was thorowly wetted in fair Water that the sides of it being squeez'd together there might be no Air left in its folds as indeed we could not afterwards upon trial discern any The neck of this Bladder was strongly tied about that of a small Glass capable of holding five full drachmes of Water the Bladder being first so compress'd that all the included Air was only in the Glass without being press'd there then the Pump being set on work after a few exsuctions the Air in the little Viol began to dilate it self and produce a small Tumor in the neck of the Bladder and as the ambient Air was more and more drawn away so the included Air penetrated farther and farther into the Bladder and by degrees listed up the sides and display'd its folds till at length it seem'd to have blown it up to its full extent Whereupon the external Air being permitted to flow back into the Receiver repuls'd the Air that had fill'd the Bladder into its former narrow receptacle and brought the Bladder to be again flaccid and wrinkled as before Then taking out the Bladder but without severing it from the Glass we did by a hole made at the top of the Bladder fill the Vessel they both made up with Water whose weight was five Ounces five Drachmes and a half Five Drachmes whereof were above-mention'd to be the contents of the Bottle So that in this Experiment when the Air had most extended the Bladder it possess'd in all above nine times as much room as it did when it was put into the Receiver And it would probably have much inlarg'd its bounds but that the Bladder by its weight and the sticking together of its sides did somewhat resist its expansion And which was more considerable the Bladder appear'd tumid enough whilst yet a pretty deal of Air was left in the Receiver whose exsuction would according to our former Observation probably have given way to a farther expansion of the Air especially supposing the dilatation not to be restrain'd by the Bladder SInce we wrote the other day the former Experiment we have met with some Glasses not very unfit for our purpose by means of which we are now able with a little more trouble to measure the expansion of the Air a great deal more accurately than we could by the help of the above-mention'd Bladder which was much too narrow to allow the Air its utmost distention We took then first a Cylindrical Pipe of Glass whose bore was about a quarter of an Inch in Diameter This Pipe was so bent and doubled that notwithstanding its being about two foot in length it might have been shut up into a smaller Receiver not a Foot high But by misfortune it crack'd in the cooling whereby we were reduced to make use of one part which was straight and intire but exceeded not six or seven Inches This little Tube was open at one end and at the other where it was Hermetically seal'd had a small Glass bubble to receive the Air whose dilatation was to be measur'd Along the side of this Tube was pasted a straight narrow piece of Parchment divided into twenty six equal parts marked with black Lines and Figures that by them might be measur'd both the included Air and its dilatation Afterwards we fill'd the Tube with Water almost to the top and stopping the open end with the Finger and inverting the Tube the Air was permitted to ascend to the above mention'd Glass bubble And by reason this ascent was very slow it gave us the opportunity to mark how much more or less than one of the twenty six divisions this Air took up By this means after a trial or two we were inabled to convey to the top of the Glass a bubble of Air equal enough as to sight to one of those Divisions Then the open end of the Tube being put into a small Viol whose bottom was cover'd with Water about half an Inch high we included both Glasses into a small and slender Receiver and caused the Pump to be set on work The event was That at the first exsuction of the Air there appear'd not any expansion of the bubble comparable to what appear'd at the second and that upon a very few exsuctions the bubble reaching as low as the surface of the subjacent Water gave us cause to think That if our Pipe had not been broken it would have expanded it self much farther Wherefore we took out the little Tube and found that besides the twenty six divisions formerly mention'd the Glass bubble and some part of the Pipe to which the divided Parchment did not reach amounted to six divisions more Whereby it appears that the Air hath take up one and thirty times as much room as before and yet seem'd capable of a much greater expansion if the Glass would have permitted it Wherefore after the former manner we let in another bubble that by our guess was but half as big as the former and found that upon the exsuction of the Air from the Receiver this little bubble did not only fill up the whole Tube but in part break through the subjacent Water in the Viol and thereby manifest it self to have prossessed sixty and odd times its former room These two Experiments are mention'd to make way for the more easy belief of that which is now to follow Finding then that our Tube was too short to serve our turn we took a slender Quill of Glass which happen'd to be at hand though it were not so fit for our purpose as we could have wished in regard it was three or four times as big at one end as the other This Pipe which was thirty Inches long being Hermetically seal'd at the slender end was almost filled with water and after the above-related manner a bubble was convey'd to the top of it and the open extreme was put into a Viol that had a little fair Water at the bottom Then the Cover by means of a small hole purposely made in it for the Glass Pipe to stand out at was cemented on to the Receiver and the Pump being set on work after some exsuctions not only the Air manifestly appear'd extended below the surface of the subjacent Water but one of the By-standers affirms that he saw some bubbles come out at the bottom of the Pipe and break through the Water This done we left off Pumping and observ'd how at the unperceiv'd leaks of the Receiver the Air got in so fast that it very quickly impell'd up the Water to the top of the Tube excepting a little space whereinto that bubble was repuls'd which had so lately possess'd the whole Tube this Air at the slender end appear'd to be a Cylinder of â…š parts of an Inch in length but when the Pipe was taken out and turn'd upside down it appear'd at the other end inferiour in bulck to a Pea. These things being thus done we took to make the Experiment the more exactly a small pair of
to agree well enough with Mr. Townley's Theory And so did as their Author was pleased to tell me some Trials made about the same time by that Noble Virtuoso and eminent Mathematician the Lord Brouncker from whose further Enquiries into this matter if his occasions will allow him to make them the Curious may well hope for something very accurate A Table of the Rarefaction of the Air. A B C D E 1 00 0 0 Subtracted from 29¾ leaves 29¾ 29¾ 1 ½ 10 â… 19 â…› 19 â…š 2 15 â…œ 14 â…œ 14 â…ž 3 20 2 8 9 4 8 9 15 12 4 22 â… 7 â…› 7 7 16 5 24 â…› 5 â… 5 19 20 6 24 â…ž 4 â…ž 4 23 24 7 25 4 8 4 2 8 4 ¼ 8 26 0 0 3 6 8 3 23 32 9 26 â…œ 3 â…œ 3 11 36 10 26 6 8 3 0 0 2 39 40 12 27 â…› 2 â… 2 23 48 14 27 4 8 2 2 8 2 â…› 16 27 6 8 2 0 0 1 55 64 18 27 â…ž 1 â…ž 1 47 72 20 28â— 1 6 8 1 9 80 24 28 2 8 1 4 8 1 23 96 28 28 â…œ 1 â…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 Trial 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 imploy vessels of such kind as are ordinary in the Torricellian Experiment we made use of a Glass-Tube of about six foot long for that being Hermetically sealed at one end serv'd out turn as well as if we could have made the 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 than 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 than an Inch of Air and in either case we were fain to rectifie the error by a small hole made with a heated Pin in the Wax and afterwards clos'd up again Fifthly Having thus included a just Inch of Air we lifted up the slender Pipe by degrees till the Air was dilated to an Inch an Inch and an half two Inches c. and observed in Inches and Eighths the length of the Mercurial Cylinder which at each degree of the Air 's expansion was impell'd above the surface of the restagnant Mercury in the Tube Sixthly The Observations being ended we presently made the Torricellian Experiment with the above-mention'd great Tube of six foot long that we might know the height of the Mercurial Cylinder for that particular day and hour which height we found to be 29¾ Inches Seventhly Our Observations made after this manner furnish'd us with the preceding Table in which there would not probably have been found the difference here set down betwixt the force of the Air when expanded to double its former dimensions and what that force should have been precisely according to the Theory but that the included Inch of Air receiv'd some little accession during the Trial which this newly-mention'd difference making us suspect we found by replunging the Pipe into the Quicksilver that the included Air had gain'd about half an eighth which we guest to have come from some little Aëreal bubbles in the Quicksilver contain'd in the Pipe so easie is it in such nice Experiments to miss of exactness We try'd also with 12 Inches of Air shut up to be dilated but being then hindred by some unwelcome avocations to prosecute those Experiments we shall elsewhere out of other Notes and Trials God permitting set down some other accurate Tables concerning this matter By which possibly we may be assisted to resolve whether the Atmosphere should be look'd upon as it usually is as a limited and bounded Portion of the Air or whether we should in a stricter sense than we did before use the Atmosphere and Aëreal part of the World for almost equivalent terms or else whether we should allow the word Atmosphere some other notion in relation to its Extent and Limits for as to its Spring and Weight these Experiments do not question but evince them But we are willing as we said to refer these matters to our Appendix and till then to retain our wonted manner of speaking of the Air and Atmosphere In the mean time to return to our last-mention'd Experiments besides that so little a variation may be in great part imputed to the difficulty of making Experiments of this nature exactly and perhaps a good part of it to something of inequality in the cavity of the Pipe or even in the thickness of the Glass besides this I say the proportion betwixt the several pressures of the included Air undilated and expanded especially when the Dilatation was great for when the Air swell'd but to four times its first extent the Mercurial Cylinder though of near 23 Inches differ'd not a quarter of an Inch from what it should have been according to Mathematical exactness the proportion I say was sutable enough to what might be expected to allow us to make this reflexion upon the whole That whether or no the intimated Theory will hold exactly for about that as I said above I dare determine nothing resolutely till I have further considered the matter yet since the Inch of Air when it was first included was shut up with no other pressure than that
therefore doth in the alledged case descend because it is thrust down by that parcel of Air which dilates its self by its own Spring Ibid. Sic deberet c. So should the Finger be rather thrust from the top of the Tube than thereby fastned to it because this Dilatation must be made as well upwards as downwards P. 6. Concipi c. It cannot be conceived how that Air should dilate it self or thrust down the Mercury unless by taking up a greater place which thing these Authors are much against asserting that Rarefaction can be made no otherways than by Corpuscles or Vacuities Chap. 3. p. 7. Si c. If you take a Tube open at both ends of a good length suppose forty Inches long and fill it with Mercury and place your Finger on the top as before taking away your lower Finger you will find the Mercury to descend even to its wonted station and your Finger on the top to be strongly drawn within the Tube and to stick close unto it Whence again it is evidently concluded that the Mercury placed in its own station is not there upheld by the external Air but suspended by a certain internal Cord whose upper end being fastned to the Finger draws and fastens it after this manner into the Tube Chap. 4. p. 8. Sumatur c. Take a Tube shorter than twenty nine Inches and an half for instance of twenty Digits not shut as hitherto at one end but with both ends open let this Tube its Orifice being immers'd in restagnant Mercury and one Finger being plac'd underneath that the Mercury to be poured in run not through be filled with Mercury and then another Finger be applied to its Orifice to close it well Which being done if you draw away your lower Finger the upper will be found to be strongly drawn and suck'd into the Tube and so stifly to adhere to it or rather to the Quicksilver as I shall hereafter shew that it will elevate the Tube it self with all the Quicksilver and make it continue to hang pendulous in the Vessel From which Experiment this Opinion is most clearly refuted For seeing according to it the Quicksilver in such a Tube but twenty Inches long must be thrust upwards by the preponderating Air it will never by it be explained how this Finger is so drawn downwards and made so strongly to stick to the Tube For it cannot by the Air thrusting upwards be thus drawn downwards p. 10 11. Quod vel c. Which is thence confirmed Because if that preponderating Air succeeds as is asserted in the place of the lower Finger which was withdrawn that is if it uphold the Quicksilver after the same manner which it was upheld by the lower Finger applied under it it is manifest according to this Opinion that the Finger on the top ought not to be more drawn downwards after the lower Finger is removed than before Seeing then that Experience teacheth the contrary it is manifest that Opinion must be false Chap. 5. p. 11 12. Quarto c. In the fourth place it is impugn'd Because thence it would follow that Quicksilver through a like Tube might be suck'd with the same easiness out of a Vessel that Water is suck'd out of the same Which notwithstanding is contrary to Experience by which we are taught that Water is easily drawn into the mouth of him that sucks whereas Quicksilver cannot be drawn thither by his utmost endeavour nay scarce unto the middle of the Tube The sequel I thus manifest Because seeing according to this Opinion that the Liquor underneath whether it be Water or Mercury may so ascend no more is requir'd but that the Air shut in the Tube may be drawn upwards by sucking which being drawn up the Liquor underneath will immediately ascend being thrust thither by the external Air now preponderating as Pecquet declares in his Anatomical Discourse p. 63. It is manifest that the Mercury may be suck'd out with the same easiness that Water is suck'd out with Which being so evidently against Experience the Opinion from whence it is deduced must needs be false p. 13. Neque hoc c. And not only this but over and above if a Glass Diabetes or Syringe be made of a sufficient length and after that the Sucker is thrust into the utmost Orifice it be placed according to use in the Mercury underneath he finds that as soon as the Sucker is drawn out the Mercury follows and ascends to the same height of two Feet and three Inches and an half And when afterwards although no greater force be added the Sucker is drawn higher he finds that the Mercury stands and follows no further and so that space is made empty which remains between the Mercury and the Sucker p. 15. Maneat igitur c. Be it therefore confirm'd by so many Arguments of which every one is sufficient in it self that Quicksilver the Experiment being made in an open place is not upheld from falling by the weight of the external Air. Cap. 6. Ibid. Argentum c. That Quicksilver in a close place is not upheld from falling by the Elater or Spring of the Air. Ibid. Cum tota c. Seeing the whole power of this Spring depends upon the already-confuted AEquilibrium of the Air with 29 Inches and an half of Quicksilver so that this Spring does neither more nor less in a close place than is done by that AEquilibrium in an open place it is manifest seeing this AEquilibrium is already shewn to be plainly fictitious and imaginary that the Spring of the Air is so likewise p. 16. Nec plus c. And that this Spring doth neither more nor less in a close place than is done by that AEquilibrium in an open place Ibid. Adde c. Add that seeing the Experiments brought in the Chapter above of the adhesion of the Finger c. are alike in a close and an open place it is necessary and certain that the same Arguments made against the AEquilibrium have force against the Spring of the Air. p. 17. Et profecto c. And really if these Authors would consider how great a difficulty there is in explaining this Spring of the Air unless the same Air by it self alone may take up a greater place I believe they would readily alter their Opinion Part 2. Chap. 1. p. 19. Constet hoc c. This appears from what has been already spoken in the preceding Chapter For the Quicksilver descending cannot so draw the Finger downwards and fasten it unto the Tube unless it be hung upon the Finger by such a Cord which by its weight it vehemently stretches as is manifest by it self Ibid. Respondeo c. I answer That this comes to pass that there may be no Vaculty seeing there is nothing else there that can succeed into the place of the descending Quicksilver Ibid. And hence is confirm'd that common Axiom used in the Schools for so many Ages past that
suspicion the Experiment about the Coals might easily suggest and which the event declar'd not to have been altogether groundless For upon the admission of the external Air the Fire that seem'd to have gone out a pretty while before did presently revive and being as it were refresh'd by the new Air and blown by the Wind made by that Air in rushing in it began again to shine and dissipate the neighbouring Fuel into Smoke as formally EXPERIMENT XIII A While after we let down into the Receiver together with a lighted piece of Match a great Bladder well tyed at the Neck but very lank as not containing actually much if any thing above a Pint of Air but being capable of containing ten or twelve times as much Our scope in this Experiment was partly to try whether or no the smoke of the Match replenishing the Receiver would be able to hinder the dilatation of the inward Air upon the exsuction of the ambient And partly to discover whether the extinction of the Fire in the Match did proceed from want of Air or barely from the pressure of its own Fumes which for want of room to expand themselves in might be suppos'd to recoyl upon the Fire and so to stifle it The event of our tryal was That at the beginning of our pumping the Match appear'd well lighted though it had almost fill'd the Receiver with its plentifull Fumes But by degrees it burnt more and more dimly notwithstanding that by the nimble drawing out the Air and Smoke the Vessel were made less opacous and less full of compressing matter as appear'd by this That the longer we pump'd the less Air and Smoke came out of the Cylinder at the opening of the Valve and consequently the less came into it before yet the Fire in the Match went but slowly out And when afterwards to satisfy our selves of its expiration we had darken'd the Room and in vain endeavoured to discover any spark of Fire as we could not for some time before by the help of Candles discern the least rising of Smoke we yet continued pumping six or seven times and after all that letting in the Air the seemingly dead Fire quickly revived and manifested its recovery by Light and store of Smoke with the latter of which it quickly began to replenish the Receiver Then we fell to pumping afresh and continued that labour so long till the re kindled Match went out again and thinking it then fit not to cease from pumping so soon as before we found that in less than half a quarter of an hour the Fire was got out for good and all and past the possibility of being recover'd by the re-admitted Air. Some Circumstances besides those already mention'd occurr'd in the making of the Experiment of which these are the principal First When the Receiver was full of Smoke if the Cylinder were emptied immediately upon the turning of the Stop-cock the Receiver would appear manifestly darken'd to his eye that look'd upon the light through it and this darkness was much less when the Receiver was much less fill'd with Fumes It was also instantaneous and seem'd to proceed from a sudden change of place and situation in the exhalations upon the vent suddenly afforded them and the Air they were mixt with out of the Receiver into the Cylinder The next thing we observed was a kind of Halo that appear'd a good while about the Fire and seem'd to be produced by the surrounding Exhalations And lastly it is remarkable That even when the Fumes seemed most to replenish the Receiver they did not sensibly hinder the Air included in the Bladder from dilating it self after the same manner for ought we could discern as it would have otherwise done So that before the Fire or the Match was quite extinct the Bladder appear'd swell'd at least to six or seven times its former capacity Since the writing of these last Lines we took a small Receiver capable of containing by guess about a pound and a half of Water and in the midst of it we suspended a lighted Match but though within one minute of an hour or there abouts from the putting in of the Match we had cemented on the Cover yet we could not make such haste but that before we began to pump the Smoke had so fill'd that small Receiver as for ought we discern'd to choke the Fire And having again and again reiterated the Experiment it seem'd still as at first that we could not close up the Vessel and pump out all the Fumes time enough to rescue the Fire from extinction whereupon we made use of this Expedient Assoon as we had pump'd once or twice we suddenly turn'd the Key and thereby gave access to the excluded Air which rushing violently in as if it had been forced thorow a pair of Bellows did both drive away the ashes fill the Glass with fresh Air and by blowing the almost extinguish'd Fire re-kindl'd it as appear'd by the Matches beginning again to smoke which before it had ceas'd to do we having by this means obtained a lighted Match in the Receiver without being reduced to spend time to close it up commanded the Air to be immediately pump'd out and found that upon the exsuction of it the Match quickly left smoking as it seem'd by reason of the absence of the Air and yet if some urgent occasions had not hinder'd us we would for greater security have try'd whether or no the Match rekindled as formerly would smoke much longer in case of no exsuction of the ambient Air. EXPERIMENT XIV TO try diverse things at once and particularly whether Fire though we found it would not long last might not be produced in our evacuated Receiver We took a Pistol of about a foot in length and having firmly tyed it to a stick almost as long as the Cavity of the Receiver we very carefully prim'd it with well dry'd Gunpowder and then cocking it we ty'd to the Tricker one end of a string whose other end was fasten'd to the Key formerly mention'd to belong to the Cover of our Receiver This done we convey'd the Pistol together with the annexed Staff into the Vessel which being clos'd up and empty'd aster the usual manner we began to turn the Key in the Cover and thereby shortning the string that reach'd from it to the Pistol we pull'd aside the Tricker and observ'd that according to our expectation the force of the Spring of the Lock was not sensibly abated by the absence of the Air from whose impetus yet some Modern Naturalists would derive the cause of the motion of Restitution in solid Bodies For the Cock falling with its wonted violence upon the Steel struck out of it as many and as conspicuous parts of Fire as for ought we could perceive it would have done in the open Air. Repeating this Experiment diverse times we also observed whether or no there would appear any considerable diversity in the Motion of the shining Sparks in
satisfactory trial was the principal fruit I promis'd my self from our Engine It being then fufficiently known that in the Experiment De Vacuo the Quick-silver in the Tube is wont to remain elevated above the surface of that whereon it leans about 27 digits I considered that if the true and only reason why the Quick-silver falls no lower be that at that Altitude the Mercurial Cylinder in the Tube is in an AEquilibrium with the Cylinder of Air suppos'd to reach from the adjacent Mercury to the top of the Atmosphere then if this Experiment could be try'd out of the Atmosphere the Quick-silver in the Tube would fall down to a level with that in the Vessel since then there would be no pressure upon the subjacent to resist the weight of the Incumbent Mercury Whence I inferr'd as easily I might that if the Experiment could be try'd in our Engine the Quick-silver would subside below 27 Digits in proportion to the exsuction of Air that should be made out of the Receiver For as when the Air is shut into the Receiver it doth according to what hath above been taught continue there as strongly compress'd as it did whilst all the incumbent Cylinder of the Atmosphere lean'd immediately upon it because the Glass wherein it is pen'd up hinders it to deliver it self by an expansion of its parts from the pressure wherewith it was shut up So if we could perfectly draw the Air out of the Receiver it would conduce as well to our purpose as if we were allow'd to try the Experiment beyond the Atmosphere Wherefore after having surmounted some little difficulties which occurr'd at the beginning the Experiment was made after this manner We took a slender and very curiously blown Cylinder of Glass of near three foot in length and whose bore had in Diameter a quarter of an Inch wanting a hairs breadth This Pipe being Hermetically seal'd at one end was at the other fill'd with Quick-silver care being taken in the filling that as few bubbles as was possible should be left in the Mercury Then the Tube being stopt with the Finger and inverted was open'd according to the manner of the Experiment into a somewhat long and slender Cylindrical Box instead of which we now are wont to use a Glass of the same form half fill'd with Quick-silver And so the liquid metal being suffered to subside and a piece of Paper being pasted on level with its upper surface the Box and Tube and all were by strings carefully let down into the Receiver And then by means of the hole formerly mentioned to be left in the Cover the said Cover was slipt along as much of the Tube as reached above the top of the Receiver And the Interval left betwixt the sides of the Hole and those of the Tube was very exquisitely filled up with melted but not over hot Diachylon and the round chink betwixt the Cover and the Receiver was likewise very carefully closed up Upon which closure there appeared not any change in the height of the Mercurial Cylinder no more than if the interposed Glass Receiver did not hinder the immediate pressure of the ambient Atmosphere upon the inclosed Air which hereby appears to bear upon the Mercury rather by virtue of its spring than of its weight since its weight cannot be supposed to amount to above two or three Ounces which is inconsiderable in comparison of such a Cylinder of Mercury as it would keep from subsiding All things being thus in a readiness the Sucker was drawn down and immediately upon the egress of a Cylinder of Air out of the Receiver the Quick silver in the Tube did according to expectation subside And notice being carefully taken by a mark fastened to the outside of the place where it stopt we caused him that managed the Pump to pump again and marked how low the Quick-silver fell at the second exsuction but continuing this work we were quickly hindred from accurately marking the Stages made by the Mercury in its descent because it soon sunk below the top of the Receiver so that we could henceforward mark it no other ways than by the eye And thus continuing the labour of pumping for about a quarter of an hour we found our selves unable to bring the Quick-silver in the Tube totally to subside because when the Receiver was considerably emptyed of its Air and consequently that little that remained grown unable to resist the Irruption of the External that Air would in spight of whatever we could doe press in at some little Avenue or other and though much could not thereat get in yet a little was sufficient to counterballance the pressure of so small a Cylinder of Quick-silver as then remained in the Tube Now to satisfy our selves farther that the falling of the Quick-silver in the Tube to a determinate height proceedeth from the AEquilibrium wherein it is at that height with the external Air the one gravitating the other pressing with equal force upon the subjacent Mercury we returned the Key and let in some new Air upon which the Mercury immediately began to ascend or rather to be impelled upwards in the Tube and continued ascending till having returned the Key it immediately rested at the height which it had then attained And so by turning and returning the Key we did several times at pleasure impell it upwards and check its ascent And lastly having given a free egress at the Stop-cock to as much of the external Air as would come in the Quick-silver was impelled up almost to its first height I say almost because it ftopt near a quarter of an Inch beneath the Paper mark formerly mentioned which we ascriâ—ed to this That there was as is usual in this Experiment some little Particles of Air engaged among those of the Quick-silver which Particles upon the descent of the Quick-silver did manisestly rise up in bubbles towards the top of the Tube and by their pressure as well as by lessening the Cylinder by as much room as they formerly took up in it hindred the Quick-silver from regaining its first height This Experiment was a few days after repeated in the presence of those excellent and deservedly Famous Mathematick Professors Dr. Wallis Dr. Ward and Mr. Wren who were pleased to honour it with their Presence And whom I name both as justly counting it an Honour to be known to them and as being glad of such Judicious and illustrious Witnesses of our Experiment and'twas by their guess that the top of the Quick-silver in the Tube was defined to be brought within an Inch of the surface of that in the Vessel And here for the Illustration of the foregoing Experiment it will not be amiss to mention some other particulars relating to it First then When we endeavoured to make the Experiment with the Tube closed at one end with Diachylon instead of an Hermetical Seal we perceived that upon the drawing of some of the Air out of the Receiver the Mercury did
Climates yet we could not believe that that difference in the Air should alone be able to make so great an one in the heights of the Mercurial Cylinders and accordingly upon enquiry we found that though the various density of the Air be not to be over-looked in this Experiment yet the main Reason why we found the Cylinder of Mercury to consist of so many Inches was this That our English Inches are somewhat inferiour in length to the digits made use of in Foreign Parts by the Writers of the Experiment The next thing I desire Your Lordship to take notice of is That the height of the Mercurial Cylinder is not wont to be found altogether so great as really it might prove by reason of the negligence or incogitancy of most that make the Experiment For oftentimes upon the opening of the inverted Tube into the Vessel'd Mercury you may observe a bubble of Air to ascend from the bottom of the Tube through the subsiding Quick-silver to the top and almost always you may if you look narrowly take notice of a multitude of small bubbles all along the inside of the Tube betwixt the Quick-silver and the Glass not now to mention the Particles of Air that lie concealed in the very Body of the Mercury Many of which upon the Quick-silver's forsaking the upper part of the Tube do break into that deserted space where they find little or no resistance to their expanding of themselves Whether this be the reason that upon the Application of warm Bodies to the emptied part of the Tube the subjacent Mercury would be depressed somewhat lower we shall not determine though it seem very probable especially since we found that upon the application of Linnen cloaths dipped in Water to the same part of the Tube the Quick-silver would somewhat ascend as if the cold had condensed the imprisoned Air that pressed upon it into a lesser room But that the deserted space is not wont to be totally devoid of Air we were induced to think by several Circumstances For when an eminent Mathematician and excellent Experimenter had taken great pains and spent much time in accurately filling up a Tube of Mercury we found that yet there remained store of inconspicuous bubbles by inverting the Tube letting the Quick-silver fall to its wonted height and by applying by degrees a red hot Iron to the outside of the Tube over against the upper part of the Mercurial Cylinder for hereby the little unheeded bubbles being mightily expanded ascended in such numbers and so fast to the deserted space that the upper part of the Quick-silver seemed to our wonder to boil We farther observed That in the trials of the Torricellian Experiment we have seen made by others and one excepted all our own we never found that upon the inclining of the Tube the Quick-silver would fully reach to the very top of the sealed end Which argued that there was some Air retreated thither that kept the Mercury out of the unreplenished space If Your Lordship should now demand what are the best expedients to hinder the intrusion of the Air in this Experiment we must answer That of those which are easily intelligible without ocular demonstration we can at present suggest upon our own trials no better than these First at the open end of the Tube the Glass must not only be made as even at the edges as you can but it is very convenient especially if the Tube be large that the bottom be every way bent inwards that so the Orifice not much exceeding a quarter of an Inch in Diameter may be the more easily and exactly stopped by the Experimenter's finger between which and the Quick-silver that there may be no Air intercepted as very often it happens that there is it is requisite that the Tube be filled as full as possibly it can be that the finger which is to stop it pressing upon the accumulated and protuberant Mercury may rather throw down some than not find enough exactly to keep out the Air. It is also an usefull and compendious way not to fill the Tube at first quite of Mercury but to leave near the top about a quarter of an Inch empty for if you then stop the open end with your finger and invert the Tube that quarter of an Inch of Air will ascend in a great bubble to the top and in its passage thither will gather up all the little bubbles and unite them with it self into one great one so that if by reinverting the Tube you let that bubble return to the open end of it you will have a much closer Mercurial Cylinder than before and need but to add a very little Quick-silver more to fill up the Tube exactly And lastly as for those lesser and inconspicuous parcels of Air which cannot this way begleaned up You may endeavour before you invert the Tube to free the Quick-silver from them by shaking the Tube and gently knocking on the outside of it after every little parcel of Quick-silver which you pour in and afterwards by forcing the small latitant bubbles of Air to disclose themselves and break by imploying a hot Iron in such manner as we lately mentioned I remember that by carefully filling the Tube though yet it were not quite free from Air we have made the Mercurial Cylinder reach to 30 Inches and above an eight and this in a very short Tube which we therefore mention because we have found by Experience that in short Tubes a little Air is more prejudicial to the Experiment than in long ones where the Air having more room to expand it self doth less potently press upon the subjacent Mercury And since we are fallen upon the consideration of the Altitude of the Mercurial Cylinder I must not conceal from Your Lordship an Experiment relating thereunto which perhaps will set both You and many of your Friends the Vertuosi on thinking and by disclosing some things about the Air or Atmosphere that have scarce hitherto been taken notice of may afford you some hints conducive to a further discovery of the subject of this Epistle EXPERIMENT XVIII WE took a Glass Tube which though it were not much above three Foot long we made choice of because it was of a more than ordinarily even thickness This we fill'd with Mercury though not with as much care as we could yet with somewhat more than is wont to be used in making the Torricellian Experiment Then having according to the manner inverted the Tube and open'd the mouth of it beneath the surface of some other Quick-silver that in the Tube fell down to the wonted height leaving as is usual some little Particles of Air in the space it deserted as we guest by observing that upon the Application of hot Bodies to the upper part of the Tube the Quicksilver would be a little depress'd Lastly having put both the Tube and the Vessel it lean'd on into a convenient Wooden frame to keep them from mischances we plac'd
For the Experiment that occasion'd this Discourse seems to make it probable enough that there may be strange Ebbings and Flowings as it were in the Atmosphere or at least that it may admit great and sudden Mutations either as to its Altitude or its Density from causes as well unknown to us as the effects are unheeded by us And that You may not think that there is nothing in Nature but our Experiment that agrees with this our conjecture we might put Your Lordship in mind of the Pains and Aches that are often complain'd of by those that have had great Wounds or Bruises and that do presage great Mutations in the Air oftentimes whilst to strong and healthy Persons no sign of any such thing appears And that is also very memorable to this purpose which I remember I have somewhere read in a Book of the Ingenious Kircherus who giving a pertinent admonition concerning the various refractions that may happen in the Air relateth That during his stay in Malta he often saw Mount AEtna though the next day notwithstanding its being extremely clear he could not see it adding that Vintemillius a very Learned Person did oftentimes from a Hill he names behold the whole Island he calls Luprica protuberant above the Sea though at other times notwithstanding a clear Sky he could not see it And though perhaps this may be in part ascribed to the various light and position of the Sun or to the various disposition of the Spectators eye or peradventure to some other cause yet the most probable cause seems to be the differing Density of the Air occasion'd by Exhalations capable to increase the refraction and consequently bring Beams to the Eye which otherwise would not fall on it We have likewise in another Treatise mention'd our having often observ'd with Telescopes a plenty of Steams in the Air which without such a help would not be taken notice of and which as they were not at all times to be seen even through a Telescope so they did sometimes especially after a shower of Rain hastily disappear and when we have visited those places that abound with Mines we have several times been told by the Diggers that even when the Sky seem'd clear there would not seldome suddenly arise and sometimes long continue a certain Steam which they usually call a damp so gross and thick that it would oftentimes put out their very Candels if they did not seasonably prevent it And I think it will easily be granted that the ascension of such Steams into this or that part of the Air and their mixing with it are very like to thicken it as on the other side either heat or the sudden condensation of the Air in another part of the Atmosphere to mention now no other causes are capable of rarefying it Nor will it very much import the main scope of our Discourse whether it be suppos'd that the copious Steams the earth sends into the Air thicken that part of the Atmosphere that receives them and make it more heavy Or that sometimes the Fumes may ascend with such celerity that though the Air be thickn'd yet they rather diminish than encrease its gravitation in regard that the quickness of their ascent not onely keeps them from gravitating themselves but may hinder the pressing downwards of many Aërial Corpuscles that they meet with in their way upwards This I say is of no great importance to our present Discourse since either way the Terrestrial Steam may here and there considerably alter the gravity or pressure of the Atmosphere Your Lordship may also be pleased to remember That by our seventeenth Experiment it appear'd that as when the Air in the Receiver was expanded more than ordinarily the Quick-silver in the Tube did proportionably subside so when the Air in the same Receiver was a little more than ordinarily compress'd it did impell up the Quick-silver in the Tube above the wonted height of betwixt six and seven and twenty digits And if to these things we annex that for ought we can find by tryals purposely made the degree of rarity or density of the Air shut up into our Receiver doth not sensibly alter its temperature as to cold or heat It will not I hope appear absurd to conceive That since the Air included in the Tube could but very saintly hinder the ascent of the Quick-silver or press it downwards Since too that included Air could scarce immediately receive any sensible alteration save either by heat or cold And since also that according to the bare density or rarity of the Air incumbent on the subjacent Quick-silver in the Vessel that in the Tube was impell'd more or less high such changes happening in the neighbouring part of the outward Air either by the ascension of gross or copious exhalations or by any other cause of which there may be divers as were capable to make considerable alterations in the consistence of the Air as to rarity and density may be able proportionably to alter the height of the Quick-silver I rather say that such alterations may be than that they are the causes of our Phaenomenon because I think it sufficient if I have propos'd conjectures not altogether irrational about a new Mystery of Nature touching which the chief things I pretend to is to give occasion to the Curious to enquire farther into it than I have been yet able to do EXPERIMENT XIX THe same Reason that mov'd us to conclude that by the drawing of the Air out of the Receiver the Mercury would descend in a Tube shorter than six and twenty digits induc'd us also to expect that by the same means Water might be brought to subside in Glass Tubes of a moderate length Though by the noble Experiment said to have been accurately made in France by Monsieur Paschal we are informed that a Tube of no less than about two and thirty Foot was found requisite to make the Experiment De vacuo succeed with Water instead of Quick-silver so tall a Cylinder of that lighter Liquor being it seems requisite to equal the Weight of a Mercurial Cylinder of six or seven and twenty digits and surmount the pressure of the Atmosphere We took then a Tube of Glass Hermetically seal'd at one end of about four foot in length and not very slender This at the open end we fill'd with common Water and then stopt that end till we had inverted the Tube and open'd it beneath the surface of a quantity of the like Water contain'd in a somewhat deep and slender Vessel This Vessel with the Tube in it was let down into the Receiver and the Receiver being clos'd up after the accustom'd manner the Pump was set on work As much of the event as concerns our present purpose was this That till a considerable part of the Air was drawn out of the Receiver the Tube continu'd top-full of Water as when it was put in it being requisite that a great part of the Air formerly contain'd
the Bladder from swimming and no more For I suppos'd that if when all things were thus order'd the Receiver were empty'd in case there were any such pressure of the Atmosphere upon Water as I was inclin'd to believe the Air within the Bladder being upon the exsuction of the Air within the Receiver freed from that pressure and being press'd onely by the small weight of the incumbent Water would considerably expand it self but whilst we were preparing Bladders for this Experiment there occurr'd an easie way for the making at once both the Discoveries I desir'd We took then a Glass Viol containing by ghess a pound and some ounces of Water this we fill'd top full and then we put into the Neck of it a Glass Pipe a pretty deal bigger than a Goose Quill open at both ends and of divers Inches in length One end of this Pipe was so put into the Neck of the Viol as to reach a little below it and then was carefully cemented thereto that no Air might get into the Viol nor any Water get out of it otherwise than through the Pipe and then the Pipe being warily fill'd about half way up to the top with more Water and a mark being pasted over aganst the upper surface of the Liquor the Viol thus fitted with the Pipe was by strings let down into the Receiver and according to the wonted manner exquisitely clos'd up in it This done we began to pump out the Air and when a pretty quantity of it had been drawn away the Water in the Pipe began to rise higher in the Pipe at the sides of which some little bubbles discover'd themselves After a little while longer the Water still swelling there appear'd at the bottom of the Pipe a bubble about the bigness of a small Pea which ascending through the Pipe to the top of the Water stay'd there a while and then broke but the Pump being nimbly ply'd the expansion of the Water so encreas'd that quickly getting up to the top of the Pipe some drops of it began to run down along the out-side of it which oblig'd us to forbear pumping a while and give the Water leave to subside within less than two Inches of the bottom of the Pipe After this the Pump being again set on work the bubbles began to ascend from the bottom of the Pipe being not all of a size but yet so big that estimating one with another they appear'd to be of the size of the smaller sort of Peas and of these we reckon'd about sixty which came up one after another besides store of smaller ones of which we made no reckoning And at length growing weary of reckoning and pumping too because we found that in spight of all our pains and industry some undiscern'd Leak or other in the Receiver hinder'd us from being able to empty it altogether we thought fit to desist for that time after tryal made of what operation the external Air being let in upon the expanded Water would have and accordingly turning the Key to let in the Air we saw as we expected that the Water in the Pipe in a moment fell down almost to the bottom of it Now of this Experiment there are two or three Circumstances yet to be mention'd which are no less than those already recited pertinent to our present purpose In the first place then when the greater part of the Air had been pump'd out of the Receiver the rising bubbles ascended so very slowly in the Pipe that their Progress was scarce discernable which seem'd to proceed from this That their bigness was such That they could not sufficiently extend themselves in the cavity of the Glass without pressing on both hands against the sides of it whereby they became of more difficult extrusion to the Water And though it may seem strange that these bubbles should be of any considerable bulk since 't is like they consisted of lesser parcels of the Air lurking in the Water than those that were vigorous enough to make their way through long before them yet they were commonly much larger than before some of them being equal in quantity to four or five Peas whether this their increase of bulk proceeded from the greater decrement of the pressure of the Air or from the Union of two or three of those numerous bubbles which were then generated below the bottom of the Pipe where we could not see what was done among them Another thing we noted in our bubbles was That whereas in ordinary ones the Air together with the thin film of Water that invests and detains it is wont to swell above the surface of the Water it swims on and commonly to constitute Hemispherical Bodies with it the little parcels of Air that came up after the Receiver was pretty well empty'd did not make protuberant bubbles but such whose upper surface was either level with or beneath that of the Water so that the upper surface being usually somewhat convex the less protuberant parts of it had a pretty quantity of Water remaining above them We also farther observ'd that whereas in the bubbles that first appear'd in the Pipe the ascending Air did as in other common bubbles make its way upwards by dividing the Water through which it pass'd in those bubbles that appear'd at the latter end of our Experiment when the pressure of the little external Air remaining in the Receiver was grown inconsiderable the ascending parcels of Air having how little more than the weight of the incumbent Water to surmount were able both so to expand themselves as to fill up that part of the Pipe which they pervaded and by pressing every way against the sides of it to lift upwards with them what Water they found above them without letting any considerable quantity glide down along the sides of the Glass So that sometimes we could see a bubble thrust on before it a whole Cylinder of Water of perhaps an Inch high and carry it up to the top of the Pipe though as we formerly noted upon the letting in the external Air these tumid bubbles suddenly relaps'd to their former inconspicuousness All these things laid together seem'd sufficiently to confirm that which the consideration of the thing it self would easily enough perswade namely That the Air and such like Bodies being under Water may be press'd upon as well by the Atmosphere as by the weight of the incumbent Water it self Hence likewise we may verify what we observ'd at the close of the foregoing Experiment namely That from the sole swelling of Water there recorded it cannot be so safely concluded that Water when freed from compression is endow'd with an Elastical power of expanding it self since thereby it appears that the Intumescence produc'd by that Experiment may at least in great part be ascribed to the numerous little bubbles which are wont to be produc'd in Water from which the pressure of the Atmosphere is in great measure taken off So apt are we to be mis-led
Repugnant to several such Phaenomena as these That if the Experiment be very well made we may by inclining the Tube impell the Mercury from its wonted station to the top of the Tube which will not happen in case the Air were before Inclination let into that deserted space That if when the Mercury is setled at its wonted station the Tube be lifted up out of the Restagnant Quicksilver the outward Air will drive up the heavy Mercurial Cylinder oftentimes with force enough to beat out the sealed end To which we shall adde onely this Experiment The Quicksilver resting at its wonted station if you carefully stop the lower Orifice under the Surface of the Restagnant Quicksilver and then lifting up the Tube that which we us'd was about three or four foot long into the Air keep it well stopt if I say you first depress one end and then the other you shall find the Quicksilver fall against the deprest extreme of the Tube with such swiftness and force as will perhaps surprize you and make you apprehend that the Tube will be either beaten out of your hand or broken Whereas if unstopping the Tube whilst the self-same quantity of Mercury remains in it you let the outward Air into the cavity unpossest by the Mercury and then if you again stop the Orifice with your finger and proceed as formerly you shall perceive the motion of the included Liquor to be very much slower and less violent than formerly by reason of the resistance of the admitted Air which will also manifestly disclose it self by the conflict and bubbles that will be produc'd betwixt the Air and Quicksilver in their hasty passing by one another to the opposite ends of the Tube If any friend of Mr. Hobbs's seeing the manifest inconveniences of this opinion shall on his behalf pretend that 't is what he calls the pure Air that passes through the body of the Quicksilver to the deserted part of the Glass Cane the answer is ready that Mr. Hobbs's expressions look so much another way that his Readers for ought I have found do generally understand him of such common Air as is displac'd by the descent of the Mercury And therefore I had reason enough to argue against what he wrote as I have newly done and however this assertion is clearly precarious and lyable to the Objections formerly alledg'd against the passing of the Air through the water To which we may adde this circumstance that in our present case it must descend into a far heavier and closer Liquor than water But perhaps it will be thought I have already said more than needed against an opinion which has been rejected as well by Plenists as Vacuists and though mention'd as to the main by several Writers as well before Mr. Hobbs asserted it as afterwards has been thought so unlikely as not to have been that I know of approv'd by any man even before the discovery of the Phaenomena of our Engine Which last words I adde because that Mr. Hobbs not pretending that any attraction intervenes in the case I see not how he can possibly make out to omit other Phaenomena the descent of the Mercury in the Tube further and further beneath its wonted station upon the Exhaustion of the Receiver and the re-ascension of the same Mercury in the same Tube as we please to let in more or less of the outward Air without admitting as much of Spring or Pressure in the Air as I need contend to have here allowed me The weight of the Terrene Particles by which at the end of the third Exposition he is reduc'd to endeavour the Solution of the Quicksilvers falling lower at the top than at the bottom of a Hill for I am willing to think that is his meaning and that 't is by the Transcribers fault rather than his that resolutely affirms the quite contrary will by no means serve his turn It being utterly improbable to imagine that the contain'd in so little a vessell as one of our Receivers can by its weight counter-balance so ponderous a Cylinder of Quicksilver Whence we may be allowed to argue that the Air sustains it by such a Pressure or Spring as we plead for whether that proceed from the Texture of the Aerial Particles or from their Motion or from both The Fourth and last of Mr. Hobbs's principal Expositions is of that Experiment of ours wherein 100. and odde pound weight being hung at the depressed Sucker the Sucker was notwithstanding impell'd up again by the Air to the top of the Cylinder Of this Phaenomenon which has not hitherto prov'd unwellcome to the Vertuous Mr Hobbs gives us the following account Haerent hic nostri which why he sayes I know not quomodo haec expedies tu A. Expedivi ante Aër enim à retractione Suctoris retrò pulsus nec locum in mundo ut supponimus pleno quò se recipiat inveniens nisi quem ipse corpora contigua suis locis pellens sibi faceret perpetuâ pulsione in Cylindrum tandem cogitur tantâ velocitate inter Cylindri concavam Suctoris convexam superficiem quant a respondere solet viribus illis magnis quas ad Suctorem revellendum necessarias expertt estis Aër autem ille quâ velocitate ingreditur eandem ingressus retinet simulque latera Cylindri aenei vi elasticâ praediti undiquaque distinet Conatur ergo Aër in Cylindro vehementer motus contra omnes partes superficiei Cylindri concavae srustra quidem dum Suctor retrahitur sed quamprimum Suctor manu emissus Aërem impellere cessat Aër ille qui ante incussus erat propter conatum in omne punctum superficiei Cylindri internae vim Aëris elasticam insinuabit se inter easdem superficies eâdem velocitate quâ impulsus fuerat id est eâ velocitate quae respondet viribus impulsionis Si ergo tanta ponderis vis Suctori appendatur quanta manuum vis erat quâ impellebatur velocitas quâ idem Aër è Cylindro exit locum in mundo pleno nullum habens quò se recipiat Suctorem rursus ad Cylindri summitatem impellet propter eandem causam quae effecit ut Suctor paulo ante impulerit Aërem Thus far our Authors passage against whose solution 't is easie to draw divers Arguments from what we have discourst against the first of his four Explications But though we refer you thither yet we will here also observe that this whole conceipt of the Aires running in and out with strange velocity between the Sucker and the Cylinder is precarious nor does he propose any one Phaenomenon to countenance it To which general Advertisement I shall adde the three following particulars First that in an Engine so contrived that the Pump lay cover'd with water when the Sucker was retracted the Atmosphere would strongly press the water against it and if the Manubrium were let go would swiftly enough repell up the Sucker into the deserted
his Explication and I am not obliged to do so I shall onely take notice of what our Author objects to prove that this Phaenomenon cannot be solv'd by the Spring of the Air in these words B. Cur non potest aqua quae cum injiceretur particulas aëris comprimebat ab iisdem particulis se explicantibus rursus rejici A. Quia locum explicatae majorem non requirunt quam compressae Quemadmodum in vase aqua pleno in qua esset multitudo anguillarum anguillas sive in se volutas sive explicatas idem semper capit locum Propellere ergo aquam per vim Elasticam quae alia non est quam motus corporum se explicantium non possunt B. Comparatio illa aëris cum aqua anguillis plena nostris credo non displicebit But the Elaterists will answer that neither can his earthly Atoms to whom he ascribes the Rejection of the water forc'd in truly fill up more parts of space at one time than at another and therefore the Objection might have been spared but indeed it reaches us not For we as Mr. Hobbs knows well are not wont to compare the Air to Eels but to Wooll and though each hair that makes up a compress'd lock of wooll do not really fill more space with wooll when extended than when crumpl'd yet when there is a congeries of these hairs compress'd together the whole fleece or congeries does by its spring endeavour to thrust away those contiguous bodies by which it is penn'd up as I have more fully explained in my Epistle so that these Aerial Corpuscles being pent up by the water forc'd into the Glas still endeavour to expand themselves by throwing it out What our Author addes in the same page as if they were mistaken that think the Experiments of the Plenists tended especially till of late to prove that the generality of them did not always mean by a Vacuum a space perfectly devoid of all corporeal substance but any space here below that is not fill'd with a visible body or at least with Air for these are my words to which I suppose Mr. Hobbs alludes To this I say it is scarce worth while to make answer the Controversie being of such small moment though I think I could easily enough do it especially since he rather excuses those that may have negligently exprest themselves than disproves what I said And since I spoke chiefly and by name of the Peripatetick Schools he may well allow that their Expressions concerning this matter were not alwayes so accurate whilst in this very passage he concludes with these words Vides quam ineptum sit ad explicationem effectuum talium advocare verba Metaphorica ut fugam vacui horrorem naturae c. quibus olim ad existimationem suam tuendam usae sunt Scholae Nor is what he adds concerning the Vacuum to be attributed to Democritus and Epicurus either clear enough or of concernment enough to our Dispute to be insisted on by us especially since I see not to what purpose he brings it in But there are in this page two particulars which though they make little or nothing against what I said of the Plenists may deserve to be taken notice of The second for I think it expedient to dispatch that first is couch'd in these words In Hydriis perforatis ideo haeret aqua quia quae per tantillum foramen exiturit adeo exigua est ut non posset ita in longitudinem se diffundere ut descendendo aditum aëri faciat per foraminum circumferentias neque aër ab exeunte aqua pulsus locum alium in mundo pleno habere potest praeterquam quem aqua deseret But this Experiment I have already examined as 't is propos'd in his Elements of Philosophy and therefore I shall now onely say to the light variation I find of it here that the reason here assign'd why the water in Gardeners pots clos'd at the top does not descend is not rightly assign'd since to omit other objections by Monsieur Paschall's Experiment it appears that though in Pipes of no great length the water will not run out yet if the Pipe be long enough though the Orifice be no wider the water will descend without giving passage to the Air at the circumference of it But the other particular here mentioned by Mr. Hobbs who thus proposes it Qui per fistulam ore aquam sugit aerem medium prius sugit quo distentum aerem externum removet qui remotus locum in pleno habere nisi proximum removendo non potest sic continua pulsione aqua tandem pellitur in fistulam succeditque aeri qui exugitur deserves a more particular consideration For this account of the ascension of Liquors by suction is not onely here given by Mr. Hobbs but for the main by the learned Gassendus himself and other Atomists and is generally acquiesc'd in by the modern Philosophers perhaps the rather because it seems not to establish or overthrow a Vacuum But though I shall not deny but that many Phaenomena of Nature may be probably explicated by this Propagation and return of Motion yet there are some Phaenomena here below which I see not how the Cartesians or the Atomists or Mr. Hobbs can explicate without admitting the Spring of the Air and which perhaps by the Spring of the Air may be explicated without the recurring to such a propagation and return of impulse Divers instances to this purpose I elsewhere consider but at present I shall propose onely one Experiment purposely devis'd to shew that both Vacuists and Plenists should admit an Elastical power in the Air. I took then a Glass-Vessel consisting of two parts the one was a Vial capable of containing about a pound of water and the other a Pipe open at both ends the lower of which reach'd within two Inches of the bottom of the Vial this Pipe was by the Glass-man fastned into the neck of the Vial not by any Cement lest it should be pretended that the Air might undiscernedly get in or out but with melted Glass of a good thickness into this Vessel by the open Pipe I at length for it is somewhat difficult pour'd water enough to swim a pretty way above the lower extreme of the pipe and then often inclin'd the Vessel to give a free intercourse betwixt the Air within the Vial and that without it that if the internal Air were comprest by the affusion of the water it might free it self as it readily did by ascending in bubbles along the inclined Pipe till the outward and inward Air were reduc'd to an equality of pressure Now if all Suction were produc'd by the pressure of the Air thrust away by the dilated Chest of him that sucks and so thrusting the water or other liquor into the Pipe at which he sucks it seems evident in our case that the water would not ascend by suction since by the contrivance of the
weigh other Bodies in its natural or ordinary consistence without at all condensing it Nay which is remarkable having convey'd a Lambs bladder about half full of Air into the Receiver we observed that though upon the drawing out of the ambient Air the imprisoned Air so expanded it self as to distend the Bladder so as to seem ready to Break it yet this rarefied Air did manifestly depress the Scale whereunto it was annexed Another thing we must not forget to mention that happened to us whilst we were making tryals concerning the weight of the Air namely that having once caus'd the Pump to be somewhat obstinately ply'd to discover the better what may be expected from the thinness of the medium in this Experiment the Imprison'd Air broke its brittle Prison and throwing the greatest part of it against the side of the Receiver dash'd it against that thick Glass into a multitude of pieces Which accident I mention partly that it may confirm what we deliver'd in our Reflexions upon the first Experiment where we considered what would probably be done by the spring of the Air Imprison'd in such Glasses in case the ballancing pressure of the ambient Air were withdrawn and partly that we may thence discern of how close a Texture Glass is since so very thin a film of Glass if I may so call it prov'd so impervious to the Air that it could not get away through the Pores but was forc'd to break the Glass in pieces to free it self and this notwithstanding the time and advantage it had to try to get out at the Pores And this I mention that neither our Experiments nor those of divers Learned Men might receive any prejudice from an Experiment which I happen'd to make divers years ago and which having been so much taken notice of by curious Men may be drawn to countenance their erroneous Opinion who would fain perswade us That Glass is penetrable by Air properly so called Our Experiment was briefly this We were distilling a certain Substance that much abounded with subtle Spirits and volatile Salt in a strong Earthen vessel of an unusual shape to which was luted a large Receiver made of the course sort of Glass which the Trades-men are wont to call green Glass but in our absence the Fire though it were to be very strong was by the negligence or mistake of those we appointed to attend it so excessively increas'd that when we came back to the Fornace we found the spirituous and saline Corpuscles pour'd out if I may so call it so hot and so copiously into the Receiver that they made it all opacous and more likely to flie in pieces than fit to be touch'd Yet being curious to observe the effects of a Distillation prosecuted with so intense and unusual a degree of heat we ventur'd to come near and observ'd among other things that on the outside of the Receiver at a great distance from the juncture there was setled a round whitish Spot or two which at first we thought might be some stain upon the Glass but after finding it to be in divers Qualities like the Oyl and Salt of the Concrete we were Distilling we began to suspect that the most subtle and fugitive parts of the impetuously ascending Steams had penetrated the substance as they speak of the Glass and by the cold of the ambient Air were condensed on the surface of it And though we were very backward to credit this suspition and therefore call'd in an Ingenious Person or two both to assist us in the Observation and have Witness of its event we continued a while longer to watch the escape of such unctuous Fumes and upon the whole matter unanimously concluded that all things consider'd the subtle parts of the distill'd matter being violently agitated by the excessive heat that pass'd through the Pores of the Glass widn'd by the same heat But this having never happen'd but once in any of the Distillations we have either made or seen though these be not a few it is much more reasonable to suppose that the perviousness of our Receiver to a Body much more subtle than Air proceeded partly from the looser Texture of that particular parcel of Glass the Receiver was made of for Experience hath taught us that all Glass is not of the same compactness and solidity and partly from the enormous heat which together with the vehement agitation of the penetrant Spirits open'd the Pores of the Glass than to imagine that such a substance as Air should be able to permeate the Body of Glass contrary to the testimony of a thousand Chymical and Mechanical Experiments and of many of those made in our Engine especially that newly recited Nay by our fifth Experiment it appears that a thin Bladder will not at its Pores give passage even to rarefied Air. And on this occasion we will annex an Experiment which hath made some of those we have acquainted with it doubt whether the Corpuscles of the Air be not less subtle than those of Water But without examining here the reasonableness of that doubt we will proceed to recite the Experiment it self which seems to teach That though Air when sufficiently compressed may perchance get entrance into narrower holes and crannies than Water yet unless the Air be forc'd in at such very little holes it will not get in at them though they may be big enough to let Water pass through them The Experiment then was this I took a fair Glass Siphon the lower end of whose longest Leg was drawn by degrees to such a slenderness that the Orifice at which the Water was to fall out would hardly admit a very small Pin This Siphon being inverted the matter was so order'd that a little Bubble of Air was intercepted in the slenderest part of the Siphon betwixt the little hole newly mention'd and the incumbent Water upon which it came to pass that the Air being not to be forc'd through so narrow a passage by so light a Cylinder of Water though amounting to the length of divers Inches as lean'd upon it hindered the farther efflux of the Water as long as I pleased to let it stay in that narrow place whereas when by blowing a little at the wider end of the Siphon that little parcel of Air was forced out with some Water the remaining Water that before continu'd suspended began freely to drop down again as formerly And if you take a Glass Pipe whether it be in the form of a Siphon or no that being for the most part of the thickness of a Mans Finger is yet towards one end so slender as to terminate in a hole almost as small as a Horse-hair and if you fill this Pipe with Water you will find that Liquor to drop down freely enough thorow the slender Extream But if you then invert the Pipe you will find that the Air will not easily get in at the same hole through which the Water passed For in the sharp end
of the Pipe some Inches of water will remain suspended which 't is probable would not happen if the Air could get in to succeed it since if the hole were a little wider the Water would immediately subside And though it be true that if the Pipe be of the length of many Inches a great part of the Water will run down at the wider Orifice yet that seems to happen for some other reason than because the Air succeeds it at the upper and narrow Orifice since all the slender part of the Pipe and perhaps some Inches more will continue full of Water And on this occasion I remember that whereas it appears by our fifth Experiment That the Aërial Corpuscles except perhaps some that are extraordinarily fine will not pass thorow the Pores of a Lambs Bladder yet Particles of Water will as we have long since observ'd and as may be easily try'd by very closely tying a little Alcalizate Salt we us'd the Calx of Tartar made with Nitre in a fine Bladder and dipping the lower end of the Bladder in Water for if you hold it there for a competent while you will find that there will strain thorow the Pores of the Bladder Water enough to dissolve the Salt into a Liquor But I see I am slip'd into a Digression wherefore I will not examine whether the Experiment I have related proceeded from hence That the springy Texture of the Corpuscles of the Air makes them less apt to yield and accommodate themselves easily to the narrow Pores of Bodies than the more flexible Particles of Water or whether it may more probably be ascrib'd to some other Cause Nor will I stay to consider how far we may hence be assisted to ghess at the cause of the ascension of Water in the slender Pipes and Siphons formerly mention'd but will return to our Bubble and take notice That we thought fit also to endeavor to measure the capacity of the Bubble we had made use of by filling it with Water that we might the better know how much Water answer'd in weight to ¾ of a Grain of Air but notwithstanding all the diligence that was used to preserve so brittle a Vessel it broke before we could perfect that we were about and we were not then provided of another Bubble fit for our turn The haste I was in My Lord when I sent away the last Sheet made me forget to take notice to you of a Problem that occurr'd to my thoughts upon the occasion of the slow breaking of the Glass Bubble in our evacuated Receiver For it may seem strange since by our sixth Experiment it appears that the Air when permitted will by its own internal Spring expand it self twice as much as Mersennus was able to expand it by the heat even of a candent AEolipile Yet the Elater of the Air was scarce able to break a very thin Glass Bubble and utterly unable to break one somewhat thicker within whose cavity it was imprison'd whereas Air pen'd up and agitated by heat is able to perform so much more considerable effects that not to mention those of Rarefaction that are more obvious the Learned Jesuit Cabaeus he that writ of the Load-stone relates That he saw a Marble Pillar so vast that three men together with display'd arms could not imbrace it and that 1000 Yoke of Oxen drawing it several ways with all their strength could not have torn it assunder quite broken off in the midst by reason of some Wood which happening to be burnt just by the Pillar the heat proceeding from the neighbouring Fir so rarefied some Air or Spirituous Matter which was shut up in the cavities of the Marble that it broke through the solid Body of the Stone to obtain room to expand it self I remember I have taken notice that probably the reason why the included Air did not break the hermetically seal'd Bubbles that remain'd intire in our emptyed Receiver was That the Air being somewhat rarefied by the flame imploy'd to close the Glass its Spring upon the recess of the heat grew weaker than before But though we reject not that ghess yet it will not in the present case serve the turn because that much smaller Glass bubbles exactly clos'd will by the included Air though agitated by the heat of a very moderate Fire be made to fly in pieces Whether we may be assisted to salve this Problem by considering that the heat doth from within vehemently agitate the Corpuscles of the Air and add its assistance to the Spring they had before I shall not now examine since I here but propose a Problem and that chiefly that by this memorable Story of Cabaeus notice may be taken of the prodigious power of Rarefaction which hereby appears capable of performing stranger things than any of our Experiments have hitherto ascrib'd to it We should hence My Lord immediately proceed to the next Experiment but that we think it fit on this occasion to acquaint You with what some former tryals though not made in our Engine have taught us concerning what we would have discover'd by the newly mention'd Bubble that broke And this the rather because a great part of this Letter supposing the gravity of the Air it will not be impertinent to determine more particularly than hitherto we have done what gravity we ascribe to it We took then an AEolipile made of Copper weighing six ounces five drachms and eight and forty grains this being made as hot as we durst make it for fear of melting the mettle or at least the Sodar was removed from the fire and immediately stopped with hard Wax that no Air at all might get in at the little hole wont to be left in AEolipiles for the fumes to issue out at Then the AEolipile being suffer'd leasurely to cool was again weighed together with the Wax that stopt it and was found to weigh by reason of the additional weight of the Wax six ounces six drachms and 39 grains Lastly the Wax being perforated without taking any of it out of the Scale the external Air was suffered to rush in which it did with some noise and then the AEolipile and Wax being again weighed amounted to six ounces six drachms and 50 grains So that the AEolipile freed as far as our fire could free it from its Air weighed less than it self when replenished with Air full eleven grains That is the Air containable within the cavity of the AEolipile amounted to eleven grains and somewhat more I say somewhat more because of the particles of Air that were not driven by the fire out of the AEolipile And by the Way if there be no mistake in the observations of the diligent Mersennus it may seem strange that it should so much differ from 2 or 3 of ours in none of which we could rarefie the Air in our AEolipile though made red hot almost all over and so immediately plung'd into cold Water to half that degree which he mentions namely to