inquired after and not in case it be Traction And such an Experimentum Crucis to speak with our Illustrious Verulam is afforded us by that noble Observation of Monsieur Paschall mentioned by the famous Pecquet and out of him by our Author namely that the Torricellian Experiment being made at the foot and in divers places of a very high Mountain of the altitude of five hundred fathom or three thousand foot he found that after he had ascended a hundred and fifty Fathom the Quicksilver was fallen two Inches and a quarter below its station at the Mountains foot and that at the very top of the Hill it had descended above three Inches below the same wonted station Whence it appears that the Quicksilver being carried up towards the top of the Atmosphere falls down the lower the higher the place is wherin the observation is made of which the reason is plain in our Hypothesis namely that the nearer we come to the top of the Atmosphere the shorter and lighter is the Cylinder of Air incumbent upon the restagnant Mercury and consequently the less weight of Cylindrical Mercury will that Air be able to counter-poise and keep suspended And since this notable Phaenomenon does thus clearly follow upon ours and not upon our Adversaries Hypothesis this Experiment seems to determine the Controversie betwixt them because in this case the Examiner cannot pretend as he does in the seventeenth and divers other of our Experiments that the Descent of the Quicksilver in the Tube is caus'd not by the Diminution of the external Airs pressure but from the preternatural Rarefaction or Distension of that external Air in the Receiver when by seeking to restore it self it endeavours to draw up the restagnant Mercury For in our present case there appears no such forcible Dilatation of that Air as in many of the Phaenomena of our Engine he is pleas'd to imagine It need therefore be no great wonder if his Adversaries do as he observes make a great account of this Experiment to prove that the Mercury is kept up in the Tube by the resistance of the external Aire Nor do I think his Answers to the Argument drawn from hence will keep them from thinking it cogent For to an Objection upon which he takes notice that they lay so much stress he replyes but two things which neither singly nor together will near amount to a satisfactory Answer But because that though Experiments made in very elevated places are noble ones and of great importance in the Controversies about the Air yet there are but very few of those that are qualified to make Experiments of that Nature who have the opportunity of making them upon high Mountains we did with the assistance of an ingenious man attempt a Tryal wherein we hoped to find a sensibly-differing Weight of the Atmospere in a far less height then that of an ordinary Hill But in stead of a common Tube we made use of a kind of Weather-glass that the included Air might help to make the event notable for a reason to be mentioned ere long and in stead of Quicksilver we employ'd common Water in the Pipe belonging to the Weather-glass that small changes in the Weight or resistance of the Atmosphere in opposit on of the included Air might be the more discernable The Instrument we made use of consisted only of a Glass with a broad Foot and a narrow Neck A B and a slender Glass-Pipe C D open at both ends which Pipe was so placed that the bottom of it did almost but not quite reach to the bottom of the bigger Glass A B within whose Neck A it was fastned with a close cement that both kept the Pipe in its place and hindred all communication betwixt the inward I I and outward K K Air save by the cavity of the Pipe C D Now we chose this Glass A B more then ordinarily capacious that the effect of the dilatation of the included Air I I might be the more conspicuous Then conveying a convenient quantity of Water H H into this Glass we carried it to the Leads of the lofty Abby-Church at Westminster and there blew in a little Air to raise the Water to the upper part of the Pipe that being above the Vessel A B we might more precisely mark the several stations of the Water then otherwise we could Afterward having suffered the Glass to rest a pretty while upon the Lead that the Air I I within might be reduc'd to the same state both as to coldness and as to pressure with K K that without having marked the station of the Water F we gently let down the Vessel by a long string to the foot of the Wall where one attended to receive it who having suffer'd it to rest upon the ground cry'd to us that it was subsided about an Inch below the mark F we had put whereupon having order'd him to put a mark at this second station of it E we drew up the Vessel again and suffering it to rest a while we observ'd the Water to be re-ascended to or near the first mark F which was indeed about an Inch above E the other And this we did that Evening a second time with almost a like success though two or three dayes after the wind blowing strongly upon the Leads we found not the Experiment to succeed quite so regularly as before yet the Water alwayes manifestly fell lower at the foot of the Wall then it was at the top which I see no cause to ascribe barely to the differing temperature of the Air above and below as to Heat and Cold since according to the general estimate the more elevated Region of the Air is caeteris paribus colder then that below which would rather check the greater expansion of the included Air at the top of the Leads then promote it But the better to avoid mistakes and prevent Objections we thought fit to try the Experiment within the Church and got into a Gallery of the same height with the Leads but the upper part of the Pipe being casually broken off we thought fit to order the matter so that the surface G of the remaining Water in the Pipe should be about an Inch higher then the surface of the Water in the Vessel And then my above-mentioned Correspondent letting down the Glass almost as soon as it was setled upon the pavement kneeling down to see how far it was subsided I found that not only it was fallen as low as the other Water but that the outward Air deprest it so far as whilest I was looking on to break in beneath the bottom of the Pipe and ascend through the Water in bubbles after which the Glass being drawn up again my Correspondent affirm'd that the Water was very manifestly re-ascended But because by the unlucky breaking of a Glass we were hindred to observe as we designed what would happen as well in a Weather-glass so contriv'd that the weight or pressure of the Atmosphere
sometimes quite contrary thereunto adds that this Experiment does strongly enough overthrow our Hypothesis of the Atmospherical Cylinder and clearly shew that the Quicksilver is not sustained by it Nam sayes he si hic ab eo sustentatum fuisset debuisset potius frigidiore tempore ascendere quam descendere eo quod aër tunc multo densior esset gravior Itaque non sustentatur argentū ab aër is aequipondio ut asseritur And by the same Argument he concludes against the Mercury's being sustained by the Spring of the Air. But in his Animadversions upon this Experiment he seems to have been too forward to reprehend for he neither well confutes my Conjecture nor substitutes so much as a plausible one in the stead of it And as to his Objection I answer First That it doth not conclude because that as sometimes the Quicksilver in the Tube did rise in warmer and fall in colder weather so at other times it did rather emulate the ascent and descent of water in a Weather-glass Secondly Though it be true that Cold is wont to condense this or that parcel of Air and that a parcel of Air may be made heavier by Condensation yet that is in regard of the ambient Air that retains its wonted laxity in which the condensed Air is weighed But our Author has not yet proved that in case the cold of the Winter should condense the whole incumbent Atmosphere it would then gravitate sensibly more upon the restagnant Quicksilver then before As a Pound of Wooll will not sensibly vary its weight though the hairs whereof it is composed be made to lye sometimes in a looser sometimes in a closer order And thirdly this Objection does as little agree with his Doctrine as with my Conjecture For in the 50. page where he gives us an account according to his principles of the rising and falling of water in a Weather-glass and compares it with the suspension of Quicksilver he tells us Hinc fit quod contracto hoc funiculo per frigus aqua illa tempore frigido ascendat descendat autem tempore calido eo quod per calorem funiculus ille dilatetur So that according to the Examiner himself the Quicksilver ought to have ascended in colder and descended in warmer weather Now although I proposed my thoughts of the difficult Phaenomenon under consideration but as a Conjecture and therefore shall be ready to alter them either upon further discovery or better information yet I see not why it should be post-posed to the Examiner's who though he rejects our Explication substitutes no other then what may be gathered from these words Ego certe non dubito quin dentur hujusmodi occultae causae quibus funiculus ille subtilis quo in tubo suspenditur argentum ut dictum est capite decimo modo producatur modo abbrevietur c. sicque argentum nunc demittat nunc elevet For since we have made it probable that the copious Fumes sometimes suddenly ascending into the Air and rolling up and down in it sometimes sensibly altering if good Authors may be credited the refraction of it and since some other causes mentioned in our eighteenth Experiment may alter the density and gravity of the Air that leans upon the restagnant Mercury I suppose the Reader will think it more intelligible and probable that alterations other then those produced by heat and cold may happen to the incumbent Atmosphere which freely communicates with the neighbouring Air and may thereby become sometimes more stufft and sometimes more destitute of adventitious Exhalations then that such changes should happen to a Funiculus included in Glass which according to our Author is impervious to the subtilest steams that are and concerning which he offers not so much as a Conjecture upon what other account it can happen to be sometimes contracted and sometimes stretch'd The 19. Experiment Upon this the Examiner has onely this short Animadversion In decimo nono ostendit aquam eodem modo per exhaustionem Recipient is descendere quo in praecedente descendere ostender at argentum vivum cujus cum eadem sit ratio non est cur amplius ei insistamus In which words since he offers nothing new or peculiar to shew any incongruity in our Explication to our principles which agree very well with the new Phaenomena of the Experiment we are content to leave the Reader to judge of the Hypotheses themselves which of the two is the more probable either ours that onely requires that the Air in the Receiver should equally resist a Cylinder of Water and of Quicksilver when their weight is but the same though their altitudes be not or the Examiner's which exacts that according to what we formerly elsewhere noted Bodies of such differing nature and texture as Quicksilver and Water should need but just the same weight or strength to rarefie them into a Funiculus The 20. Experiment In his Examen of this Experiment our Author makes me infer from the Phaenomena he repeats that not onely the Air but the Water also has a Spring But though I suspect not that he does wilfully mistake my sense yet by what I write in this and the following Experiments the Reader may well enough perceive that I spoke but very doubtfully of a Spring in the water nay and that I did in the 154. page expresly teach That the intumescence of it might at least in great part proceed from that of the small parcels of Air which I thought to be usually harboured in the body of that liquor But whereas I ascribe the appearance of the Bubbles in the water to this that upon the exhaustion of some of the Air incumbent on the water the pressure of what remains is much debilitated whereby the little Particles of Air lurking in the Water are allowed to expand themselves into bubbles he rejects this Explication as manifestly false Nam sayes he si it a sieret deberent profecto hujusmodi bullulae non è fundo vasis sic ascendere uti tam in hoc quam in sequentibus experiment is in quibus de istis bullis agitur semper asseritur sed è superiore parte aquae ubi minus premuntur ut per se est manifestum But why he should be here so peremptory I confess I do not for all this Objection yet see For in the bottom of the next page he sayes he will not deny but that Aerial Particles latitant in the other parts of the water he had before spoken of the bottom of it may be extended into bubbles by his way of Rarefaction And that we particularly mentioned the rising of bubbles even from the bottom of the water was because that circumstance seem'd to deserve a peculiar note and not as he seems to imagine as if the bubbles did not also rise from the superior parts of the liquor since we did take notice of it about the middle of the 149 page And we often in this and
Quicksilver doth not onely touch the top of the Glass but stick to it That Nature wreaths a little rarefied Air into a strong rope even able to draw up Quicksilver p. 28 29. That Rarefaction is performed by a certain unknown force or vis divulsiva p. 30. That thin Surfaces are left successively one after another that these Surfaces are contrived into strings that may be stretch'd without being made more slender c. p. 31. The illustration of the manner how his Funiculus is made from the rarefaction of Wax or Tallow in a lighted Candle is considered p. 32. and shewed not to be apposite ibid. Divers other difficulties and improbabilities manifested in the Funicular Hypothesis p. 33. Of the inward Spring necessary to the contraction of his Funiculus p. 33 34. An Argument from a Pendulum's moving freely in an exhausted Receiver that the medium it moves in doth not consist of an innumerable exceedingly-stretch'd strings p. 35. Chap. 3. The Aristotelean Rarefaction proposed by the Adversary examined What Rarefaction and Condensation is p. 36. Three wayes of explicating how Rarefaction is made p. 36 37. Absurdities in resolving the Magdeburg Experiment by the Aristotelean way of Rarefaction p. 38. The inconveniences of the several Hypotheses compared p. 39. The difficulties in the Adversaries explaining Rarefaction by Bodies infinitely divisible p. 41. The difficulties of explaining it by supposing Bodies made up of parts indivisible p. 43 44. The difficulties wherewith his Condensation is incumbred as that it infers Penetration of Dimensions c. p. 46. Chap. 4. A Consideration pertinent to the present Controversie of what happens in trying the Torrecellian and other Experiments at the top and feet of Hills That the Funicular Hypothesis is but an Inversion of the Elastical one supposing a Spring inwards the other outwards one performing its effects by Pulsion the other by Traction p. 48. That these tryals on the tops and feet of Hills determine the case for the Authors Hypothesis p. 49. The truth of the Observation of Monsieur Paschall confirmed p. 50. and the several tryals that have been made of it related ibid. A tryal of the Authors from the Leads of the Abbey-Church at Westminster p. 51 52 53. That the subsidence of the Mercury at the top of a Hill proceeds from the lightness of the Atmospherical Cylinder there p. 54. The relation of an Experiment lately made at Hallifax Hill in confirmation of the former p. 56. Chap. 5. Two new Experiments touching the measure of the force of the Spring of the Air compress'd and dilated That it is capable of doing far more then the necessity of the Authors Hypothesis requires p. 57. The first Experiment of compressing Air by pouring Mercury into a crooked Tube related p. 58. Wherein the same Air being brought to a degree of density twice as great obtains a Spring twice as strong as before p. 59. A Table of the Condensation of the Air according to this Experiment p. 60. Particular Circumstances observed in the making the Experiment p. 61. How far the Spring of the Air may be increased p. 62. Of the decrement of the force of dilated Air p. 63. A Table of the Rarefaction of the Air p. 64. Particular Circumstances in making the Experiment whence this Table was drawn p. 65 66. That the free Air here below appears to be near as strongly comprest by the weight of the incumbent Air as it would be by the weight of a Mercurial Cylinder of 28. or 30. Inches p. 67. PART III. Wherein what is objected against Mr. Boyle's Explications of particular Experiments is answered The entrance into this Part of the Discourse with an advertisement how far onely it will be requisite to examine the Adversaries assertions and explications the Hypotheses on both sides being before considered p. 69 70. A defence of the first and second Experiments concerning the intrusion of the Finger into the Orifice of the Valve of the evacuated Receiver p. 70. A defence of the third Experiment why the Sucker being drawn down there is no greater difficulty in the end then in the beginnin of the gdepression p. 71 72. Of the fourth Experiment touching the swelling of a Bladder upon the exhaustion of the ambient Air and proportionably to that exhaustion p. 72 73. The Authors and the Funicular Hypothesis in the explication of this Phaenomenon compared ibid. Of the fifth Experiment p. 73. Of the eighth Experiment about the breaking of a Glass-Receiver which was not globular upon the exhaustion of the inward Air p. 74. Whether it were more likely to be broken by the pressure of the Atmosphere without or a contraction of a string of Air within ibid. Of the ninth Experiment p. 75. Whether the breaking of the Vial outwards in the exhausted Receiver was caused by the pressure of the Atmosphere through the Tube which was open to the ambient Air ibid. Of the 17. Experiment p. 76 77 78 79. The Torrecellian Experiment being made within the Receiver whether the descent and ascent of the Mercury in the Tube under and above its wonted station be caused by the debilitated and strengthned Spring of the Air ibid. Of the 18. Experiment p. 79 80. Whether the Authors or the Funicular Hypothesis assign the more probable cause why a Cylinder of Mercury did in Winter rise and fall in the Tube sometimes as water in a weather-glass according to the laws of Heat and Cold and sometimes contrary thereunto ibid. Of the 19. Experiment p. 81. Of the 20. Experiment p. 82 83. Some mistakes in the Adversary of the Authors meaning about the Spring of the Water and the places whence the bubbles arose ibid. The Hypotheses compared ibid. Of the 31. Experiment p. 84 85 86. Of the cause why the Marbles fell not asunder in the exhausted Receiver though a weight of four Ounces were hung at the lower stone ibid. Whether the account of the Author or Adversary be more satisfactory ibid. Of the 32. and 33. Experiments of the re-ascent of the Sucker and its carrying up a great weight with it upon the exhaustion of the Receiver p. 86 87. How the flesh and neighbouring bloud of a Patient is thrust up into a Cupping-glass ibid. Of the 37. Experiment and the cause of the appearance of light or whiteness therein p. 87. Of the 40. and 41. Experiments concerning the cause of the sudden death of Animals in the exhausted Receiver p. 88 89. Of the 42. and 43. Experiments p. 90. The Conclusion p. 91 92. FINIS ERRATA PAge 13. line 19. lege which pressure notwithstanding The. p. 14. l. 21. Hydrargyrum deprehendit p. 29. l. 29. ut validissimam conficiant cat p. 31. l. 27. quendam funiculum per. p 58. l. 2. alamp p. 69. l. 9. Physico-Mechanical p. 70. l. 19. Boylianis p. 72. l. 17. removal Our p. 74. l. 29. quam ut ob figuram illam resistendo minus idoneam resistere potuerint About the History of Flame of Heat of Colours of the Origine of Qualities and Forms c. Pag. 20. Pag. 16. Pag. 17. Pag. 15. Pag. 12. Pag. 14. Pag. 8. Gass Phys Sect. 1. Lib. 2. Pag. 204. De nupero Inanis Experimento Pag. 19. Pag. 19. 20. Pag. 20. Pag. 21. Pag. 21. Pag. 11. Pag. 24. Pag. 48. Pag. 22. Pag. 25. Pag. 38. Pag. 38. Pag. 40. Pag. 40 41. Pag. 41. Pag. 43 44. Pag. 42. Pag. 160. Pag. 169. Pag. 163. Chap. 5. Pag. 175◠Pag. 159. Pag. 66. Pag 68. Pag. 50. †Mr. Croon one of the learned Professors of Gresham Colledge * Dr. Hen. Power See the second Figure * Probably these or the like words did manifest Pressure are here omitted for the Mountaine-Aire there seems to have acted rather by its Weight then Elasticity Page 11. See the 5. Figure See Part 2. C 5. Sed contra manifestè See also in the 43. Experim these passages And this Effervescence was so great in the upper part of the water c. As also The Effervescence was confin'd to the upper part of the water unless c. See more concerning this Objection in the Answer to it as 't is propos'd by Mr. Hobbes
Air at pleasure upon the restagnant Mercury and consequently weakning and increasing its pressure we might make it more clearly appear then hither to had been done by Experiment that the suspension of the Mercurial Cylinder and the height of it depended upon the greater or lesser pressure of the Air. But against our Explication of this Experiment which has had the good fortune to convince and satisfie many ingenious men the Examiner objects nothing in particular contenting himself to have recourse here also to his Funiculus Yet two observations of ours he is pleased to take notice of The first is that though the Quicksilver were exactly shut up into our Receiver after the manner newly declared yet the suspended Quicksilver did not descend whence having said that I argue that it is now sustained not by the Counterpoise of the Atmosphere but by the Spring of the Air shut up in the Receiver he subjoyns onely this Sed rectius sane infertur Cylindrum illum nihil ibidem antea praestitisse But whether this be not gratis dictum we leave the Reader to collect from what we have formerly discourst in the second Part of this Defence of the Spring of the Air especially from that Experiment by which it appears That Spring may sustain a far higher Cylinder of Quick-silver In the second Observation he mentions of ours he summarily recites our Explication of the descent and ascent of the Mercury in the Tube by the debilitated and strengthned Spring of the Air. But without finding fault with our application of that principle to the Phaenomena he sayes that he has sufficiently refuted the principle it self in the fourth Chapter which how well he has done we have already seen and therefore explicates the matter thus Dico igitur sayes he argentum per illam exhaustionem sic in tubo descendere quod deorsum trahaâ—ur ab aëre qui incumbit argento restagnanti siquidem incumbens ille aër jam per exhaustionem valde rarefactus extensus sese vehementer contrahit contrahendo conatur etiam subjectum sibi argentum restagnans è suo vasculo elevare unde fit ut argento illo restagnante minus jam gravitante in fundum sui vasculi argentum quod est in tubo descendat ut per se patet Adeoque mirum non est quod ingrediente postea aëre externo rursum argentum ascendat cum per illum ingressum vis illa sic elevans argentum restagnans debilitetur But this Explication supposing such a Funiculus as we have already shewn to be but fictitious the Reader will easily gather what is to be judged of it from what has been already delivered Wherefore I shall onely subioyn that by this Explication were it admitted there is onely an account given of that part of our seventeenth Experiment which relates to the descent of the Mercury below its wonted height and its re-ascent to it But as for our having by the forcing in some more Air into the Receiver impell'd the Quicksilver to a considerably-greater height then 't is wont to be sustain'd at in the Torricellian Experiment I confess I understand not how the Examiner gives an account of it in the following words which are immediately annex'd to those we last recited of his and which are all that he employes to explicate this notable Phaenomenon Atque hinc etiam redditur ratio alterius quod ibidem quoque notaîur nempe quod per violentam intrusionem aëris externt in Recipientem ascenderit argentum notabiliter supra digitos 29½ Nam sicut per extractionem aëris argentum infra stationem detrahitur sic etiam per intrusionem novi supra eandem elevabitur For in this passage I see not how he himself does not rather repeat the matter of fact then give any account how it is perform'd And if it be alledged on his behalf That according to his principles it may be said that upon the pressure of the adventitious Air upon the restagnant Mercury the Funiculus in the Tube that was not able before to draw it up above 29½ Inches is now enabled to draw it up higher I demand upon what account this new Air does thus press against the restagnant Mercury and impell up and sustain that in the Tube It will not be said that 't is by its weight for as much Mercury as may be thus impell'd up above the usual station will weigh a great many times more then the Air forc'd into the Receiver And therefore it remains that the additional Air counterpoises the additional Mercury by its Spring And if we consider withall that there 's no reason to doubt especially considering what we have formerly delivered upon tryal touching the power of comprest Air to impell up Quicksilver but that had we not been afraid of breaking our Vessel we might by forcing more Air into the Receiver have impell'd it up to the top of the Tube and kept it there we shall scarce deny but that supposing there could be no such Funiculus as our Examiner's in rerum natura the pressure of the incumbent Air alone might suffice to keep a correspondent Cylinder of Mercury suspended and that without any attraction of the restagnant Mercury by a Funiculus of violently distended Air in the Receiver the Quicksilver in the Tube may be made to rest at any height greater or lesser provided it exceed 30. Inches onely because its weight is just able to counterbalance the pressure of the contiguous Air. I know not whether I may not adde to express an unwillingness to omit what some may think proper to do my Adversary right that it may be said for the Examiner that he in the 11. page acknowledging with us a power in the Air to recover its due extension if it be crouded into less room then its disposition requires a man may from that principle solve the Phaenomena in question by saying that the Air in the Receiver being forcibly comprest by the intrusion of fresh Air into the same vessel does by its endeavour to recover its due expansion press upon the restagnant Mercury and force up some of it into the Tube But this Explication though it agree with what the Author teaches in a place very distant from his Notes upon our 17. Experiment now under debate yet still 't is not clear to me how by what he sayes in these Notes the Phaenomenon is accounted for as the word Hinc imports it to be But otherwise I need not quarrel with the Explication since without recurring to the Funiculus for the sustaining of the additional Mercury the solution of the Phaenomenon is given upon the same principle that I employ The 18. Experiment Our Examiner in his Animadversion upon the 18. Experiment having recited my Conjecture at the cause why a Cylinder of Mercury did in Winter rise and fall in the Tube sometimes as Water is wont to do in a Weather-glass according to the laws of heat and cold and
not amiss to make use now and then of some such opportunities to illustrate the matter it self under consideration Which I the rather did for these two Reasons First because I find that except by some able Mathematicians and very few other contemplative men the Doctrine of the Spring of the Air at least as I have proposed it is not yet sufficiently apprehended and therefore needs to be inclucated Insomuch that through a great part of some late Discourses of men otherwise eminently learned written against other Elaterists not me there seems to run so great and clear a mistake perhaps for want of skill in the Hydrostaticks that I can scarce impute it to any thing but to their not throughly understanding the Hypothesis they would confute And next because I was willing to lay down in my Answer to the Objections I examin'd the grounds of answering such other Arguments as may be built upon the same or the like Principles And perhaps I may truly enough say that in the following Treatise I have already in effect answered several Discourses written some before and some since mine by learned men about the Torricellian and other new Experiments relating to a Vacuum though I forbore to mention the names or words of the Authors because I found not that my Writings or Experiments were as yet known to them To these things I may adde that I thought the Discourses of Linus the fitter to be insisted on because he seems to have more diligently then some others who yet venture to dispute against it enquired into our Doctrine And I shall not scruple to say thus much of an Adversary and one to whom I gave no provocation to be so that though I dare not speak in general of those that have written either about the Weight of the Air or else For or Against a Vacuum because as I acknowledge in the first Chapter following I cannot yet procure the Books of divers learned men especially of those great Personages Robervall Balianus and Casatus yet among the Writers I have hitherto met with who have recourse to the Aristotelean Rarefaction and Condensation in the Controversies under debate scarce any seems to have contrived his Hypothesis better then our Linus Not that I think his Principle is either true or at least to such as I intelligible but that the Funiculus he assumes being allow'd him he may for a Reason to be touch'd a little below make out though not all the Phaenomena of my Experiments yet many more of them then most other Plenists that deny the Spring of the Air can deduce from their Hypotheses if granted And in regard that whereas we ascribe to the Air a Motion of Restitution outwards he attributes to it the like Motion inwards it cannot but happen that though the Principles cannot both be true yet many of the Phaenomena may be explicable by which of them soever is granted because of this I say it is not so easie as many ingenious Readers may be apt to think to draw pertinent Objections from Experience against the Adversary I have to deal with Which Irepresent lest as some may think I have employ'd more Arguments then I needed so others should think I have omitted many as indeed I have omitted some that I might pertinently have employ'd But there is another sort of Persons besides those I mention'd at the beginning of this Preface to whom I must addresse the remaining part of it namely to those who seem troubled that I suffer my self to be diverted either by Linus or Mr. Hobbs from perfecting those Experimental Treatises that are lying by me almost promis'd by the learned Publisher of the Latine Edition of my Essays and from prosecuting those wayes of enquiry into the Nature of things wherein they are pleas'd to think I may be more serviceable to reall Learning and the Lovers of it And I confess that these Mens Reasons and Perswasions have so far prevailed with me that after what I have done in the two following Treatises to Vindicate my Writings from the Objections made against them by two Learned men of very differing Hypotheses and thereby to shew in some measure that I am not altogether unacquainted with the way of defending oppos'd Truths I have laid aside the thoughts of writing any more distinct or entire Polemicall Treatises about the Subjects already disputed of And to this I am invited by several other Reasons besides what I have newly intimated For first as I elsewhere declare it was not my chief Design to establish Theories and Principles but to devise Experiments and to enrich the History of Nature with Observations faithfully made and deliver'd that by these and the like Contributions made by others men may in time be furnish'd with a sufficient stock of Experiments to ground Hypotheses and Theorys on And though in my Physico-Mechanicall Epistle and my Specimens I have ventur'd some Conjectures also at the Causes of the Phaenomena I relate lest the Discourse should appear to inquisitive Readers too jejune yet as I formerly said I propos'd my Thoughts but as Conjectures design'd though not only yet chiefly to excite the Curiosity of the Ingenious and afford some hints and assistance to the Disquisitions of the Speculative And accordingly I have not forborn to mention divers things which judicious Readers may easily perceive I foresaw that many would think unfavourable to the Opinions I inclin'd to So that for me to leave Experimental for Controversial Studies were a course unsuitable to the principal scope of my Writings Next though I have adventur'd to improve the Doctrine of the Spring and Weight of the Air by some Supplements where I found it deficient and to recommend it by some new Illustrations and Arguments deduc'd from my Experiments yet the Hypotheses themselves for the main being the Opinions also of far learneder Men then I it might be thought injurious both to them and to our common Cause if I should needlesly go about to hinder them from the Honour of Vindicating the Truths we agree in especially some of them being Excellent Mathematicians and others Eminent Naturalists whose Concern to maintain the Hypotheses against Objections if any shall arise is equal to mine and whose leisure and abilities far exceed those of a Person who both is sickly and hath other employments enough and who if he were far better skil'd in Geometry then he pretends to be hath such a weakness in his Eyes as makes him both unwilling and unfit to engage in any Study where the conversing with Mathematical Schemes is necessary Thirdly nor do I see much cause to doubt that the things I have deliver'd will notwithstanding my silence be left undefended The forwardness I have already observ'd in divers Virtuosi to Vindicate those Writings which they are pleas'd to say have convinc'd them and to save me the labour of penning the following Treatises scarce permitting me such an Apprehension Especially since there are some things that will much
is a new one flowing from the lucid body that darts its corporeal beams quite through the Glass and Space we dispute about which for want of such Corpuscles were not just before visible And supposing light not to be made by a trajection of Atoms through Diaphanous bodies but a propagation of the impulse of lucid bodies through them yet it will not thence necessarily follow that the deserted part of the Tube must be full As in our 27. Experiment though many of those gross Aerial Particles that appear'd necessary to convey a languid sound were drawn out of our Receiver at the first and second Exsuction yet there remain'd so many of the like Corpuscles that those that were wanting were not miss'd by the sense though afterwards when a far greater number was drawn out they were so there may be matter enough remaining to transmit the impulse of light though betwixt the Particles of that matter there should be store of vacuities intercepted Whereas our Author pretends to prove not onely that there is no coacervate Vacuity in the space so often mentioned but absolutely that there is none For 't is in this last sense as well as the other that the Schools and our Author who defends their Opinion deny a Vacuum But notwithstanding what we have now discours'd as in our 17. Experiment we declin'd determining whether there be a Vacuum or no so now what we have said to the Examiners Argument has not been to declare our whole sense of the Controversie but onely to shew that though his Hypothesis supposes there is no Vacuum yet his Arguments do not sufficiently prove it which may help to shew his Doctrine to be precarious for otherwise the Cartesians though Plenists may plausibly enough whether truly or no I now dispute not decline the necessity of admitting a Vacuum in the deserted space of the Tube by supposing it fill'd with their second and first Element whose Particles they imagine to be minute enough freely to pass in and out through the Pores of Glass But then they must allow the pressure of the outward Air to be the cause of the suspension of the Quicksilver for though the materia coelestis may readily fill the spaces the Mercury deserts yet that within the Tube cannot binder so ponderous a liquor from subsiding as low as the restagnant Mercury since all the parts of the Tube as well the lowermost as the uppermost being pervious to that subtile matter it may with like facility succeed in whatever part of the Tube shall be for saken by the Quicksilver The Examiners second Argument in the same place is That since the Mercurial Cylinder is not sustain'd by the outward Air it must necessarily be that it be kept suspended by his internal string But since for the proof of this he is content to refer us to the third Chapter our having already examin'd that allows us to proceed to his third Argument which is That the Mercurial Cylinder resting in its wonted station does not gravitate as may appear by applying the Finger to the immers'd or lower Orifice of the Tube Whence he infers that it must of necessity be suspended from within the Tube And indeed if you dexterously apply your Finger to the open end of the Tube when you have almost but not quite lifted it out of the restagnant Mercury which circumstance must not be neglected though our Author have omitted it that so you may shut up no more Quicksilver then the Mercurial Cylinder is wont to consist of you will find the Experiment to succeed well enough Which makes me somewhat wonder to find it affirm'd that the learned Maignan denies it not but that you will feel upon your Finger a gravitation or pressure of the Glass-Tube and the contained Mercury as of one body but that you will not feel any sensible pressure of the Mercury apart as if it endeavoured to thrust away your Finger from the Tube But the reason of this is not hard to give in our Hypothesis for according to that the Mercurial Cylinder and the Air counterpoising one another the Finger sustains not any sensibly-differing pressure from the ambient Air that presses against the Nail and sides of it and from the included Quicksilver that presses against the Pulp But if the Mercurial Cylinder should exceed the usual length then the Finger would feel some pressure from that surplusage of Quicksilver which the Air does not assist the Finger to sustain So that this pleasant Phaenomenon may be as well solv'd in our Hypothesis as in the Examiners in which if we had time to clear an Objection which we fore-see might be made but might be answer'd too we would demand why when the Mercury included in the Tube is but of a due altitude it should run out upon the removal of the Finger that stops it beneath in case it be sustain'd onely by the internal Funiculus and do according to his Doctrine when the Funiculus sustains it emulate a solid body if the pressure of the external Air has not as our Author teaches it not to have any thing to do in this matter And if some inquisitive person shall here object That certainly the Finger must feel much pain by being squeez'd betwixt two such pressures as that of a Pillar of thirty Inches of Quick-silver on the one side and an equivalent pressure from the Atmospherical Pillar on the other it may readily be represented that in fluid bodies such as are those concern'd in our Difficulty a solid body has no such sense of pressure from the ambient bodies as unless Experience had otherwise instructed us we should perhaps imagine For not to mention that having inquired of a famous Diver whether he found himself sensibly compressed by the water at the bottom of the Sea he agreed with the generality of Divers in the Negative I am inform'd that the learned Maignan did purposely try that his hand being thrust three or four Palmes deep into Quicksilver his fingers were not sensible either of any weight from the incumbent or of any pressure from the ambient Quicksilver The reason of which whether that inquisitive man have given it or no is not necessary in our present Controversie to be lookt after To these three Arguments the Examiner addes not a fourth unless he design to present it us in this concluding passage Huc etiam faciunt insignes librationes quibus argentum subito descendens agitatur Idem enim hic fit quod in aliis Pendulis ab alto demissis fieri solet But of this Phaenomenon also 't is easie to give an account in our Hypothesis by two several wayes whereof the First which is proper chiefly when the Experiment is made in a close place as our Receiver is That the Quicksilver by its sudden descent acquires an impetus superadded to the pressure it has upon the score of its wonted gravity whereby it for a while falls below its station and thereby
Nor will it necessarily follow that the space which the flame seems to take up should contain neither Air nor Aether nor any thing else save the parts of that flame because the eye cannot discern any other body there For even the smoke ascending from the snuff of a newly-extinguish'd Candle appears a dark pillar which to the eye at some distance seems to consist of smoke whenas yet there are so many Aerial and other invisible Corpuscles mingled with it as if all those parts of smoke that make a great show in the Air were collected and contiguous they would not perhaps amount to the bigness of a Pins head as may appear by the great quantity of steams that in Chymical Vessels are wont to go to the making up of one drop of Spirit And therefore it does not ill fall out for our turn that the Examiner to inforce his former Example alledges the turning of a particle of Quicksilver into vapour by putting fire under it for if such be the Rarefaction of Mercury 't is not at all like to make such a Funiculus as he talks of since those Mercurial Fumes appear by divers Experiments to be Mercury divided and thrown abroad into minute parts whereby though the body obtain more of Surface then it had before yet it really fills no more of true and genuine space since if all the particular little spaces fill'd by these scatter'd Corpuscles were reduc'd into one as the Corpuscles themselves often are in Chymical Operations they would amount but to one total space equal to that of the whole Mercury before rarefaction But these Objections against this Explication are not all that I have to say against our Adversaries Funiculus it self For I farther demand how the Funiculus comes by such hooks or graple-irons or parts of the like shape to take fast hold of all contiguous bodies and even the smoothest such as Glass and the calm surfaces of Quicksilver Water Oyle and other fluids And how these slender and invisible hooks cannot onely in the tersest bodies find an innumerable company of ears or loops to take hold on but hold so strongly that they are able not alone to lift up a tall Cylinder of that very ponderous metall of Quicksilver but to draw inwards the sides of strong Glasses so forcibly as to break them all to pieces And 't is also somewhat strange that Water and other fluid bodies whose parts are wont to be so easily separable should when the Funiculus once layes hold on the superficial Corpuscles presently emulate the nature of consistent bodies and be drawn up like Masses each of them of an intire piece though even in the exhausted Receiver they appear by their undulation when they are stir'd by Bubbles that pass freely through them and many other signs to continue fluid bodies It seems also very difficult to conceive how this extenuated substance should acquire so strong a spring inward as the Examiner all along his book ascribes to it Nor will it serve his turn to require of us in exchange an Explication of the Airs spring outward since he acknowledges as well as we that it has such a spring I know that by calling this extenuated substance a Funiculus he seems plainly to intimate that it has its spring inward upon the same account that Lute-strings and Ropes forcibly stretch'd have theirs But there is no small disparity betwixt them for whereas in strings there is requir'd either wreathing or some peculiar and artificial texture of the component parts a rarefaction of Air were it granted does not include or infer any such contrivance of parts as is requisite to make bodies Elastical And if the Cartesian Notion of the cause of Springiness be admitted then our extenuated substance having no Pores to be pervaded by the materia subtilis to which besides our Author also makes Glass impervious will be destitute of Springiness And however since Lute-strings Ropes c. must when they shrink inwards either fill up or lessen their Pores and increase in thickness as they diminish in length our Examiners Funiculus must differ very much from them since it has no Pores to receive the shrinking parts and contracts it self as to length without increasing its thickness Nor can it well be pretended that this self-contraction is done ob fugam vacui since though it should not be made a Vacuum would not ensue And if it be said that it is made that the preternaturally stretch'd body might restore it self to its natural dimensions I answer That I am not very forward to allow acting for ends to bodies inanimate and consequently devoid of knowledge and therefore should gladly see some unquestionable Examples produc'd of Operations of that nature And however to me who in Physical enquiries of this nature look for efficient rather then final causes 't is not easie to conceive how Air by being expanded in which case its force like that of other rarify'd bodies seems principally to tend outwards as we see in fired Gun-powder in Aeolipiles in warm'd Weather-glasses c. should acquire so prodigious a force of moving contiguous bodies inwards Nor does it to me seem very probable that when for instance part of a polish'd Marble is extended into a Funiculus that Funiculus does so strongly aspire to turn into Marble again I might likewise wish our Author had more clearly explicated how it comes to pass which he all along takes for granted that the access of the outward Air does so much and so suddenly relax the tension of his Funiculus since that being according to him a real and Poreless body 't is not so obvious how the presence of another can so easily and to so strange a degree make it shrink But I will rather observe that 't is very unlikely that the space which our Adversary would have replenish'd with his Funicular substance should be full of little highly-stretcht strings that lay fast hold of the Surfaces of all contiguous bodies and alwayes violently endeavour to pull them inwards For we have related in our 26. Experiment that a Pendulum being set a moving in our exhausted Receiver did swing to and fro as freely and with the string stretch'd as streight as for ought we could perceive it would have done in the common Air. Nay the Balance of a Watch did there move freely and nimbly to and fro which 't is hard to conceive those bodies could do if they were to break through a medium consisting of innumerable exceedingly-stretch'd strings On which occasion we might adde that 't is somewhat strange that these strings thus cut or broken by the passage of these bodies through them could so readily have their parts re-united and without any more ado be made intire again And we might also take notice of this as another strange peculiarity in our Authors Funiculus That in this case the two divided parts of each small string that is broken do not like those of other broken strings shrink and
Quicksilver being poured in to fill up the bended part of the Glass that the surface of it in either leg might rest in the same Horizontal line as we lately taught there was more and more Quicksilver poured into the longer Tube and notice being watchfully taken how far the Mercury was risen in that longer Tube when it appeared to have ascended to any of the divisions in the shorter Tube the several Observations that were thus successively made and as they were made set down afforded us the ensuing Table A Table of the Condensation of the Air. A A B C D E 48 12 00 Added to 29⅛ makes 29 2 16 29 2 16 46 11½ 01 7 16 30 9 16 30 6 16 44 11 02 13 16 31 15 16 31 12 16 42 10½ 04 6 16 33 8 16 33 1 7 40 10 06 3 16 35 5 16 35 38 9½ 07 14 16 37 36 15 19 36 9 10 2 16 39 4 16 38⅞ 34 8½ 12 8 16 41 10 16 41 2 17 32 8 15 1 16 44 3 16 43 11 16 30 7½ 17 15 16 47 1 16 46⅗ 28 7 21 2 16 50 5 16 50 26 6½ 25 3 16 54 5 16 53 10 13 24 6 29 11 16 58 13 16 58 2 8 23 5¾ 32 3 16 61 5 16 60 18 23 22 5½ 34 15 16 64 1 16 63 6 11 21 5¼ 37 15 16 67 1 16 66 4 7 20 5 41 9 16 70 11 16 70 19 4 3 4 45 74 2 16 73 11 19 18 4½ 48 12 16 77 14 16 77⅔ 17 4¼ 53 11 16 82 12 16 82 4 17 16 4 58 2 16 87 14 16 87⅜ 15 3¾ 63 15 16 93 2 16 93⅕ 14 3½ 71 5 16 100 7 16 99 6 7 13 3¼ 78 11 16 107 12 16 107 7 13 12 3 88 7 16 117 9 16 116 4 8 A A. The number of equal spaces in the shorter leg that contained the same parcel of Air diversly extended B. The height of the Mercurial Cylinder in the longer leg that compress'd the Air into those dimensions C. The height of a Mercurial Cylinder that counterbalanc'd the pressure of the Atmosphere D. The Aggregate of the two last Columns B and C exhibiting the pressure sustained by the included Air. E. What that pressure should be according to the Hypothesis that supposes the pressures and expansions to be in reciprocal proportion For the better understanding of this Experiment it may not be amiss to take notice of the following particulars 1. That the Tube being so tall that we could not conveniently make use of it in a Chamber we were fain to use it on a pair of Stairs which yet were very lightsom the Tube being for preservations sake by strings so suspended that it did scarce touch the Box presently to be mentioned 2. The lower and crooked part of the Pipe was placed in a square wooden Box of a good largness and depth to prevent the loss of the Quicksilver that might fall aside in the transfusion from the Vessel into the Pipe and to receive the whole Quicksilver in case the Tube should break 3. That we were two to make the observation together the one to take notice at the bottom how the Quicksilver rose in the shorter Cylinder and the other to pour in at the top of the longer it being very hard and troublesome for one man alone to do both accurately 4. That the Quicksilver was poured in but by little and little according to the direction of him that observed below it being far easier to pour in more then to take out any in case too much at once had been poured in 5. That at the beginning of the Operation that we might the more truly discern where the Quicksilver rested from time to time we made use of a small Looking-glass held in a convenient posture to reflect to the eye what we desired to discern 6. That when the Air was so compress'd as to be crouded into less then a quarter of the space it possess'd before we tryed whether the cold of a Linen Cloth dipp'd in water would then condense it And it sometimes seemed a little to shrink but not so manifestly as that we dare build any thing upon it We then tryed likewise whether heat would notwithstanding so forcible a compressure dilate it and approching the flame of a Candle to that part where the Air was pent up the heat had a more sensible operation then the cold had before so that we scarce doubted but that the expansion of the Air would notwithstanding the weight that opprest it have been made conspicuous if the fear of unseasonably breaking the Glass had not kept us from increasing the heat Now although we deny not but that in our Table some particulars do not so exactly answer to what our formerly intimated Hypothesis might perchance invite the Reader to expect yet the Variations are not so considerable but that they may probably enough be ascribed to some such want of exactness as in such nice Experiments is scarce avoidable But for all that till further tryal hath more clearly informed me I shall not venture to determine whether or no the intimated Theory will hold universally and precisely either in Condensation of Air or Rarefaction all that I shall now urge being That however the tryal already made sufficiently proves the main thing for which I here alledge it since by it 't is evident that as common Air when reduc'd to half its wonted extent obtained near about twice as forcible a Spring as it had before so this thus-comprest Air being further thrust into half this narrow room obtained thereby a Spring about as strong again as that it last had and consequently four times as strong as that of the common Air. And there is no cause to doubt that if we had been here furnisht with a greater quantity of Quicksilver and a very strong Tube we might by a further compression of the included Air have made it counter-balance the pressure of a far taller and heavier Cylinder of Mercury For no man perhaps yet knows how near to an infinite compression the Air may be capable of if the compressing force be competently increast So that here our Adversary may plainly see that the Spring of the Air which he makes so light of may not onely be able to resist the weight of 29. Inches but in some cases of above an hundred Inches of Quicksilver and that without the assistance of his Funiculus which in our present case has nothing to do And to let you see that we did not a little above inconsiderately mention the weight of the incumbent Atmospherical Cylinder as a part of the weight resisted by the imprisoned Air we will here annex that we took care when the Mercurial Cylinder in the longer leg of the Pipe was about an hundred Inches high to cause one to suck at the open Orifice whereupon as we expected the Mercury in the Tube did notably ascend Which considerable Phaenomenon cannot be ascribed
to our Examiners Funiculus since by his own confession that cannot pull up the Mercury if the Mercurial Cylinder be above 29. or 30. Inches of Mercury And therefore we shall render this reason of it That the pressure of the incumbent Air being in part taken off by its expanding it self into the Suckers dilated chest the imprison'd Air was thereby enabled to dilate it self manifestly and repel the Mercury that comprest it till there was an equality of force betwixt the strong Spring of that comprest Air on the one part and the tall Mercurial Cylinder together with the contiguous dilated Air on the other part Now if to what we have thus delivered concerning the compression of Air we adde some Observations concerning its spontaneous Expansion it will the better appear how much the Phaenomena of these Mercurial Experiments depend upon the differing measures of strength to be met with in the Airs Spring according to its various degrees of Compression and Laxity But before I enter upon this subject I shall readily acknowledge that I had not reduc'd the tryals I had made about measuring the Expansion of the Air to any certain Hypothesis when that ingenious Gentleman Mr. Richard Townely was pleased to inform me that having by the perusal of my Physico-Mechanical Experiments been satisfied that the Spring of the Air was the cause of it he had endeavoured and I wish in such attempts other ingenious men would follow his example to supply what I had omitted concerning the reducing to a precise estimate how much Air dilated of it self loses of its Elastical force according to the measures of its Dilatation He added that he had begun to set down what occurred to him to this purpose in a short Discourse whereof he afterwards did me the favour to shew me the beginning which gives me a just Curiosity to see it perfected But because I neither know nor by reason of the great distance betwixt our places of residence have at present the opportunity to enquire whether he will think fit to annex his Discourse to our Appendix or to publish it by it self or at all and because he hath not yet for ought I know met with fit Glasses to make an any-thing-accurate Table of the Decrement of the force of dilated Air our present design invites us to present the Reader with that which follows wherein I had the assistance of the same person that I took notice of in the former Chapter as having written something about Rarefaction whom I the rather make mention of on this occasion because when he first heard me speak of Mr. Townley's suppositions about the proportion wherein Air loses of its Spring by Dilatation he told me he had the year before and not long after the publication of my Pneumatical Treatise made Observations to the same purpose which he acknowledged to agree well enough with Mr. Townley's Theory And so did as their Author was pleased to tell me some Tryals made about the same time by that Noble Virtuoso and eminent Mathematician the Lord Brouncker from whose further Enquiries into this matter if his occasions will allow him to make them the Curious may well hope for something very accurate A Table of the Rarefaction of the Air. A B C D E 1 00 0 0 Subttracted from 29¾ leaves 29¾ 29¾ 1 1 2 10â… 19â…› 19â…š 2 15â…œ 14â…œ 14â…ž 3 20 2 8 9 4 8 9 15 12 4 22â… 7â…› 7 7 16 5 24â…› 5â… 5 19 20 6 24â…ž 4â…ž 4 23 24 7 25 4 8 4 2 8 4¼ 8 26 0 0 3 6 8 3 23 32 9 26â…œ 3 1 8 3 11 36 10 26 6 8 3 0 0 2 39 40 12 27â…› 2â… 2 23 48 14 27 4 8 2 2 8 2â…› 16 27 6 8 2 0 0 1 5â— 64 18 27â…ž 1â…ž 1 47 72 20 28 â— â— 1 6 8 18 9 0 24 28 2 8 1 4 8 1 23 96 28 28â…œ 1â…œ 1 1 16 32 28 4 8 1 2 8 0 119 128 A. The number of equal spaces at the top of the Tube that contained the same parcel of Air. B. The height of the Mercurial Cylinder that together with the Spring of the included Air counterbalanced the pressure of the Atmosphere C. The pressure of the Atmosphere D. The Complement of B to C exhibiting the pressure sustained by the included Air. E. What that pressure should be according to the Hypothesis To make the Experiment of the debilitated force of expanded Air the plainer 't will not be amiss to note some particulars especially touching the manner of making the Tryal which for the reasons lately mention'd we made on a lightsome pair of stairs and with a Box also lin'd with Paper to receive the Mercury that might be spilt And in regard it would require a vast and in few places procurable quantity of Quicksilver to employ vessels of such kind as are ordinary in the Torriccllian Experiment we made use of a Glass-Tube of about six foot long for that being Hermetically sealed at one end serv'd our turn as well as if we could have made the Experiment in a Tub or Pond of seventy Inches deep Secondly We also provided a slender Glass-Pipe of about the bigness of a Swans Quill and open at both ends all along which was pasted a narrow list of Paper divided into Inches and half quarters Thirdly This slender Pipe being thrust down into the greater Tube almost fill'd with Quicksilver the Glass helpt to make it swell to the top of the Tube and the Quicksilver getting in at the lower orifice of the Pipe fill'd it up till the Mercury included in that was near about a level with the surface of the surrounding Mercury in the Tube Fourthly There being as near as we could guess little more then an Inch of the slender Pipe left above the surface of the restagnant Mercury and consequently unfill'd therewith the prominent orifice was carefully clos'd with sealing Wax melted after which the Pipe was let alone for a while that the Air dilated a little by the heat of the Wax might upon refrigeration be reduc'd to its wonted density And then we observ'd by the help of the above-mentioned list of Paper whether we had not included somewhat more or somewhat less then an Inch of Air and in either case we were fain to rectifie the error by a small hole made with an heated Pin in the Wax and afterwards clos'd up again Fifthly Having thus included a just Inch of Air we listed up the slender Pipe by degrees till the Air was dilated to an Inch an Inch and an half two Inches c. and observed in Inches and Eighths the length of the Mercurial Cylinder which at each degree of the Airs expansion was impell'd above the surface of the restagnant Mercury in the Tube Sixthly The Observations being ended we presently made the Torricellian Experiment with the above-mention'd great Tube of six foot long that we might know the height of the Mercurial Cylinder for that particular day
may be context yet our Explication will have this advantage in point of probability above his That whereas he denies not that the Air has Spring and Weight as we deny his Funiculus to have any other then an imaginary existence and whereas he acknowledges that by the Instrument the Air about the Bladder is exhausted to shew that there needs no more then that and consequently no Funiculus to draw asunder the sides of the Bladder we can confirm our Explication by the formerly mentioned Experiment of the ingenious Paschall who carrying a flaccid Foot-ball from the bottom to the top of a high Mountain found it to swell proportionably as he ascended and as the weight and pressure of the ambient Air decreased and likewise to shrink again as he descended And yet in this case there is no recourse to be had to a Funiculus of violently-rarefi'd Air to draw asunder every way the sides of the Foot-ball But however the Examiner will be able to defend his Explication it may suffice us that he has objected nothing against ours The 5. Experiment Against the cause we assign of the fifth Experiment he likewise objects nothing but onely ascribes the breaking of the Bladder to the self-contraction of the rarefi'd Air in the Receiver And therefore referring the Reader to what we have newly said about the last Experiment we will with our Author pass over the sixth and seventh to which he has no quarrel and proceed to the eighth The 8. Experiment This is that wherein we mention our having broke a Glass-Receiver which was not globular by the exhaustion of most of the inward Air whereby its debilitated pressure became unable to resist the unweakned pressure of the outward Air. But this Explication the Examiner confidently rejects in these words At profecto non videtur credibile mollissimum hunc aërem tam vehementer vitrum tantae praesertim crassitudin is quantae ibidem dicitur undique sic comprimere ut illud perfring at as if it were more credible that the little Air within which according to him is so much thinner then common Air should be able to act more powerfully upon the Glass then the Air without which himself confesses to be a heavy body and which not onely reaches from the surface of the Earth to the top of the highest Mountains but which as may not improbably be argued from what we have elsewhere delivered may for ought we know to the contrary be heaped upon the Receiver to the height of some hundreds of Miles nay to I know not how many thousands in case the Atmosphere be not a bounded port on of the Air but reach as high as It. As for the Explication he substitutes in these words Verius itaque respondetur ideo sic fractum esse illud vitrum quia per exhaustionem illam latera ejus vehementius introrsum sint attracta quam ut ob figuram illam resistendo minus idoneam resistere potuerunt Cum enim inclusus aër lateribus vitri firmissimè adhaereat nihil aliud erit aërem illum sic exhaurire quam satagere latera vitri introrsum flectere By what we have already discoursed about the Funiculus the Reader may easily discern what is to be answered Nor does our Author here shew us any way by which his imaginary strings should take such fast hold of the sides of the Glass as to be able to draw them together notwithstanding the resistance they find from the close texture of the Body to be broken The 9. Experiment Our Explication of the ninth Experiment he handles very severely for having briefly recited it he proposes his Objection against it thus Sed profecto nimis longè videtur hoc à veritate recedere potestque vel inde solum satis refutari quia si tanta sit pressura aeris sic per tubum illum in phialam descendent is ut ipsam phialam perfringat deberet profecto inclusam aquam cui immergitur ille tubus valde quoque ante fractionem phialae commovere bullulasque in eadem excitaro c. ut constat siquis insufflando per illum tubulum aquam vel mediocriter sic premat At certum est aquam antequam frangatur sit phiala nec tantillum moveri ut experienti constabit But I do confess I do for all this think our Explication more true then well considered by our Author For the putting of water into the Vial that was broken was done as is clearly intimated in the beginning of our Narrative upon a particular design as indeed we tryed divers other things with our Engine not so much with immediate reference to the Spring of the Air as to make use of such Tryals in some other of our Writings And accordingly in the second Tryal mentioned in the same Experiment the water was omitted But notwithstanding this water the sides of the Glass being exposed to the pressure of the Atmosphere had that whole pressure against them before the exhaustion of the Receiver so that there needed no such blowing in of the Air afresh as our Author imagines to effect the breaking of the Vial it being sufficient for that purpose that the pressure against the convex superficies of it was taken off by the exhaustion of the Receiver the pressure against the concave superficies remaining as great as ever And therefore we need not altogether deny what the Examiner sayes that Licet clausus superne fuisset tubulus ille codem tamen modo fracta sine dubio fuisset phiala For since in such cases the Air as we have often taught is shut up with the whole pressure of the Atmosphere upon it it may almost as easily break the Glass as if it were unstopt And accordingly we mention in the 36. Experiment the breaking of a thin Glass Hermetically seal'd upon the recess of the ambient Air. But how confidently soever our Author speaks I thought fit to adde the word almost because we observed in the 39. Experiment that such thin Vials and thick ones will not break are subject upon the withdrawing of the ambient Air to retch a little whereby the Spring of the Air within the Vial might in some cases I say in some be so far weakned as not to be able to break it unless assisted by the pressure of the Atmosphere wherewith it communicates and which leans upon it And when the Vial does actually begin to break then the pursuing pressure of the outward Air upon the yielding Air within the Vial may help to throw the parts of the Glass more forcibly asunder All the Experiments from the 9. to the 17. exclusively our Examiner leaving uncensured we may with him advance to the consideration of the 17. The 17. Experiment defended In this we relate how when we made the Torricellian Experiment we shut up the restagnant Mercury together with the Tube and the suspended Mercurial Cylinder of about 29. Inches in our Receiver that by drawing off and letting in the