plain enough that I take the Air in the obvious Acception of the word, for part of the Atmosphere which we breath, and wherein we move. Nor do I find that any other of my Readers do otherwise understand me. But Mr. Hobbs seems to think he has sufficiently confuted me, if in some cases he have prov'd (which whether he have done well or no is not here to be examin'd) that there is a subtile substance, which he calls AEther (but which I wish he had better explain'd) in some places which I take not to be fill'd with Air; and that the AEther has or has not some Accidents which I deny or as∣cribe to the Air. Whereas I deny not but that the Atmosphere or fluid Body that surrounds the terraqueous Globe, may, besides the grosser and more solid Corpuscles wherewith it a∣bounds, consist of a thinner Matter, which for distinction sake I also now and then call Ethereal. And therefore though I did not think my self oblig'd to declare against either the Atomical or the Cartesian Hypothests touching the Nature of the Air, yet I propos'd the later too as probable (which as it excludes a Vacuum, so it makes the Air consist in great part of a Celestial Matter.) And my incidental Explications of the Rarefaction and Condensation of the Air, together with my comparing it to a Fleece of Wooll, sufficiently declare that I take it not to be a Homogeneous Body; and though there be Air intercepted betwixt the Hairs of Wooll, yet in case I should prove that a Box were not so full of Wooll as before, because the most part of the Hairs had been taken out, I should

not think he argued well against me, that should onely prove that the Box contain'd as much of Matter, consisting of Air and Wooll together, afterwards as before. Nor do I think Mr. Hobbs has in divers passages, wherein he supposes he dis∣putes against me, much more directly contradicted what I teach concerning the Air, if that word be rightly and in my sense understood. And on this occasion I must crave leave to add, that whereas he is pleas'd to intimate that I misrepresent the Cartestan Hypothests, ascribing that to the Air which Des Car∣tes does to Water; If the Reader think it worth while to compare the Summary Account I give of that Hypothests, with what Des Cartes himself has taught in his 45, 46, & 47. Articles of the fourth Part of his Principles, wherein that Author com∣prises his Doctrine of the Nature of the Air, he will quickly find, that whether or on Mr. Hobbs be mistaken, I am not unless it be in estimating his Hypothests by what he teaches in his Principles, which were published after his Meteors, and more elaborately written. And as for that particular, which alone Mr. Hobbs alledges, namely, that he makes not the Parts of Air but of Water so flexible: Des Cartes's Words in the 46. Article are these; Cum ejus Particulae ferè omnes sint flexiles in star mollium plumularum veltenuium funiculorum, &c. And as for what Mr. Hobbs subjoyns, Sed quisquis talis sup∣position is Author fuit, parum refert. Nam ipsa Hypothesis, in qua motus supponitur materiae subtilis sine causa velocissimus, & praeterea Corpusculorum innumer abiles vertigines diversae ab illius Materiae unico motu generatae, vix sani hominis est. I cannot but in Gratitude to such a Personage declare my dislike, to find him upon so slight an Occasion so coursly us'd for an Opini∣on the Censurer of it does no better confute, and Which is thought to be in some particulars not so unlike his own. And perhaps I should be afear'd that Mr. Hobbs's speaking so severely of one that was at least a famous Geometrician, might reflect upon the English Civility in the opinion of Strangers, if I did not hope that those who have read Doctor Ward's

Exercitation will look upon this censure of the Cartesian Doctrine by Mr. Hobbs, as provoked by that severe Judgment of Des Cartes mentioned by the Doctor in these words; Nempe hoc est quod alicubi admiratus est * 1.5 magnus Cartesius; nusquam eum, sive verum, sive falsum posuerit, rectè aliquid ex suppositionibus, ra∣tiocinando inferre.

CHAP. III. Wherein the Weight and Spring of the Air are asserted against Mr. Hobbs.

HAving thus dispatch'd those general Considerations I thought expedient to premise, my proposed Method leads me in the next place to consider that Mr. Hobbs does not, that I remember, deny the truth of any of the matters of fact I have deliver'd. Nor does he, if my memory fail me not, labor to prove that the Explications I have given of my Experiments, are not agreeable to the Doctrine I propos'd: But rather thinks fit to reject our two grand Hypotheses them∣selves, The Weight, and the Spring of the Air. And there∣fore it will suffice us in this Chapter briefly, but not slightly, to prove what he is unwilling to grant.

And first, that the Air (in the sense wherein we take the word) is not devoid of Weight, we have prov'd by divers Experiments: which having more fully deliver'd in the Book it self, it may in this place suffice now to name them.

One then of these Experiments that prove the Air's Gra∣vity, is, that we found a blown Bladder carefully weighed in an exact pair of Scales, manifestly heavier when full of Air, than when the Air was let out.

Next it has been observ'd in our 36. Experiment, that an AEolipile, being well heated, and the little hole left at the top of the Pipe being stopt, when it was thus hot; upon the opening of that hole, when the AEolipile was grown cold again, the external Air rushing in with a wistling noise at

the foremention'd Orifice, made the AEolipile weigh so much more than it did just before the external Air got in, that it a∣mounted, by computation, to near a thousandth part of the Weight of an equal bulk of Water. And though some difficulty may perhaps be mov'd touching the accurateness of the proportion this way found out, betwixt the gravities of those Bodies; yet that the one as well as the other is actually heavy (which is all that we here need contend for) the Experiment sufficiently manifests.

Thirdly, in the Magdeburgick Experiment, (mention'd at the beginning of our Epistle) the ingenious makers of it found, that, having before weighed the great Receiver they were to exhaust, and having done the like after the extracti∣on of the Air, they found it to weigh one whole * 1.6 Ounce and 3/10; quod sane (saies the learned Publisher, though a Peripatetick) luculentissimum est argu∣mentum gravitatis aëris.

Fourthly, in our 36. Experiment we relate our having weighed the Air, and that shut up in Bodies in our exhausted Receiver, wherein of two Bodies of differing Natures (the one a blown Bladder, and the other a Glass Bubble) that were aequiponderant each to a more solid Weight before the Air was pumpt out, that which included a good quantity of Air did manifestly preponderate after the exhaustion.

And to these four we might adde other proofs to the same purpose; But that these contain in them such a variety of Cases, that I think it would be superfluous.

But now let us see what Mr. Hobbs objects against the newly∣mention'd Experiment of the Bladder weighed in the exhausted Receiver, (for the others he quarrels not with,) Quod quidem lanx (saith he) in qua est vesica, magis deprimi∣tur * 1.7 quam altera, certi esse possunt, oculis testibus: Quod autem id à gravitate aëris naturali accidit, certi esse non possunt; prae∣sertim si quae sit gravitatis causa efficiens nesciunt. But I know not whom Mr. Hobbs will perswade, that a man cannot be

sure that Lead is in Specie heavier than Cork, unless he knows what is the efficient cause of Gravity. And Mr. Hobbs speaks in his 30. Chapter (where he expresly treats of that Subject) as if that had not been explain'd by any man, and consequent∣ly not by any Writer of Staticks: (and perhaps I am therein somewhat of his mind) And yet sure all these Writers, treat∣ing of the Proportion of Heavy Bodies, did not write they knew not what. And, though he mentions his own Hypo∣thesis, as that than which nothing is more likely; yet I think I could frame Objections against it, that would not easily be answer'd, if my present task requir'd it; or if I found his opinion, in this point, embrac'd, as yet, by men of Note. Wherefore I shall now say no more of it than he himself doth namely, that according to his Doctrine, It may well be thought to determine (for it is a certain consequent) that heavy Bodies descend with less and less velocity, as they are * 1.8 more and more remote from the AEquator; and that at the Poles themselves they will either not descend at all, or not descend by the Axis: which whether it be true or false, Experience must determine. Which till it have done in his favour (an event I do not expect) I hope he will allow me to distrust his Hypothesis.

But to return to our Experiment. The Account he gives why the Bladder does propend (for so he loves to speak) is this, Quod vesica sive follibus sive flatu oris * 1.9 distenta sit, gravior sit quam eadem vesica non distenta, negare¦nolo, propter majorem quantitatem Atomorum follibus, vel Corpusculorum fuligineorum ab halitu inflatorum. Ab experi∣mento autem quod fit à vesica inflata nihil colligunt quod sit satis certum. Oportuit lancibus imponere duo vasa pondere aequa∣lia, quorum alterum esset accuratè clausum, alterum apertum: Sic enim non inflatus sed inclusus tantum aër ponderatus esset. Quando igitur aërem sic ponderatum videbis, meditabimur postea quid dicendum sit de Phaenomeno quod retuleris. But, as to the First part of this passage, it does not deny the gravity of what we call the Air; but onely endeavours

to shew what Parts they are that make it heavy. And as to the Second, he seems to mistake the present Case. For, there is no need that the Air in the Bladder be, before the exhausti∣on of the Receiver, (in which the foregoing (fifteenth) Page declares he Supposes the Experiment to be made) heavier than the outward Air. Wherefore when he subjoyns that from this Experiment we collect nothing quod sit satis certum, the Af∣firmation is not an Inference, but Precarious. And as for the annexed way whereby he would wish to have an Experiment made fit to infer the gravity of the Air, if he had not. over-look'd what I have delivered in the beginning of the 36. Ex∣periment, he would easily have perceiv'd that we did make a Trial much of the same nature with that he desires. For we weighed in our Receiver the Air, in a Glass Hermetically sealed; wherein it was not (to use his Expression) inflated, but onely included. This is what he here objects against the gravity of the Air in the other place (Pag. 8. & 9.) where he saies something to this Controversie; he inculcates also that we should first explicate what is Gravity, and then adds, Quod Atmosphaerae insunt permistae corpori AEthereo multae tum aquae tum etiam terrae particulae, facile persuadeor; * 1.10 sed quod in medio AEthere, sursum, deorsum, quaquaversum motae, nec semper alterae alteris innitentes gravitent, inconcep∣tibile est. To which he adds two or three Reflexions, whose Examen being here unnecessary, would require more time than perhaps it would (in reference to the present Controversie) deserve: for we are now enquiring not how the Air comes to gravitate, but whether or no it have gravity. And since in his Elements of Philosophy he grants, and gives * 1.11 his Reason for it, That if Air be blown into a hollow Cylinder, or into a Bladder, it will increase the Weight of either of them a little: and since here he likewise confesses (as we have just now seen) that there are mingled with the AEther many aqueous and earthly (and consequently heavy) Particles: he confesses that which we labor to evince; namely, that the

Air is not devoid of Weight. And it concerns us no more than himself, to shew how the Corpuscles, upon whose account the Air is heavy, make it so. And this being what Mr. Hobbs in several places thinks fit to object against the Gravity of the Air; the Reader will, I suppose, easily take notice that he has left the Experiment of the AEolipile, and some others, unanswered. Though these alone prove that the Air is a mani∣fest Weight even when it is not comprest, but retains its laxity. Having said thus much to evince against Mr. Hobbs the Gravity of the Air, let us now examine whether it have not also a Spring (in the sense we take that word in.) This though Mr. Hobbs be pleas'd * 1.12 to call (as he also does the weight of the Air) a Dream; yet he does himself grant, in effect, as much as is requisite to prove the Spring of the Air, in the sense I contend for it. For taking upon him to give account (how good an one we shall see anon) of that known Experiment wherein the Air is comprest in a Glass Bottle by the forcible injection of Water, which Water, when the Glass is unstop't, the Air does again throw out in recovering its former Dimensions; of this Ex∣periment (I say) he gives this account (Pag. 24.) Aër quo ab initio Sphaera plenus erat à Corpusculis illis terreis motus motu circulari simplice, vi injectionis coactus, qui quidem purus est exit (aquam injectam penetrans) in aërem extrinsecum, locum relinquens aquae; sequitur ergo Corpusculis illis terreis minus relinqui loci in quo motum suum naturalen exercere possint: ita∣que in se mutuo impingentes aquam urgent ad egressum; egredi∣entem aër externus (quia universum supponitur esse plenum) penetrat, locumque egredientis aëris successivè occupat, donec Corpuscula, quantitate aëris eadem restituta, libertatem motui suo naturalem recipiant.

But how little this comes short of granting as much Spring to the Air as the Cartesians do, and as I need require, may easily be judg'd by divers passages in our Book; and parti∣cularly

by our proposing as not improbable, the Cartesian way of explicating the Spring of the Air; according to which the Corpuscles that swim in the AEther, being each hindred by the neighbouring ones from the freedom of its motion, they beat off one another (which Mr. Hobbs would have them do:) whence it comes to pass that, in any assign'd portion of Air here below, the Corpuscles that compose that portion, beaten off by one another, do make the whole portion tend to ob∣tain (though not exactly to fill up) more room, and conse∣quently to emulate a Spring, like that which we scruple not to ascribe to a comprest Fleece of Wooll, because of a like endeavour to expand it self.

We may enforce this by another passage of Mr. Hobbs's, that speaks expresly enough to our present purpose, where he gives this Reason of one of the Phaenomena of our Engine, Quoniam per suctoris retractionem aër purus impulsus * 1.13 erat, partes autem terreae impulsae non erant; major erat ratio particularum terrearum quae extra Cylindrum suctori contiguae erant, ad aërem purum, in quo motum suum exercebant, post revulsionem * 1.14 quam ante: quare particulae illae motae minus habentes loci ad motum suum naturalem exercendum, aliae aliis im∣pingebant, & propellebant: necesse ergo erat, ut particulae quae suctoris superficiei contiguae erant suctorem propellerent. To which we may adde, that Mr. Hobbs himself seems rather to reject other mens wayes of proposing the Spring of the Air, than resolutely to deny the thing it self. For, Vidisti (sayes he) jam Elastrum illud aëris quod supponunt, aut impossibile esse, aut recurren∣dum esse ad Hypothesin Hobbianam. * 1.15

But besides Mr. Hobbs's Concessions in the passages newly recited, and some others; we can prove the Spring of the Air

by many of the Phaenomena of our Engine, which we have deduc'd from it, and of which he does not offer any other way of Explication. Wherefore we shall now content our selves to prove the Spring of the Air by two Experiments: The one not mention'd in our Epistle, and the other much oppos'd by Mr. Hobbs.

And first, if you make the Torrecellian Experiment in a Tube of between two foot and half and three foot in length, and if, when the Mercury rests at its wonted Station, you dexterously stop the Orifice of the Tube with your Finger (that Orifice being lifted up as near the surface of the restag∣nant Mercury as it can be, without giving admission to the external Air) and if then you quite lift up the Tube thus stopt into the free Air you shall feel upon your Finger little or no gravitation or pressure from the Weight of the Mercurial Cylinder, distinct from the Weight of the Tube: because (as we have more fully explicated this Phae∣nomenon elsewhere) the gravity of the Quicksilver * 1.16 is balanc'd by that of the outward Air that thrusts the Finger against it. But if you invert the Tube, and having let in the Air at the Orifice, stop it again with your Finger, and again let the Mercurial Cylinder lean upon that Finger; you shall then find your Finger strongly prest, and endeavour'd to be thrust away: which new pressure, since it cannot come from the Mercury, that being the very same that was in the Tubebefore, nor from the Weight of the admitted Air, which perhaps may not amount to so much as a grain, to what can we rationally ascribe it but to the Spring of the included Air, whose force will be as well manifest to the Eye as the Finger, if the Tube be unstopt under the surface of the restagnant Mercury; for then that in the Glass will not rest as before at the usual Station, but be deprest beneath it a good way, perhaps some Inches? And if you make the Torrecellian Ex∣periment in a short Tube seal'd at neither end, but stopt a∣bove and below with your Fingers, you shall find, upon the

unstopping of the upper Orifice a new and forcible pressure upon the Finger that keeps the lower Orifice stopt, made by the gravitation of the external Air, which was before kept off from leaning upon the Mercurial Cylinder by the upper Finger; the Pulp of which Finger by that gravitating Air was before thrust into the deserted Cavity of the Tube (as we have elsewhere discourst, in a fuller measure, of these Ex∣periments.) Which will evince against Mr. Hobbs, both the Spring of the Air and Gravity of the Atmosphere; since he is as little as I for ascribing these Phaenomena to the efficacy or absence of my other Antagonist's imaginary Funiculus.

The other Experiment I shall mention is the Fourth in our Epistle; namely, that of the swelling and shrinking of a Blad∣der hung in our Receiver, according as the ambient Air, and consequently its pressure, is withdrawn or suffer'd to return. But though this Experiment be so congruous to our Hypo∣thesis, that 'tis generally acquiesc'd in by those Ingenious men that have hitherto seen it; yet Mr. Hobbs is pleas'd to reject our Explication, and substitute another in these Words, which are all he has concerning this matter. Quia Cuticula omnis ex filiculis constat, quae propter figuras, contact∣um * 1.17 per omnia punct a accuratum habere non possunt, pervia ergo est vesica, cum sit cuticula, nec aëri tantum, sed etiam aquae, qualis est sudor. Eadem ergo aëris per vim incussi est compressio intra vesicam quae extra, cujus conatus, propter viam motuum undiqua{que} decussatam, tendit undiquaque ad superficiem vesicae concavam. Quare necessarium est ut undiqua{que} intumescat, & crescente conatûs vehementiâ tandem laceretur. But, if this be a sufficient Answer to such an Experiment, I confess I fear it will be harder than we are yet aware of to prove any thing by Experiments.

For first, how unlike is it to be true what he affirms, and what his Reply supposes, namely, that such Bladders as we us'd are readily pervious to the Air; when easie Experience shewes us, that by leasurely compressing such blown bladders

betwixt our hands, we shall rather break them (as we have try'd) than squeeze out the Air at the Pores? So that the rest of his Answer being built upon what is so repugnant to com∣mon Experience, will not need a particular Consutation: but however ex abundanti we will adde, that in our 36. Experi∣ment, we relate that by the exhaustion of the Air we likewise broke a Glass Hermetically seal'd; and to say that Glass also is pervious to Air, were to affirm what the greatest part of his Book supposes to be false. Besides, whereas there is not any sensible and unquestionable Phaenomenon to prove that the Receiver is full of any such aër per vim incussus as he would have, we see plainly that when the Air does manifest∣ly get into the Receiver, the Bladder is not thereby made to swell, but strangely to shrink. Moreover since (according to Mr. Hobbs) the Bladder is pervious to the Air, and the Air within the Receiver is universally comprest, as well that which is within the Bladder as that which is without it; how comes it to pass, that the Air that bears against the Convex Surface of the Bladder does not resist that which is contiguous to the Concave Superficies of the same; And at least how comes the Bladder to be broken by the Air, which, accord∣ing to Mr. Hobbs, can get in and out at pleasure? And lastly, to shew that to the swelling of the Bladder there needs noth∣ing but the Spring of the included Air, and not such vehem∣ent agitation of the ambient Air as Mr. Hobbs supposes to be made in our Engine; It appears by the elsewhere-mention'd Experiment of Monsieur Paschal, that in the free and ordinary Air a Foot-ball half blown up will swell more and more the nearer it is carried to the top of an high Mountain; where the incumbent Cylinder of the Atmosphere is shorter, and its Weight lighter: and will, for the contrary Reason, grow more and more flag'd, the nearer it approaches again to the foot of the Mountain.

Though I doubt not but the Arguments employ'd in this Chapter will be sufficient to convince impartial Readers; yet

I shall adde by way of Inforcement, that whereas Mr. Hobbs ascribes the Weight of the Air in Bladders to the earthy Cor∣puscles intruded by him that blows them up; and attributes the Spring of the Air in the Wind gun and in the Phaenomena of our Engine, to the violent Motion the Air is put into by the vehement impulses of the Rammer or Sucker: our Doctrine may be evinc'd by Experiment, wherein the Air in its natural and wonted state operates without being forcibly comprest or put into motion by us. This may appear by the two sorts of Experiments to be made upon high Mountains, which we have mention'd and urg'd in the Second Part of our Defence against the Learned Linus. Wherefore referring the Reader thither, we shall now onely in very few words mention the substance of them.

The First Experiment is, That it has been found upon Tryal, both formerly in France and since in England, that the Quick∣silver in the Torricellian Experiment falls notably lower at the top of a Mountain than at the foot, (by Monsieur Pas∣chal's observation upon a Hill (far higher than those the Experi∣ment was try'd on here) the difference was so great, as to amount, as the most ingenious Pecquet, a happy promoter of Experi∣mental Learning, informs us, to above three Inches) which we say is caused by this, that the Atmospherical Cylinder is much lighter, as well as shorter, at the top of the Mountain than at the bottom: and Mr Hobbs disallows not the Experiment, but yet gives onely this account of it, Sed & particulae illae quae interspersae aëri it a moventur ut supposuimus, * 1.18 magis confertae sunt ad radicem montis quàm in summo, nam hoc quo{que} supposuimus. But what then? how does the plenty of these interspers'd Particles hinder the Mercurial Cylinder from descending at the bottom of the Hill as much as at the top, un∣less by their gravity or pressure? And 'tis very unlikely that the Earthy Atomes, contiguous to the restagnant Mercury at the bottom of the Hill, should be able by their weight to keep suspended a Cylinder of Mercury of above three Inches,

unless the contiguous Air were gravitated upon by the weight of other incumbent parts of the Atmosphere.

The other of the two mentioned Experiments is briefly this, That a Termoscope being carried from the bottom to the top of a Hill, the included Air, instead of shrinking in that colder Region, manifestly dilated it self, and notably de∣press'd the water. An effect which I see not to what it can well be attributed but to the spring of the included Air, which having not near so great a pressure against it from the Atmo∣sphere incumbent on the restagnant and suspended water, was able to make it self more room than before it could; and since that pressure of the Atmosphere depends for ought ap∣pears upon its gravity, the same Experiment may argue both the spring of the Air and its weight.

And this may suffice for our third Chapter, wherein hav∣ing evinc'd against Mr. Hobbs our grand Hypothesis of the weight and Spring of the Air, I hope we have dispatched the chief part of our work; since as for the particular Explicati∣ons we deduce from these Hypotheses, there are but very few, if any, that he endeavours to prove incongruous to them. Yet after we shall have (in the following Chapter) consider'd upon what grounds he prefers his Doctrine before ours, we shall (God permitting) in two or three other Chapters gather up the things that he objects against some particular Opinions and Explications by us delivered, and examine them.

CHAP. IV. Wherein Mr. Hobbs's principal Explications of the Phaeno∣mena of the Authors Engine are Examined.

OF the Hypotheses that Mr. Hobbs assumes to explicate the Phaenomena of our Engine, himself gives us a summary in this passage, (pag. 10.) intellêxtiergo Hypotheses meas, 1. Quod aëri interspersae sunt particulae multae terreae praeditae motu circulari simplice, naturae congenito. 2. Quod major est quantitas earum par∣ticularum in aëre propè adterram quàm in aëre à terra remotiore.

Now here I might at the beginning take notice, that there are other things which he takes for granted. As, first, Non dari Vacuum, which as we have already seen he has not well evinced, nor I think easily will upon the grounds he proceeds on. Next, that our common Air is chiefly composed of an AEthereal substance, which methinks he should have proved; since for the most part the Vacuists (and such he will needs have his Adversaries to be) admit not that pure Air of his. Thirdly, that the Air, at least the pure Air, is easily divisible into parts always fluid and always Air. Indeed he sayes of this Assumption, * 1.19 Nec suppono tantùm, sed credo; but neither to suppose nor to believe, is to prove. And what he adds, † 1.20 Ne{que} est qui hactenus ullam ad∣duxit rationem, quare ita esse non potest; if it were true, would conclude little, since many things have not been, and perhaps cannot be, proved to be true; of whose not being possible no proof has been given. We might, I say, mention and examine these other Assumptions of our Author, but for bre∣vities sake we will consider those two lately recited from him.

And as for the second of them, bateing the peculiar motion he is pleas'd to ascribe to the earthy Particles, I shall not con∣tend with him about that Hypothesis; and therefore shall now onely consider the other. The Motus circularis simplex it self, which he imagines in the Sun and the terrestrial Globe, I shall not need to examine, since Dr. Ward (a person whom, wthout disparagement to a famous man, I may affirm to be ati least as esteemed for Astronomy as Mr. Hobbs) has expresly endeavoured to confute it, and that not without some derision, (which yet I willingly forbear to imitate) by Arguments that I cannot learn Mr. Hobbs has yet answered. And I am in∣formed that the learned Dr. Wallis, and others intend, some Animadversions on this Motion. But restraining our present consideration to what this Dialogue suggests to me, This Assumption to me seems very precarious, since I know not any unquestionable Example or Experiment whereby it can

be made out, that any small parcel of matter has such a motus circularis simplex as he ascribes to each of these innumerable earthy and (as himself adds in the same page) aqueous Par∣ticles. The onely Argument he brings in that page to prove that each Atome would have this motion, if all the rest of the earth were annihilated, does not to me seem clear. For, not to mention that it is still by many learned men doub∣ted whether the Terrestrial Globe it self have it; nor to ex∣amine whether or no he assigns a good Natural cause of it; it is not always true, that each minute part of a Homogene∣ous body (which yet 'twill be hard to prove the Terrestrial Globe to be) has in every respect the same qualities with the whole; As the roundness which a small drop of Water or Quicksilver is commonly observed to have when it leans upon a dry or greasie plain, is not to be met with in great portions of either of those Liquors, though placed upon the same plain. And Mr. Hobbs as well as we makes the terrene Atoms in the Air to have gravity, which yet is a quality that does not properly belong to the whole Globe of the Earth; nor is it manifest why, because the Terrestrial Globe moves in a vast Circle about the Sun, each particular Atom of it must describe a small Circle in the Air about I know not what Cen∣tre. And since he teaches in his second Hypothesis, and a few lines before it, That the Air, near the Earth abounds with such Terrene Corpuscles, 'tis not likely they should be per∣mitted to exercise such a regular motion as he attributes to them; but hitting against one another, they must in pro∣bability be put into almost as various and confused a motion as Des Cartes ascribes to his Terrestrial Particles swimming in the Atmosphere. That which some will, I doubt not, pe∣culiarly wonder at in Mr. Hobbs's Hypothesis is, that he makes this regular motion of each Atom naturae suae congenitus: For Philosophers that are known to wish very well to Reli∣gion, and to have done it good service, have been very shie of having recourse, as he has, to Creation, for the explain∣ing

of particular Phaenomena. And the Cartesians will think it at least as allowable for them to suppose the Motion he will not grant in their Materia subtilis, as for Mr. Hobbs to assume it in his Particulae terreae: especially since he seems to make each such Atom put into and kept in a regular motion; whereas they assume but the having of one general impulse given to the whole mass of Matter. Those likewise that fancie a Spring properly so called in particular Aerial Cor∣puscles, will hence perhaps take occasion to think they may suppose an ingenite motion fit for their turn, as well as he an ingenite motus circularis simplex. How well like wise this Hypothesis will agree with his Fundamental Doctrine, That Nihil movetur nisi à corpore contiguo & moto, I leave to him to consider. As also whether or no Gassendus, and those other Atomists that admit Creation, may not hence counte∣nance their grand supposition of the congenite motion of A∣toms, which granted would destroy the best part of Mr. Hobbs's Philosophy. But whatever becomes of this motus circularis simplex, I need not be much solicitous, having formerly shewn, that the admission of it would not disprove what I have delivered concerning the Spring of the Air: and therefore leaving Mr. Hobbs to dispute it out, if he think fit, with his other Adversaries, I will proceed to the main Ex∣plications, wherein Mr. Hobbs endeavours to prefer his Doctrine about the Phaenomena of our Engine before ours. And these I find to be the four that ensue.

The first and principal of these is that wherein he strives to prove, That by the Exhaustion of our Cylinder no Vacuum is produced, and to give of the Experiment it self a very dif∣fering account from ours. This he does in the following passage; which, by reason of its importance in our present Controversie, we shall set down verbatim: Dum Suctor (sayes he) retrahitur, quanto relict us locus major fit, tanto minus loci relinquitur aëri externo, qui re∣trusus * 1.21 à Suctore moto versus externa, proximum sibi aërem si∣militer

movet, & hic alium, & sic continuè, ita ut necesse sit aërem tandem compelli in locum desertum à Suctore, & intrare inter superficiem Suctoris convexam & Cylindri concavam: supposito enim aëris partes esse infinitè subtiles, impossibile est ut viâ illâ qua retrahitur Suctor, illae non se insinuent. Primò enim, contactus superficierum istarum per omnia puncta perfec∣tus esse non potest, quia ipsae superficies fieri infinitè laeves non¦possunt. Deinde vis illa quae ad Suctorem revellendum adhibe∣tur, cavitatem Cylindri aliquantulum distendit. Postremo, si in confinio duarum dictarum superficierum ingrediatur una tan∣tum atomus dura, aër purus eâ viâ ingreditur conatu quan∣tumvis debili. . Poteram etiam computasse aërem illum qui prop∣ter eandem causam insinuasset se per Cylindri valvulam. Subla∣tam ergo vides consequentiam à retractione Suctoris ad locum vacuum. Sequuturum hoc quo{que} est, aëremillum qui est in locum à Suctore desertum impulsus, quia magnâ vi impulsus est, motu valde celeri & per circuitum inter summum & imum in Cylin∣dro moveri; cum nondum sit quod motum ejus possit debilitare: Scis autem nihil esse quod sibi motum aut impertiri possit aut di∣minuere. But this Ratiocination containeth divers things ly∣able to exceptions; and in order to the examining of it I must premise, That I know not why Mr. Hobbs should here con∣fine his discourse to the Pump without taking notice of the Glass, for whose evacuation 'twas designed. Wherefore for easier considerations sake we will consider, how this dis∣course will account for the Exhaustion of the Receiver, as well as for the Cylinder; for we usually empty them both in the same tryals. And he being obliged to explicate the Ex∣haustion of the one as well as the other, it will be conveni∣ent to take into consideration the Receiver also, because that being of Glass and transparent, we can better see what happens in it than in the opacous Cylinder. This premised, we may now proceed to the Exceptions themselves. And, first, I do not clearly see by this Explication how he avoids a Vacuum: For, according to his first words, the external

Air is displac'd by the motion of the Sucker outward, and this displac'd Air must move that which is next to it, and that the next, and so onward, (whether in infinitum or no he declares not;) so that at length (tandem) the Air must be compell'd into the place deserted by the Sucker: so that till this returning Air get in betwixt the Sucker and the Cylinder, how appears it from this Discourse, that the deserted space was not empty for some little while? For, certainly, all these motions of the Air forward and backward could not be per∣form'd in an instant; as may appear by the motion of Sounds and Echo's, whose Velocity is reducible to measure. Second∣ly, though he takes his Adversaries to be Vacuists, yet (to give an account of these Phaenomena) he supposes the Pleni∣tude of the World; as may appear both by express passages in his Dialogue, and by his here rendring no other probable cause of the Airs getting into the room relinquish'd by the Sucker. But, because I have not here taken upon me the person of a Vacuist, I shall offer some other Considerations. I wish then, thirdly, that Mr. Hobbs had declared from whence the regress of the Airs impulsion should begin; for that may well be required from one that, making the World full, and for ought appears (the Celestial Globes excepted) fluid, al∣lows us to believe it infinite, if the Magistrate shall please to enjoyn us that belief. Fourthly, I demand what necessity there is there should be such a forcible return of the impulse, as is requisite to thrust in the Air at so narrow a passage as that between the Sucker and Cylinder. For, why may not that impulse when diffused in the vast ambient Medium, be so communicated and blended among the differing motions of the other parts of it, as not to return again from whence it begun? As we see that a Voice, though strong, will not move the Air beyond a certain distance smartly enough to be reflected in an Echo to the Speaker: and a stone cast into a Lake will have the Waves it makes diverted from returning to the place they began at. Fifthly, I do not likewise see

that 'tis prov'd, or probable, what Mr. Hobbs affirms of so thick a Cylinder as ours, that it should be distended by the depressing of the Sucker. But this I insist not on; for the main thing that is peculiar in Mr. Hobbs's Explication is, That as much Air as is driven away by the Sucker, gets presently in again betwixt it and the Cylinder: wherefore let us ex∣amine that a little. I say then, that by the Air which is so supposed to get in, he either means, in the usual sense and in ours, the Common Air, such as we live and breathe in; or he does not.

If he do speak of such Air, I can plainly prove by several Experiments, that our Engine is in great part devoid of it.

For, first, if there be a contrivance made, whereby the whole Pump may be covered with Water, one may, as we have tryed, plainly see the Air that is drawn out of the Re∣ceiver, at each reciprocation of the Sucker, pass in great bub∣bles out of the Valve through the water.

Next, it appears by the Magdeburg Experiment formerly mentioned, that by reason of the recess of the Air, the Globe of Glass, whence it went out, was diminish'd in weight a∣bove an Ounce. Thirdly the same truth may be proved by the Experiments formerly mentioned of the swelling of a Bladder, and the breaking of an Hermetically-seal'd Glass upon the recess of the ambient Air: these Experiments having been already vindicated from Mr. Hobbs's very improbable Expli∣cations of them. Fourthly, the same may be prov'd by the breaking of weak or ill-figur'd Receivers inwards; of which in our Hypothesis the reason is clear, but not in Mr Hobbs's. But, fifthly, (not to multiply Instances, though that were easie for me) what I contend for may be sufficiently prov∣ed by this one Phaenomenon, That though, if the Receiver being full of common Air the Key be turned under water, the water will not at all be spurted up at the open Orifice: yet the like being done after the Exhaustion of the Receiver, we have had divers Gallons of water violently impell'd into

the cavity of the Glass; which could not happen if it were full of Air, both in regard there can be no probable cause assigned why the water should be thus spurted up; and be∣cause the Receiver being already full of Air, either two bo∣dies must be contained in one place, and so we must allow Penetration of Dimensions; or else common Air, to which Glass is impervious, must pass through the water, which we conclude it does not, because no such bubbles are made in the external water as would appear if common Air past through it: Nay, so little of this common Air was sometimes left in the Globe us'd at Magdeburg, that when the water was suffered to rush in, it reduced the Air into less by the beholders estimate than the thousandth part of the capacity of the Globe: And even if our Receiver be unstopt, not under water, but in the open Air, the ambient Air will vio∣lently press in with a noise great and lasting enough to argue that the Glass was far from being full of such Air before.

And thus we may argue against Mr. Hobbs, if he would have the Engine, when we call it exhausted, fill'd with common Air, as his words in the recited passage (where he talks of the external Air, and that impell'd into the Cylinder, with∣out differencing them) seem to intimate. But because by some other passages of this Dialogue he may be favourably thought to mean, that the pure Air (as he speaks) is that which gets in by the sides of the Sucker into the Pump, and so into the Receiver; let us consider his Explication in this sense also. And not to urge, that it had not been amiss if, to a∣void ambiguity, he had more clearly exprest himself, and named that Other here, as well as he elsewhere calls it so: not to urge this, I say, I desire it may be taken notice of that if Mr. Hobbs take the Air in this Second Notion, he op∣poses not what I have delivered; the Air I pretend to be pumpt out of the Receiver being the common Air, which consists in great part of grosser Corpuscles than the AEthereal substance; and therefore I might safely pass on to another

subject. But I consider further, that even this explication of Mr. Hobbs's will be lyable to the two first Inconveniences lately objected against the other in favour of the Vacuists; and to divers of those things besides, that are objected in the following parts of that Discourse. Next I observe again, that though the Pump be all the while kept under water, yet the Exhaustion of the Cylinder and Receiver will be made as well as in the open Air: I demand then of Mr. Hobbs, how the pure Air gets in by the sides of the Sucker that is immers'd in water? I presume that for want of a more plausible Answer he will here say, (as he elsewhere does in an almost parallel case) That the Air passes through the body of the water to fill up that de∣serted space, that must otherwise be void: But then I appeal to any rational man, whether I am obliged to believe so un∣likely a thing upon Mr. Hobbs's bare affirmation. If I be, I must almost despair to prove things by Experiments; and if he will allow me to expect from him as much as he seems to do from me, I shall scarce despair to maintain almost any Hypothesis I please: For, besides that he does not so much as pretend by any Phaenomenon to countenance this bold as∣sertion, there are Phaenomena that make against it. For I know not how many Experiments shew us, that when Air passes through Water, it makes bubbles there, which in our case do not appear. And besides, I see not why the out∣ward Air should not rather impell the water (as we see it frequently does in such cases) than be supposed to dive so strangely and unperceivedly through it. When also the dili∣gently-exhausted Receiver is unstopt under water, he that observes how the water rushes in with a stream as big as the passage will give leave, will hardly imagine that at the self-same time as much Air as there gets in water can pass through the same hole without being perceiv'd. But it may by Plenists be said in Mr. Hobbs's behalf, and it seems the most that can be said, that either his Explication or a Vacuum must be admitted. To which I reply, First, that he

has not evinc'd there can be no Vacuum; having endeavour∣ed to prove it but by a single Experiment, which at best does not more strongly plead against a Vacuum than this does for it. Next that we have lately made it probable, that by his Ex∣plication he does not avoid the necessity of a Vacuum. And thirdly, that a Plenist without having recourse to Mr. Hobbs's precarious diving of the Air, may more probably decline the necessity of yielding a Vacuum by saying, according to the Principles of the Cartesians, (the subtilest and wariest Cham∣pions for a Plenum I have yet met with) that the AEther is by the impulse of the depressed Sucker and the resistance of the ambient Bodies squeez'd in at the pores of the Glass or Cylinder into the cavity of the vessel, as fast as room is there made for it. And I confess, I somewhat wonder at Mr. Hobbs's being averse to this way of salving the objected Dif∣ficultie, since (a little above the middle of that passage of his we have so long been examining) he supposes the parts of the Air to be infinitely subtile; which if they are, I know not what pores can be too narrow for them to insinuate them∣selves into. But, to press this no further, I must here take notice, that whether the cavity of the Receiver be resolved to be (totally or in part) empty or full of Mr. Hobbs's AE∣therial Body, or the Cartesians Celestial matter; the violent rushing in of the water, when the vessel is unstopt under that Liquor, and divers other Phaenomena which will not be ascri∣b'd to the subtile matter within (to which they attribute not any attraction) sufficiently argue that there is in the Exter∣nal Air a far greater power of pressing inwards, than there is within of resisting; and consequently such a Weight or Spring in that Air as my Epistle challenges to it. I had al∣most forgot to Answer the last lines of Mr. Hobbs's so often mentioned passage, where he would have the Air that he supposes to be impell'd into the Sucker, to move very swift∣ly betwixt the top and bottom of it. And so elsewhere he would have the same Air, when it gets into the cavity of the

Receiver. But having tired my self, as I fear I have you, by dwelling so long upon one passage; I will skip somewhat that I here approve not in the Ratiocination, and onely say, that when a light Bladder is suspended in the cavity of the Receiver, it betrays no such motion as is here imagined; nay, the flame of a Taper, as our Epistle mentions, was not blown out, nor (for ought appeared) stir'd by this suppos'd wind: to which I shall adde, that Smoke produced in the Receiver whilst it remained exhausted, was not by this ve∣hement motion of the Air blown about the Receiver, as is particularly set down in our Appendix, promised by the Translator of the newly-mentioned Treatise. But if you let in the Common external Air at the Stop-cock, that indeed will rush in with Noise and Violence, and whirle about the Bladder that hung quietly enough before.

Having thus examined Mr. Hobbs's First solemn Explicati∣on, I now proceed to the next, wherein he undertakes to give an account by his Hypothesis of the Reason, Why in our Engine, if the Manubrium of the deprest Sucker happens to slip out of the Pumpers hand, the Sucker is carryed up again towards the top of the Cylinder. But since this Explication is such, that though he mentions it as his first, presently after the Recital of his two Hypotheses, he himself is pleas'd to confess in the last page of his Book, that 'tis Erronious; I shall forbear to vex it, thinking such acknowledgments more fit to be imitated whenever there is the like occasion, than to be discouraged. But as for the Explication which at the end of his Dialogues he substitutes for his Retracted one, I confess to me 'tis so obscure, that I know not well what to make of it. But, as far as upon consideration I can understand it, it is coincident with that, which in our Method will be call'd his Fourth Explication; with which that it may the better agree, seems one of the chief Reasons of his altering it from what we had proposed at first. Wherefore we should pre∣sently fall upon examining them both together; but that be∣tween

them I meet with an Explication (which in our rec∣koning is the Third) of the Torricellian Experiment.

And here he spends many words to prove the Opinion he had whether proposed or adopted in his Elements of Philosophy; namely, that the place deserted by the suspen∣ded Mercury is not empty, but full of Air. But because this Exposition assumes what he has not yet Demonstrated, viz. Non dari Vacuum, and because the Torricellian Experi∣ment as 'tis wont to be made is none of the Phaenomena of our Engine; I shall refer you to what those Learned men Doc∣tor Ward and Moranus have prosessedly, and the first of them largely enough, written against Mr. Hobbs's Explicati∣on, (yet without making all that either of them teaches mine:) Because, for my part, it will suffice me to argue, as I did before, that if he takes the Air in the common sense of the Word (and that wherein his Readers generally under∣stand him) his conceipt is manifestly Repugnant to several such Phaenomena as these. That if the Experiment be very well made, we may by inclining the Tube impell the Mer∣cury from its wonted station to the top of the Tube; which will not happen in case the Air were before Inclination let into that deserted space. That if when the Mercury is setled at its wonted station, the Tube be lifted up out of the Restag∣nant Quicksilver, the outward Air will drive up the heavy Mercurial Cylinder oftentimes with force enough to beat out the sealed end. To which we shall adde onely this Experi∣ment: The Quicksilver resting at its wonted station, if you carefully stop the lower Orifice under the Surface of the Restagnant Quicksilver, and then lifting up the Tube (that which we us'd was about three or four foot long) into the Air, keep it well stopt, if, I say, you first depress one end and then the other, you shall find the Quicksilver fall against the deprest extreme of the Tube with such swiftness and force, as will perhaps surprize you, and make you apprehend that the Tube will be either beaten out of your hand or broken:

Whereas if unstopping the Tube whilst the self-same quanti∣ty of Mercury remains in it, you let the outward Air into the cavity unpossest by the Mercury, and then if you again stop the Orifice with your finger, and proceed as formerly, you shall perceive the motion of the included Liquor to be very much slower and less violent than formerly, by reason of the resistance of the admitted Air: which will also manifestly disclose it self by the conflict and bubbles that will be pro∣duc'd betwixt the Air and Quicksilver in their hasty passing by one another to the opposite ends of the Tube.

If any friend of Mr. Hobbs's seeing the manifest inconveni∣ences of this opinion, shall on his behalf pretend that 'tis what he calls the pure Air, that passes through the body of the Quicksilver to the deserted part of the Glass Cane; the answer is ready, that Mr. Hobbs's expressions look so much another way, that his Readers (for ought I have found) do generally understand him of such common Air as is displac'd by the descent of the Mercury. And therefore I had reason enough to argue against what he wrote, as I have newly done; and however, this assertion is clearly precarious, and lyable to the Objections formerly alledg'd against the passing of the Air through the water. To which we may adde this circumstance, that in our present case it must descend into a far heavier and closer Liquor than water. But perhaps it will be thought, I have already said more than needed a∣gainst an opinion which has been rejected as well by Plenists as Vacuists; and though mention'd as to the main by several Writers, as well before Mr. Hobbs asserted it as afterwards, has been thought so unlikely, as not to have been (that I know of) approv'd by any man, even before the discovery of the Phaenomena of our Engine. Which last words I adde, because that Mr. Hobbs not pretending that any attraction intervenes in the case, I see not how he can possibly make out, to omit other Phaenomena, the descent of the Mercury in the Tube further and further beneath its wonted station,

upon the Exhaustion of the Receiver, and the re-ascension of the same Mercury in the same Tube, as we please to let in more or less of the outward Air; without admitting as much of Spring or Pressure in the Air as I need contend to have here allowed me. The weight of the Terrene Particles, by which, at the end of the third Exposition, he is reduc'd to endeavour the Solution of the Quicksilvers falling lower at the top than at the bottom of a Hill, (for I am willing to think that is his meaning, and that 'tis by the Transcribers fault rather than his, that resolutely affirms the quite contrary) will by no means serve his turn: It being utterly improbable to imagine, that the contain'd in so little a vessell as one of our Receivers can by its weight counter-balance so pon∣derous a Cylinder of Quicksilver: Whence we may be al∣lowed to argue that the Air sustains it by such a Pressure or Spring as we plead for, whether that proceed from the Tex∣ture of the Aerial Particles, or from their Motion, or from both.

The Fourth and last of Mr. Hobbs's principal Expositions is of that Experiment of ours, wherein 100. and odde pound weight being hung at the depressed Sucker, the Suck∣er was notwithstanding impell'd up again by the Air to the top of the Cylinder. Of this Phaenomenon (which has not hitherto prov'd unwellcome to the Vertuous) Mr Hobbs gives us the following account.

Haerent hic nostri: (which why he sayes I know not) quomodo haec expedies tu? * 1.22

A. Expedivi ante. Aër enim à retractione Suctoris retrò pulsus, nec locum in mundo (ut supponimus pleno) quò se re∣cipiat inveniens, nisi quem ipse, corpora contigua suis locis pel∣lens, sibi faceret, perpetuâ pulsione in Cylindrum tandem cogi∣tur, tantâ velocitate inter Cylindri concavam & Suctoris con∣vexam superficiem, quant a respondere solet viribus illis magnis quas ad Suctorem revellendum necessarias expertt estis. Aër au∣tem ille, quâ velocitate ingreditur, eandem ingressus retinet,

simul{que} latera Cylindri aenei (vi elasticâ praediti) undiqua{que} distinet. Conatur ergo Aër in Cylindro vehementer motus con∣tra omnes partes superficiei Cylindri concavae; srustra quidem dum Suctor retrahitur: sed quamprimum Suctor manu emissus Aërem impellere cessat, Aër ille qui ante incussus erat, propter conatum in omne punctum superficiei Cylindri internae & vim Aëris elasticam, insinuabit se inter easdem superficies eâdem velocitate quâ impulsus fuerat, id est, eâ velocitate quae respon∣det viribus impulsionis. Si ergo tanta ponderis vis Suctori ap∣pendatur quanta manuum vis erat quâ impellebatur, velocitas quâ idem Aër è Cylindro exit, locum in mundo pleno nullum habens quò se recipiat, Suctorem rursus ad Cylindri summita∣tem impellet, propter eandem causam quae effecit ut Suctor paulo ante impulerit Aërem. Thus far our Authors passage: a∣gainst whose solution 'tis easie to draw divers Arguments from what we have discourst against the first of his four Ex∣plications. But though we refer you thither, yet we will here also observe, that this whole conceipt of the Aires run∣ning in and out with strange velocity between the Sucker and the Cylinder is precarious; nor does he propose any one Phaenomenon to countenance it. To which general Adver∣tisement I shall adde the three following particulars. First, that in an Engine so contrived, that the Pump lay cover'd with water, when the Sucker was retracted, the Atmo∣sphere would strongly press the water against it; and if the Manubrium were let go, would swiftly enough repell up the Sucker into the deserted cavity of the Cylinder. Which being a case Parallel to that under consideration, let any unbiass'd Person judge how likely it is, that the Air could perform all these Excursions without exciting bubbles, not∣withstanding the Waters constant interposition betwixt it and the Cylinder. Secondly, that there is as little probabi∣lity in what our Author teaches in those words Conatur ergo Aër, &c. I might here repeat what we formerly mention'd of the breaking of our Receivers inwards, not outwards; and

I might adde, that I see no reason why the Conatus of the Included Air, if its Conatus were granted, should be frus∣traneous, when the Sucker is deprest. But I will rather de∣mand, Why, if the Air within have so strong an endeavour outwards, as to stretch the thick sides of the Bras. Cylinder, as Mr. Hobbs (with what probability, let any man judge) would have it; I demand, I say, why this Air does not throw out the Wooden Peg or Valve, which we have often to our trouble seen thrown out with great force and noise, when the deprest Sucker being thrust up again whiles there was Air in the Cylinder, we forgot to leave the Valve open; though in this case the Air that drove out the Peg was far enough from stretching the Cylinder. And I further demand, how it comes to pass, that, if having stopt the hole of the Cylinder with your finger instead of the Peg, you swiftly depress the Sucker, you shall be so far from feeling a Pres∣sure outwards against the Pulp of the finger from any thing contain'd in the cavity of the Cylinder, that your finger will be strongly, and perhaps not without some pain, prest in by the ambient Air; in so much that 'twas this Phaeno∣menon, and one somewhat like it in the Torricellian Experi∣ment, that seem to have ingag'd my other Adversary, the Learned Linus, to maintain a conceipt quite contrary to Mr. Hobbs's, and imagine in the deserted cavity of the Cylinder, not a distending, but violently contracting substance. Third∣ly. That as to the last part of the passage under considerati∣on, beginning at si ergo, &c. which seems to me somewhat intricate, I do not so clearly understand why the Air that is impell'd in so swiftly betwixt the Cylinder and the Sucker, should not resist the swift Egress Mr. Hobbs ascribes to the included Air by the same passage: nor why this impell'd Air, that has so strong an endeavour outward, should never de∣press the Sucker (against whose upper part it must bear as well as against the Cylinder) as well as the same Air dif∣fusing its Motion through the vast ambient Medium, can

enable the external Air to thrust up the Sucker again; espe∣cially, since during such a depression of the Sucker (as we have mention'd not to happen) made by the Rebound of the Air, forcibly impell'd in from the close bottom of the Cylinder, the Air from without may all the while, with congruity enough to Mr. Hobbs's principles, get in between the said Sucker and the Cylinder. But not to insist upon these niceties: I say, that the lifting up of the Sucker either is not necessary to prevent a Vacuum, or that in some cases it will be hard to shew how a Vacuum can by Mr. Hobbs be a∣voided. For when the deprest Sucker is ready to be thurst up again, if you hang a somewhat greater weight at it than an hundred and odde pounds, it shall not be lifted up at all. And I shall make this further improvement of the Ex∣periment under consideration, that whereas this progress and regression of the impulse of the external Air cannot reasonably be suppos'd to be very lasting, you may by a competent weight detain the Sucker deprest, till the ambient Air is as quiet as it uses to be; and yet if then you take off the overplus of weight, and perhaps a little more, in case the Pump have been very stanch, the Sucker and the great weight appended will notwithstanding be carried up: which 'tis no way likely it could be by the impulse of the outward Air, which had time to decay and be confounded. And as for the inward Air, beside that we have proved, that it has no such conatus outwards as Mr. Hobbs pretends, why should not that, were it granted, throw out the Sucker rather than cause it to be impell'd inward; it being no way likely, that in case some Air should get out of the cavity of the Cylinder, it could so move the outward Air, as that the reflex of that im∣pulse should make that free outward Air bear more strongly against the outside of the Sucker than the inside of the same Sucker is prest against by the included Air, whose impetus is incomparably less diffused? But not to be thought a more nice and diligent Opponent than the matter requires, I shall

drive this Discourse no further: but rather desire it may be observ'd in general, that whatever be resolv'd to be in the Cavity of the Cylinder when the Sucker is deprest; yet since 'tis manifest, that it is at least in great part devoid of common Air, and since the Sucker with the appended weight may, if the Instrument leak not, be impell'd up, when in all probability those forced Undulations of the Air, that may be supposed to have been made by the Sucker, have ceast; the Cartesians, Mr. Hobbs, and those others that will not have recourse to the un-intelligible attraction of some rare∣fied substance within, must ascribe so strange a Phaenomenon to the pressure of the Air without. But I shall no further press this Fourth Objection, partly because 'tis added to the other three onely ex abundanti, and partly because this Chapter is grown so long already

I know indeed that after the Exposition last recited out of Mr. Hobbs, he makes the Academian Dialogist confess, that the rest of the Phaenomena of our Engine may also not uneasily be reduc'd to his principles. But perhaps they that take notice of the variety of those Phaenomena we have set down in our Treatise, will scarce be of his mind; and those that have considered what has been discours'd in this Chapter against his four principal Explications, and what I am about to subjoyn in the following part of this Treatise, concerning divers other Solutions that he gives, Will perhaps be inclined to think that others may be like these, without being there∣fore necessarily true.

CHAP. V. In which divers scattered Explications and other passages in Mr. Hobbs's Dialogue are examined.

I Proceed then to the Fifth Chapter, in which and the next I glean up and examine divers scatter'd passages, where∣in he offers at somewhat by way of Argument against some things we had delivered in our Epistolical Treatise: I say,

what he offers by way of Argument; for as to those passages that do but either praise himself or disparage his Adversaries, I have almost as little leisure as inclination to take notice of them, and do not much apprehend that the Virtuosi (e∣specially such as know us both) will think what I write the less rational for being civil; or will let me suffer in their Opi∣nions for neglecting to trouble them in aPhilosophical Con∣troversie, with matters that do but very little belong to it.

To skip then what Mr. Hobbs is pleased to say in the first Page of his Dialogue, concerning some disputable discover∣ies about Sensation, which he challenges to himself; and to pass by divers other things in the second or third following pages, which relate to him, or to the Society he writes against, rather than to the nature of the Air; we should begin with the Opinion he thinks fit in the fifth page to impute to us, as if we distinguish'd what is fluid from what is not so, onely (for so his Ratiocination imports) by the bigness of the parts of which a Body consists: But designing in an Appendix to be subjoyned to this Discourse to examine what I find in this Dialogue dispersed touching Fluidity, I shall now onely say, that he does very much mistake and mis-represent my Doc∣trine of Fluidity; wherein I expresly teach, That the prin∣cipal cause or condition of it is not the size, but the mo∣tion of the small parts that compose the fluid body.

To take up then the particulars we are to examine, in the order (as far as conveniently may be) wherein I find them lye in the Authors Dialogue, and passing by at present those things which either we have considered already, or are not to consider in this place; The first particular that offers it self to be taken notice of, is this passage at the bot∣tom of the twelfth page;

B. In vas apertum infudimus aquam, in aqua fistulam * 1.23 statuimus erectam, longam, exilissimam; observavimus autem aquam è vase subjecto in erectam fistulam ascendisse.

A. Nec mirum; nam superficiem aquae, particulae aëri inter∣spersae

aquae{que} contiguae motu suo verberabant, ita ut aqua non potuit in fistulam non ascendere, & sensibiliter quidem in fistu∣lam valde angustam.

To this I say, that 'tis manifest by what I write in my Epistle, that I did not then take upon me, nor do I under∣take in this place, to assign the true reason of the propos'd Phaenomenon. An Attempt of this kind has been since ad∣dress'd to me, which being ingenious, if not also true, may be consulted. In the mean time I cannot but declare that I am no way satisfied with Mr. Hobbs's Exposition: For, to say nothing of the motion he ascribes to the particles dis∣persed through the Air, he leaves the difficulty unsolved, since there being common Air as well within the Cavity of the slender Pipes as without it, he neither shews, nor so much as offers at, a reason why the pressure of the Air with∣in should not resist the pressure of the same kind of Air without; as we see it does in greater Pipes. And possibly he would have past by this particular, if he had not over∣look'd the Advertisement I gave towards the close of the 35. Experiment, That it would concern those who should un∣dertake to shew the causes of this Phaenomenon to bethink themselves also of a reason why, if the Experiment be tryed with Quicksilver instead of Water, the Surface of the Li∣quor will instead of being higher, be lower within the Pipe than without it: Whereas if Mr. Hobbs's Explication be suffi∣cient, why should not the contrary happen in Quicksilver as well as in Water?

The next passage I have to consider is in the 13. page thus set down; Siquis post impulsionem revulsionem{que} Suctoris aliquoties repetitam, Epistomium superni * 1.24 orificii Recipientis conetur extrahere, inveniet illud valde gra∣vitare, tanquam si multarum librarum pondus ab eo penderet. Vnde contingit hoc?

A. Ab aëris qui est in Recipiente fortissimo conatu circulari facto à violento ingressu aëris inter superficiem Suctoris convexam

& Cylindri concavam, generato per iteratam illam impulsio∣nem revulsionem{que} Suctoris, quam vos perperam vocatis exucti∣onem aëris. Nam propter naturae plenitudinem, Epistomium extrahi non potest, quin aër qui est in Recipiente (Epistomio contiguus) una extrahendus sit. Qui quidem aer, si quiesceret, facillimè Epistomium sequeretur: sed dum velocissimè circuit, satis difficulter sequitur; id est, videtur esse valde gravis.

B. Verisimile est: Nam ut aër novus in Recipiens paulatim admittitur, etiam apparentem illam gravitatem paulatim perdit.

But, I do not much fear that this Explication will keep the Experiment from continuing to be thought by ingenious men, a notable Confirmation of our Hypothesis. For, to pass by something that, though I am no way satisfied with, cannot well be examined in few words; I answer, First, that if there be such a vehement circular endeavour as he imagi∣nes of the Air in the Receiver, by which motion he else∣where teaches (as we have seen above) that the Air rushes out with violence enough to make the Atmosphere lift up in our Cylinder above an hundred pound weight; I see not why it should not rather throw out the stopple under con∣sideration, than hinder its extraction. And I see not why, when the external Air is re-admitted at the stop-cock into the exhausted Receiver, and thereupon there does sensibly follow for a little while a whirling about of the included Air, the stopple, that just before seemed so much to resist the being drawn out, should cease to make any such re∣sistance. Nor do I see how the plenitude of Nature should, as is here intimated, hinder the extraction of the stopple: For, according to the Plenists, the World and the Receiver must be at all times equally full. And if the contiguous Air must for Mr Hobbs's reason necessarily be extracted with the stopple in one case, I see not why the like should not happen in another. But since Mr. Hobbs is pleased to call us Experimentarian Philosophers, let us shew that such Explicati∣ons as these of his need not make us asham'd of the name. I say

then, that it appears by our Experiments that there is no such Fortissimus conatus circularis in the exhausted Receiver as he pretends; but that there is indeed an endeavour of the Am∣bient Atmosphere to press inwards the parts of the Glass and Cover that are contiguous to it. For, as I have also noted already, a light Bladder suspended in the cavity of the Re∣ceiver betrayed no such motion as Mr. Hobbs here supposes. To which I shall now adde, that neither were a pair of Scales suspended within the same Cavity; nor was a long Magnetical Needle that rested upon the point of another Needle, at all whirled about by this imaginary motion of the Air. Besides, if you leisurely loosen the Brass stopple, so that it may be very near, but not contiguous, to the sides of the Socket, you shall manifestly perceive a strong current of Air to flow into the Receiver at that passage: And more than once, when instead of that piece of Brass we stopt the hole in the Cover with our Cement, one might observe sometimes whilst we were pumping, sometimes after we had done pumping, that the outward Air by degrees de∣press'd the superficies of the Cement expos'd to it, and made it concave, and now and then would break through it, thrusting it inward with great violence and noise.

In the same page our Author rectifies, after his way, an∣other of our Explications in these words; Vidimus item aquam demissam in Recipiens post Suctoris aliquot * 1.25 reciprocationes ita bullire, ac st supposito igne fervesceret.

A. Id quo{que} accidit propter velocitatem aëris, ut dictum est, in Recipiente circumeuntis; nisi forte aquam illam dum bullit calidam quo{que} esse deprehendatis. Nam si certi essemus illam calescere, alia causa Phaenomeni excogitanda esset.

B. Imo certi sumus quod non calescit sensibiliter.

A. Quid ergo tali aquae motui conferre posse putas majorem vel minorem Atmosphaerae gravitatem?

B. Ne{que} illum motum attribuunt, puto, Atmosphaerae.

But, I confess, I see not how the circular motion of the

Air within the Receiver could in a Vial with a long neck produce such effects as in my Epistle are recited: especially I see not how such a wind passing along the Surface of the Water could raise so many and so strangely-big bubbles, which seemed many of them to rise from the lower parts of the Wa∣ter, and swell'd notably as they ascended; and how such a wind should carry up the most part of the Water through the long neck of the Vial, and as it were spout into the Receiver.

As for what he sayes about the gravity of the Atmosphere, 'tis plain enough that my conjecture ascribes the Phaenome∣non to the taking off, not the gravity of the external Air, but of the pressure of the Air within the Receiver; though I see not why the removal of the weight of the Atmosphere, if it could be out of the Engine effected, should not have a like operation.

And (to answer Mr. Hobbs's Question as it should have been put) that which I think the greater or lesser pressure of the Air confers to this Phaenomenon is this, That whereas common Experience shews us, that water by being heated is expan∣ded, and has bubbles generated in it; and whereas our former Experiments, especially the 28. have made it appear, that there is wont to be in water and other liquors Aerial Particles, which tend to expand themselves, and do actually do so, in numerous bubbles, when the pressure of the incumbent Air is considerably lessened: In the present Phaenomenon that pressure being by the exhaustion of the Receiver taken off, the Aerial particles and agitated Vapours that abound in the hot water are allowed to expand themselves, as before they could not, and to make such numerous and great bubbles, that thereby a good part of the water is carried out of the Vial. So that I somewhat wonder what makes Mr. Hobbs speak as if there were no sensible heat of the water under consider∣ation, since 'tis expresly said that it was put in hot; and if it were put in cold, could by no pumping be brought to the

least shew of Effervescence. And as for his Explication of the Phaenomenon, the Experimentarian Philosophers need not the Objection lately made against it; For I have al∣ready evinced by Experiments, that there is in our exhausted Receivers no such peculiar motion of the Air as he ascribes the Phaenomenon to; nay, when there is manifestly a whirl∣ing about the Air in the Glass upon the admission of the external Air, the production of numerous bubbles in the water presently ceaseth. And therefore I see not why Mr. Hobbs might not have let alone my Conjecture, (for I pro∣pos'd it, and look upon it, as no more) unless he could either have disproved it better, or substituted a more pro∣bable one than he has in its place.

As for what he-adds in these words, Ab hoc experimenta manifestum est, quod Recipiens per exuctionem hanc quam vocatis Aeris, non sit vacuum. Nam moveri * 1.26 aqua non potuit nisi à movente aliquo moto & contiguo. * 1.27 Phaenomenum hoc demonstrationem suppositionis meae continere videtur non infirmam. I am not obliged to answer it, but leave that to those that are profest Vacuists; against whom I must doubt whether his Ratiocination will conclude, though the consequence be not manifest to me. For himself allows his Terrestrial Atoms an innate circular motion, which consequently needs not depend upon some body contiguous and moved; and the Vacuists will say, that the particles of the water being strongly agitated when it was put into the Receiver, (whether by fiery Corpuscles swarming in it, or otherwise) and the resistance of the incumbent Air being taken off, the Phaenomenon would be produced just as it is, though we should suppose no other body to succeed in the room of the exhausted Air. And besides, though some sub∣tile particles of active matter should get in to agitate the Aqueous and Aerial Corpuscles, yet (they may say) there is no necessity that such minute particles should be numerous enough to fill up exactly all the little spaces deserted by the

Air. And even upon this supposition, as it would not fol∣low that such relinquish'd spaces were all of them quite emp∣ty; so would not the Phaenomenon at all prove, much less manifestly prove, that they were quite full. And since an actual heat, that is, a brisk and various Agitation of its small parts, is requisite to the boyling of the water in this Experi∣ment; perhaps others will not think it more absurd, that the re∣moval of the pressure of the Air should occasion this expan∣sive motion in the water, than that which Mr. Hobbs must allow, that in Air comprest by Quicksilver, or some other weight, the removal of that pressure is sufficient to make that Air expand it self by the flying abroad of its parts.

And whereas Mr. Hobbs urges this other Argument against the Vacuists, Praeterea dic mihi, bullientem aquam potuistin' conspicere? * 1.28

B. Quidni?

A. Nonne visionem fieri concedunt vestri per actionem conti∣nuam ab objecto ad oculum? Nonne etiam putant actionem esse motum, & omnem motum esse corporis? Quomodo ergo potuit ab objecto, nempe aqua, ad oculos tuos motus per vacuum (id est, per non corpus) derivare?

B. Non affirmant nostri it a vacuum esse Recipiens, ut nul∣lus omnino aër relict us sit.

A. Nil refert an totum Recipiens vacuum sit, an magna ejus pars; nam utrumvis supponatur, derivatio motus ab objecto ad oculum intercipietur.

B. Ita videtur, nec habeo quod respondeam. The Vacuists will perhaps answer him as I answered Franciseus Linus to an almost like Objection. And those of them (which make far the greatest number) who plead but for an interspersed Vacuum, will perhaps tell him, that they take Vision to be made not by such a Propagation of Impulse as he does, but by a Trajection of Effluvia, that issuing out of the Sun, and tra∣versing the Diaphanous bodies interpos'd, rebound from the object to the eye. And according to this Doctrine they

may ask Mr. Hobbs, why a motion may not be made through a Vacuum or non corpus? nay, how it can naturally be stopt in vacuo where there is nothing to resist it? But Con∣troversies of this nature it lyes not upon me to pro∣secute.

In the 14. page Mr. Hobbs having recited that Experi∣ment of ours, of killing Animals included in our Receiver by the exhaustion of the Air in two or three minutes of an hour, subjoyns these words, Credin'tu animalia ista¦tam cito interempta esse eo quod carerent aëre? Quo∣modo * 1.29 ergo sub aquam vivunt Urinatores, quorum aliqui (assue∣ti à pueritiâ) caruere aëre per horam integram? Inclusa in Re∣cipiente animalia occidit motus ille idem vehementissimus, quo distenduntur rumpuntur{que} inclusae vesicae. But, though he sayes no more in this place concerning this matter, yet it seems he either much liked his own Conjectures, or greatly disliked mine, since in his Epistle Dedicatory to the learned. Sorberius he singles out this sole Phaenomenon to explicate; Ego contra (sayes he there) ne{que} aërem exugi posse, ne{que} inclu∣sum animal (etsi exuctus esset) tam cito moriturum esse existimo. Actio quidem quam mors illa sequitur videri potest vel suctio quaedam (& propterea exuctione conclusi aëris interfici animal, respiratione sublatâ) vel etim compulsio aëris ab omni parte ver∣sus caentrum sphaerae cui animal includitur; & sic videri potest mori à tenacitate compressi aëris, quast aqua suffocatum; nimi∣rum haustum in intima pulmonum aërem solito tenaciorem, inter arteriam & venam pulmonis, cursum sanguinis intercipiendo sistere. But, as I proposed my Coniecture doubtingly, and profess my self to be in a further enquiry about the use of the Air and of Respiration; so I must still think, that we want some further or clearer discovery about that matter, notwithstanding what has been delivered concerning it by Mr. Hobbs. For his Argument against my Conjecture is in the passage that propose, it answer'd by himself: for he plain∣ly intimates that Divers who can live without Air (which

yet I might question, if he means without any Air at all) for a whole hour, are accustomed to it from their Childhood. Wherefore, unless the Animals that dyed in my Engine had been for a long time framed by degrees to live without Air, it will not follow that the want of it could not dispatch them in a short time, as ordinary men may be drowned in a few minutes. And having purposely let down some Mice and small Birds into a deep Glass fill'd with water, and kept them from emerging by a Weight tyed to their legs or tayls, though some lived longer than others, yet I observed them to be kill'd fast enough to keep my Conjecture from being incredible: especially the last we made tryal of, though a large and lusty Mouse, appear'd to be quite dead within somewhat less than one minute, measured by the Vibrations of a Pen∣dulum. And we particularly took notice, that before drown∣ing divers bubbles, which seemed to be the respired Air, came out of their mouths, and ascended through the water.

And as for the Explication that Mr. Hobbs would recom∣mend instead of mine, not to urge that I could wish he had been pleas'd to shew us how the tenacious Air he imagines to be inspired comes to produce those strange Convul∣sions and other Symptomes mentioned in my Epistle; not to urge this, I say, we have already disproved the supposi∣tion his Opinion is built on, namely, that there is in the ex∣hausted Receiver such a motus vehementissimus as he pretends: besides that he shews not how this motion comes to kill the included Animals which I was wont to keep, not near the Centre of the Receiver, where he seems to think this moti∣on most operative, but near the bottom of it, that the in∣cluded Animal might have something firm under his feet. Nor does it at all clear the difficulty, that he would have this motion the same whereby included Bladders are disten∣ded and broken. For, besides that 'tis very hard to con∣ceive how the tenacity of the Air, or its beating from all parts upon the convex Surface of an almost quite empty

Bladder, (for in such also the Experiment he refers to will succeed) should make it burst outwards; besides this (I say) we have already proved that the distension and breaking of Bladders in our Receiver proceeds not from any such motion of the neighbouring Air as is here presumed, but from a quite differing, if not from a contrary cause.

In the same page our Author makes a digression from the Engine, and discourses of another Experiment which I have long since often made: but though his Explication be lyable enough to just Exceptions, (as I can make good if it be re∣quired) yet because the Experiment is none of those I de∣livered, I shall leave it to be examined by others: and for the same reason I forbear to meddle with that he has in the next page concerning the Wind-gun, as to what he has in the same 16. page in these words, Placet mihi tua magis Hypothesis quam illa de vi aëris elastica: nam * 1.30 video quod à veritate illius veritas dependet vel vacui vel pleni; sed à veritate hujus nihil sequitur in neutram partem quaestionis. Aëris, inquit, structura similis est compressae lanae. Bene est. Lana fit ex filis. Recte. Sed cujus figurae? Si Parallelopipedi, nulla potestesse compressio partium: si non Parallelopipedi, erunt inter fila illa spatia quaedam relicta; quae si vacua sunt, suppo∣nunt Vacuum, ad probandum quod Vacuum est possibile; si plena, plenum dicunt quod vacuum putant. To this passage, I say, I cannot but represent, that the Question is not, whether from the Hypothesis that ascribes a Spring to the Air, depends the proof of a Vacuum or a Plenum, but whether the Hypo∣thesis it self be true or no. For, sure there are many things certain in Natural Philosophy, from whose truth that of a Plenum or a Vacuum cannot be deduc'd. And to what he addes concerning the structure of the Aërial Particles, the Vacuists may tell him, that they make no such Argument as he is pleased to make for them; and do not commonly im∣ploy the Figure of the Aërial Particles to prove a Vacuum, but other Arguments, such as Mr. Hobbs has not yet well

answered: and having by them, as they judge, prov'd inter∣spersed Vacuities, they might without inconvenience suppose in an Aërial Corpuscle little empty Pores, upon whose ac∣count it may be capable of compression, in case they should think fit (which I know not that any of them does) to assign it the Figure of a Parallelopipedon. But this Controversie the Vacuists may, if they please, prosecute. In the same page Mr. Hobbs begins, and in the next he continues, a long dis∣course concerning the going out of fire in our Receiver up∣on the exhaustion of the Air: the passage is too prolix, and does too little concern the Spring of the Air to be here to∣tally transcribed, or examined Period by Period. In summe, he indeavours to do two things: the one is to reduce what happens to kindled Coals placed in our Engine to what hap∣pens in certain Mines, wherein when some thick damps as∣cend, both Charcoals and Candles are soon extinguished thereby: the other is to shew, that by the Reciprocation of the Sucker, the Air impell'd first into the Cylinder, and then into the Receiver, is put into such a motion as gives it a cer∣tain middle consistence, as he speaks, betwixt the consistence of pure Air and that of Water. But I shall not need to ex∣amine this second part of his discourse, because I deny the first; and being able to disprove the thing it self, namely, the thickness of the Air in the exhausted Receiver, I need not spend time about what he teaches de modo.

To examine then onely the first of the above mentioned particulars, I shall begin with observing that his story of the damp to be met with in Mines is more largely set down by Mr. Hobbs in that Chapter of his Elements of Philosophy, where he treats of Gravity; in which place he seems to men∣tion it (to use his own Expression) as a story of doubtfull credit, which 'tis not like he would have done if had then seen it. Which I mention, not that I deny the story for the main, nor that I would bring Mr. Hobbs into a suspicion of relating things untrue as matters of fact, his enemies them∣selves

having not accused him of such a meanness; but because, if he have not since observed the thing himself, there may easily be a mistake in some of the circumstances: as for in∣stance, the number of Minutes wherein the thick Air choaks the fire; and 'tis upon that circumstance that the validity of what he deduces from the observation chiefly depends. But, however the matter fare with these subterraneal Damps, we have already proved by several of the Experiments of our Engine, that in the exhausted Receiver there is no such mo∣tion of the Air as is here supposed. And it may be suffici∣ently proved, that whatever remains in the Receiver is not such a substance as Mr. Hobbs would have it: for that, he here tells us, is of a consistence betwixt Air and Water; and in the above cited place of his Elements he sayes, that 'tis not much lighter than Water. But by the Magdeburgick Ex∣periment (we have already had occasion to mention two or three times) 'tis evident that the Receiver by being exhausted of common Air is so far from growing heavier, much less so much heavier as it must if it were filled with a substance not much lighter than Water, that it lost above an Ounce of its former weight. And to this agrees what we see happen in AEolipiles, that grow lighter when the Air is expell'd. Be∣sides, if the Receiver be in our present case filled with a substance whose consistence is so much nearer that of Water than is our common Air, as Mr. Hobbs would have it; how chance a Pendulum should not move very sensibly slower in it, when in Water the Diadromes are so exceedingly much more slow? And the breaking of an Hermetically-seal'd bub∣ble in our Receiver outwards, when the Air was much ex∣hausted, and not before, together with divers other Experi∣ments that might be easily applyed to this purpose, in our Epistle, do sufficiently evince, that 'tis not a thicker and far heavier Air, but a more yielding and lighter, that remains after Pumping in the Cavity of our Receiver. And thus much as to Mr. Hobbs's discourse upon our Experiment. But

as for the thing it self, it appears that when I related it I thought it might admit a further enquiry: And indeed there may be so many ways of extinguishing Fire (as we see that the flame of a Candle may be blown out by the wind, or quenched in water, or put out by the compression of a pair of Snuffers, or suffocated for want of Air to receive its fu∣liginous steams, or (if that be a different way) stifled by the thick Exhalations of deep Mines or of new Wine) that as 'tis not in all cases so easie to assign the true cause of the extincti∣on of fire, so 'tis unsafe to conclude with Mr. Hobbs, that because a Candle or a live Coal may a great way under ground be extinguisht by a thick Damp, therefore the effect must proceed from the like cause in our Receiver, where there is no sign of any Damp or unusual thickness of the Air, but of the contrary.

But let us follow Mr. Hobbs to the next passage, wherein he seems fond enough of playing the Censor. For, speaking of our 11. Experiment, wherein the Coals that seemed al∣most dead in our exhausted Receiver, being taken out into the Air began to shine again, having made his Academian Dialogist say, Fuere eorum aliqui qui remansisse dixerunt in carbonibus illis (quanquam extincti videbantur) par∣ticulas quasdam igneas, quae admisso aëre ventilate caete∣ram * 1.31 molem denuo accenderent: The other (by whom Mr. Hobbs is meant) answers him, Nae illi quae dicerent non videntur co∣gitasse, sed sortitos esse. This is very severe. But let us see what weighty reason he has to be so: Credin' tu in carbone ignito partem aliquam non carbonem, sed ig∣nem * 1.32 esse; aut in candente ferro partem inesse quod ferrum non sit sed ignis? But some will think that by these words he does rather propose than prove his Opinion: wherefore let us hear his Ratiocination, which he annexes in the following words, Ab unica scintilla magnae urbis incendium na∣sci potest. Atqui si ignis corpus ab ignito diversum sit, * 1.33 non plures potuere esse partes igneae in toto incendio quam in una

illa scintillula. Videmus corpora diversorum generum à luce Solis tam per refractionem quam reflexionem factam in speculis comburentibus accendi posse: ne{que} tamen quenquam esse credo qui putet particul is igneas à Sole eject as transire posse per substan∣tiam globuli crystallini. In aëre intermedio ignis nullus est. But I doubt his Adversaries will say, that he is so far from having in this passage well confuted their Opinions, that he seems not to have well understood them: For they will tell him, that they teach not that the fire is materially differ∣ent from every part of the fewel; but that the igneous Corpuscles, whilst they are divided, blended and opprest with the others, have not the power to shine or burn, till being by some spark or other body actually burning, or by some other equivalent cause extricated, they flock together in swarms, and then are able to burn and shine, that is, to appear fire: Which fire is yet but a part of the fewel; as appears by the Phlegme, Ashes, and perhaps other incombus∣tible parts of the Coal or other fewel. So that the Atomists and divers others will not allow what Mr. Hobbs infers a∣bout an incendium. And whereas he tells us he believes that no body thinks, Particulas igneas à Sole eject as transire posse per substantiam globuli crystallini; he seems to me to have very little heeded the Epicurean Hypothesis. For, not onely the learned Gassendus, but I know not how many other Atomists (besides other Naturalists) Ancient and Modern, expresly teach the Sun-beams to consist of fiery Corpuscles, trajected through the Air, and capable of passing through Glass; whereby these Authors give an account of those specula us∣toria that burn by reflexion. These things I represent, not that I intend here to adopt the Atomists Opinion of the na∣ture of Fire, of which I am not obliged to declare my thoughts here, and have done it elsewhere; but to shew that Mr. Hobbs's Arguments are not a sufficient ground for so heavy a Censure. And if a Coal be kindled at one end, though Mr. Hobbs would have the kindled end a Coal, not Fire; yet if he

please to hold it in his naked hand, he may find that differs enough from the other end to deserve another name. And I, that but related a Phaenomenon, did not perhaps express my self much less warily, if not more so, than Mr. Hobbs him∣self. For whereas my words are these, We presently took out the Coals, in which it seems there had remained some little Parcels of fire, rather covered than totally * 1.34 quench'd: for in the open air the Coals began to be rekindled in several places: Mr. Hobbs even in his Elements of Philoso∣phy speaks thus upon a somewhat-like occasion, If a Grate filled with Coals throughly kindled, and burning ne∣ver so brightly, be let down, as soon as ever it is below * 1.35 C. the fire will begin to grow pale, and shortly after (loosing its light) be extinguisht, no otherwise than if it were quencht in water: but if the Grate be drawn up again presently, while the Coals are still very hot, the fire will by little and little be kindled again, and shine as before.

As for the reason Mr. Hobbs assigns of our Experiment in the lately mentioned passage of his Dialogue, being grounded upon such a thickness of the Air in the * 1.36 Receiver as we have already disproved, it needs not to be examined. And lastly, as to what he subjoynes in these words, Quando autem est quod de homine vere pro∣nunciare possumus quod est mortuus, sive (quod idem * 1.37 est) animam expiravit. Cognitum enim est homines nonnullos pro mortuis habitos, postridie elatos revixisse.

A. De puncto temporis quo anima à corpore separatur difficile est statuere. Perge igitur ad experimenta alia.

I confess I see not why that needless Question might not have been well spared, if he designed to give it no better Answer.

CHAP. VI. Wherein other passages of Mr. Hobbs's Dialogue that concern the Author are examin'd

WHat our Author has in the 19. page concerning a Bladder has been already examined, wherefore I pro∣ceed to the next passage in the same page, which is this; B. Si acus magnete excitus libere pendeat intra Recipiens, se∣quetur tamen ille motum ferri quod circumducitur extra Recipi∣ens. Item object a intus posita ab iis qui extra sunt videbuntur, & soni intus facti audientur, omnia haec aeque post at{que} ante exuctionem aëris, nisi quod soni sunt aliquanto post quam ante debiliores.

A. Manifestissima haec sunt signa Recipientis semper pleni, nec posse inde exugi aërem. Quod autem soni inde sentiantur debiliores, signum est consistentiae aëris. Consistentia autem aëris à motu ejus est per lineas diametraliter oppositas. But I meet with few of the Vacuists, who, even in the Torricellian Experiment, think the place relinquished by the Quicksilver to be perfectly void, most of them allowing, that though it be not quite full of body, yet it may contain some of the Earth's magnetical steams, or of those igneous Corpuscles that flow from the Sun, or both of them. Now against these who would from our Experiments deduce but onely an interspersed Vacuum, I see not that the Phaenomena mention∣ed by Mr. Hobbs do conclude half so manifestly as he pre∣tends: For, as to the motion of the Needle within the Re∣ceiver, 'tis known that they are wont to ascribe Magnetical Attraction to certain Effluvia, that issuing out of the Load∣stone are subtile enough to pass through the Pores of the closest bodies without excepting Glass; so that although the Receiver were quite empty'd before, the Needle might be wrought upon by Magnetical Corpuscles, that need not be supposed to fill the 10th. part of the Receiver. I know in∣deed that Mr. Hobbs has another Hypothesis of the Phaenomena

of the Loadstone, but I know that divers learned Writers have absolutely rejected it, and not one such that I have heard of has approved it. And as for the other two Phae∣nomena here mentioned by Mr. Hobbs, the Atomists may an∣swer, That the first (touching Objects seen in the Receiver) has been shewn already not to overthrow their Doctrine: and that the other (concerning the Debilitation of Sounds) makes against him, not for him; since we have already dis∣proved that consistence of the Air whereto he ascribes it. And the same Arguments that overthrow that Opinion may make it seem somewhat strange, that he should subjoyn our Experiment of two like Pendula, whose Vibrations we found not manifestly to differ within and without our exhausted Receiver. For the former should move far slower than the other according to Mr. Hobbs's Conceit, that the Receiver, when we say 'tis exhausted, is filled with a substance of a middle consistence betwixt * 1.38 pure Air and Water, and not much lighter than Water. But whether the Receiver be in such cases adequately full or no, the Vacuists may further consider. For its being granted to be full would not overthrow either of my Hypotheses, namely, the Weight and Spring of the Air.

In the same 19. and some following pages Mr. Hobbs, has a long Discourse against my Conjecture at the reason I pro∣pose in my 31. Experiment, why (as I there express it) if the exquisitely polisht Surfaces of two flat pieces of Marble be so congruous to each other, that upon their mutual application there results an immediate contact, they will stick so fast to∣gether, that he that lifts up the uppermost shall, if the un∣dermost be not exceeding heavy, lift up that too, and sustain it aloft in the free Air. The Conjecture it self is in the same page thus set down, That the lower superficies of that (un∣dermost) stone being freely exposed to the Air, is prest * 1.39 upon by it; whereas the uppermost surface being contiguous to

the superiour stone, is thereby defended from the pressure of the Air, which consequently pressing the lower stone against the up∣per hinders it from falling, as we have elsewhere more fully declared. Which last words I therefore omit not, because they shew that I handle this matter in this place but inciden∣tally, and may make use of what I have deliver'd where I treat of it more expresly; as I have since done in Print in the History of Fluidity and Firmness, which Mr. Hobbs appears to have seen by those censures of some passages of it that I shall hereafter examine.

His whole Discourse concerning my Conjecture, and his Scheme, would be too prolix to be entirely inserted. But the thing his Discourse drives at is to shew, that neither the Spring nor Weight of the Air have any thing to do with this Phaenomenon: and therefore when he had made his Academian relate, that two coherent Marbles suspended in our Receiver did not fall asunder upon the exhaustion of it, he subjoyns that it was, Quia nihil istic erat quod ageret Atmosphaerae pon∣dus; and annexes, Experimento hoc excogitari contra opinionem eorum qui Vacuum asserunt aliud argumentum * 1.40 fortius aut evidentius non potuit. Nam si duorum cohaerentium alterutrum secundum eam viam in qua jacent ipsae contiguae su∣perficies propulsum esset, facile separarentur, aëre proximo in locum relictum successivè semper influente; sed illa ita divellere, ut simul totum amitterent contactum, impossibile est, mundo pleno. Oporteret enim aut motum fieri ab uno termino ad alium in instante, aut duo corpora eodem tempore in eodem esse loco: quorum utrumvis dicere est absurdum. But how this should be so cogent and manifest an Argument against the Vacuists I confess I do not well discern. For that which it proves (if it prove any thing) seems to be, That in case the cohering Marbles could be so severed as to lose at once their whole contact, the world might be concluded not to be full: But I see not how it thence follows, that therefore there can be no Vacuum. For my part I would demand, whether the so

strong cohesion of the Marbles be necessary or not to the plenitude of the world. If it be, how chance a sufficient weight hung to the lower Marble can immediatley draw them asunder? and if it be not, why does not Mr. Hobbs assign some other cause of their so strong adhesion, if it depend neither upon the Spring nor Weight of the Air? As for the non-separation of the two Marbles in our Receiver, I have said in the same 31. Experiment, that the cause may probably be the pressure of the Air remaining in the Receiver not suf∣ficiently exhausted. And this Conjecture I have more fully defended in what I have written about it against Franciscus Linus, where I shew, that 'tis no way unlikely the remaining Air should be able to sustain a weight of four or five Ounces hanging at the lower Marble, since the free Air was able to support between 400. and 500. Ounces hanging at the same.

But Mr. Hobbs tells us, that the cause I assign of the cohe∣sion of our Marbles is lyable to huge inconveniences; of the greatness of which we may judge by the first of them Confi∣tentur (sayes he) tum ipsi tum alii omnes, ponderatio∣nem omnem conatum esse per lineas rectas undiqua{que} ad * 1.41 centrum terrae; & proinde non Cylindrum vel Columnam fieri, sed per Pyramidem, cujus vertex est centrum terrae, basis pars superficiei Atmosphaerae. As if it were much material whether a body whose Basis is scarce two Inches Diameter, and whose length amounts to some thousands of Miles, be considered as a Cylinder or a Piramid. Certainly Stevinus and other learned Writers of the Hydrostaticks would scarce have made this an Objection, since they scruple not to make it a postu∣latum, that all not very distant Perpendiculars be looked upon as parallel, though they allow such Perpendiculars would meet in the Centre of the Earth. What he adds partly in these words, Conatus ergo punctorum omnium ponder∣antium propagabitur ad superficiem Marmoris superioris * 1.42 antequam possit propagari ulterius (puta) ad terram, and partly in the following lines, to prove that the whole endeavour of

the Pyramid that leans upon the upper Marble is terminated there, and that there is no endeavour of the Atmosphere a∣gainst the under-superficies of the lowermost Marble; This Ratiocination seems grounded, partly upon a Conceit of his about the nature of Gravity, according to which I see not why any Body plac'd between the sides of that Pyramid or rather Cone, whereof the upper-superficies of the higher Marble is the Basis, should descend upon the account of gravi∣ty; and partly from a mistake of my Opinion: for I do no where, that I know of, speak as if I thought this sustentation of the lower Marble were performed by little Globules or other mi∣nute bodies protruding one another directly towards the Cen∣tre of the Earth, and rebounding from a perfectly smooth superficies; nor need I say, that the lower stone is sustained by the pressure of the self-same pillar of the Atmosphere that is incumbent on the upper, since other parts of the Atmos∣phere, some on the one hand and some on the other, pressing obliquely upon the uneven surface of the Earth, may have their pressure upward terminated against the lower surface of the undermost Marble. And in the mentioned History of Fluidity and Firmness, speaking (pag. 187.) of the adhesion of flat Glasses, (and the reason is the same in our flat Marbles) I plainly deduce it from the pressure of the fluid Air, which, like a liquor, diffusing it self upon the surface of the Ter∣restrial Globe, because its descent is there resisted, does, like water and other liquors, press almost equally every way, and strongly endeavour to thrust away any body against which it can bear; so that whereever the pressure is taken off from one part of a body and not from the opposite, that body will be prest toward that part, whether it be downwards, or side∣wards, or upwards, where that formerly-equal resistance is removed. And this Explication I do in that Discourse back with Considerations and Experiments, which Mr. Hobbs is not pleased to take any notice of; wherefore I hold it not amiss to adde here two or three other experiments to one of those mentioned there.

First then, an AEolipile being by heat freed from Air as much as you can, if the little hole at the extremity of the neck, by which the Air gets in and out, be presently and carefully stopt with Wax, and afterwards suffer'd to cool, there will not be in the Cavity of the AEolipile a resistance any thing near equal to the pressure of the outward Air. And there∣fore if you perforate the Wax, that Air will violently be im∣pell'd in at the unstopt Orifice, whether the neck be held parallel or perpendicular to the Horizon, or in any other si∣tuation in respect of the Centre of the Earth. And the like will happen if the AEolipile be unstopt under water.

Next, I relate in the mentioned History, that having drawn some of the Air out of a large Glass with a narrow mouth, and thereby destroyed the equality of force betwixt the weight of the outward Air, and the now weakned spring of the inward; I found that by immediately applying a flat body to the Orifice of the Vessel, that body was readily lif∣ted up and sustain'd in the Air as long as I pleas'd, though the weight of it exceeded 20. Ounces.

Thirdly, I lately met with the relation of an Experiment which does abundantly make out the power of the ambient Atmosphere to press bodies against each other, when it can∣not get between their internal surfaces. For the ingenious Author of the Magdeburgick Experiment writes to the indus∣trious Schottus, that having caused two Copper Plates to be made almost in the form of Scales a little above half an Ell in Diameter, and exactly congruous if laid upon one another; Has (sayes our Jesuite) si mutuo sibi imponit, & aërem extrahit, adeo ab externi aëris gravitate * 1.43 compressae at{que} unitae tenentur, ut sex viri robusti eas divellere non possint. Quod si tandem adhi∣bito omni conatu divellantur, crepitum edunt sclopeti aut Musque∣tae explosioni non minorem; quamprimum vero per claviculum feu Epistomium apertum vel minimus aditus laxatur aëri, sponte separantur.

And, Fourthly, if a Glass Vial (such as will be anon more fully describ'd) have a Pipe open at both ends so fitted into it, that no Air can get in or out betwixt the neck and it; and if the Vial be so far filled with water, that the lower end of the Pipe be well immersed therein; if then you suck at the upper end of the Pipe, the water will ascend to a good height; which argues its being forc'd upwards by the oblique pressure of the Air in the Vial; for 'tis onely in the Pipe and not in the Vial that there is any Air in the same Perpen∣dicular with the Water that is impell'd up.

But let us follow Mr. Hobbs a little further. Having ask'd this Question, Sed vis illa elastica quam in aëre esse dicunt, nihilne ad marmor sustinendum conferre potest? he answers, Nihil omnino; non enim conatus in aëre est * 1.44 ullus ad centrum terrae magis quam ad aliud quodvis punctum Universi. Quoniam enim gravia omnia tendunt à circumferen∣tia Atmosphaerae ad centrum terrae, & inde rursus ad circum∣ferentiam Atmosphaerae per easdem lineas reflexas, conatus sur∣sum conatui deorsum aequalis erit, & proinde mutuo se perimentes neutrâ conabuntur viâ. But that the Spring of the Air may perform somewhat in the case proposed, I hope the newly-mention'd Experiments have evinc'd. And the reason he annexes to his Negative, as also the difficult Example he sub∣joyns, of a man lying in the bottom of the Sea, seem rather oppos'd to the Weight than the Spring of the Air. But we have already both by Experiments and by his own Concessi∣ons sufficiently prov'd that the Air is not devoid of gravity; and that it likewise gravitates upon the terraqueous Globe, which in this page he seems to deny, we have proved by divers reasons, and particularly in our 25. Experiment by the vast expansion of Air under Water, when the pressure of the incumbent Air was taken off from the Water.

As for the Scheme he annexes, I confess I do not well see what he drives at in it; at least if it be intended for a Confuta∣tion of the Conjecture I have been defending: nor am I the

onely person that complain of his writing often enough ob∣scurely. And as far as we can judge by the conclusion couch'd in these words Non potest ergo pars, BC. (which in the Ex∣plication of the Scheme he calls, Pars Atmosphaerae intra to∣tam posita ubicun{que}) (propter magnitudinem) quantumvis gra∣vis sit descendere, ne{que} ergo premere sive gravitare; his No∣tions about Gravity are somewhat strange, and probably either do not concern us, or will be found repugnant to those Experiments on which our Conjecture is grounded.

And as for what he adds, Si possibile esse negarem, ut diligentiâ & arte humanâ duae superficies corporum * 1.45 duorum inter se per omnia puncta ita accurate congruae fiant, ut ne minimo quidem corpusculo creabili transitus permittatur, non video quomodo illi aut suam Hypothesim tueri, aut negati∣onem nostram improbitatis arguere jure possent: I confess I do not see how this Argumentation proves any thing against the Interest, either of the Weight, or so much as of the Spring of the Air in the cohesion of our Marbles. For, provided that the Corpuscles of the Air get not in between the two stones, the pressure of the Air may well suffice to keep them together. And, lastly, as for that modest passage (that im∣mediately precedes the words newly recited) wherein he sayes, Vtra{que} illa phantasia, tum gravitatis At∣mosphaerae, tum vis Elasticae sive Antitupiae aëris, * 1.46 somnium erat. Siquidem autem illis concederetur esse aliquam in filiculis aëris Antitupiam, quaeret{que} aliquis, unde illa cur∣vata quidem sed quiescentia moverentur rursus ad rectitudinem, deberent illi, si Physici haberi volunt, causam ejus aliquam pos∣sibilem assignare: We have already given an account why we forbore to assign a cause of the motion of Restitution; but methinks Mr. Hobbs might have, for the speaking so, chosen a fitter place than this, where he gives me so far an oppor∣tunity to tell him again, that he should, if he would be thought a Naturalist, have assigned some cause of the Phae∣nomenon about which he had all this while been desputing:

which since even he himself has declin'd to do, perhaps the Phaenomenon will be thought somewhat difficult, and my at∣tempt at discovering the cause of it will be at least excused.

But after having so long dwelt upon the consideration of our Marbles, it is high time to proceed to what remains.

In the 24. page Mr. Hobbs has that passage I formerly re∣cited touching the Glass-Fountains, out of which water is thrown up by compress'd Air. But though I as well as others have made use of such Fountains, invented by Vincenzo Vin∣centi of Urbin, and was unsatisfied with the account he gives of their Phaenomena; yet in regatd some learned men, and particularly Dr. Ward, have already examined his Explicati∣on, and I am not obliged to do so; I shall onely take notice of what our Author objects to prove that this Phaenomenon cannot be solv'd by the Spring of the Air, in these words:

B. Cur non potest aqua, quae cum injiceretur parti∣culas aëris comprimebat, ab iisdem particulis se expli∣cantibus * 1.47 rursus rejici?

A. Quia locum explicatae majorem non requirunt quam com∣pressae. Quemadmodum in vase aqua pleno, in qua esset mul∣titudo anguillarum, anguillas sive in se volutas sive explicatas idem semper capit locum. Propellere ergo aquam per vim Elasti∣cam, quae alia non est quam motus corporum se explicantium, non possunt.

B. Comparatio illa aëris cum aqua anguillis plena, nostris, credo, non displicebit.

But the Elaterists will answer, that neither can his earthly Atoms, to whom he ascribes the Rejection of the water forc'd in, truly fill up more parts of space at one time than at ano∣ther; and therefore the Objection might have been spared: but indeed it reaches us not. For we, as Mr. Hobbs knows well, are not wont to compare the Air to Eels, but to Wooll: and though each hair that makes up a compress'd lock of wooll, do not really fill more space with wooll when extended than when crumpl'd; yet when there is a congeries of these hairs

compress'd together, the whole fleece or congeries does by its spring endeavour to thrust away those contiguous bodies by which it is penn'd up, as I have more fully explained in my Epistle; so that these Aerial Corpuscles, being pent up by the water forc'd into the Glas, still endeavour to expand themselves by throwing it out.

What our Author addes in the same page, as if they were mistaken that think the Experiments of the Plenists tended (especially till of late) to prove that the generality of them did not always mean by a Vacuum a space perfectly devoid of all corporeal substance, but any space here below that is not fill'd with a visible body, or at least with Air, (for these are my words to which I suppose Mr. Hobbs alludes) To this, I say, it is scarce worth while to make answer, the Controversie being of such small moment, (though I think I could easily enough do it) especially since he rather excuses those that may have negligently exprest themselves, than disproves what I said. And since I spoke chiefly and by name of the Peripatetick Schools, he may well allow that their Expressions concerning this matter were not alwayes so accurate, whilst in this very passage he concludes with these words, Vides quam ineptum sit ad explicationem effectuum talium advocare verba Metaphorica, ut fugam vacui, horrorem naturae, &c. * 1.48 quibus olim ad existimationem suam tuendam usae sunt Scholae. Nor is what he adds concerning the Vacuum to be attributed to Democritus and Epicurus either clear enough, or of con∣cernment enough to our Dispute, to be insisted on by us; especially since I see not to what purpose he brings it in.

But there are in this page two particulars, which, though they make little or nothing against what I said of the Plenists, may deserve to be taken notice of.

The second (for I think it expedient to dispatch that first) is couch'd in these words, In Hydriis perforatis ideo haeret aqua, quia quae per tantillum foramen exiturit, adeo exigua est,* 1.49 ut non posset ita in longitudinem se diffun∣dere,

ut descendendo aditum aëri faciat per foraminum circum∣ferentias; ne{que} aër ab exeunte aqua pulsus locum alium (in mun∣do pleno) habere potest praeterquam quem aqua deseret.

But this Experiment I have already examined as 'tis pro∣pos'd in his Elements of Philosophy; and therefore I shall now onely say to the light variation I find of it here, that the reason here assign'd why the water in Gardeners pots clos'd at the top does not descend, is not rightly assign'd, since (to omit other objections) by Monsieur Paschall's Ex∣periment it appears, that though in Pipes of no great length the water will not run out, yet if the Pipe be long enough, though the Orifice be no wider, the water will descend with∣out giving passage to the Air at the circumference of it.

But the other particular here mentioned by Mr. Hobbs, who thus proposes it, Qui per fistulam ore aquam sugit, aerem medium prius sugit, quo distentum aerem externum removet; qui remotus locum (in pleno) habere nisi * 1.50 proximum removendo non potest, & sic continua pulsione aqua tandem pellitur in fistulam, succedit{que} aeri qui exugitur; de∣serves a more particular consideration. For this account of the ascension of Liquors by suction is not onely here given by Mr. Hobbs, but for the main by the learned Gassendus himself, and other Atomists, and is generally acquiesc'd in by the modern Philosophers; perhaps the rather, because it seems not to establish or overthrow a Vacuum. But though I shall not deny but that many Phaenomena of Nature may be probably explicated by this Propagation and return of Motion; yet there are some Phaenomena here below, which I see not how the Cartesians, or the Atomists, or Mr. Hobbs can explicate without admitting the Spring of the Air, and which perhaps by the Spring of the Air may be explicated without the recurring to such a propagation and return of impulse. Divers instances to this purpose I elsewhere consider, but at present I shall propose onely one Experiment purposely devis'd to

shew that both Vacuists and Plenists should admit an Elastical power in the Air. I took then a Glass-Vessel consisting of two parts; the one was a Vial capable of con∣taining about a pound of water, and the other a Pipe open at both ends, the lower of which reach'd within two Inches of the bottom of the Vial: this Pipe was by the Glass-man fastn∣ed into the neck of the Vial, not by any Cement, lest, it should be pretended that the Air might undiscernedly get in or out, but with melted Glass of a good thickness: into this Vessel by the open Pipe I at length (for it is somewhat difficult) pour'd water enough to swim a pretty way above the lower extreme of the pipe, and then often inclin'd the Vessel, to give a free intercourse betwixt the Air within the Vial and that without it, that if the internal Air were comprest by the affusion of the water it might free it self, as it readily did by ascending in bubbles along the inclined Pipe, till the outward and inward Air were reduc'd to an equality of pressure. Now if all Suction were produc'd by the pressure of the Air, thrust away by the dilated Chest of him that sucks, and so thrusting the water or other liquor into the Pipe at which he sucks, it seems evident, in our case, that the water would not ascend by suction: since by the contrivance of the Vessel, the Air thrust away by him that sucks cannot at all come to bear or press upon the water. And yet, whether the Pipe were inclin'd or erected, the water did according to my expectation easily enough ascend, upon suction, to the top of the Pipe, and ran over into my mouth. I say, easily enough, because that though the Spring of the Air pent up in the Vial were able, upon the decrease of the pressure of the out∣ward Air, occasion'd by my sucking, to impell the water strongly enough into the Pipe; yet, when a pretty quantity of water had been so impell'd up, the included Air gaining thereby more room to expand it self, its spring was thereby so far weakned, that the water ascended far less easily than in ordinary suction. The other circumstances worth noting in

this Experiment belong not to this place; and what has been delivered may, I hope, suffice for the purpose 'tis alledg'd for. Onely one particular I shall here adde, by way of confirm∣ation of what I said touching the weakn'd Spring of the Air, and it is this; That partly to shew some, who yet embrace the Opinion of the Schools, that the ascension of the water in the Pipe did not proceed from any such tendency in the water it self to ascend for prevention of a Vacuum, and partly for other reasons that concern not this place, I did carefully take out the water by degrees, till the lower end of the Pipe was but very little under the surface of the water, though in the cavity of the Pipe the water, as it usually will be in Pipes that are not wide, was a pretty deal higher: then suffering the Vessel to rest, and sucking at the upper end of the Pipe, the water (as I foresaw it would be) was impell'd up, yet without reaching near the top, till the surface of it was fallen a little below the bottom of the Pipe. But then, though I continu'd sucking, no more water ascended into the Pipe, but the Air passing through it towards my mouth, did in its passage toss up the water that was already in the Pipe, and turn it into bubbles, (of a strong bigness when the cavity of the Pipe would permit it) which broke (not without noise) one after another: and thus the ascending Air for a pretty while kept the water in the Pipe from falling back to that in the Vial. But when I remov'd my mouth, the Spring of the Air remaining in the Cavity of the Vial, being debi∣litated by the recess of the Air I had (as men are wont to speak) suck'd out, it was not able to resist the pressure of the outward Air, and accordingly the water in the Pipe was not onely depress'd into the Vial, but the outward Air forc'd its way in many bubbles, and not without some noise, through the water contiguous to the bottom of the Pipe, till the pressure of the included Air and that of the Atmosphere were reduc'd to an equality.

But in the same 25. page our Author tells us, that the

Society he writes against would have the cause of Filtrati∣on, and that of the passage of water through Siphons, to be the same. To which he annexes, this peremptory passage, Id vero impossibile est. Nam in Siphone nisi ambo crura aquâ impleantur, aqua è pelvi non ascendet. Ascensionis causa in pannum est motus ille terrearum atomorum quae aquae contiguae sunt, motus (inquam) circularis simplex, aëri in quo moventur communicatus; quae atomi aquam ferientes in materi∣am laneam incutiunt, incussae autem magis magis{que} madefaciunt, donec madida tota sit. Cum vero madida tota sit, &c. Thus far he; but the passage in my Epistle, upon which he seems to have grounded his Opposition, is but this (wherewith I begin my 35. Experiment) Some learned Mathematicians (I meant the industrious Schottus and some Cartesians) have of late ingeniously endeavoured to reduce Filtres to Siphons; but still the cause of the ascension of water and other liquor both in Siphons and in Filtration needing (for ought we have yet found) a clearer discovery and explication, we were desirous to try, &c. So that neither did I ascribe this reduction (of Filtres to Siphons) to a Society which was not then in being, nor perhaps so much as design'd; nor did I adopt it my self; but express'd a desire to have it further examin'd. But as for the cause of Filtration it self, I may take a fitter opportunity to dis∣course of it; in the mean time I doubt whether the reason here assign'd by Mr. Hobbs will not seem as well precarious, as the motus circularis simplex of earthly Atoms, whereon it is grounded. Nor does his Explication render a reason why Quicksilver will not ascend the 14. part as high in the Filtre, though in part immers'd into it, as water, nay, will not reach so high where 'tis contiguous to the Filtre, as where 'tis not: nor why it should begin to ascend, since, for ought he shews to the contrary, the pressure of the Air, even in the sense he takes the Air, ought to be the same on that part of the Surface of the Liquor which is contiguous to the Filtre, and on any other part of the same Surface. To which I shall

onely adde, that as resolutely as Mr. Hobbs sayes 'tis impossible for the water to ascend out of the Vessel into a Siphon, un∣less both the legs be fill'd with that Liquor, he would pro∣bably have spoken more warily, and distinguish'd betwixt Siphons, if he had been pleased to take notice of what I relate in the-forementioned 35. Experiment, of a small Glass-Siphon I devis'd, whereof when the shorter leg was but dipp'd in wa∣ter, the Liquor did presently as it were of it self run down the longer leg. Which Experiment, besides other consider∣ations, may induce us to suspect that the nature of Siphons and of Filtration may not yet be so throughly understood, as not to deserve a further enquiry.

But to draw at length towards a Conclusion of our trou∣blesome Examen; it remains onely that I take some notice of the general Corollary that Mr. Hobbs is pleased to deduce from his whole Discourse, of the Experiments exhibited in our Engine.

A. Fateris ergo (says he) nihil hactenus à Col∣legis tuis promotam esse scientiam causarum naturali∣um, * 1.51 nisi quod unus eorum machinam invenerit qua motus exci∣tari aeris possit talis, ut partes sphaerae simul undiqua{que} tendant ad centrum, & ut Hypotheses Hobbianae, ante quidem satis probabiles, hinc reddantur probabiliores.

B. Nec fateri pudet; nam, Est aliquid prodire tenus, si non datur ultra.

A. Quid tenus; Quorsum autem tantus apparatus & sumptus machinarum factu difficilium, ut eatenus tantum prodiretis quantum ante prodierat Hobbius? cur non inde potius incepistis ubi ille desiit? cur principiis ab eo positis non estis usi? Cum{que} Aristoteles recte dixisset, Ignorato motu ignorari naturam, quo∣modo tantum in vos suscipere onus ausi estis, &c.

As to what he sayes to the disparagement of the Assem∣bly, and in his own praise, the laws I prescribed my self at the beginning of this Discourse forbid me to reply to what is more likely, amongst civil and judicious Readers, to pre∣judice his own reputation than theirs he is so displeased with.

And as for that which he assigns to be the use of our Engine, I shall very willingly leave it to the ingenious to judge what use may be made of it. But as for this mentioned by Mr. Hobbs, if he means here, as he elsewhere teaches (pag. 13. and 19.) that the Motion he speaks of is produc'd by that of the Air impell'd betwixt the sides of the Sucker and the Cylinder; perhaps it will be thought I have sufficiently prov∣ed, that 'tis not any of its uses, so far is it from being its chief or onely use. But I consess I somewhat wonder Mr. Hobbs should quarrel with me, (for 'tis I that in my Epistle em∣ploy the following Verse) for saying,

Est aliquid prodire tenus, si non datur ultra.

And this not, as some would perhaps suspect, because I do not imitate him, in speaking of my self, as he does of himself, but because he thinks the expression too arrogant. For since he here confesses that his Hypotheses are by this Engine rendered more probable, some will perchance think that to be enough to entitle my Experiment to some degree of usefulness, unless Mr. Hobbs's Doctrine of the Air had found more embracers than before these seasonable, though despised, Experiments it was observed to have. But, since either of us may be partial in his own case, I am very well content to leave others to judge both whether my Expression have been guilty of Arrogance, and how much he has done more than prodire tenus in all the past long Discourse against me, when they have considered what new Experiment or matter of fact Mr. Hobbs has therein added to enrich the History of Nature, what new Truths he has discovered, or what Errors (except one of his own in the last page) he has well confuted. These things, I say, I am very well content to leave to be judged of by all dis-interessed persons, with∣out being much discouraged by the differing strain wherein Mr. Hobbs thinks fit to speak of his own performances and mine, or invited to imitate him in that way of writing, my Endeavours (such as they are) having hitherto been favoured

with such a Reception among the Virtuosi, that possibly I may have almost as little need as reason to commend them.

But 'tis somewhat trouble some work to argue long with a man that's angry with an Expression, which perhaps none but he would have found fault with for want of modesty; and therefore as I have lest un-recited several provoking and very undeserved Expressions he emploies in the same page, and even that passage, where to prove our Naturalists and Mathematicians professed they would not receive Truth com∣ing from him, he alledges onely a saying (whether true or no I examine not) of Dr. Owen, who, besides that his pro∣fession was Divinity, not Philosophy or Mathematicks, nei∣ther is nor ever was of our Society; as, I say, I have (for the reason newly intimated) declin'd taking notice of mat∣ters of this nature; so I will not now stay to enquire why he urges us, whom he would have men take for Vacuists, with the Authority of Aristotle, whom on other occasions he is wont to use with as little respect as if he were a Mem∣ber of our Society. Nor shall I now examine, why here and elsewhere he sends us to his own Writings for the Doc∣trine of Motion, as if, to omit ancienter Authors, such great Personages as Galilaeo, Mersennus, Verulam, Des-Cartes, Gas∣sendus, Balianus, Foannes Marcus Marci, Honoratus Fabris, (not to mention other Moderns, nor those of our own as∣sembly, as the eminently learned Sir Kenelme Digby, and the others, whom their Modesty forbids me here to name) had not most of them learnedly, and some of them copiously, written of Local Motion before Mr. Hobbs's Books, where he treats of it, came abroad into the World. This, I say, I shall not insist on, because I would hasten to a Conclusion. Onely one thing I must adde, that where∣as he accuses us of devising elaborate and sumptuous Engines, I do not fear to find so many Readers of his mind, that I need make them Excuses for what perhaps will obtain their Thanks. And whatever Mr. Hobbs may think, for my part I freely confess, that I love Truth so well, that I do not think, no

onely my Pains and Charges, but even what I rate much higher, my Time it self, too much for the discovery of Truth; or (that Mr. Hobbs may not think me partial) even for the establishment of such Truths as, though discover'd by some, are yet as far more generally opposed than imbraced.

There remain yet some other pages of Mr. Hobbs's. Dia∣logue, wherein he speaks of Fire, and Cold, and Ice, and Light, and Colours, and Fluidity, and Hardness, and Thickness, and Ethicks, and Politicks, and the Duplication of the Cube, and the Quadrature of the Circle, and several other Subjects. But these I forbear to meddle with, not that I approve them all, or the greatest part, but partly, because I am too much tired already to be fond of engaging in Controversies that I am not tyed to meddle with, (except what concerns Fluidity and Firmness, which I shall, God willing, examine by it self;) partly, because divers passages relate to Persons, not Things: partly, because I do not much fear that Mr. Hobbs will find e∣very Reader so easie and complaisant as he makes his Acade∣mian, who in many passages of the Dialogue speaks not un∣sutably to what he does in the last page ofit, where he ex∣cepts but one particular (and that is neither the Duplication of the Cube, nor the Squaring of the Circle) when he tells Mr. Hobbs, Discedo jam multo (ut mihi videor) quam ante certi∣or, & quae dixifti omnia teneo & probo: and partly, because Mr. Hobbs has some things, as about Fire, and certain Col∣ours, which I am not forward to reject, though the Consider∣ations that incline me to some such Opinions be perhaps very differing from the Grounds on which he proposes them. And indeed as well my Nature as my Custom forbids me to scruple to learn, if I can, of Persons much less famous than Mr. Hobbs. 'Tis far from my humour to write against all that every man sayes, that (how causlesly soever) writes against me; and I am almost as much indisposed to reject as to embrace, with∣out distinction, whatever it be that this or that man teaches.

CHAP. VII. (Being an APPENDIX to the past Discourse) Wherein is examin'd what Mr. Hobbs teaches concerning Fluidity and Firmness.

ALthough Mr. Hobbs do not name me for the Maintainer of the Opinions which I have proposed in the History of Fluidity and Firmness, and which he censures: yet since that History, after having been mentioned in the Book I have hitherto been defending, was published a good while before Mr. Hobbs's Dialogue; and since some of the chief particulars he censures or takes notice of, are delivered there, and some of them perchance no where else; I think it may concern me to examine what he sayes either against my Opini∣ons, or in favour of his own, touching Fluidity and Firmness. And if it be said that he meant not his Objections particularly against me, but rather against some other person, who may have liked such Opinions: I shall answer, That I am content to leave to others the defence of their particular Opinions, and to have as much of the following Discourse as is concern∣ed in this Allegation, looked upon as written onely upon this supposition, that my writings are those he designs to oppose. But there being other things in what he discourses about Flu∣idity and Firmness, which for the reasons freshly intimated I think fit here to consider, I chuse to gather up together the passages touching these subjects which I find scattered in his Dialogue, that I may have the better opportunity to clear up the matter it self under debate.

But, before I go further, I must at the very entrance of this Discourse take notice, that in the fifth page, where Mr. Hobbs begins to dispute against our Notion of Fluidity, he very much mistakes my Opinion, as may appear by these words, which he puts into the mouth of his Academian, Sed pleri{que} nostrum naturam fluidam à non fluida distingui∣mus * 1.52 magnitudine partium ex quibus corpus aliquod constat, & quasi compingitur: Ita{que} non modo aërem; aquam & liquorum

omnem, sed etiam cinerem & pulverem, tanquam fluida contem∣plamur. Et fluida ex non fluidis composita esse posse non nega∣mus; nam divisibilitatem illam infinitam non concoquimus. To which he answers, Divisio quidem infinita concipi non potest, divisibilitas autem facile. Ego contra, distinctionem non capio intra fluida & non fluida quam sumitis à magnitudine partium; nam si caperem, ruina illa sive rudera illa quae jacent in Ecclesia Paulina mibi dicenda essent fluida: sin propter nimiam lapidum magnitudinem fluida illa esse negaveritis, defini mihi magnitu∣dinem illam quam habens pars ruentis muri, propter eam sit dicenda fluida. Tu vero qui divisibilitatem infinitam non ca∣pis, dic mihi quae tibi apparet causa, quare Deo omnipotenti difficilius esse putem creare corpus fluidum, & cujus partes actu diffluant, omni data atomo minus, quam creare Oceanum. Ita{que} desperare me facis omnem conventus vestri fructum, dicendo quod putant aërem, aquam, & caetera fluida constare ex non fluidis, tanquam si murum, cujus ruentes lapides aliquous{que} dis∣currunt, dicerent esse fluidum. Si sic loquendum est, nihil non est fluidum; nam etiam marmor comminui potest in partes omni atomo Epicureana minores. Thus he. But in my History, though I make the smalness of the parts whereof a body con∣sists one of the requisites to its being fluid; yet at the end of the 13. Section I call the various agitation of those Par∣ticles the principal qualification of all, and in the beginning of the 14. Section I call it the cheif condition of a fluid body. And therefore he much mistakes, if he thinks that we alwayes consider Ashes and Dust as fluids absolutely speaking. But as he * 1.53 somewhere tells us, that by Fire he understands the combustible matter it self, not simply and alwayes, but then onely when, &c. So neither do I look upon the Dust of Alabaster, (to my words about which, I suppose, he has a respect in the pas∣sage under consideration) as a fluid body simply and alwayes; for I clearly teach the contrary, but onely when and whilst its parts are not alone reduced to a competent small∣ness, but are also actually put into such a various agitation as

makes the body they compose (even according to Mr. Hobbs's own Definition, which is, That Fluid bodies are those whose parts may by very weak endeavour be * 1.54 separated from one another) emulate a fluid body by the very easie Cession of its component Corpus∣cles, and by its boyling like a liquor. By this the Reader may discern how little that makes against me which Mr. Hobbs talks, and seems to do it seriously, of the Ruines of Pauls; as if according to my Opinion, Ruina illa sive rudera a quae ja∣cent in Ecclesia Paulina dicenda essent fluida. For 'tis most evident that I require in the parts of a fluid body both minu∣teness and such a motion along each other as makes them ea∣sily yeild to the touch: which qualifications how well they belong to the ruines of Pauls, is, I think not very difficult to determine; though in the same passage Mr. Hobbs do again make use of the like example, to which he subjoyns. Si sic loquendum est, nihil non est fluidum; which how little it follows from my Doctrine about Fluidity there needs not a quick-sighted Reader to discern. As for the Reason he an∣nexes in these words, Nam etiam marmor comminui potest in partes omni atomo Epicureana minores; I would gladly know by what art Mr. Hobbs can divide Marble into lesser Parti∣cles than such as are naturally indivisible, (for such Epicurus makes his Atoms to be:) nor do I see how, in case this could be done, it proves, that there is not any thing that is not fluid. For I say that the blocks of Marble before Com∣minution are not fluid, either according to him or according to me; nay, the greatest Comminution imaginable would not, according to my Doctrine, make a lump of Marble fluid, unless the heap composed of the parts, how minute soever, were actually and variously set a moving amongst themselves. But he would perhaps have spoken more warily, if he had considered the difference there is betwixt saying that all things are fluid, and saying, as I do, that there are many bodies that are now solid, which by Comminution, Motion, and other requisite alterations, may be made parts of a fluid body:

As hard Ice may be turned into fluid Water, and Quick∣silver precipitated per se into a red Powder, may be reduced to running Mercury. As for what he sayes of an infinite divisibility of body, it is scarce in this place worth while to examine it.

For I have shewn in the History of Firmness, that this Di∣visibility (which I had then considered) does no way over∣throw my Doctrine of Fluidity; nor does Mr. Hobbs here an∣swer what I there discourse. Besides that indeed I donot so well understand what he means and drives at, when he sayes that Divisio quidem infinita concipi non potest, Divisibilitas autem facile. For since in this very passage and within a very few lines he has recourse in this matter to God's Omnipotence, I see not why an infinite division cannot be as well conceived as an infinite divisibility, since sure an Omnipotent Agent is able to do what is possible to be done; and why else should a body be called infinitely divisible? Besides, when Mr. Hobbs has recourse to what God can do, (whose Omnipotence we have both great reason to acknowledge) it imports not to the Controversie about Fluidity to determine what the Al∣mighty Creator can do, but what he actually has done. And, lastly, whereas my Adversary requires to have the magnitude defined which a part of a falling Wall ought to have to deserve the name of fluid; first, he should have clearly proved that Flu∣idity belongs to any one single part of matter how minute so∣ever, and not rather to an aggregate of Particles. And next I say those Corpuscles that compose a fluid body may be of several sizes, as those of Water, Oyl, and Quicksilver, provided they be little enough to be put into the agitation requisite to give the aggregate they make up the qualities that are wont to denominate bodies fluid; and 'tis no more requisite for me to define precisely the magnitudes of the parts of a fluid body, than for Mr. Hobbs in his Definition above-re∣cited to define (which he will not easily do) what precise degree of endeavour must be signified by that very weak en∣deavour, by which if the parts of a body can be separated

from one another, he thinks fit to call them fluid. But though I thought it not amiss to make these Animadversions upon Mr. Hobbs's Ratiocination, yet as to the Opinion it self, for whose sake he speaks so severely and so despairingly of our Society, if it be con∣sidered as I propos'd it, he shews me as yet no cause at all to re∣nounce it. For that which I taught is this, That if a solid body be reduc'd into parts minute enough, those solid Corpuscles, whilst they are put into a convenient motion, may become parts of a fluid body. And against this Mr. Hobbs's indignation seems stronger than his Argument: For that which he objects being as we have lately seen, that at this rate all bodies must be fluid; 'tis evident by what I have already argued, that he infers this Absurdity not from my Opinion, but his own mistake of it: nor did I content my self with the proofless proposal of my Conjec∣ture, but I delivered in several parts of the often mention'd His∣tory particular Experiments to evince what I taught: As that a consistent coagulum of pure spirits of Urine and Wine may by bare digestion be turned into a permanent liquor; and that the fluid body of Quicksilver may without any sensible addition be turned into a permanent dry Powder, and may again in a trice by bare heat be turned into a lastingly fluid body. Whereto I added other Experiments, which together with these Mr. Hobbs would possibly have thought fit to answer, if he had found it easie for him to do so.

After this passage extant in Mr. Hobbs's fifth page that I have all this while been examining, I remember nothing in his Dia∣logue that requires to be insisted on about Fluidity and Firm∣ness, till we come to the 29. page, where having asked what cause the Academians assign of Hardness, 'tis answered that some of them assign three: to which Mr. Hobbs so far agrees as to say, Quin corpuscula (qualia sunt atomi quas supponit * 1.55 Lucretius at{que} etiam Hobbius) jam ante dur a facile possint ab ali∣qua dict arum causaram compingi, it a ut totum ex illis factum durum fiat, dubitandum non est. But then he would have us assign the cause of that he calls durum primum. But after some discourse, wherein he is pleased to approve an Objection of mine against some learned men that ascribe all Cohesion of bodies to a

certain Glue, he answers himself the Objection he frames against my Doctrine about Hardness, and thereby allowed me to proceed to what he further presses in these words, Si dura ex primis du∣ris fieri dicant, quare non & fluida fieri putant ex primis fluidis? An creari fluida maxima potuere, ut aether, min∣ima * 1.56 non potuere? Qui Corpusculum durum aut fluidum primus fecit, potuit, si libuisset, illud fecisse tum majus, tum minus quocun{que} corpore dato. Quod si fluidum fiat ex non fluidis, ut vos dicitis, & durum ex duris tantum, nonne sequitur ex fluidis primis ne{que} fluidum fieri ne{que} durum? But against this passage I have divers things to represent. For, first, (not now to mention that it may be que∣stioned with what propriety one part of matter more than ano∣ther may be called primum durum) he should have told us what he means by his prima fluida, and how he proves that there are any such; which since he has not done, 'twill be at least as hard for a considering man to acquiesce in his Question as to answer it. For my part, I know no fluid body upon whose account, as of an Ingredient, all others are fluid. And, I think, 'twill be hard for Mr. Hobbs to shew that Water, Quicksilver, and purely-rectifi'd Chymical Oyles (to name now no other liquors) do consist of such fluida prima as he teaches, whereto they owe all their Flui∣dity. And 'tis plain by several Experiments delivered in our His∣tory, and even by the obvious changes of Water and Ice into one another, that 'tis the motion, rest, and the texture of the Corpuscles which compose a Body, that make it firm or fluid. As for what Mr. Hobbs demands, whether the smallest Fluids im∣aginable could not as well have been created as the AEther, it proves nothing against me, the Question not being, what might have been made, but what is so. And he should have answered the Arguments I * 1.57 alledge to make it impro∣bable that a fluid body is, as he would perswade us in his Book † 1.58 De Corpore, alwayes divisible into bodies equally fluid, as Quantity into Quan∣tities. 'Tis true, he there tells us that, though many others do not, He understands by Fluidity that which is made such by Nature equally in every part of the fluid body, in such manner as water seems fluid, and to divide it self into parts perpetually fluid. But whe∣ther

others will take this for a clear Notion of Fluidity I think may well be doubted; and he should not barely say, but prove, (which, I think he will find hard to do) that the Corpuscles of water divide themselves so as he teaches, since we see, that not onely they cannot penetrate Glass, but are unable to be driven in at the Pores of more open bodies, which other liquors easily pierce into. And, lastly, as to Mr. Hobbs's Question, Quod si flu∣idum fiat &c. 'tis easie to foresee what according to my Doctrine I may answer: For, not to mention that the Argumentation is invalid, unless by Fluidum he mean Omne fluidum, I reply, That till he have explained what he means by his Fluida prima, and proved that there are such, the Question needs no Answer. Besides that whatever he upon mistakes strives to infer, my Doctrine is so far from affirming that there are many parts of matter of which neither fluid nor hard bodies can be made, that I teach, as we have lately seen, that there are multitudes of parts that may, by being reduced to a sufficient smalness and put into a convenient motion, or by being brought to a mutual contact and rest, be made to constitute either a fluid body or a firm one: as may be exemplified in the formerly-mentioned instances of two subtile liquors that immediately composed a consistent body; and of Quicksilver, which without additaments was made some∣times a Powder, and sometimes a liquor. What Mr. Hobbs addes in the next page about the difficulty of explain∣ing the Diaphaneity of Glass or Crystal, in case they * 1.59 consisted of Corpuscles hard and implicated, or having their Pores in any way whatsoever disjoyned, I must not now insist on; since besides that such a disquisition would require almost a Volume, the true and general cause of Transparency in bodies is in my poor Opinion one of the abstrusest things in Natural Phy∣losophy; and Mr. Hobbs's Explication of it (though none of his worst Conceits) has for ought I can find fallen short of satisfying the Curious, as well as those of other men have done. But to me, that have not taken upon me to write Elements of Phylo∣sophy, it is enough that I have by competent Experiments and other Proofs confirm'd the truth of my Doctrine about the cause of Firmness; though I attempt not to explicate the other quali∣ties

of the same bodies, whose Explication my undertaking does not exact. Wherefore I hope I may now hasten to conclude this Appendix, with spending a few words on the Notion of Fluidity and Firmness Mr. Hobbs would substitute instead of mine. For, having now (perhaps but too prolixly) exam∣ined what he has been pleased to object against my doctrine, I shall not need spend time to vindicate the Experiments and Considerations whereon I built it, Mr. Hobbs, for reasons best known to himself, not having thought fit to take notice of them.

Mr. Hobbs's Theory of Fluidity and Firmness is thus deliver∣ed by himself;

B. Quaenam duri & fluidi sunt principia?

A. Quid aliud nisi fluidi quidem, Quies, duri autem, * 1.60 Motus quidam ad illum effectum producendum idoneus? Per Quie∣tem intelligo duar am partium inter se quietem cum se mutuo tangunt quidem, sed non premunt: Nam & fluida moveri tota possunt reten∣ta fluiditate, & dura quiescere, ut tamen partes eorum moveantur.

I doubt not but this will to most Readers seem a Paradox. And as for his Ratiocination contain'd in the two last lines, I shall readi∣ly allow him that Fluida moveri tota possunt retent a fluiditate, since that I think agrees at least as well with my Hypothesis as his: but whereas he adds that hard bodies may rest, and yet their parts be moved, that may in one case be conceived, and in another not. For indeed the implicated parts of a firm body may be made to tremble or a little vibrate as it were to and fro, as those of a sounding Bell do, or as in a Hedge the branches and twigs may be shaken by the wind, whilst the trees and bushes themselves conti∣nue rooted in the ground. But that in a body the constituent Corpuscles should all or most of them be moved quite out of their places in respect of one another, as was lately shewn to happen in fluids, and yet the body continue hard, is more requisite than easie to be proved.

But Mr. Hobbs contents himself to alledge in favour of his strange Notion touching Fluidity and Firmness three particulars, which, I confess, afford me not the least satisfaction.

The first is drawn from what he formerly taught touching the

swift motion of the Air in our Cylinder; which example (as he calls it) having repeated, he adds, At{que} hinc manifestum est vehementem esse in aëre it a moto & clauso compressionem, * 1.61 quantam scilicet efficere potest vis illa qua incussus erat; at{que} etiam à tanta compressione aliquem gradum consistentiae fieri, quanquam consistentia aquae minorem. Quod si esset in iisdem particulis aëris omnibus, praeter motum illum quo alter a alteram premit, motus ille circularis simplex, is{que} satis vehemens, impossibile fere esset unam earum à suo circello dimoveri, quin reliquis particulis resistentibus, totus simul premeretur, idest, totum durum esset: durum enimest totumillud, cujus nulla cedit parsnisi cedente toto. Vides ergoposse fieri duritiem in fluidissimo aëre per motum hunc circularem simplicem particularem, quibus duo motus contrarii ante dederant vertiginem.

But, I confess, I do not see how the Motus circularis simplex he talks of should give such a hardness to the fluid Air: nor is it manifest to me how the Air that perfectly fills the Cylinder can be by motion compress'd, especially so far as to obtain thereby a degree of consistence fit to be mentioned, as he speaks of it, when (without adding the word much, or any other equivalent term) he sayes that yet 'tis less than the consistence of water. For the Cylinder being, according to him, perfectly full of Air, I see not how the Pumping can make the Cavity (to use his own ex∣pression elsewhere) fuller than full; nor consequently can com∣press the Air to a consistence any thing near that of water, with∣out penetration of Dimensions. But these things were menti∣oned onely ex abundanti, for the violent motion it self of the Air in the Cylinder (which motion the Argument supposes) has been already, in the Examen of one of the former passages of his Dialogue, sufficiently manifested to be contrary to Experience.

The second thing Mr. Hobbs alledges is his Conceit of the Ge∣neration of Flesh within the Muscles of the humane body. But besides that he takes for granted two or three things which many learned Anatomists and Physicians, even among the Mo∣derns, will scarce allow him, and which he does not prove: be∣sides this, I say, (which I may elsewhere have occasion to con∣sider further) the account he gives of the Generation of Flesh from these suppositions, is far from being evidently enough de∣duc'd

to vie for clearness with many of those Experiments which I have alledged in favour of the Opinion he opposes. And whereas he adds, At{que} talis quidem esse potest causa effi∣ciens Duri primi, Duri autem secundi, id est, Duri à co∣haesione * 1.62 durorum primorum, causa potest esse motus ille idem circu∣laris simplex conjunctus cum contactu eorundem superficiali, vel eti∣am intricatione: Not again to say any thing to his durum primum, I confess I do not see how the motus circularis simplex should need to be superadded to the Contact or Intrication of the cohering firm Corpuscles, to procure a Cohesion, to which'tis needless, and which in divers cases may be rather hindered than furthered by it.

The third thing that Mr. Hobbs alledges is not so much a confirmation of his own Doctrine, as an Objection, as he seems to think, against that of his Adversaries. For, Si sup∣ponamus (sayes he presently after his last-recited words) * 1.63 cum illis, duritiei causam esse magnitudinem aut crassitiem parti∣um, quam rationem reddere poterimus, cur durior vel firmior sit aqua congelata, quam est eadem aqua ante congelationem? But it may easily be replyed, That we make not the bigness or grosness of the parts of a body the onely or chief cause of its hardness, but their rest by one another, which the parts of frozen water have; whereas those of unfrozen water have it not, but are in a state of Fluidity, and consequently not of Firmness. Which may be illustrated by what I * 1.64 elsewhere relate of pure Oyle of Aniseeds, and a substance I distilled out of Benzoin, both which bodies were sometimes fluid and sometimes consistent, as the greater or lesser warmth of the Air kept their parts in a due motion or suffered them to rest.

But in exchange of these few & unconcluding arguments, which are all that Mr. Hobbs alledges to countenance his Paradox, how many Experiments and Reasons mightwe transcribe out of our His∣tory of Fluidity and Firmness in favour of the contrary Truth?

And as Critical as Mr. Hobbs appears in laying down the re∣quisites of a good Hypothesis, I must make bold to the two con∣ditions he mentions (pag. 11.) Vt sit conceptibilis (idest, non ab∣surda) (which whether it be enough I now dispute not) & Vt ab

ea concessa inferri possit Phaenomeni necessitas, to adde a third, namely, That it be not inconsistent with any other Truth or Phaenomenon of Nature. Which third condition whether divers of Mr. Hobbs's Hypotheses (which himself in this place calls miran∣dae) do not want, we have in part already considered in the Trea∣tise to which this is an Appendix; and (as I newly intimated) I might further shew as to his Notion of Fluidity and Firmness, if I would here repeat all the Experiments mentioned in my Hi∣story of them, though they be not all that I have made ready to the same purpose against another opportunity: but partly weari∣ness, and partly a natural unwillingness to repeat, induces me ra∣ther to refer my Reader thither. Which when I do, I do not forget that Mr. Hobbs appears offended at me and others for troubling our selves to make un-obvious Experiments. But that I may not repeat what in divers Treatises I represent con∣cerning the Usefulness of such Experiments, I shall now onely oppose to the Authority of Mr. Hobbs in this Dialogue, wherein he has been pleased to chuse those he calls the Experimentarian Phi∣losophers for his Adversaries, the Authority and Reason of the same Mr. Hobbs in another Dialogue (published but the year be∣fore) where one of his two Discoursers having said, Qui corpora corporibus admovendo, nova & mirabilia ostendunt Na∣turae opera, mirum in modum incendunt animos homi∣num * 1.65 amore Philosophiae, & ad causas investigandas non parum instigant, eo{que} nomine laude digni sunt: the other confirms it by adding, It a est; nam historiam Naturalem (si∣ne qua scientia Naturalis frustra quaeritur) locupletant. And how∣soever Mr. Hobbs needed not have recourse to such Experiments as he would be thought to disapprove, (I mean Elaborate ones) to discern that his Notions do not over-well agree with the Phae∣nomena. For, if there be not a various motion in the small parts of Water and such liquors, whence is it that a lump of common Salt being thrown into a pot of water is there dissolved into mi∣nute bodies, whereof many are carried to the very top of the wa∣ter, and are so exquisitely diffused and mingled with the liquor, that each least drop of it contains numbers of Saline Corpuscles? And if motion be the cause rather of hardness than fluidity, how

comes it to pass that in frosty weather Ice is by heat (which Mr. Hobbs will not deny to be motion, or an effect of it) turned from a hard to a fluid body? And that Metals, as Gold and Sil∣ver, &c. whilst they are either cold, or exposed but to a mode∣rate heat are firm and consistent bodies; and by a violent heat, which does manifestly give their parts a various and vehement agitation, (as appears by their sudden dissipating of Spittle, Greace, and far more stable bodies, cast upon them, into smoak) are put into a fluidity, which upon their removal from the fire they quickly exchange for firmness?

But since the want of more to say would not in haste put a Pe∣riod to this Discourse, I am content to let my Haste break it off; especially since after I have thus examined what Mr. Hobbs teaches concerning Fluidity and Firmness, either here, or in that Section of his Elements where he pretends to define them, I think I need not fear that a Doctrine which I have perhaps with some care endeavoured to establish, for the main, upon Experiments, should be overthrown by Opinions whose grounds are but such as we have already seen; and in pleading for which the Author is plea∣sed not onely to leave almost all my Arguments untouch'd, but not so much as to offer at explicating by his Principles any of those numerous and important Phaenomena of Fluidity and Firm∣ness delivered in the Treatise he opposes.

And now leaving Mr. Hobbs to apply my self to the Reader, I have to the things hitherto discourst but this one thing to adde concerning them, That as little cause as Mr. Hobbs has hitherto given me to distrust what I have written of Fluidity and Firm∣ness; yet I am not now more confident of my Conjectures than I was, when toward the end of the Preface to the History of these two Qualities I spoke diffidently enough of the Theorical part of that Treatise. And I freely confess, that the great diffi∣culty of things, and the little abilities I find my self furnisht with to surmount it, do often in general beget in me a great distrust even of things whereof my Adversaries Objections give me not any.

FINIS.

Notes

• * 1.1

  Cap. 26. Sect. 2.
• * 1.2

  In some Dia∣logues of Heat and Flame.
• * 1.3

  Pag. 18.
• * 1.4

  Pag. 8.
• * 1.5

  Wardi Exer. in Philosoph. Hobbian. pag. 188.
• * 1.6

  Exper. Mag∣deburgicum a∣pud Schotum, pag. 446.
• * 1.7

  Pag. 15.
• * 1.8

  Elem. of Phil. Ch. 30. Sect. 4.
• * 1.9

  Pag. 16.
• * 1.10

  Pag. 9.
• * 1.11

  Chap. 30. Sect. 10.
• * 1.12

  Utraque enim illa phan∣t sia tum gravitatis At∣mosphaerae, tum vis Ela∣sticae sive antitupiae aë∣ris, somnium erat. Dial. p. 21.
• * 1.13

  Pag. 11.
• * 1.14

  The Motions therefore of those small Bodies (speaking of the Earthy Particles in the Air) will be less and less free, by how much the quantity of the inje∣cted Water is greater and grea∣ter: so that by their Motion fal∣ling upon one another, the same Bodies will mutually compress each other, and have a perpetu∣al endeavour of regaining their liberty, and of depressing the Water that hinders them. Elem. Chap. 30. Sect. 9.
• * 1.15

  Pag. 8.
• * 1.16

  In our De∣fence against Linus.
• * 1.17

  Pag. 19.
• * 1.18

  Pag. 12.
• * 1.19

  Pag. 4.
• † 1.20

  Ioid.
• * 1.21

  Pag. 5.
• * 1.22

  Page 22.
• * 1.23

  Pag. 12.
• * 1.24

  Page 13.
• * 1.25

  Page 13.
• * 1.26

  Page 3.
• * 1.27

  Ita{que}
• * 1.28

  Page 13, 14.
• * 1.29

  Page. 14.
• * 1.30

  Page 16.
• * 1.31

  Page 18.
• * 1.32

  Page 18.
• * 1.33

  Page 1••.
• * 1.34

  Page 79.
• * 1.35

  Chap. 30. Sect. 14.
• * 1.36

  Page 18.
• * 1.37

  Page. 18.
• * 1.38

  Compare that in the 30. Chap. 14. Sect. of his Phy∣sicks with that of his Dialogue, page 15, 16.
• * 1.39

  Page 6.
• * 1.40

  Page 10.
• * 1.41

  Page. 20.
• * 1.42

  Page 20.
• * 1.43

  Schot. Mech. Hyd. Pneumat. pag. 461.
• * 1.44

  Pag. 20, 21.
• * 1.45

  Page 22.
• * 1.46

  Page 21, 22.
• * 1.47

  Page 24.
• * 1.48

  Page 25.
• * 1.49

  Page 25.
• * 1.50

  Page 25.
• * 1.51

  Page. 23.
• * 1.52

  Page 5.
• * 1.53

  Hobbs de Corp. ch. 27.
• * 1.54

  Mr. Hobbs de Corpore, cap. 26. part. 4.
• * 1.55

  Page 29.
• * 1.56

  Page 30.
• * 1.57

  History of. Firm∣ness, page, 227. and elsewhere.
• † 1.58

  Chap. 16. Sect. 4.
• * 1.59

  Page 31.
• * 1.60

  Page 30.
• * 1.61

  Page 30.
• * 1.62

  Page. 31.
• * 1.63

  Page. 31.
• * 1.64

  In the History of Fluidity and Firmness.
• * 1.65

  Mr. Hobbs in Examinat. & Emendatione, &c. Dialog. 6.