ANIMADVERSIONS UPON MR. Hobbes' PROBLEMATA DE VACUO.  
By the Honourable ROBERT boil, Fellow of the Royal Society.  
LONDON, Printed by William Godbid, and are to be Sold by Moses Pitt, at the Angel over against the little North Door of St. Paul's Church. 1674.   

PREFACE.  
UPON the coming abroad of Mr. Hobbes' Problemata Physica, finding them in the hands of an Ingenious Person, that intended to write a Censure of them, which several Employments private and public have, it seems, hindered him to do; I began, as is usual on such occasions, to turn over the leaves of the Book, to see what particular things it treated of. This I had not long done before I found, by obvious passages in the third Chapter, or Dialogue, as well as by the Title, which was Problemata de Vacuo, that I was particularly concerned in it; upon which I desired the Possessor of the Book, who readily consented, to leave me to examine that Dialogue, on which condition I would leave him to deal with all the rest of the Book. Nor did I look upon the Reflections I meant to make as repugnant to the Resolutions I had taken against writing Books of Controversy, since the Explications, Mr. Hobbes gave of his Problems, seemed to contain but some Variations of, or an Appendix to, his Tract De Natura Aeris, which, being one of the two first pieces that were published against what I had written, was one of those that I had expressly reserved myself the liberty to answer. But the Animadversions I first made upon Mr. Hobbes' Problems De Vacuo, having been casually mislaid ere they were finished; before I had occasion to resume my task, there past time enough to let me perceive, that his Doctrine, which 'twill easily be thought that the Vacuists disapproved, was not much relished by most of the Plenists themselves, the modernest Peripatetics and the Cartesians; each of them maintaining the Fullness of the World, upon their own grounds, which are differing enough from those of our Author, the natural Indisposition I have to Polemical Discourses, easily persuaded me to let alone a Controversy, that did not appear needful: And I had still persisted in my silence, if Mr. Hobbes had not as 'twere summoned me to break it by publishing again his Explications, which in my Examen of his Dialogue De Natura Aeris I had shown to be erroneous.  
And I did not grow at all more satisfied, to find him so constant as well as stiff an Adversary to interspersed Vacuities, by comparing what he maintains in his Dialogue De Vacuo, with some things that he teaches, especially concerning God, the Cause of Motion, and the Imperviousness of Glass, in some other of his writings that are published in the same Volume with it. For since he asserts that there is a God, and owns Him to be the Creator of the World; and since on the other side the Penetration of Dimensions is confessed to be impossible, and he denies that there is any Vacuum in the Universe; it seems difficult to conceive, how in a World that is already perfectly full of Body, a Corporeal Deity, such as he maintains in his Append. ad Leviath. cap. 3, can have that access even to the minute parts of the Mundane Matter, that seems requi● site to the Attributes and Operations that belong to the Deity, in reference to the World. But I leave Divines to consider what Influence the conjunction of Mr. Hobbes' two Opinions, the Corporeity of the Deity, and the perfect Plenitude of the World, may have on Theology. And perhaps I should not in a Physical Discourse have taken any notice of the proposed Difficulty, but that, to prevent an Imputation on the Study of Nature's Works, (as if it taught us rather to degrade than admire their Author,) it seemed not amiss to hint (in transitu) that Mr. Hobbes' gross Conteption of a Corporeal God, is not only unwarranted by found Philosophy, but ill befriended even by his own.  
My Adversary having proposed his Problems by way of Dialogue between A. and B; 'twill not, I presume, be wondered at, that I have given the same form to my Animadversions; which come forth no earlier, because I had divers other Treatises, that I was more concerned for, to publish before them.  
But because it will probably be demanded, why on a Tract that is but short, my Animadversions should take up so much room? It will be requisite, that I here give an account of the bulk of this Treatise.  
And first, having found that there was not any one Problem, in whose Explication, as proposed by Mr. Hobbes, I saw cause to acquiesce, I was induced for the Readers ease, and that I might be sure to do my Adversary no wrong, to transcribe his whole Dialogue, bating some few Transitions, and other Clauses not needful to be transferred hither.  


Credo, (says Mr. Hobbes in his Dialogus Physicus:) 
De Nat Aeris, p. 13.  Nam motus hic Restitutionis, Hobbii est, & ab illo primo & solo explicatus in Lib. de Corpore, cap. 21. Art. 1. Sine qua Hypothesi, quantuscunque labour, arse, sumptus, ad rerum Naturalium invisibiles causas inveniendas adbibeatur, frustra erit. And speaking of the Gentleman (to whom it were not here proper for me so give Epithets) that used to meet at Gresham-College, and are known by the Name of the Royal Secrety, he thus treats them and their way of Enquiring into Nature: Conveniant, studia conferant, Experimenta faciant quantum volunt, nisi & Principiis utantur mess, nihil proficient.  A. 
Pateris ergo nihil bactenus à Collegis tuis promotam esse scientium Causarum Naturalium, nisi quod Unus eorum Machinam invenerit, quâ motus excitari Aeris possit talis, ut partes Sphaerae simul undiquaque tendant ad Centrum, & ut Hypotheses Hobbianae, antè quidem satis probabiles, hinc reddantur probabiliores.  B. 
Nec fateri pudet; nam est aliqu●d prodire tenus, si non datur ultra.  A. 
Quid tinus? quorsum autem tantus apparatus & sumptus Machinarum factu difficilium, ut eatenus tantum productis quantum ante prodi●rat Hobbius? Cut non inde potius incepistis ubi ille desiit? Cur Principiis ab illo positis non estis usi? Cumque Aristoteles recte dixit, ignorato motu ignorari Naturam, etc.  
— Ad Causas autem, propter quas proficere ne pau●usum quidem potuistis, nec poter●tis, accedunt etiam ●liae, ut odium Hobbii, etc.   Next, I was not willing to imitate Mr. Hobbes, who recites in the Dialogue we are considering the same Experiments that he had already mentioned in his Tract De Natura Aeris, without adding as his own (that I remember) any new one to them. But my unwillingness to tyre the Reader with bare Repetitions of the Arguments I employed in my Examen of that Tract, invited me to endeavour to make him some amends for the exercise of his patience by inserting, as occasion was offered, five or six new Experiments, that will not perhaps be so easily made by every Reader that will be able (now that I have perspicuously proposed them) to understand them.  
And lastly, since Mr. Hobbes has not been content to magnify himself and his way of treating of Physical matters, but has been pleased to speak very slightingly of Experimentarian Philosophers (as he styles them) in general, and, which is worse, to disparage the making of elaborate Experiments; I judged the thing, he seemed to aim at, so prejudicial to true and useful Philosophy, that I thought, it might do some service to the less knowing, and less wary, sort of Readers, if I tried to make his own Explications enervate his Authority, and by a somewhat particular Examen of the Solutions he has given of the Problems I am concerned in, show, that 'tis much more easy to undervalue a frequent recourse to Experiments, than truly to explicate the Phaenomena of Nature without them. And since our Author, speaking of his Problemata Physica, (which is but a small Book) scruples not to tell His Majesty, to whom he dedicates them, that he has therein comprised (to speak in his own terms) the greatest and most probable part of his Physical Meditations; and since by the alterations, he has made in what he formerly writ about the Phaenomena of my Engine, he seems to have designed to give it a more advantageous form: I conceive, that by these selected Solutions of his, one may, without doing him the least injustice, make an estimate of his way of discoursing about Natural things. And though I would not interess the credit of Experimentarian Philosophers in no considerabler a Paper than this; yet if Mr. Hobbes' Explications and mine be attentively compared, it will not, I hope, by them be found, that the way of Philosophising he employs, is much to be preferred before that which he undervalues.   

ANIMADVERSIONS UPON MR. Hobbes' Problemata de VACUO.  A. 
MAy one, without too bold an inquisitiveness, ask, what Book you are reading so attentively?  B. 
You will easily believe you may, when I shall have answered you, that 'twas Mr. Hobbes' lately published Tract of Physical Problems, which I was perusing.  A. 
What progress have you made in it?  B. 
I was finishing the third Dialogue or Chapter when you came in, and finding myself, though not named, yet particularly concerned, I was perusing it with that attention which it seems you took notice of.  A. 
Divers of your Experiments are so expressly mentioned there, that one need not be skilled in deciphering to perceive that you are interessed in that Chapter, and therefore seeing you have heedfully read it over, pray give me leave to ask your Judgement, both of Mr. Hobbes' Opinion, and his Reasonings about Vacuum.  B. 
Concerning his Opinion, I am sorry I cannot now satisfy your Curiosity, having long since taken, and ever since kept, a Resolution to decline, at least until a time that is not yet come, the declaring myself either for or against the Plenists. But as to the other part of your Question, which is about Mr. Hobbes' Arguments for the absolute Plenitude of the World, I shall not scruple readily to answer, that his Ratiocinations seem to me far short of that cogency, which the noise he would make in the world, and the way wherein he treats both ancient and modern Philosophers that descent from him, may warrant us to expect.  A. 
You will allow me the freedom to tell you, That, to convince me, that your resentment of his explicating divers of the Phaenomena of your Pneumatic Engine otherwise than you have been wont to do, (and perhaps in terms that might well have been more civil,) has had no share in dictating this Judgement of yours; the best way will be, that entering for a while into the party of the Vacuists you answer the Arguments he alleges in this Chapter to confute them.  B. 
Having always, as you know, forborn to declare myself either way in this Controversy, I shall not tie myself strictly to the Principles and Notions of the Vacuists, nor, though but for a while, oppose myself to those of the Plenists: But so far I shall comply with your Commands, as either upon the Doctrine of the Vacuists, or upon other grounds, to consider, whether this Dialogue of Mr. Hobbes have cogently proved his, and the Schools, Assertion, Non dari Vacuum; and whether he has rightly explained some Phaenomena of Nature which he undertakes to give an account of, and especially some produced in our Engine, whereof he takes upon him to render the genuine Causes. And this last inquiry is that which I chiefly design.  A. 
By this I perceive, that if you can make out your own Explications of your Adversaries Problems de Vacuo, and show them to be preferable to his, you will think you have done your work, and that 'tis but your secondary scope to show, that in Mr. Hobbes his way of solving them, he gives the Vacuists an advantage against Him, though not against the plenists in general.  B. 
You do not mistake my meaning, and therefore without any further Preamble, let us now proceed to the particular Phaenomena considered by Mr. Hobbes; the first of which is an Experiment proposed by me in the one and thirtieth of the Physicomechanical Experiments concerning the Adhesion of two flat and polished Marbles, which I endeavoured to solve by the pressure of the Air. And this Experiment Mr. Hobbes thinks so convincing an one to prove the Plenitude of the World, that, though he tells us he has many cogent Arguments to make it out, yet he mentions but this one, because that, he says, suffices.  A. 
The Confidence he thereby expresses of the great force of this Argument does the less move me, because, I remember, that formerly in his Elements of Philosophy he thought it sufficient to employ one Argument to evince the Plenitude of the World, and for that one he pitched upon the Vulgar Experiment of a Gardeners Watering-Pot: But, whether he were wrought upon by the Objections made to his Inference from that Phaenomenon in your Examen of his Dialogue De Natura Aeris, or by some other Considerations, I will not pretend to divine. But I plainly perceive, he now prefers the Experiment of the cohering Marbles.  B. 
Of which it will not be amiss, though the passage be somewhat long, to read you his whole Discourse out of the Book I have in my hand.  A. 
'Tis fit that you, who for my sake are content to take the pains of answering what he says, should be eased of the trouble of reading it, which I will therefore, with your leave, take upon me. His Discourse then about the Marbles is this:  A. 
Ad probandam Universi Plenitudinem, nullum nostin' Argumentum cogens?  B. 
Imò multa: Unum autem sufficit ex eo sumptum, Quod duo corpor a plana, si se mutuò secundùm amborum planitiem communem tangant, non facile in instant divelli possunt; successiuè verò facillimè. Non dico, impossibile esse duo durissima Marmora ita coharentia divellere, sed difficile; & vim postulare tantam, quanta sufficit ad duritiem lapidis superandam. Siquidem verò majore vi ad separationem opus sit quam illa, quâ moventur separata, id signum est non dari Vacuum.  A. 
Assertiones illae demonstratione indigent. Primò autem ostend, quomodo ex duorum durissimorum corporum, conjunctorum ad superficies exquisite laeves, diremptione difficili, sequatur Plenitudo Mundi?  B. 
Si duo plana, dura, polita Corpora (ut Marmora) collocentur unum supra alterum, ita ut eorum superficies se mutuò per amnia puncta exactè, quantum fieri potest, contingant, illa sine magna difficultate ita divelli non possunt, ut eodem instante per omnia puncta dirimantur. Veruntamen Marmora eadem, si communis eorum superficies ad Horizontem erigatur, aut non valde inclinetur, alterum ab altero facillimè (ut scis) etiam solo pondere dilabentur. Nun causa hujus rei haec est, Quod labenti Marmori succedit Aer, & relictum locum semper implet?  A. 
Certissimé. Quid ergo?  B. 
Quando verò eadem uno instante divellere conaris, nun multo major vis adhibenda est; Quam ob causam?  A. 
Ego, & mecum (puto) omnes cansam statuunt, Quod spatium totum inter duo illa Marmora divulsa, simul uno instante implere Aer non potest, quantacunque celeritate fiat divulsio.  B. 
An qui spatia in Aere dari vacua contendunt, in illo Aere solo dari negant qui Marmora illa conjuncta circumdat?  A. 
Minimè, sed ubique interspersa.  B. 
Dum ergo illi, qui Marmor unum ab altero revellentes Aerem comprimunt, & per consequens Vacuum exprimunt, Vacuum faciunt locum per revulsionem relictum; nulla ergo separationis erit difficultas, saltem non major quam est difficultas corpora eadem movendi in Aere postquam separata fuerint. Itaque quoniam, concesso Vacuo, difficult as Marmora illa dirimendi nulla est, sequitur per difficultatis experientiam, nullum esse Vacuum.  A. 
Recte quidem illud infers. Mundi autem Plenitudine supposita, quomodo demonstrabis possibile omnino esse ut divellantur?  B. 
Cogita primo Corpus aliquod ductile, nec nimis durum, ut ceram, in duas partes distrahi, quae tamen partes non minus exacte in communi plano se mutuo tangunt quam laevissima Marmora. Jam quo pacto distrahatur ●era, consideremus. Nun perpetuo attenuatur donec in filum evadat tenuissimum, & omni dato crasso tenuius, & sie tandem divellitur? Eodem modo etiam durissima columna in duas partes distrahetur, si vim tantam adhibeas, quanta sufficit ad resistentiam duritiei superandam. Sicut enim in card parts primò extimae distrahuntur, in quarum locum succedit Aer; ita etiam in Corpore quantumlibet duro Aer locum subit partium extimarum, quae primae Vulsionis viribus dirumpuntur. Vis autem quae superat resistentiam partium extimarum Duri, facilè superabit resistentiam reliquarum. Nam resistentia prima est à Toto Duro, reliquarum verò semper à Residuo.  A. 
It a quidem videtur consideranti, quam Corpora quaedam, praesertim verò durissima, fragilia sint.  
Does this Ratiocination seem to you as cogent, as it did to the Proposer of it?  B. 
You will quickly think it does not, and perhaps you will think it should not, if you please to consider with me some of the Reflections that the Reading of it suggested to me.  
And first, without declaring for the Vacuists Opinion, I must profess myself unsatisfied with Mr. Hobbes' way of arguing against them: For, where he says, Dum ergo illi qui Marmor unum ab altero revellentes Aerem comprimunt & per consequens Vacuum exprimunt, Vacuum faciunt locum per revulsionem relictum; nulla ergo separationis erit difficultas, saltem non major quam est difficultas corpora eadem movendi in Aere postquam separata fuerint. Itaque quoniam, concesso Vacuo, difficultas Marmora illa dirimendi nulla est, sequitur per difficultatis experientiam, nullum esse Vacuum. Methinks he expresses himself but obscurely, and leaves his Readers to guess, what the word Dum refers to. But that which seems to be his drift in this passage, is, that, since the Vacuists allow interspersed Vacuities, not only in the Air that surrounds the conjoined Marbles, but in the rest of the ambient Air, there is no reason, why there should be any difficulty in separating the Marbles, or at least any greater difficulty than in moving the Marbles in that Air after their separation. But, not to consider, whether his Adversaries will not accuse his phrase of squeezing out a Vacuum as if it were a Body, they will easily answer, that notwithstanding the Vacuities they admit in the ambient Air, a manifest reason may be given in their Hypothesis of our finding a difficulty in the Divulsion of the Marbles. For, the Vacuities they admit being but interspersed, and very small, and the Corpuscles of the Atmosphere being according to them endowed with Gravity, there leans so many upon the upper surface of the uppermost Marble, that that stone cannot be at once perpendicularly drawn up from the lower Marble contiguous to it, without a force capable to surmount the weight of the Aerial Corpuscles that lean upon it. And this weight has already so constipated the neighbouring parts of the ambient Air, that he, that would perpendicularly raise the upper Marble from the lower, shall need a considerable force to make the Revulsion, and compel the already contiguous parts of the incumbent Air to a subingression into the pores or intervals intercepted between them. For the Conatus of him, that endeavours to remove the upper Marble, whilst the lower surface of it is fenced from the pressure of the Atmosphere by the Contact of the lower Marble which suffers no Air to come in between them, is not assisted by the weight or pressure of the Atmosphere, which, when the Marbles are once separated, pressing as strongly against the undermost surface of the upper Marble, as the incumbent Atmospherical Pillar does against the upper surface of the same Marble, the hand that endeavours to raise it in the free Air has no other resistance, than that small one of the Marbles own weight to surmount.  A. 
But what say you to the Reason that Mr. Hobbes, and, as he thinks, all others give of the difficulty of the often mentioned Divulsion, namely, Quòd spatium totum inter duo illa Marmora divulsa simul uno instante implere Aer non potest, quant acunque celeritate fiat divulsio.  B. 
I say, that, for aught I know, the Plenists may give a more plausible account of this Experiment, than Mr. Hobbes has here done; and therefore abstracting from the two opposite Hypotheses, I shall further say, That the genuine Cause of the Phaenomenon seems to be that which I have already assigned; and that difficulty of raising the upper stone that accompanies the Airs not being able to come in all at once, to possess the space left between the surfaces of the two Marbles upon their separation, proceeds from hence, that, till that space be filled with the Atmospherical Air, the hand of him that would lift up the superior Marble cannot be fully assisted by the pressure of the Air against the lower surface of that Marble.  A. 
This is a Paradox, and therefore I shall desire to know on what you ground it?  B. 
Though I mention it but as a Conjecture proposed ex abundanti▪ yet I shall on this occasion countenance it with two things; the first▪ that, since I declare not for the Hypothesis of the Plenists as 'tis maintained by Mr. Hobbes, I am not bound to allow, what the common Explication, adopted by my Adversary, supposes; namely, that either Nature abhors a Vacuum (as the Schools would have it,) or that there could be no Divulsion of the Marbles, unless at the same time the Air were admitted into the room that Divulsion makes for it. And a Vacuist may tell you, that, provided the strength employed to draw up the superior Marble be great enough to surmount the weight of the Aerial Corpuscles accumulated upon it, the divulsion would ensue, though by Divine Omnipotence no Air or other Body should be permitted to fill the room made for it by the divulsion; and that the Air's rushing into that space does not necessarily accompany, but in order of Nature and time follow upon, a separation of the Marbles, the Air that surrounded their contiguous surfaces being by the weight of the collaterally superior Air impelled into the room newly made by the divulsion. But I shall rather countenance what you call my Paradox by an Experiment I purposely made in our Pneumatical Receiver, where having accommodated two flat and polished Marbles, so that the lower being fixed, the upper might be laid upon it and drawn up again as there should be occasion, I found, that if, when the Receiver was well exhausted, the upper Marble was by a certain contrivance laid flat upon the lower, they would not then cohere as formerly, but be with great ease separated, though it did not by any Phaenomenon appear, that any Air could come to rush in, to possess the place given it by the recess of the upper Marble, whose very easy avulsion is as easily explicable by our Hypothesis; since the pressure of that little Air, that remained in the Receiver, being too faint to make any at all considerable resistance to the avulsion of the upper Marble, the hand that drew it up had very little more than the single weight of the stone to surmount.  A. 
An Anti-plenist had expected, that you would have observed, that the difficult separation of the Marbles in the open Air does rather prove, that there may be a Vacuum, than that there can be none. For in case the Air can succeed as fast at the sides as the divulsion is made, a Vacuist may demand, whence comes the difficulty of the separation? And if the Air cannot fill the whole room made for it by the separated Marbles at the same instant they are forced asunder, how is a Vacuum avoided for that time, how small soever, that is necessary for the Air to pass from the edges to the middle of the room newly made?  B. 
What the Plenists will say to your Argument I leave them to consider; but I presume, they will be able to give a more plausible account of the Phaenomenon we are treating of, than is given by Mr. Hobbes.  A. 
What induces you to dislike his Explication of it?  B. 
Two things; the one, that I think the Cause he assigns improbable; and the other, that I think another, that is better, has been assigned already.  
And first, whereas Mr. Hobbes requires to the Divulsion of the Marbles a force great enough to surmount the hardness of the stone, this is asserted gratis, which it should not be; since it seems very unlikely, that the weight of so few pounds as will suffice to separate two coherent Marbles of about an Inch, for instance, in Diameter, should be able to surmount the hardness of such solid stones as we usually employ in this Experiment. And though it be generally judged more easy to bend, if it may be, or break a broader piece of Marble caeteris paribus, than a much narrower; yet, whereas neither I, nor any else that I know, nor I believe Mr. Hobbes, ever observed any difference in the resistance of Marbles to separation from the greater or lesser thickness of the stones; I find by constant experience, that, caeteris paribus, the broadness of the coherent Marbles does exceedingly increase the difficulty of disjoining them: Insomuch that, whereas not many pounds, as I was saying, would separate Marbles of an Inch, or a lesser, Diameter; when I increased their Diameter to about four Inches, if I misremember not, there were several Men that successively tried to pull them asunder without being able by their utmost force to effect it.  A. 
But what say you to the Illustration, that Mr. Hobbes, upon the supposition of the World's Plenitude, gives of our Phaenomenon by drawing asunder the opposite parts of a piece of Wax?  B. 
To me it seems an Instance improper enough. For first, the parts that are to be divided in the Wax are of a soft and yielding consistence, and according to him of a ductile, or, if you please, of a tractile nature, and not, as the parts of the coherent Marbles, very solid and hard. Next, the parts of the Wax do not stick together barely by a superficial contact of two smooth Planes, as do the Marbles we are speaking of; but have their parts implicated, and as it were entangled with one another. And therefore they are far from a disposition to slide off, like the Marbles, from one another, in how commodious a posture soever you place them. Besides 'tis manifest, that the Air has opportunity to succeed in the places successively deserted by the receding parts of the attenuated Wax; but 'tis neither manifest, nor as yet well proved by Mr. Hobbes, that the Air does after the same manner succeed between the two Marbles, which, as I lately noted, are not forced asunder after such a way, but are, as himself speaks, severed in all their points at the same instant.  A. 
I know, you forget not what he says of the dividing of a hard Column into two parts by a force sufficient to overcome the resistance of its hardness.  B. 
He does not here either affirm, that he, or any he can trust, has seen the thing done; nor does he give us any such account of the way wherein the Pillar is to be broken, whether in an erected, inclined, or horizontal posture; nor describe the particular circumstances that were fit to be mentioned in order to the solution of the Phaenomenon. Wherefore, till I be better informed of the matter of fact, I can scarce look upon what Mr. Hobbes says of the Pillar, as other than his Conjecture, which now I shall the rather pass by, not only because the case is differing from that of our polished Marbles, which are actually distinct Bodies, and only contiguous in one Commissure; but also, because I would hasten to the second reason of my dislike of Mr. Hobbes' Explication of our Phaenomenon, which is, that a better has been given already, from the pressure of the Atmosphere upon all the superficial parts of the upper Marble save those that touch the Plane of the lower.  A. 
You would have put fair for convincing Mr. Hobbes himself, at least would have put him to unusual shifts, if you had succeeded in the attempt you made, among other of your Physicomechanical Experiments, to disjoin two coherent Marbles, by suspending them horizontally in your Pneumatical Receiver, and pumping out the Air that environed them; for, from your failing in that attempt, though you rendered a not improbable Reason of it, Mr. Hobbes took occasion, in his Dialogue De Natura Aeris, to speak in so high a strain as this: Nihil isthic erat quod ageret pondus; Experimento hoc excogitari contra opinionem eorum qui Vacuum asserunt aliud argumentum fortius aut evidentius non potuit. Nam si duorum cohaerentium alterutrum secundùm eam viam, in qua jacent ipsae contiguae superficies, propulsum esset, facile separarentur, Aere praximo in locum relictum successiuè 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 instant, aut duo corpora eodem tempore in eodem esse loco: Quorum utrumvis dicere, est absurdum.  B. 
You may remember, that where I relate that Experiment, I expressed a hope, that, when I should be better accommodated than I then was, I might attempt the Trial with prosperous success, and accordingly afterwards, having got a lesser Engine than that I used before, wherewith the Air might be better pumped out and longer kept out, I cheerfully repeated the Trial. To show then, that when two coherent Marbles are sustained horizontally in the Air, the Cause, why they are not to be forced asunder, if they have two or three Inches in Diameter, without the help of a considerable weight, is the pressure I was lately mentioning of the ambient Air; I caused two such coherent Marbles to be suspended in a large Receiver, with a weight at the lowermost, that might help to keep them steady, but was very inconsiderable to that which their Cohesion might have surmounted; then causing the Air to be pumped by degrees out of the Receiver, for a good while the Marbles stuck close together, because during that time the Air could not be so far pumped out, but that there remained enough to sustain the small weight that endeavoured their divulsion: But when the Air was further pumped out, at length the Spring of the little, but not a little expanded, Air, that remained, being grown too weak to sustain the lower Marble and its small clog, they did, as I expected, drop off▪  A. 
This will not agree over-well with the confident and triumphant expressions just now necited.  B. 
I never envied Mr. Hobbes' forwardness to triumph, and am content, his Conjectures be recommended by the confidence that accompanies them, if mine be by the success that follows them. But to confirm the Explication given by me of our Phaenomenon, I shall add, that as the last mentioned Trial, which I had several times occasion to repeat, shows, that the cohesion of our two contiguous Marbles would cease upon the withdrawing of the pressure of the Atmosphere; so by another Experiment I made, it appears, that the supervening of that pressure sufficed to cause that Cohesion. For, in prosecution of one of the lately mentioned Trials, having found, that when the Receiver was well exhausted, two Marbles, though considerably broad, being laid upon one another after the requisite manner, their adhesion was, if any at all, so weak, that the uppermost would be easily drawn up from off the other; we laid them again one upon the other, and then letting the external Air flow into the Receiver, we found, according to expectation, that the Marbles now cohered well, and we could not raise the uppermost but accompanied with the lowermost. But I am sensible, I have detained you too long upon the single Experiment of the Marbles: And though I hope the stress Mr. Hobbes lays on it will plead my excuse, yet to make your Patience some amends, I shall be the more brief in the other particulars that remain to be considered in his Dialogue De Vacuo. And 'twill not be difficult for me to keep my promise without injuring my Cause, since almost all these particulars being but the same which he has already alleged in his Dialogue De Natura Aeris, and I soon after answered in my Examen of that Dialogue, I shall need but to refer you to the passages where you may find these Allegations examined, only subjoyning here some Reflections upon those few and slight things, that he has added in his Problems De Vacuo.  A. 
I may then, I suppose, read to you the next passage to that long one, you have hitherto been considering, and it is this: Ad Vacuum nunc revertor: Quas causas sine suppositione Vacui redditurus es illorum effectuum, qui ostenduntur per Machinam illam quae est in Collegio Greshamensi?  B. 
Machina illa—  B. 
Stop here, I beseech you, a little, that, before we go any further, I may take notice to you of a couple of things that will concern our subsequent Discourse.  
Whereof the first is, that it appears by Mr. Hobbes' Dialogue about the Air, that the Explications he there gave of some of the Phaenomena of the Machina Boyliana, were directed partly against the Virtuosos, that have since been honoured with the Title of the Royal Society, and partly against the Author of that Engine, as if the main thing therein designed were to prove a Vacuum. And since he now repeats the same explications, I think it necessary to say again, that if he either takes the Society or me for professed Vacuists, he mistakes, and shoots beside the mark; for, neither they nor I have ever yet declared either for or against a Vacuum.  
And the other thing I would observe to you, is, that Mr. Hobbes seems not to have rightly understood, or at least not to have sufficiently heeded in what chiefly consists the advantage, which the Vacuists may make of our Engine against him: For, whereas in divers places he is very solicitous to prove, that the cavity of our Pneumatical Receiver is not altogether empty, the Vacuists may tell him, that since he asserts the absolute plenitude of the World, he must, as indeed he does, reject not only great Vacuities, but also those very small and interspersed ones, that they suppose to be intercepted between the solid corpuscles of other bodies, particularly of the Air: So that it would not confute them to prove, that in our Receiver, when most diligently exhausted, there is not one great and absolute Vacuity, or, as they speak, a Vacuum coacervatum, since smaller and disseminated Vacuities would serve their turn. And therefore they may think their Pretensions highly favoured, as by several particular effects, so by this general Phaenomenon of our Engine, that it appears by several Circumstances, that the Common or Atmospherical Air, which, before the pump is set a work, possessed the whole cavity of our Receiver, far the greatest part is by the intervention of the pump made to pass out of the cavity into the open Air, without being able, at least for a little while, to get in again; and yet it does not appear by any thing alleged by Mr. Hobbes, that any other body succeeds to fill adequately the places deserted by such a multitude of Aerial corpuscles.  A. 
If I guess aright, by those words, (viz. it appears not by any thing alleged by Mr. Hobbes,) you design to intimate, that you would not in general prejudice the Plenists.  B. 
Your conjecture was well founded: For I think divers of them, and particularly the Cartesians, who suppose a subtle Matter or Aether fine enough to permeate glass, though our common Air cannot do it, have not near so difficult a task to avoid the Arguments the Vacuists may draw from our Engine, as Mr. Hobbes, who, without having recourse to the porosity of glass, which indeed is impervious to common Air, strives to solve the Phaenomena, and prove our Receiver to be always perfectly full, and therefore as full at any one time as at any other of common or Atmospherical Air, as far as we can judge of his opinion by the tendency or import of his Explications.  A. 
Yet, if I were rightly informed of an Experiment of yours, Mr. Hobbes may be thereby reduced either to pass over to the Vacuists, or to acknowledge some Aetherial or other matter more subtle than Air, and capable of passing through the pores of glass; and therefore, to show yourself impartial between the Vacuists and their Adversaries in this Controversy, I hope you will not refuse to gratify the Plenists by giving your friends a more particular account of the Experiment.  B. 
I know which you mean, and remember it very well. For, though I long since devised it, yet having but the other day had occasion to peruse the Relation I writ down of one of the best Trials, I think I can repeat it, almost in the very words, which, if I mistake not, were these:  
There was taken a Bubble of thin white glass, about the bigness of a Nutmeg, with a very slender stem, of about four or five Inches long, and of the bigness of a Crows-quill. The end of the Quill being held in the flame of a Lamp blown with a pair of Bellows, was readily and well sealed up, and presently the globous part of the glass, being held by the stem, was kept turning in the flame, till it was red hot and ready to melt; then being a little removed from the flame, as the included Air began to lose of its agitation and spring, the external Air manifestly and considerably pressed in one of the sides of the Bubble. But the glass being again, before the cold could crack it, held as before in the flame, the rarified Air distended and plumped up the Bubble; which being the second time removed from the flame, was the second time compressed; and, being the third time brought back to the flame, swelled as before, and removed, was again compressed, (either this time or the last by two distinct cavities;) till at length, having satisfied ourselves, that the included Air was capable of being condensed or dilated without the ingress or egress of Air (properly so called) we held the Bubble so long in the flame, strengthened by nimble blasts, that not only it had its sides plumped up, but a hole violently broken in it by the over-rarified Air, which, together with the former watchfulness, we employed from time to time to discern if it were any where cracked or perforated, satisfied us that it was till then entire.  A. 
I confess, I did not readily conceive before, how you could, (as I was told you had,) make a solid Vessel, wherein there was no danger of the Airs getting in or out, whose cavity should be still possessed with the same Air, and yet the Vessel be made by turns bigger and lesser. And, though I presently thought upon a well stopped bladder, yet I well foresaw, that a distrustful Adversary might make some Objections, which are by your way of proceeding obviated, and the Experiment agrees with your Doctrine in showing, how impervious we may well think your thick Pneumatick Receivers are to common Air, since a thin glass Bubble, when its pores were opened or relaxed by flame, would not give passage to the Springy particles of the Air, though violently agitated; for if those particles could have got out of the pores, they never would have broke the Bubble, as at length a more violent degree of Heat made them do; nor probably would the Compression, that afterwards ensued of the Bubble by the ambient Air, be checked near so soon, if those Springy Corpuscles had not remained within to make the resistance. Methinks, one may hence draw a new proof of what I remember you elsewhere teach, that the Spring of the Air may be much strengthened by Heat. For, in our case, the Spring of the Air was thereby enabled to expand the compressed glass, it was imprisoned in, in spite of the resisting pressure of the external Air; and yet, that this pressure was considerable, appears by this, that the weight of so small a Column of Atmospherical Air, as could bear upon the Bubble, was able to press in the heated glass, in spite of the resistance of its tenacity and arched figure.  B. 
Yet that which I mainly designed in this Experiment was, (if I were able) to show and prove at once, by an Instance not liable to the ordinary exceptions, the true Nature of Rarefaction and Condensation, at least of the Air. For, to say nothing of the Peripatetic Rarefaction and Condensation, strictly so called, which I scruple not to declare, I think to be physically inconceptible or impossible; 'tis plain by our Experiment, that, when the Bubble, after the Glass had been first thrust in towards the Centre, was expanded again by heat, the included Air possessed more room than before, and yet it could perfectly fill no more room than formerly, each Aerial Particle taking up, both before and after the heating of the Bubble, a portion of space adequate to its own bulk; so that in the Cavity of the expanded Bubble we must admit either Vacuities interspersed between the Corpuscles of the Air, or that some fine Particles of the Flame, or other subtle matter, came in to fill up those Intervals, which matter must have entered the Cavity of the Glass at its pores: And afterwards, when the red-hot Bubble was removed from the flame, it is evident, that, since the grosser particles of the Air could not get through the Glass, which they were not able to do, even when vehemently agitated by an ambient Flame, the Compression of the Bubble, and the Condensation of the Air, which was necessarily consequent upon it, could not, supposing the Plenitude of the World, be performed without squeezing out some of the subtle matter contained in the cavity of the Bubble, whence it could not issue but at the pores of the Glass. But I will no longer detain you from Mr. Hobbes his Explications of the Machina Boyliana; to the first of which you may now, if you please, advance.  A. 
The passage I was going to read, when you interrupted me, was this:  B. 
Machina illa eosdem effectus producit, quos produceret in loco non magno magnus inclusus ventus.  A. 
Quomodo ingreditur istuo ventus? Machinam nosti Cylindrum esse cavum, sneum, in quem protruditur Cylindrus alius solidus ligneus, coriotectus, (quem suctorem dicunt) ita exquisitè congruens, ut ne minimus quidem Aer inter corium & aes intrare (ut putant) possit.  B. 
Scio, & quò Suctor facilius intrudi possit, foramen quoddam est in superiori parte Cylindri, per quod Aer (qui suctoris ingressum alioqui impedire possit) emittatur. Quod foramen aperire possunt & clandere quoties usus postulat. Est etiam in Cylindri cavi recessu summo datus aditus Aeri in globum concavum Vitreum, quem etiam aditum claviculâ obturare & aperire possunt quoties volunt. Denique in globo vitreo summo relinquitur foramen satis amplum, (claviculâ item claudendum & recludendum) ut in illum quae volunt immittere possint, experiendi causâ  B. 
The imaginary wind to which Mr. Hobbes here ascribes the effects of our Engine, he formerly had recourse to in the 13th page of his Dialogue, and I have sufficiently answered that passage of it in the 45th and 46th pages of my Examen, to which I therefore refer you.  A. 
I presume, you did not overlook the comparison Mr. Hobbes annexes to what I last read out of his Problems, since he liked the conceit so well, that we meet with it in this place again, though he had formerly printed it in his Dialogue De Natura Aeris. The words (as you see) are these: Tota denique Machina non multum differt, si naturam ejus spectes, à Sclopeto ex Sambuco, quo pueri se delectant, imitantes Sclopetos militum, nisi quòd major sit, & majori arte fabricatus, & pluris constet.  B. 
I could scarce, for the reason you give, avoid taking notice of it. And if Mr. Hobbes intended it for a piece of Ralliery, I willingly let it pass, and could easily forgive him a more considerable attempt than this, to be revenged on an Engine that has destroyed several of his opinions: But, if he seriously meant to make a Physical Comparison, I think he made a very improper one. For, not to urge, that one may well doubt how he knows, that in the enclosed cavity of his Potgun, there is a very vehement wind, (since that does not necessarily follow from the compreffion of the included Air:) In Mr. Hobbes' Instrument, the Air, being forcibly compressed, has an endeavour to expand itself, and when it is able to surmount the resistance of its prison, that part that is first disjoined is forcibly thrown outwards; whereas in our Engine it appears by the passage lately cited of our Examen, that the Air is not compressed but expanded in our Receiver, and if an intercourse be opened, or the Vessel be not strong enough, the outward Air violently rushes in: And if the Receiver chance to break, the fragments of the glass are not thrown outwards, but forced inwards.  A. 
So that, whether or no Mr. Hobbes could have pitched upon a Comparison more suitable to his Intentions, he might easily have employed one more suitable to the Phaenomena.  B. 
I presume, you will judge it the less agreeable to the Phaenomena, if I here subjoin an Experiment, that possibly you will not dislike; which I devised to show, not only that in our exhausted Receivers there is no such strong endeavour outwards, as most of Mr. Hobbes' Explications of the things that happen in them are built upon, but that the weight of the Atmospherical Air, when 'tis not resisted by the counterpressure of any internal Air, is able to perform what a weight of many pounds would not suffice to do.  A. 
I shall the more willingly learn an Experiment to this purpose, because in your Receivers, the rigidity of the glass keeps us from seeing, by any manifest change of its figure, whether, if it could yield without breaking, it would be pressed in, as your Hypothesis requires.  B. 
The desires to obviate that very difficulty, for their satisfaction, that had not yet penetrated the grounds of our Hypothesis, made me think of employing, instead of a Receiver of Glass, one of a stiff and tough, but yet somewhat flexible, Metal. And accordingly having provided a new Pewter Porringer, and whelmed it upside down upon an Iron plate fastened to (the upper end of) our Pneumatical Pump, we carefully fastened by Cement the orifice to the plate, and though the inverted Vessel, by reason of its stiffness and thickness and the convexity of its superficies, were strong enough to have supported a great weight without changing its figure; yet, as soon as by an exsuction or two the remaining part of the included Air was brought to such a degree of expansion, that its weakened Spring was able to afford but little assistance to the tenacity and firmness of the Metal, the weight of the pillar of the incumbent Atmosphere (which by reason of the breadth of the Vessel was considerably wide also) did presently and notably depress the upper part of the Porringer, both lessening its capacity and changing its figure; so that instead of the Convex surface, the Receiver had before, it came to a Concave one, which new figure was somewhat, though not much, increased by the further withdrawing of the included and already rarified Air. The Experiment succeeded also with an other common Porringer of the same Metal. But in such kind of Vessels, made purposely of Iron plates, it will sometimes succeed and sometimes not, according to the Diameter of the vessel and the thickness of the plate, which was sometimes strong enough and sometimes too weak to resist the pressure of the incumbent Air. And sometimes I found also, that the vessel would be thrust in, not at the top but side-ways, in case that side were the only part that were made too thin to resist the pressure of the Ambient; which Phaenomenon I therefore take notice of, that you may see, 〈◊〉 that powerful pressure may be exercised laterally as well as perpendicularly.  
Perhaps this Experiment, and that I lately recited of an Hermetically sealed Bubble, by their fitness to disprove Mr. Hobbes 's Doctrine, may do somewhat towards the letting him see, that he might have spared that not over-modest and wary expression, where speaking of the Gentlemen that meet at Gresham-College, (of whom I pretend not to be one of the chief) he is pleased to say, Experimenta faciant quantum volunt, nisi Principiis utantur meis nihil proficient. But let us, if you please, pass on to what he further alleges to prove, that the space in the exhausted Receiver, which the Vacuists suppose to be partly empty, is full of Air. (Video (says A.) si suctor trudatur usque ad fundum Cylindri Aenei, obturenturque for amina, Secuturum esse, dum suctor retrahitur, locum in Cylindro cavo relictum fore vacuum. Nam ut in locum ejus succedat Aer, est impossibile. To which B. answers, Credo equidem, suctorem cum Cylindri cavi superficie satis arctè cohaerere ad excludendum stramen & plumam, non autem Aerem neque Aquam. Cogita enim, quod non ita accuratè congruerent, quin undiquaque interstitium relinqueretur, quantum tenuissimi capilli capax esset. Retracto ergo suctore, tantum impelleretur Aeris, quantum viribus illis conveniret quibus Aer propter suctoris Retractionem reprimitur, idque sine omni difficultate sensibili. Quanto autem interstitium illud minus esset, tantum ingrederetur Aer velocius: Vel si contactus sit, sed non per omnia puncta, etiam tunc intrabit Aer, modò suctor majore vi retrahatur. Postremò, etsi contactus ubique exactissimus sit, vi tamen satis auctâ per cochleam ferream, tum corium cedet, tum ipsum es; atque ita quoque ingredietur Aer. Credin' tu, possibile esse duas superficies ita exactè componere, ut has compositas esse supponunt illi; aut corium ita durum esse, ut Aeri, qui Cochleae ope incutitur, nihil omnino cedat? Corium quanquam optimum admittit aquam, ut ipse scis, si fortè fecisti unquam iter vento & pluvia 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉. It aque dubitare non potes, quin retractus Suctor tantum Aeris in Cylindrum adeoque in ipsum Recipiens incutiat, quantum sufficit ad locum semper relictum perfectè implendum. Effectus ergo, qui oritur à Retractione suctoris, alius non est quam ventus, ventus (inquam) uchementissimus, qui ingreditur undiquaque inter Suctoris superficiem convexam, & Cylindri aenei concavam, proceditque (versâ claviculâ) in cavitatem globi Vitrei, sive (ut vocatur) Recipientis.  
The Substance of this Ratiocination having been already proposed by Mr. Hobbes in his Dialogue of the Air, the 11th page, I long since answered it in the 30th and some of the following pages of my Examen; and therefore I shall only now take notice in transitu of some slight whether additions or variations, that occur in what you have been reading. And, first, I see no probability in what he gratìs asserts, that so thick a Cylinder of Brass, as made the chief part of the pump of our Engine, should yield to the Sucker, that was moved up and down in it, though by the help of an Iron rack; and whereas he adds, that the leather, that surrounds the more solid part of the Sucker, would yield to such a force; it seems, that that compression of the leather should by thrusting the solid parts into the pores make the leather rather less than more fit to give passage to the Air; nor would it however follow, notwithstanding Mr. Hobbes' Example, that, because a Body admits Water, it must be pervious to Air: For I have several times, by ways elsewhere taught, made Water penetrate the pores of Bladders, and yet Bladders resist the passage of the Air so well, that even when Air included in them was sufficiently rarified by Heat, or by our Engine, it was necessary for the Air to break them before it could get out; which would not have been, if it could have escaped through their pores. What Mr. Hobbes inculcates here again concerning his ventus vehementissimus, you will find answered in the place of my Examen I lately directed you to.  A. 
We may then proceed to Mr. Hobbes' next Explication, which he proposes in these terms:  A. 
Causam video nunc unius ex Machinae mirabilibus, nimirum cur Suctor, postquam est aliquatenus retractus & deinde amissus, subitò recurrit ad Cylindri summitatem. Nam Aer, qui vi magna fuit impulsus, rursus per repercussionem ad externa vi eadem revertitur.  B. 
Atque hoc quidem Argumenti satis est etiam solum, quòd locus à suctore relictus non est Vacuus. Quid enim aut attrahere aut impellere suctorem potuit ad locum illum unde retractus erat, si Cylindrus fuisset vacuus? Namut Aeris pondus aliquod id efficere potuisset, falsum esse satis supra demonstravi ab eo quod Aer in Aere gravitare non potest. Nosti etiam, quod cum è recipiente Aerem omnem (ut illi loquuntur) exegerint, possunt tamen trans vitrum id quod intus fit videre, & sonum, si quis fiat, inde audire. Id quod solum, etsi nullum aliud Argumentum esset (sunt autem multa,) ad probandum, nullum esse in Recipiente Vacuum, abundè sufficit.  B. 
Here are several things joined together, which the Author had before separately alleged in his often-mentioned Dialogue. The first is, the Cause he assigns of the ascension of the Sucker forcibly depressed to the bottom of the exhausted Cylinder, and then let alone by him that pumped; to which might be added, that this ascension succeeded, when the Sucker was clogged with an hundred pound weight. This Explication of Mr. Hobbes you will find examined in the 33th and 39th, and some ensuing pages of my Discourse. And as to his denying, that the weight or pressure of the Air could drive up the Sucker in that Phaenomenon, because the Air does not weigh in Air, we may see the contrary largely proved in divers places of my Examen, and more particularly and expressly in the four first pages of the third Chapter. And whereas he says in the last place, that the visibility of Bodies included in our Receivers, and the propagation of Sound, (which, by the way, is not to be understood of all Sound that may be heard, though made in the exhausted Receiver,) are alone sufficient Arguments to prove no Vacuum: I have considered that passage in the answer I made to the like allegation in the 45th page of the Examen; and shall only observe here, that, since the Vacuists can prove, that much of the Air is pumped out of the exhausted Receiver, and will pretend, that, notwithstanding many interspersed Vacuities, there may be in the Receiver corporeal substance enough to transmit Light and stronger Sounds, Mr. Hobbes has not performed what he pretended, if he have but barely proved, that there may be Substances capable of conveying Light and Sound in the cavity of our Receiver, since he triumphantly asserts, Nullum esse in Recipienti Vacuum. But we may leave Mr. Hobbes and his Adversaries to dispute out this point, and go on to the next passage.  A. 
Which follows in these words:  
Ad illud autem, quod si Vesica aliquatenus inflata in Recipiente includatur, paulo post per exuctionem aeris inflatur vehementius & dirumpitur, quid respondes?  B. 
Motus partium Aeris undiquaque concurrentium velocissimus & per concursum in spatiis brevissimis numeroque infinitis gyrationis velocissimae vesicam in locis innumerabilibus simul & vi magna, instar totidem terebrarum, penetrate, praesertim si vesica, antequam immittatur, quò magis resistat aliquatenus inflat a sit. Postquam autem Aer penetrans semel ingressus est, facile cogitare potes, quo pacto deinceps vesicam tendet, & tandem rumpet. Verùm si antequam rumpatur, versâ claviculâ, Aer externus admittatur, videbis vesicam propter vehementiam motus temperatam diminutâ tensione rugosiorem. Nam id quoque observatum est. Jam si haec, quam dixi, causa minùs tihi videatur verisimilis, vide an tu aut alius quicunque imaginari potest, quo pacto vesica distendi & rumpi possit à viribus Vacui, id est, Nihili.  B. 
This Explication Mr. Hobbes gave us in the 19th page of his Dialogue De Natura Aeris, and you may find it at large confuted in the latter part of the third Chapter of my Examen. Nor does, what he here says in the close about the Vires Vacui or Nihili, deserve to detain us, since there is no reason at all, that the Vacuists should ascribe to nothing a power of breaking a Bladder, of whose rupture the Spring of the included Air supplies them so easily with a sufficient Cause.  
After what Mr. Hobbes has said of the breaking of a Bladder, he proceeds to an Experiment which he judges of affinity with it, and his Academian having proposed this Question:  
Unde fit ut animalia tam cito, nimirum spatio quatuor minutorum horae, in recipiente interficiantur?  
For answer to it our Author says:  B. 
Nun animalia sic inclusa insugunt in Pulmones Aerem vehementissimè motum? Quo motu necesse est ut transitus sanguinis ab uno ad alterum cordis ventriculum interceptus, non multò pòst sistatur. Cessatio autem sanguinis, Mors est. Possunt tamen animalia cessante sanguine reviviscere, si Aer externus satis maturè intromittatur, vel ipsa in Aerem temperatum, antequam refrixerit sanguis, extrahantur.  
This Explication is not probable enough, to oblige me to add any thing about it to what I have said in the 49th and the two following pages of my Examen; especially the most vehement motion, ascribed to the Air in the Receiver, having been before proved to be an Imaginary thing. You may therefore, if you please, take notice of the next Explication.  
[Idem Aer (says he) in Recipiente Carbones ardentes extinguit, sed & illi, si, dum satis calidi sunt, eximantur, relucebunt. Notissimum est, quòd in fodinis Carbonum terreorum (cujus rei experimentum ipse vidi) saepissime è lateribus foveae ventus quidam undiquaque exit, qui fossores interficit ignemque extinguit, qui tamen reviviscunt si satis cito ad Aerem liberum extrahantur.]  
This Comparison which Mr. Hobbes here summarily makes, he more fully displayed in his Dialogue De Natura Aeris, and I considered, what he there alleged, in the 52th page and the two next of my Examen. And, though I will not contradict Mr. Hobbes in what he historically asserts in this passage; yet I cannot but somewhat doubt, whether he mingles not his conjecture with the bare matter of fact. For, though I have with some curiosity visited Mines in more places than one, and proposed Questions to Men that have been conversant in other Mines, both elsewhere and in England (and particularly in Derbyshire where Mr. Hobbes lived long;) yet I could never find, that any such odd and vehement wind, as Mr. Hobbes ascribes the Phaenomenon to, had been by them observed to kill the Diggers, and extinguish well-lighted Coals themselves: And indeed, it seems more likely, that the damp, by its tenacity or some peculiarly malign quality, did the mischief, than a wind, of which I found not any notice taken; especially since we see, what vehement winds Men will be able to endure for a long time, without being near-killed by them; and that it seems very odd, that a wind, that Mr. Hobbes does not observe to have blown away the Coals, that were let down, should be able (instead of kindling them more fiercely) to blow them out.  A. 
The last Experiment of your Engine, that your Adversary mentions in these Problems, is delivered in this passage:  A. 
Si phialam aquae in Recipiens dimiseris, exucto Aere bullire videbis aquam. Quid ad hoc Respondebis?  B. 
Credo sanè in tanta Aeris motitatione saltaturam esse aquam, sed ut calefiat nondum audivi. Sed imaginabile non est, Saltationem illam à Vacuo nasci posse.  B. 
This Phaenomenon he likewise took notice of, and attempted to explicate in his abovementioned Dialogue, which gave me occasion in the 46th and 47th pages of my Examen, to show how unlikely 'tis, that the vehement motion of the Air should be the cause of it; but he here tells us, that 'tis not imaginable, that this dancing of the water (as he is pleased to call it) proceeds from a vacuum, nor do I know any Man that ever pretended, that a vacuum was the efficient cause of it. But the Vacuists perhaps will tell him, that, though the bubbling of the water be not an effect of a vacuum, it may be a proof of it against him; for they will tell him, that it has been formerly proved, that a great part of the Atmospherical Air is by pumping removed out of our exhausted Receiver, and consequently can no more, as formerly, press upon the surface of the water. Nor does Mr. Hobbes show what succeeds in the room of it; and therefore it will be allowable, for them to conclude against him (though not perhaps against the Cartesians) that there are a great many interspersed Vacuities left in the Receiver, which are the occasion, though not the proper efficient cause, of the Phaenomenon. For they will say, that the Springy Particles of the yet included Air, having room to unbend themselves in the spaces deserted by the Air that was pumped out, the Aerial and Springy Corpuscles, that lay concealed in the pores of the water, being now freed from the wont pressure that kept them coiled up in the liquor, expanded themselves into numerous bubbles, which, because of their comparative lightness, are extruded by the water, and many of them appear to have risen from the bottom of it. And Mr. Hobbes' vehement wind, to produce the several Circumstances of this Experiment, must be a lasting one. For, after the agitation of the Pump has been quite left off, provided the external Air be kept from getting in, the bubbles will sometimes continue to rise for an hour after. And that which agrees very well with our Explication and very ill with that of Mr Hobbes's, is, that, when by having continued to pump a competent time, the water has been freed from the Aerial particles that lurked in it before, though one continue to pump as lustily as he did, yet the water will not at all be covered with bubbles as it was, the Air that produced them being spent; though, according to Mr. Hobbes' Explication, the wind in the Receiver continuing, the dance of the water should continue too.  A. 
I easily guess, by what you have said already, what you may say of that Epiphonema wherewith Mr. Hobbes (in his 18th page) concludes the Explications of the Phaenomena of your Engine. [Spero jam te certum esse, says he, nullum esse Machinae illius Phaenomenon, quo demonstrari potest ullum in Universo locum dari corpore omni vacuum.]  B. 
If you guessed aright, you guessed that I would say, that as to the Phaenomena of my Engine, my business was to prove, that he had not substituted good Explications of them in the place of mine, which he was pleased to reject. And as for the proving a Vacuum by the Phaenomena of my Engine, though I declared that was not the thing intended, yet I shall not wonder, that the Vacuists should think those Phaenomena give them an advantage against Mr. Hobbes. For, though in the passage recited by you he speak more cautiously than he is won to do, yet, by what you may have already observed in his Argumentations, the way he takes to solve the Phaenomena of our Engine, is by contending, that our Receiver, when we say it is almost exhausted, is as full as ever (for he will have it perfectly full,) of common Air; which is a conceit so contrary to I know not how many Phaenomena, that I do not remember I have met with or heard of any Naturalist, whether Vacuist or Plenist, that having read my Physicomechanical Experiments and his Dialogue, has embraced his opinion.  A. 
After what you have said, I will not trouble you with what he subjoins about Vacuum in general, where having made his Academian say, [Mundum scis finitum esse, & per Consequens vacuum esse oportere totum illud Spatium quod est extra mundum infinitum. Quid impedit quo minus vacuum illud cum Aere mundano permisceatur?] He answers: De rebus transmundanis nihil scio. For I know, that it concerns not you to take notice of it. But possibly the Vacuists will think, he fathers upon them an Impropriety they would not be guilty of, making them speak, as if they thought, the ultra-mundan Vacuum were a real Substance that might be brought into this World and mingled with our Air. And since, for aught I know, Mr. Hobbes might have spared this passage, if he had not designed it should introduce the slighting answer he makes to it; I shall add, that by the account Mr. Hobbes has given of several Phaenomena within the World, 'tis possible, that the Vacuists may believe his Profession of knowing nothing of things beyond it.  
After the Experimenta Boyliana (as your other Adversary calls them;) Mr: Hobbes proceeds to the Torricellian Experiment, of which he thus discourses:  A. 
Quid de experimento censes Torricelliano, probante Vacuum per Argentum vivum hoc modo: est in seq. figurae ad A, pelvis sive aliud vas, & in eo Argentum vivum usque ad B; est autem C D tubus vitreus concavus repletus quoque Argento vivo. Hunc tubum si digito obturaveris erexerisque in vase A, manumque abstuleris, descendet Argentum vivum à C; verùm non effundetur totum in pelvim, sed sistetur in distantia quadam, puta in D. Nun ergo necessarium est, ut pars tubi inter C & D sit vacua? Non enim puto negabis quin superficies tubi concava & Argenti vivi convexa se mutuo exquisitissimè contingant.  B. 
Ego neque nego contactum, neque vim Consequentiae intelligo.  
By which passage it seems that he still persists in the solution of this Experiment, which he gave in his Dialogue De Natura Aeris, and formerly did, for the main, either propose, or adopt, in his Elements of Philosophy.  B. 
This opinion or explication of Mr. Hobbes I have, as far as concerns me, considered in the 36th, and some ensuing pages, of my Examen, to which it may well suffice me to refer you. But yet let me take notice of what he now alleges:  B. 
Si quis (says he) in Argentum vivum, quod in vase est, vesicam immerserit inflatam, nun illa amotâ manu emerget?  A. 
It a certè, etsi esset vesica ferrea vel ex materia quacunque praeter Aurum.  B. 
Vides igitur ab Aere penetrari posse Argentum vivum.  A. 
Etiam, & quidem illâ ipsâ vi quam à pondere accipit Argenti vivi.  
I confess this Allegation did a little surprise me: It concerned Mr. Hobbes to prove, that as much Air, as was displaced by the descending Mercury, did at the orifice of the Tube, immersed in stagnant Mercury, invisibly ascend to the upper part of the pipe. To prove this he tells us, that a bladder full of Air being depressed in Quicksilver, will, when the hand that depressed it is removed, be squeezed up by the very weight of the Mercury, whence it follows, that Air may penetrate Quicksilver. But I know not, who ever denied, that Air environed with Quicksilver may thereby be squeezed upwards; but, since even very small bubbles of Air may be seen to move in their passage through Mercury, I see not, how this Example will at all help the Proposer of it. For 'tis by mere accident, that the Air included in the bladder comes to be buoyed up, because the bladder itself is so; and if it were filled with Water instead of Air, or with Stone instead of Water, it would nevertheless emerge, as himself confesses it would do, if it were made of Iron, or of any Matter besides Gold, because all other Bodies are lighter in specie than Quicksilver. But since the emersion of the bladder is manifest enough to the sight, I see not how it will serve Mr. Hobbes' turn, who is to prove that the Air gets into the Torricellian Tube invisibly; since 'tis plain, that even heedful observation can make our Eyes discover no such trajection of the Air; which (to add that enforcement of our Argument) must not only pass unseen through the sustained Quicksilver, but must likewise unperceivedly dive, in spite of its comparative lightness, beneath the surface of the ponderous stagnant Mercury, to get in at the orifice of the erected Tube. But let us, if you please, hear the rest of his Discourse about this Experiment.  A. 
Though it be somewhat prolix, yet, according to my custom hitherto, I will give it you verbatim.  B. 
Simul atque Argentum vivum descenderit ad D, altius erit in vase A quam antè, nimirum plus erit Argenti vivi in vase quam erat ante descensum, tanto quantum capit pars tubi C, D. Tanto quoque minus erit Aeris extra tubum quam ante erat. Ille autem Aer qui ab Argento vivo loco suo extrusus est, (suppositâ universi plenitudine) quò abire potest nisi ad eum locum, qui in tubo inter C & D à descensu Argenti vivi relinquebatur? sed quâ, inquies, viâ in illum locum successurus est? Quà, nisi per ipsum corpus Argenti vivi Aerem urgentis? Sicut enim omne grave liquidum, sui ipsius pondere, Aerem, quem descendendo prennt, ascendere cogit (si via alia non detur) per suum ipsius corpus; ita quoque Aerem quem premit ascendendo, (si via alia non detur) per suum ipsius corpus transire cogit. Manifestum igitur est, supposità mundi plenitudine posse Aerem externum ab ipsa gravitate Argenti vivi cogi in locum illum inter C & D. Itaque phaenomenon illud necessitatem vacus nondemonstrat. Quoniam autem corpus Argenti vivi penetrationi, quae fit ab Aere, non nihil resistit, & ascensioni Argenti vivi in vase A resistit Aer; quando illae duae resistentiae aequales erunt, tunc in tubo sistetur alicubi Argentum vivum; atque ibi est D.  B. 
In answer to this Explication I have in my Examen proposed divers things, which you may there meet with: And indeed his Explication has appeared so improbable to those that have written of this Experiment, that I have not found it embraced by any of them, though, when divers of them opposed it, the Phaenomena of our Engine were not yet divulged. Not then needlessly to repeat what has been said already, I shall on this occasion only add one Experiment, that I afterwards made, and it was this: Having made the Torricellian Experiment (in a strait Tube) after the ordinary way, we took a little piece of a fine Bladder, and raising the Pipe a little in the stagnant Mercury, but not so high as the surface of it, the piece of Bladder was dexterously conveyed in the Quicksilver, so as to be applied by one's finger to the immersed orifice of the Pipe, without letting the Air get into the Cavity of it; then the Bladder was tied very strait and carefully to the lower end of the Pipe, whose orifice (as we said) it covered before, and then the Pipe being slowly lifted out of the stagnant Mercury, the impendent Quicksilver appeared to lean but very lightly upon the Bladder, being so near an exact Aequilibrium with the Atmosperical Air, that, if the Tube were but a very little inclined, whereby the gravitation of the Quicksilver, being not so perpendicular, came to be somewhat lessened, the Bladder would immediately be driven into the orifice of the Tube, and to the Eye, placed without, appear to have acquired a concave superficies instead of the convex it had before. And when the Tube was reerected, the Bladder would no longer appear sucked in, but be again somewhat protuberant. And if, when the Mercury in the Pipe was made to descend a little below its station into the stagnant Mercury, if, I say, at that nick of time the piece of Bladder were nimbly and dexterously applied, as before, to the immersed orifice, and fastened to the sides of the Pipe, upon the lifting the Instrument out of the stagnant Mercury, the Cylinder of that Liquor being now somewhat short of its due height, was no longer able fully to counterpoise the weight of the Atmospherical Air, which consequently, though the Glass were held in an erected posture, would press up the Bladder into the orifice of the Pipe, and both make and maintain there a Cavity sensible both to the Touch and the Eye.  A. 
What did you mainly drive at in this Experiment?  B. 
To satisfy some Ingenious Men, that were more diffident of, than skilful in, hydrostatics, that the pressure of the external Air is capable of sustaining a Cylinder of 29 or 30 Inches of Mercury, and upon a small lessening of the gravitation of that ponderous liquor, to press it up higher into the Tube. But a farther use may be made of it against Mr. Hobbes' pretention. For, when the Tube is again erected, the Mercury will subside as low as at first, and leave as great a space as formerly was left deserted at the top; into which how the Air should get to fill it, will not appear easy to them, that, like you and me, know by many trials, that a Bladder will rather be burst by Air than grant it passage. And if it should be pretended, either that some Air from without had yet got through the Bladder, or that the Air, that they may presume to have been just before included between the Bladder and the Mercury, made its way from the lower part of the Instrument to the upper; 'tis obvious to answer, That 'tis no way likely, that it should pass all along the Cylinder unseen by us; since, when there are really any Aerial Bubbles, though smaller than Pins heads, they are easily discernible. And in our case, there is no such resistance of the Air to the ascension of the stagnant Mercury, as Mr. Hobbes pretends in the Torricellian Experiment made the usual way.  A. 
But, whatever becomes of Mr. Hobbes' Explication of the Phaenomenon; yet may not one still say, that it affords no advantage to the Vacuists against him?  B. 
Whether or no it do against other Plenists, I shall not now consider; but I doubt, the Vacuists will tell Mr. Hobbes, that he is fain in two places of the Explication, we have read, to suppose the Plenitude of the World, that is, to beg the thing in question, which 'tis not to be presumed they will allow.  A. 
But may not Mr. Hobbes say, that 'tis as lawful for him to suppose a Plenum, as for them to suppose a Vacuum.  B. 
I think he may justly say so; but 'tis like they will reply, that, in their way of explicating the Torricellian Experiment, they do not suppose a Vacuum at to Air, but prove it. For they show a great space, that having been just before filled with Quicksilver, is now deserted by it, though it appeared not, that any Air succeeded in its room; but rather, that the upper end of the Tube is either totally or near totally so devoid of Air, that the Quicksilver may without resistance, by barely inclining the Tube, be made to fill it to the very top: Whereas Mr. Hobbes is fain to have recourse to that which he knows they deny, the Plenitude of the World, not proving by any sensible Phaenomena, that there did get in through the Quicksilver Air enough to fill the deserted part of the Tube, but only concluding, that so much Air must have got in there, because, the World being full, it could find no room any where else; which the Vacuists will take for no proof at all, and the Cartesians, though Plenists, who admit an Etherial matter capable of passing through the pores of Glass, will, I doubt, look upon but as an improper Explication.  A. 
I remember on this occasion another Experiment of yours, that seems unfavourable enough to Mr. Hobbes' Explication, and you will perhaps call it to mind when I tell you, that 'twas made in a bended Pipe almost filled with Quicksilver.  B. 
To see whether we understand one another, I will briefly describe the Instrument I think you mean. We took a Cylindrical Pipe of Glass, closed at the upper end, and of that length, that being dexterously bend at some Inches from the bottom, the shorter leg was made as parallel as we could to the longer: In this Glass we found an expedient, (for 'tis not easy to do,) to make the Torricellian Experiment, the Quicksilver in the shorter leg serving instead of the stagnant Quicksilver in the usual Baroscope, and the Quicksilver in the longer leg reaching above that in the shorter about eight or nine and twenty Inches. Then, by another artifice, the shorter leg, into which the Mercury did not rise within an Inch of the top, was so ordered, that it could in a trice be Hermetically sealed, without disordering the Quicksilver. And this is the Instrument that I guess you mean.  A. 
It is so, and I remember, that it is the same with that, which in the Paradox about Suction you call, whilst the shorter leg remains unsealed, a Travelling Baroscope. But when I saw you make the Experiment, that leg was Hermetically sealed, an Inch of Air in its natural or usual consistence being left in the upper part of it, to which Air you outwardly applied a pair of heated Tongues.  B. 
Yet that, which I chiefly aimed at in the Trial, was not the Phaenomenon I perceive you mean; for, my design was, by breaking the Ice for them, to encourage some, that may have more skill and accommodation than I then had, to make an attempt that I did not find to have been made by any; namely, to reduce the Expensive force of Heat in every way included Air, if not in some other Bodies also, to some kind of measure, and, if 'twere possible, to determine it by weight. And I presumed, that at least the event of my Trial would much confirm several Explications of mine, by showing, that Heat is able, as long as it lasts, very considerably to increase the Spring or pressing power of the Air. And in this conjecture I was not mistaken; for, having shut up, after the manner newly recited, a determinate quantity of uncomprest Air, which, (in the Experiment you saw,) was about one Inch; we warily held a pair of heated Tongues near the outside of the Glass, (without making it touch the Instrument, for fear of breaking it,) whereby the Air being agitated was enabled to expand itself to double its former Dimensions, and consequently had its Spring so strengthened by Heat, that it was able to raise all the Quicksilver in the longer leg, and keep up or sustain a Mercurial Cylinder of about nine and twenty Inches high, when by its expansion it would, if it had not been for the Heat, have lost half the force of its elasticity. But whatever I design in this Experiment, pray tell me, what use you would make of it against Mr. Hobbes.  A. 
I believe, he will find it very difficult to show, what keeps the Mercury suspended in the longer leg of the Travelling Baroscope, when the shorter leg is unstopped, at which it may run out; since this Instrument may, as I have tried, be carried to distant places, where it cannot with probability be pretended, that any Air has been displaced by the fall of the Quicksilver in the longer leg, which perhaps fell long before above a mile off. And when the shorter leg is seal'd, it will be very hard for Mr. Hobbes to show there the odd motions of the Air, to which he ascribes the Torricellian Experiment. For, if you warily incline the Instrument, the Quicksilver will rise to the top of the longer leg, and immediately subside, when the Instrument is again erected, and yet no Air appears to pass through the Quicksilver interposed between the ends of the longer and the shorter leg. But that which I would chiefly take notice of in the Experiment, is, that upon the external application of a hot Body to the shorter leg of the Baroscope, when 'twas sealed up, the included Air was expanded from one Inch to two, and so raised the whole Cylinder of Mercury in the longer leg, and, whilst the heat continued undiminished, kept it from subsiding again. For, if the Air were able to get unseen through the body of the Quicksilver, why had it not been much more able, when rarified by Heat, to pass through the Quicksilver, than for want of doing so to raise and sustain so weighty a Cylinder of Mercury? I shall not stay to inquire on this occasion, how Mr. Hobbes will, according to his Hypothesis, explicate the rarefaction of the Air to double its former dimensions, and the condensation of it again; especially since, asserting that part of the upper leg, that is unfilled with the Quicksilver, to be perfectly full of Air, he affirms that, which I doubt he cannot prove, and which may very probably be disproved by the Experiment you mention in the Discourse about Suction, where you show, to another purpose, that in a Travelling Baroscope, whose shorter leg is sealed, if the end of the longer leg be opened, whereby it comes indeed to be filled with Air, the pressure of that Air will enable the subjacent Mercury notably to compress the Air included in the shorter leg.  B. 
I leave Mr. Hobbes to consider what you have objected against his Explication of the Torricellian Experiment; to which I shall add nothing, though perhaps I could add much, because I think it may be well spared, and our Conference has lasted long already.  A. 
I will then proceed to the last Experiment recited by Mr. Hobbes in his Problemata de Vacuo.  A. 
Si Phialam, collum habentem longiusculum, candèmque omni Corpore praeter Aerem vacuam ore sugas, continuoque Phialae os aquae immergas, videbis aquam aliquousque ascendere in Phialam. Quî fieri hoc potest nisi factum sit Vacuum ab exuctione Aeris, in cujus locum possit Aqua illa ascendere?  B. 
Concesso Vacuo, oportet quaedam loca vacua fuisse in illo Aere, etiam qui erat intra Phialam ante suctionem. Cur ergo non ascendebat Aqua ad ea implenda absque suctione? Is qui sugit Phialam, neque in ventrem quicquam, neque in pulmones, neque in os è Phiala exugit. Quid ergo agit? Aerem commovet, & in partibus ejus conatum sugendo efficit per os exeundi, & non admittendo, conatum redeundi. Ab his conatibus contrariis componitur circumitio intra Phialam, & conatus exeundi quaquaversum. Itaque Phialae ore aquae immerso, Aer in subject am aquam penetrate è Phiala egrediens, & tantundem aquae in Phialam cogit.  
Praeterea vis illa magna suctionis facit, ut sugentis labra cum collo Phialae aliquando arctissimè cohaereant propter contactum exqusitissimum.  B. 
As to the first Clause of Mr. Hobbes' account of our Phaenomenon, the Vacuists will easily answer his Question by acknowledging, that there were indeed interspersed Vacuities in the Air contained in the Vial before the suction; but they will add, there was no reason, why the Water should ascend to fill them, because, being a heavy body, it cannot rise of itself, but must be raised by some prevalent weight or pressure, which then was wanting. Besides, that there being interspersed Vacuities as well in the rest of the Air that was very near the Water, as in that contained in the Vial, there was no reason, why the Water should ascend to fill the Vacuities of one portion of Air rather than those of another. But when once by suction a great many of the Aerial Corpuscles were made to pass out of the Vial, the Spring of the remaining Air being weakened, whilst the pressure of the ambient Air, which depends upon its constant Gravity, is undiminished, the Spring of the internal becomes unable to resist the weight of the external Air, which is therefore able to impel the interposed Water with some violence into the Cavity of the Glass, till the Air, remaining in that Cavity, being reduced almost to its usual Density, is able by its Spring, and the weight of the Water got up into the Vial, to hinder any more Water from being impelled up. For, as to what Mr. Hobbes affirms, that, Is qui so get Phialam neque in ventrem quicquam, neque in pulmones, neque in os quicquam exugit: How it will agree with what he elsewhere delivers about Suction. I leave him to consider. But I confess, I cannot but wonder at his confidence, that can positively assert a thing so repugnant to the common sentiments of Men of all opinions, without offering any proof for it. But I suppose, they that are by trial acquainted with Sucking, and have felt the Air come in at their mouths, will prefer their own experience to his authority. And as to what he adds, that the Person that sucks agitates the Air, and turns it within the Vial into a kind of circulating wind, that endeavours every where to get out; I wish, he had shown us by what means a Man that sucks makes this odd Commotion of the Air; especially in such Vials as I use to employ about the Experiment, the orifice of whose neck is sometimes less than a Pins head.  A. 
That there may be really Air extracted by Suction out of a Glass, me thinks you might argue from an Experiment I saw you make with a Receiver which was exhausted by your Pump, and consequently by Suction. For I remember, when you had counterpoised it with very good Scales, and afterwards by turning a stop-cock, let in the outward Air, there rushed in as much Air to fill the space that had been deserted by the Air pumped out, as weighed some scruples (consisting of twenty grains a piece) though the Receiver were not of the largest size.  B. 
You did well to add that Clause; for, the Magdobargic Experiment, mentioned by the industrious Schottus, having been made with a vast Receiver, the readmitted Air amounted to a whole ounce and some drachms. But to return to Mr. Hobbes, I fear not that he will persuade you, that have seen the Experiment he recites, that as soon as the neck of the Vial is unstopped under water, the Air, that whittled about before, makes a sally out, and forces in as much water. For, if the orifice be any thing large, you will, instead of feeling an endeavour to thrust away your finger that stopped it, find the pulp of your finger so thrust inward, that a Peripatetic would affirm that he felt it sucked in. And that Intrusion may be the Reason, why the lip of him that sucks is oftentimes strongly fastened to the orifice of the Vials neck, which Mr. Hobbes ascribes to a most exquisite contact, but without clearly telling us, how that extraordinary contact is effected. And when your finger is removed, instead of perceiving any Air go out of the Vial through the water, (which, if any such thing happen, you will easily discover by the bubbles,) you shall see the water briskly spring up in a slender stream to the top of the Vial, which it could not do, if the Cavity were already full of Air. And to let you see, that, when the Air does really pass in or out of the Vial immersed under water, 'tis very easy to perceive its motions, if you dip the neck of the Vial in water, and then apply to the globulous part of it either your warm hands or any other competent Heat, the internal Air being rarified; you shall see a portion of it, answerable to the degree of Heat you applied, manifestly pass through the water in successive bubbles, whilst yet you shall not see any water get into the Vial to supply the place deserted by that Air. And if, when you have (as you may do by the help of sucking) filled the neck and part of the belly of the Vial with water, you immerse the orifice into stagnant water, and apply warm hands to the globulous part as before, you will find the water in the Vial to be driven out, before any bubbles pass out of the Vial into the surrounding water; which shows, that the Air is not so forward to dive under the water, (and much less under so ponderous a liquor as Quicksilver,) as Mr. Hobbes has supposed.  A. 
That 'tis the Pressure of the external Air, that (surmounting the Spring of the internal) drives up the water into the Vial we have been speaking of, does, I confess, follow upon your Hypothesis: But an Experimentarian Philosopher, as Mr. Hobbes calls you among others, may possibly be furnished with an Experiment to confirm this to the Eye.  B. 
You bring into my mind what I once devised to confirm my Hypothesis about Suction, but found a while since that I had omitted it in my Discourse about that Subject. And therefore I shall now repeat to you the substance at least of the Memorial that was written of that Experiment, by which the great interest of the weight of the Atmospherical Air in Suction will appear, and in which also some things will occur, that will not well agree with Mr. Hobbes' Explication, and prevent some of his Allegations against mine.  A. 
Having not yet met with an Experiment of this nature, such an one as you speak of will be welcome to me.  B. 
We took a Glass Bubble, whose long stem was both very slender and very Cylindrical; then by applying to the outside of the Ball or globulous part a convenient heat, we expelled so much of the Air, as that, when the end of the pipe was dipped in water, and the inward Air had time to recover its former coolness, the water ascended either to the top of the pipe or very near it. This done, we gently and warily rarified the Air in the Cavity of the Bubble, till by its expansion it had driven out almost all the water that had got up into the stem, that so it might attain as near as could be to that degree of heat and measure of expansion, that it had when the water began to rise in it. And we were careful to leave two or three drops of water unexpelled at the bottom of the pipe, that we might be sure, that none of the included Air was by this second rarefaction driven out at the orifice of it; as the depression of the water so low assured us, on the other side, that the included Air wanted nothing considerable of the expansion it had when the water began to ascend into the pipe. Whilst the Air was in this rarified state, we presently removed the little Instrument out of the stagnant water into stagnant Quicksilver, which in a short time began to rise in the pipe. Now, if the ascension of the liquor were the effect of Nature's Abhorrence of a Vacuum; or of some internal principle of Motion; or of the Compression and propagated Pulsion of the outward Air by that which had been expelled; why should not the Mercury have ascended to the top of the pipe, as the water did before? But de facto it did not ascend half, or perhaps a quarter so far; and if the pipe had been long enough, as well as 'twas slender enough, I question, whether the Mercury would have ascended (in proportion to the length of the stem) half so high as it did.  
Now of this Experiment, which we tried more than once, I see not, for the reason lately expressed, how any good account will be given without our Hypothesis, but according to That 'tis clear.  A. 
I think I perceive why you say so; for the Ascension of Liquors being an effect of the prevalency of the external Airs pressure against the resistance it meets with in the Cavity of the Instrument, and the Quicksilver being bulk for bulk many times heavier than water, the same surplusage of pressure that was able to impel up water to the top of the pipe, ought not to be able to impel up the Quicksilver to any thing near that height. And if it be here objected, as it very plausibly may be, that the raised Cylinder of Mercury was much longer than it ought to have been in reference to a Cylinder of Water, the proportion in gravity between those two Liquors (which is almost that of fourteen to one) being considered; I answer, that when the Cylinder of Water reached to the pipe, the Air possessed no more than the Cavity of the globulous part of the Instrument, being very little assisted to dilate itself by so light a Cylinder as that of Water: But when the Quicksilver came to be impelled into the Instrument by the weight of the external Air, that ponderous Body did not stop its ascent as soon as it came to be equiponderant to the formerly expelled Cylinder of Water; because, to attain that height, it reached but a little way into the pipe, and left all the rest of the Cavity of the pipe to be filled with part of that Air, which formerly was all shut up in the Cavity of the Bubble; by which means the Air, included in the whole Instrument, must needs be in a state of expansion, and thereby have its Spring weakened, and consequently disabled to resist the pressure of the external Air, as much as the same included Air did before, when it was less rarified; on which account, the undiminished weight or pressure of the external Air was able to raise the Quicksilver higher and higher, till it had obtained that height, at which the pressure, compounded of the weight of the Mercurial Cylinder and the Spring of the internal Air (now less rarified than before,) was equivalent to the pressure of the Atmosphere or external Air.  B. 
You have given the very Explication I was about to propose▪ wherefore I shall only add, that, to confirm this Experiment by a kind of Inversion of it, we drove by heat a little Air out of the Bubble, and dipped the open end of the pipe into Quicksilver, which by this means we made to ascend till it had filled about a fourth part or less of the pipe, when that was held erected. Then carefully removing it without letting fall any Quicksilver, or letting in any Air, we held the orifice of the pipe a little under the surface of a Glass full of Water, and applying a moderate heat to the outside of the Ball, we warily expelled the Quicksilver, yet leaving a little of it to make it sure that no Air was driven out with it; then suffering the included Air to cool, the external Air was found able to make the Water not only ascend to the very top of the pipe, and thence spread itself a little into the Cavity of the Ball, but to carry up before it the Quicksilver that had remained unexpelled at the bottom of the stem. And if in making the Experiment we had first raised, as we sometimes did, a greater quantity of Quicksilver, and afterwards drove it out, the quantity of Water, that would be impelled into the Cavity of the pipe and ball, would be accordingly increased.  A. 
In this Experiment 'tis manifest, that something is driven out of the Cavity of the Glass before the Water or Quicksilver begins to ascend in it: And here also we see not, that the Air can pass through the pores of Quicksilver or Water, but that it drives them on before it, without sensibly mixing with them. In this Experiment there appears not at all any Circular Wind, as Mr. Hobbes fancies in the sucked Vial we are disputing of, nor any tendency outwards of the included Air upon the account of such a Wind; but, instead of these things, that the ascension of the Liquors into the Cavity of the pipe depends upon the external Air, pressing up the Liquors into that Cavity, may be argued by this, that the same weight of the Atmosphere impelled up into the pipe so much more of the lighter Liquor, Water, than of the heavier Liquor, Mercury.  B. 
You have said enough on this Experiment; but 'tis not the only I have to oppose to Mr. Hobbes his Explication: For, that there is no need of the sallying of Air out of a Vial, to make the Atmospherical Air press against a Body that closes the orifice of it, when the pressure of the internal Air is much weakened; I have had occasion to show some Virtuosos, by sucking out, with the help of an Instrument, a considerable portion of the Air contained in a Glass; for having then, instead of unstopping the orifice under water, nimbly applied a flat Body to it, the external Air pressed that Body so forcibly against it, as to keep it fastened and suspended, though 'twere clogged with a weight of many ounces.  A. 
Another Experiment of yours Mr. Hobbes' Explication brings into my mind, by which it appears, that, if there be such a Circular Wind, as he pretends, produced by Suction in the Cavity of the Vial, it must needs be strangely lasting. For I have seen more than once, that, when you have by an Instrument sucked much of the Air out of a Vial, and afterwards carefully closed it, though you kept the slender neck of it stopped a long time, perhaps for some weeks or months, yet when 'twas opened under water, a considerable quantity of the Liquor would be briskly impelled up into the neck and belly of the Vial. So that, though I will not be so pleasant with Mr. Hobbes, as to mind you on this occasion of those Writers of Natural Magic, that teach us to shut up Articulate, Sounds in a Vessel, which being transported to a distant place and opened there, will render the Words that are committed to it; yet I must needs say, that so lasting a Circular Wind, as, according to Mr. Hobbes, your Experiments exhibited, may well deserve our wonder.  B. 
Your admiration would perchance increase, if I should assure you, that having with the Sunbeams produced smoke in one of those well-stopped Vials, this Circular Wind did not at all appear to blow it about, but suffered it to rise, as it would have done if the included Air had been very calm. And now I shall add but one Experiment more, which will not be liable to some of the things as invalid as they are, which Mr. Hobbes has alleged in his account of the Vial, and which will let you see, that the weight of the Atmospherical Air is a very considerable thing; and which may also incline you to think, that, whilst Mr. Hobbes does not admit a subtler Matter than common Air to pass through the Pores of close and solid Bodies, the Air he has recourse to will sometimes come too late to prevent a Vacuum. The Experiment, which was partly accidental, I lately found registered to this sense, if not in these words: [Having, to make some Discovery of the weight of the Air, and for other purposes, caused an Aeolipile, very light considering its bulk, to be made by a famous Artist, I had occasion to put it so often into the fire for several Trials, that at length the Copper scaled off by degrees, and left the Vessel much thinner than when it first came out of the Artificers hands; and a good while after, this change in the Instrument being not in my thoughts, I had occasion to employ it, as formerly, to weigh how many grains it would contain of the Air at such a determinate constitution of the Atmosphere, as was to be met with, where I than chanced to be. For the making this Experiment the more exactly, the Air was by a strong, but warily applied, fire so carefully driven away, that, when clapping a piece of Sealing-wax to the Pin-hole, at which it had been forced out, we hindered any communication betwixt the Cavity of the Instrument and the external Air, we supposed the Aeolipile to be very well exhausted, and therefore laid it by, that, when it should be grown cold, we might, by opening the orifice with a Pin, again let in the outward Air, and observe the increase of weight that would thereupon ensue: But the Instrument, that, as I was saying, was grown thin, had been so diligently freed from Air, that the very little that remained, and was kept by the Wax from receiving any assistance from without, being unable by its Spring to assist the Aeolipile to support the weight of the ambient Air; this external fluid did by its weight press against it so strongly, that it compressed it, and thrust it so considerably inwards, and in more than one place so changed its figure, that, when I showed it to the Virtuosos that were assembled at Gresham-Colledge, they were pleased to command it of me to be kept in their Repository, where I presume it is still to be seen.  
FINIS.   

NEW EXPERIMENTS About the PRESERVATION OF BODIES IN VACUO BOYLIANO.  
By the Honourable ROBERT boil, Fellow of the Royal Society.  
LONDON, Printed by William Godbid, and are to be Sold by Moses Pitt, at the Angel over against the little North Door of St. Paul's Church. 1674.