NEW EXPERIMENTS Physico-Mechanicall Touching the Air. NEW EXPERIMENTS Physico-Mechanicall, Touching The SPRING of the AIR, and its EFFECTS, (Made, for the most part, in a New PNEUMATICAL ENGINE) Written by way of LETTER To the Right Honourable Charles Lord Viscount of Dungarvan, Eldest Son to the EARL of CORK. By the Honourable Robert boil Esq OXFORD: Printed by H: Hall, Printer to the University, for Tho: Robinson. 1660. To the Reader. ALthough the following Treatise being far more prolix than becomes a Letter, and then I at first intended it; I am very unwilling to increase the already excessive bulk of the Book by a Preface, yet there are some particulars that I think myself obliged to take notice of to the Reader, as things, that will either concern him to know, or me to have known. In the first place then: If it be demanded why I publish to the World a Letter, which by its Style and divers Passages, appears to have been written as well For, as To a particular Person; I have chief these two things to answer: The one, That the Experiments therein related, having been many of them tried in the presence of Ingenious Men; and by that means having made some noise among the Virtuosos (insomuch that some of them have been sent into Foreign Countries, where they have had the luck not to be despised) I could not without quite tiring more than one Amanuensis, give out half as many Copies of them as were so earnestly desired, that I could not civilly refuse them. The other, That intelligent Persons in matters of this kind persuaded me, that the publication of what I had observed touching the Nature of the Air, would not be useless to the World; and that in an Age so taken with Novelties as is ours, these new Experiments would be grateful to the Lovers of free and real Learning: So that I might at once comply with my grand Design of promoting Experimental and Useful Philosophy, and obtain the great satisfaction of giving some to ingenious Men; the hope of which, is, I confess, a temptation that I cannot easily resist. Of my being somewhat prolix in many of my Experiments, I have these Reasons to render, That some of them being altogether new, seemed to need the being circumstantially related, to keep the Reader from distrusting them: That divers Circumstances I did here and there set down for fear of forgetting them, when I may hereafter have occasion to make use of them in my other Writings: That in divers cases I thought it necessary to deliver things circumstantially, that the Person I addressed them to, might without mistake, and with as little trouble as is possible, be able to repeat such unusual Experiments: and that after I consented to let my Observations be made public, the most ordinary Reason of my prolixity was, That foreseeing that such a trouble as I met with in making those trials carefully, and the great expense of time that they necessarily require, (not to mention the charges of making the Engine, and employing a man to manage it) will probably keep most men from trying again those Experiments; I thought I might do the generality of my Readers no unacceptable piece of service, by so punctually relating what I carefully observed, that they may look upon these Narratives as standing Records in our new Pneumaticks, and need not reiterate themselves an Experiment to have as distinct an Idea of it, as may suffice them to ground their Reflections and Speculations upon. And because sometimes 'tis the Discourse made upon the Experiment that makes it appear prolix, I have commonly left a conspicuous interval betwixt such Discourses, and the Experiments whereunto they belong, or are annexed; that they who desire only the Historical part of the account we give of our Engine, may read the Narratives, without being put to the trouble of reading the Reflections too: Which I here take notice of, for the sake of those that are well versed in the New Philosophy, and in the Mathematics; that such may skip what was designed, but for such Persons as may be less acquainted even then I, with matters of this nature (scarce so much as mentioned by any Writer in our Language) and not for them from whom I shall be much more forward to learn, then to pretend to teach them. Of my being wont to speak rather doubtfully, or hesitantly, then resolvedly, concerning matters wherein I apprehend some difficulty, I have in another Treatise (which may, through God's Assistance, come abroad ere long) given a particular, and I hope a satisfactory account: Wherefore I shall now defend my Practice but by the Observation of Aristotle, who somewhere notes, That to seem to know all things certainly, and to speak positively of them, is a trick of bold and young Fellows: Whereas those that are indeed intelligent and considerate, are wont to employ more wary and diffident Expressions, or (as he speaks) 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉. There are divers Reflections, and other Passages in the following Epistle, and even some Experiments (occasionally mentioned) which may seem either impertinent or superfluous, but are not so: Being purposely written, either to evince some truth opposed, or disprove some erroneous conceit maintained, by some eminent New Philosopher, or by some other Ingenious Men, who, I presumed, would easily forgive me the having on such occasions purposely omitted their Names; though an inquisitive Person will probably discover divers of them, by the mention of the Opinions disproven in the Experiments I am excusing. Ever since I discerned the usefulness of speculative Geometry to Natural Philosophy, the unhappy Distempers of my Eyes, have so far kept me from being much conversant in it, that I fear I shall need the pardon of my Mathematical Readers, for some Passages, which if I had been deeply skilled in Geometry, I should have treated more accurately. And indeed, having, for Reasons elsewhere deduced, purposely kept myself a stranger to most of the new Hypotheses in Philosophy, I am sensible enough that the Engine I treat of has prevailed with me to write of some subjects which are sufficiently remote from those I have been most conversant in. And having been reduced to write the greatest part of the ensuing Letter at a distance, not only from my Library, but from my own Manuscripts, I cannot but fear that my Discourses do not only want many choice things wherewith the Learned Writings of others might have enriched or embellished them: But that partly for this Reason, and partly for that touched upon a little before, It is possible I may have mentioned some Notions already published by others, without taking notice of the Authors, not out of any design to defraud deserving Men, but for want of knowing such particulars to have been already published by them: Especially the Experiments of our Engine being themselves sufficient to hint such Notions as we build upon them. The order of the Experiments every Reader may alter, as suits best with his own Design in perusing them: For not only all those betwixt whom there is an Affinity in Nature (by belonging to one subject) are not always placed one by another, but they are not still set down so much as in the order wherein they were made; but most commonly in that casual one wherein my occasions induced me to dispatch them to the Press. And, which is worse, I did usually send quite away the former Experiments, before the later were written, or perhaps so much as made: Whereby I lost the advantage of correcting and supplying the Imperfections of what I had formerly written, by the light of my subsequent Trials and Discoveries. Besides all this, the distemper in my eyes forbidding me not only to write myself so much as one Experiment, but even to read over myself what I dictated to others. I cannot but fear, that besides the Author's mistakes, this Edition may be blemished by many, that may be properly imputed to a very unskilful Writer (whom I was often times by haste reduced against my custom to employ) and may have escaped the Diligence of that Learned Friend, that does me the favour to oversee the Press; especially there being the distance of two days journey betwixt it and me. I need not perhaps represent to the equitable Reader, how much the strange Confusions of this unhappy Nation, in the midst of which I have made and written these Experiments, are apt to disturb that calmness of Mind, and ●ndistractedness of Thoughts, that are wont to be requisite to Happy Speculations. But I presume, that by all these things put together, he will readily perceive, That I have been so far from following the Poets prudent Counsel touching the slow Publication of Books designed to purchase credit by, — Nonumque prematur in Annum that I suffer this Treatise to come abroad into the World with a multitude of Disadvantages. But if it be demanded, why then I did not make it fit for the Press before I sent it thither? my Answer must be, That not at first imagining that this sort of Experiments would prove any thing near so troublesome, either to make, or to Record, as I afterwards found them, I did, to engage the Printer to dispatch, promise him to send him the whole Epistle in a very short time: So that although now and then the occasional vacations of the Press, by reason of Festivals, or the absence of the Corrector, gave me the leisure to exspaciate upon some subject; yet being oftentimes called upon to dispatch the Papers to the Press, my promise, and many unexpected Avocations, obliged me to a haste, which, though it have detracted nothing from the Faithfulness of the Historical part of our Book, has (I fear) been disadvantageous enough to all the rest. And I made the less scruple to let the following Papers pass out of my hands, with all their Imperfections; because, as the public Affairs, and my own, were then circumstanced, I knew not when (if at all) I should be again in a condition to prosecute Experiments of this kind; especially, since (to omit my being almost weary of being, as it were, confined to one sort of Experiments) I am preingaged (if it please God to vouchsafe me Life and Health) to employ my first leisure in the publication of some other Physiological Papers, which I thought 'twould make me much the fit to take in hand, if I first dispatched all that I had at this time to write touching our Engine. I have this further to add, by way of Excuse, That as it has been my design in publishing these Experiments to gratify Ingenious men; so, if I have not been much flattered, I may hope that the various hints to be met with in the following Letter, will (at least) somewhat awaken men's thoughts, & excite them to new speculations (such as perhaps even inquisitive men would scarce else light upon) and I need not despair, that even the examination of such new Suspicions and Inquiries will hence also, at least Occasionally, be facilitated: I said Occasionally, because it being, as 'tis proverbially said, Facile Inventis addere. It seems not irrational to expect, that our Engine itself, and divers of our Experiments, will be much promoted by the Industry of Inventive and Mathematical Wits, whose contrivances may easily either correct or supply, and consequently surpass many of those we have made use of. And, particularly, if Men by skill and patience can arrive both to evacuate such Receivers as ours, till there be no more Air left in them, than there seems to have remained in the Glasses made use of about the Magdeburgick Experiment (hereafter to be mentioned) and to keep out the Air for a competent while, the Usefulness and Discoveries of our Engine, will not be a little advanced. And perhaps that may belong to it, which I remember Seneca speaks of Nature, Initiatos (says he) nos credimus, in Vestibulo ejus haeremus: For being now in a place where we are not quite destitute of moderately skilful Artificers, we have, since the Conclusion of the following Letter, made some Additions to our Engine, by whose help we find (upon some new trials) that we may be able, without much of new trouble, to keep the ambient Air out of the exhausted Receiver for a whole day; and perhaps we should be able to keep it out much longer, if before we shall have dispatched some urgent Affairs, and published some Papers for which a kind of Promise is thought to make us Debtors to the Press, we could be at leisure to prosecute such Experiments, as may possibly afford a Supplement to the following Treatise, from which I shall now no longer detain the Reader. Friendly Reader, I Know all Persons that have a public Spirit for the Advancement of Learning, will think much that this piece came not out in a Language of more general Use, than this you see it now attired in; especially since the Excellent Noble Person, who is the Author, is known to be well able himself (being almost universally a Linguist) to have given it either the Old Latin, or the newer French Dress. But if it be an Honour to a Language to be preferred, and this Honour breeds sometimes an Emulation, as anciently it did between the Greeks and Romans, it cannot be thought unhandsome for an English Nobleman to have preferred his own: And it may be a sufficient Reason for the Gentry of Foreign Parts to learn our Speech, or keep Interpreters, that they are sure to have for their requital, from many of our English Writers (as here from this piece) much curiously ingenious, and profitable Learning. But as to this particular (give me leave to use Words from a Story) Since the Mountain cannot come to Mahomet, Mahomet will go to the Mountain: I mean thus; Because many witty Men, Persons of Honour and Estate especially, may be supposed to be able to make a better account, by employing their Studies and Time on Matter than Words, and so are justly impeded from learning Languages; And because (as I may judge) the noble Author is willing to oblige all Men, He has already provided, that this piece shall shortly be done into Latin, that so it may come home to divers worthy Persons in its Stream, who cannot travel to find it out in its first Origine. Having therefore leave so to do, I cannot forbear to give the World the Advertisement of this Latin Edition, lest some skilful Artist should take needless pains about a Work, which will, ere long (by God's furtherance) be done to his Hands; For such unprofitable expenses of Study have too frequently happened, and too much to the disadvantage of Learning, for want of a sufficient Correspondence and Intercourse between such as are exercised in the Mines of Wisdom. This is all the trouble I shall at present give you: Nor shall I need mind thee, if you have a true gust for the Book you read, to have an honour and thankful regard to the Person that has favoured us with the Communication of these his Trials, & is manifestly so great a Patron and Friend to Experimental Learning, and all true Wisdom; for should you fail in this, you might deservedly be deprived of some other Observations on the same subject, which the Author, I hear, has made since the finishing of this Treatise. I desire to be excused that I do not make Excuses for the slowness of the Publication, hoping that the long expectation you have had of it, will enhance, and not diminish your delight in the enjoyment of a piece like to be, amongst the students in accurate Philosophy, of so general acceptance. Farewell. R: Sh. A Summary of the chief Matters treated of in this Epistolical Discourse. THe Proaemium, wherein is set down the occasion of this Discourse, 1. The motives that induced the Author thereunto, 2 etc. The hints he received, 5. The things wherein this Engine excels any that have yet been made use of, 6 etc. The description of the Engine and its parts, 8 etc. The way of preparing and using it, 15 etc. The division of the Experiments tryable thereby into two sorts, and the difficulty of excluding the Air. 18 etc. The first Experiment, touching the manner of pumping out the Air, and by what degrees the Receiver is emptied, ●0, etc. A digression touching the Spring or Elastical power of the Air, with an attempt for a Mechanical Explication thereof, necessary to be premised for the explanation of the Phaenomena, exhibited in this and the subsequent Experiments. 22 etc. The second Experiment, touching the pressure of the Air against the sides of the Bodies it environs, 37 etc. with a digressive Explication of the pressure of the Air included within an ambient Body. 39 etc. The third Experiment, touching the force requisite to draw down the Sucker, 42 etc. The Opinion of an eminent Modern Naturalist examined. 44 etc. The fourth Experiment, touching the swelling of a Bladder; with the degrees by which it increases, 45 etc. Another Opinion of a Learned Author examined. 48 etc. The fifth Experiment, touching the breaking of a Bladder in the Receiver, 49 etc. And of another by heat. 52 The sixth Experiment, of divers ways by which the elastical expansion of the Air was measured. 52 &c The seventh Experiment, touching what Figure does best resist the pressure of the Air. 62 etc. The eighth Experiment, tending to a further Demonstration of the former, from the breaking of glass a Helmet inward. 64 etc. The ninth Experiment, contains a further confirmation from the breaking of a Glass outward, 66 etc. with an Experiment to prove, that these Phaenomena proceed not from an invincible Fuga vacui 69. A description of other small Receivers, and their Conveniencies, 70 etc. A Receipt for the making of a Composition to Cement cracked Glasses. 73 The tenth Experiment, touching the flaming of Candles enclosed in the Receiver. 74 etc. The eleventh Experiment, touching the burning of Coals, 78. And the lasting of the excandescence of an included piece of Iron. 80. The twelfth Experiment concerning the burning of Match. 82 The thirteenth Experiment, concerning the further prosecution of the preceding, tending to prove the extinction of the Fire in the former Experiments, not to have proceeded from the pressure of the Fire by the Fumes, 84. Some remarkable Circumstances of it, 86. The Experiment of Match tried in a small Receiver. 87 The fourteenth Experiment, touching the striking Fire, and kindling of Powder with the Lock of a Pistol in the evacuated Receiver. 88 etc. The fifteenth Experiment, touching the unsuccessfulness of kindling included Bodies with a burning Glass, and the Author's intention to prosecute it further. 102 The sixteenth Experiment, concerning the operation of the Loadstone. 105, etc. The seventeenth Experiment, touching the gradual descent of the Quicksilver in the Torricellian Experiment, 106 etc. Some observable Circumstances concerning it, 112 etc. The same Experiment tried in one of the small Receivers, 115. How this Experiment may be made use of to know the strength of the pressure of the Air for every degree of Rarefaction, 1●6 etc. The trial of the same Experiment in a Tube not two foot long, 118. The raising of the Mercurial Cylinder, by the forcing of more Air into the Receiver, 119. Some Allegations for and against a Vacuum considered, 1●0 etc. Some Advertisements concerning the inconveniencies that may arise from the diversity of measures made use of for the defining the Altitute of the Mercurial Cylinder; and from the neglect of little parcels of Air apt to remain between the Mercury and the concave surface of the Tube, 123 etc. Some Expedients for the more exact filling the Tube, 127. The height the Author once found of the Mercurial Cylinder, according to English measure. 128. The eighteenth Experiment, containing a new Observation touching the variation of the height of the Mercurial Cylinder in the same Tube, with an offer at the reason thereof. 129 etc. The 19th Experiment, touching the subsiding of a Cylinder of Water, 140 etc. The same tried in a small Receiver. 143 The 20th Experiment, touching the Elater of Water, with a digressive Experiment to the same purpose 144 etc. The 21 Experiment, being a prosecution of the former Enquiry, by Experimenting the Generation of Bubbles under Water, a recital of some notable Circumstances, with some observable Corollary's deduced therefrom. 147 etc. The 22d Experiment, tending to a determination of the Enquiry proposed in the former Experiment, by proving the matter of these Bubbles from their permanency to be Air: The Experiments tried in the great and small Receivers, evincing the same thing, 155 etc. An Experiment wherein there appeared Bubbles in Quicksilver, 160. The Author's Inference, 162. A digressive Enquiry, whether or no Air may be generated anew; with several Histories and Experiments, tending to the resolving and clearing thereof, 162 etc. The Author's excuse for so long a Digression. 181 The 23d Experiment, containing a further Enquiry touching Bubbles made with common and distilled Water. 182 The 24th Experiment, wherein the inquiry is prosecuted with other Liquors, as with Salad Oil, Oil of Turpentine, a Solution of Tartar, Spirit of Vinegar, Red-wine, Milk, Hen's Eggs, Spirit of Urine, Spirit of Wine and Water, Spirit of Wine. 187 etc. The wonderful expansion of the Spirit of Wine. 194 The 25th Experiment, touching the expansion and gravity of the Air under water. 195 etc. The 26th Experiment, touching the Vibrations of a Pendulum. 202 etc. The 27th Experiment, touching the propagation of sound: And the Author's intention of trying some other Experiments, for the further elucidation thereof. 210 etc. The 28 Experiment, touching the sudden eruption of Bubbles from the water, when the airs pressure was speedily removed. 214 The 29 Experiment, touching the cause of the ascent of Fumes and Vapours, wherein 'tis proved (from the several motions, which the Fumes of a strange smoking Liquor, of the Authors, were observed to have in the Receiver, upon the exsuction of the Air) that the reason of their ascent proceeds from the gravity of the ambient air, and not from any positive levity of their own. 217 etc. The 30 Experiment, concerning the nature of a fluid Body, illustrated by the example of smoke which in several circumstances seems very much to resemble the property of a fluid Body, 224 etc. A conjecture of the cause of the Sun's undulation. 228 The 31 Experiment, concerning the Phaenomena of two flat Marbles exactly plained and wrought together, and the true reason thereof, 229. The Author's intention for the further prosecution thereof, & what hindered him; the reason why the under Marble did not fall from the upper (being only conjoined with Spirit of Wine) when the Receiver was evacuated. And a notable relation concerning the cohesion of flat Bodies. 231 etc. The 32 Experiment, touching the forcible pressure of the Air against the outward superficies of a Valve, fastened upon the stop-cock of the Receiver. The Diameter of it, and the weight it sustained. 233 etc. The 33 experiment, touching the great pressure of the Air against the under superficies of the Sucker, 236 etc. what weight was requisite to depress it, & what weight it would lift and carry up with it, 239 etc. what improvement & use there may be made of this experiment, 242. A Discourse touching the nature of Suction, proving that fuga vacui is not the adequate cause thereof. 243 etc. The 34th Experiment, containing several attempts for the weighing of light Bodies in the exhausted Receiver. 258 etc. The 35th Experiment, touching the cause of filtration, and the rising of Water in Siphons', 262 etc. A relation of a new kind of Siphon, of the Authors, upon the occasion of trying the Experiment lately observed by some Frenchmen, and further improved by himself; and some conjectures touching the cause of the exhibited Phaenomena. 267 etc. The 36th Experiment, touching the weighing of a parcel of Air in the exhausted Vessel; and some other Observations for the explication thereof, 272 etc. An accidental Experiment, tending to the further confirmation of the Author's Reflections upon the first Experiment; with a digressive Observation, noting the subtle penetrancy of some Spirits, to exceed by far that of the Air, 275 etc. And some other Experiments to show the difficulty of the ingress of the Air into the pores or holes of some bodies into which Water will readily insinuate itself, 279 etc. with a conjecture at the cause thereof, 282. The Author returns to the prosecution of the inquiry after the gravity of the Air: But first, (upon the occasion of the tenacity of a thin Bubble of Glass) sets down his thoughts concerning the strange exuperancy of strength in Air, agitated by heat, above what the same has unagitated, 283 etc. And then proceeds to the examination of the weight of the Air by an Aeolipile, and compares the result thereof, with that of Mersennus, 286. The Opinions and Experiments of divers Authors, and some of his own, touching the proportion of weight betwixt Water and Air, are compared and examined by the Author, 288. The result thereof, 290. Mersennus his observation reconciled, with that of the Author; and the proportion between the gravity of Water and Air about London, 291 etc. After the recital of the Opinions of several Writers, touching the proportion of gravity between Water and Quick silver, the Author sets down his own trials, made several ways, together with his conclusion therefrom, 293 etc. The use he makes of this inquiry for the guessing at the height of the Atmosphere, 297. What other Experiments are requisite to the determination thereof. 299 etc. The 37th Experiment, touching the strange and odd Phaenomenon, of the sudden flashes of light in the cavity of the Receiver; the several circumstances and difficulties of it, with some attempts towards the rendering at reason thereof, 301, etc. The Difficulty of so doing further shown from the consideration of the various changes of Air which do not immediately fall under our senses, 315. this last proposition proved by several observations. 316. The 38. Experiment, touching the freezing of water, 319. etc. A problem, (concerning the great force wherewith a freezing Liquor extends its self,) proposed upon the Consideration of divers admirable effects wrought thereby. 320 etc. The 39 Experiment, containing an inquisition after the temperature of the substance that remained in the cavity of the Receiver, after the Air was well exhausted. The relation of a Phaenomenon, seeming to proceed from the sw●lling of the Glass. With an advertisement concerning the pliableness of Glass in small prices. 322. etc. The 40. Experiment, touching the difficulty that occurred in making trial whether rarified Air were able to sustain flying infects. 326. &c The 41. Experiment, Exhibiting several trials touching the respiration of divers sorts of animals included in the Receiver, 328, etc. With a digression containing some doubts touching respiration wherein are delivere● several Experiments relating thereunto. 335 etc. The 42. Experiment, touching the differing operation▪ of corrosive Liquors in the emptied Receiver and in the open Air. 384 The 43. Experiment, touching the spontaneous Ebullition of warm Liquors in the exhausted Receiver. 388 The Conclusion. 394 TO THE LORD OF DUNGARVAN, My Honoured and Dear NEPHEW. My Dear Lord, REceiving in your last from Paris, a desire that I would add some more Experiments to those I formerly sent You over: I could not be so much your Servant as I am, without looking upon that Desire as a Command; and consequently, without thinking myself obliged to consider by what sort of Experiments it might the most acceptably be obeyed. And at the same time, perceiving by Letters from some other Ingenious Persons at Paris, that several of the Virtuosos there, were very intent upon the examination of the Interest of the Air, in hindering the descent of the Quicksilver, in the famous Experiment touching a Vacuum: I thought I could not comply with your Desires in a more fit and seasonable manner, then by prosecuting and endeavouring to promote that noble Experiment of Torricellius: and by presenting your Lordship an account of my attempts to illustrate a subject, about which, it's being so much discoursed of where you are, together with your inbred Curiosity, and love of Experimental Learning, made me suppose you sufficiently inquisitive. And though I pretend not to acquaint you, on this occasion, with any store of new Discoveries, yet possibly I shall be so happy, as to assist you to know somethings which you did formerly but suppose; and shall present you, if not with new Theories, at least with new Proofs of such as are not yet become unquestionable. And if what I shall deliver, have the good fortune to encourage and assist you to prosecute the Hints it will afford, I shall account myself, in paying of a duty to you, to have done a piece of Service to the Commonwealth of Learning. Since it may highly conduce to the advancement of that Experimental Philosophy, the effectual pursuit of which, requires as well a Purse as a Brain, to endear it to hopeful Persons of your Quality: who may accomplish many things which others can but wish or, at most, but design, by being able to employ the Presents of Fortune in the search of the Mysteries of Nature. And I am not faintly induced to make choice of this Subject, rather than any of the expected Chemical ones, to entertain your Lordship upon, by these two Considerations: The one, That the Air being so necessary to humane Life, that not only the generality of Men, but most other Creatures that breath, cannot live many minutes without it; any considerable discovery of its Nature, seems likely to prove of moment to Mankind. And the other is, That the Ambient Air, being that whereto both our own Bodies, and most of the others we deal with here below, are almost perpetually contiguous; not only its alterations have a notable and manifest share in those obvious effects, that men have already been invited to ascribe thereunto such as are the various distempers incident to humane Bodies, especially if crazy, in the Spring, the Autumn, and also on most of the great and sudden changes of Wether) but likewise, that the further discovery of the nature of the Air, will probably discover to us, that it concurs more or less to the exhibiting of many Phaenomena, in which it hath hitherto scarce been suspected to have any interest. So that a True Account of any Experiment that is New concerning a thing, wherewith we have such constant and necessary intercourse, may not only prove of some advantage to humane Life, but gratify Philosophers, by promoting their Speculations on a Subject which hath so much oppurtunity to solicit their Curiosity. And I should immediately proceed to the mention of my Experiments, but that I like too well that worthy saying of the Naturalist Pliny, Benignum est & plenum ingenui pudoris, In Praesat. lib. 1. fateri per quos profeceris, not to conform to it, by acquainting your Lordship, in the first place, with the Hint I had of the Engine I am to entertain you of. You may be pleased to remember, that a while before our separation in England, I told you of a Book that I had heard of, but not perused, published by the industrious Jesuit Schottus, wherein 'twas said, He related how that ingenious Gentleman Otto Gericke, Consul of Magdeburg, had lately practised in Germany a way of emptying Glass Vessels, by sucking out the Air at the mouth of the Vessel, plunged under water: And you may also perhaps remember, that I expressed myself much delighted with this Experiment, since thereby the great force of the external Air (either rushing in at the opened Orifice of the emptied Vessel, or violently forcing up the Water into it) was rendered more obvious and conspicuous, than in any Experiment that I had formerly seen. And though it may appear by some of those Writings I sometimes ●hew'd your Lordship, that I had been solicitous to try things upon the same ground; yet in regard this Gentleman was beforehand with me in producing such considerable effects, by means of the exsuction of Air, I think myself obliged to acknowledge the Assistance, and Encouragement the Report of his performances hath afforded me. But as few inventions happen to be at first so complete, as not to be either blemished with some deficiencies needful to be remedied, or otherwise capable of improvement: so when the Engine we have been speaking of, comes to be more attentively considered, there will appear two very considerable things to be desired in it. For first, the Wind-Pump (as some body not improperly calls it) is so contrived, that to evacuate the Vessel there is required the continual labour of two strong men for divers hours. And next (which is an imperfection of much greater moment) the Receiver, or Glass to be emptied, consisting of one entire and uninterrupted Globe and Neck of Glass; the whole Engine is so made, that things cannot be conveyed into it, whereon to try Experiments: So that there seems but little (if any thing) more to be expected from it, than those very few Phaenomena that have been already observed by the Author, and Recorded by Schottus. Wherefore to remedy these Inconveniences, I put both Mr. G. and R. Hook (who hath also the Honour to be known to your Lordship, and was with me when I had these things under consideration) to contrive some Air Pump, that might not, like the other, need to be kept under water (which on divers occasions is inconvenient) & might be more easily managed: And after an unsuccessful trial or two of ways proposed by others, the last named Person fitted me with a Pump, anon to be described. And thus the first Imperfection of the Germane Engine, was in good measure, though not perfectly, remedied: And to supply the second defect, it was considered that it would not perhaps prove impossible to leave in the Glass to be emptied, a hole large enough to put in a Man's Arm clothed; and consequently other Bodies, not bigger than it, or longer than the inside of the Vessel. And this Design seemed the more hopeful, because I remembered, that having several years before often made the Experiment De Vacuo with my own hands; I had, to examine some conjectures that occurred to me about it, caused Glasses to be made with a hole at that end, which uses to be sealed up, and had nevertheless been able, as occasion required, to make use of such Tubes, as if no such holes had been left in them; by devising stopples for them, made of the common Plaster called Diachylon: which I rightly enough guessed, would, by reason of the exquisite commixtion of its small parts, and closeness of its texture, deny all access to the external Air. Wherefore, supposing that by the help of such Plasters, carefully laid upon the commissures of the stopple and hole to be made in the Receiver, the external Air might be hindered from insinuating itself between them into the Vessel, we caused several such Glasses, as you will find described a little lower, to be blown at the Glass-house; and though we could not get the Workmen to blow any of them so large, or of so convenient a shape as we would fain have had; yet finding one to be tolerably fit, and less unfit than any of the rest, we were content to make use of it in that Engine: Of which, I suppose, you by this time expect the Description, in order to the Recital of the Phaenomena exhibited by it. To give your Lordship then, in the first place, some account of the Engine it self: It consists of two principal parts, a glass Vessel, and a Pump to draw the Air out of it. The former of these (which we, with the Glassmen, shall often call a Receiver, for its affinity to the large Vessels of that name, used by Chemists) consists of a Glass with a wide hole at the top, of a cover to that hole, and of a stop-cock fastened to the end of the neck, at the bottom. The shape of the Glass, you will find expressed in the first Figure of the annexed Scheme. And for the size of it, it contained about 30 Wine Quarts, each of them containing near two pound (of 16 Ounces to the pound) of water: We should have been better pleased with a more capacious Vessel, but the Glassmen professed themselves unable to blow a larger, of such a thickness and shape as was requisite to our purpose. At the very top of the Vessel, (A) you may observe a round hole, whose Diameter (BC) is of about four inches; and whereof, the Orifice is encircled with a lip of Glass, almost an inch high: For the making of which lip, it was requisite (to mention that upon the by, in case your Lordship should have such another Engine made for you) to have a hollow and tapering Pipe of Glass drawn out, whereof the Orifice above mentioned was the Basis, and then to have the cone cut off with a hot Iron, within about an Inch of the Points (BC.) The use of the lip, is to sustain the cover delineated in the second Figure; where (DE) points out a brass Ring, so cast, as that it doth within and without cover the lip (BC) of the first Figure, and is cemented on upon it with a strong and close Cement. To the inward tapering Orifice of this Ring (which is about three Inches over) are tightly ground the sides of the Brass stopple (FG;) so that the concave superficies of the one, and the convex of the other, may touch one another in so many places, as may leave as little access, as possible, to the external Air: And in the midst of this cover is left a hole (HI) of about half an inch over, environed also with a ring or socket of the same metal, and fitted likewise with a brass stopple (K) made in the form of the Key of a stop-cock, and exactly ground into the hole (HI) it is to fill; so as that though it be turned round in the cavity it possesses, it will not let in the Air, and yet may be put in or taken out at pleasure, for uses to be hereafter mentioned. In order to some of which, it is perforated with a little hole, (8) traversing the whole thickness of it at the lower end; through which, and a little brass Ring (L) fastened to one side, (no matter which) of the bottom of the stopple (FG) a string (8, 9, 10) might pass, to be employed to move some things in the capacity of the emptied Vessel; without any where unstopping it. The last thing belonging to our Receiver, is the stop-cock designed in the first Figure by (N.) for the better fastening of which to the neck, and exacter exclusion of the Air, there was soldered on to the shank of the Cock (X) a Plate of Tin, (MTUW) long enough to cover the neck of the Receiver. But because the cementing of this was a matter of some difficulty, it will not be amiss to mention here the manner of it, which was, That the cavity of the tin Plate was filled with a melted Cement, made of Pitch, Rosin, and Wood-ashes, well incorporated; and to hinder this liquid Mixture from getting into the Orifice (Z) of the shank, (X) that hole was stopped with a Cork, to which was fastened a string, whereby it might be pulled out of the upper Orifice of the Receiver; and then, the glass neck of the Receiver being well warmed, was thrust into this Cement, and over the shank whereby it was effected, that all the space betwixt the tin Plate and the Receiver, and betwixt the internal superficies of the Receiver, and the shanck of the Cock, was filled with the Cement; and so we have dispatched the first and upper part of the Engine. The undermost remaining part consists of a Frame, and of a sucking Pump, or as we formerly called it, an Air Pump, supported by it: The Frame is of Wood, small, but very strong, consisting of three legs, (111) so placed, that one side of it may stand perpendicular, that the free motion of the hand may not be hindered. In the midst of which frame, is transversly nailed a board, (222) which may not improperly be called a Midriff, upon which rests, and to which is strongly fastened, the main part of the Pump itself, which is the only thing remaining to be described. The Pump consists of four parts, a hollow Cylindre, a Sucker, a handle to move that Sucker, and a valve. The Cylindre was (by a pattern) cast of brass; it is in length about 14 inches, thick enough to be very strong, notwithstanding the Cylindrical cavity left within it; this cavity is about three inches Diameter, and makes as exact a Cylindre as the Artificer was able to boar. This hollow Cylindre is fitted with a sucker, (4455) consisting of two parts, the one (44) somewhat less in Diameter then the cavity of the Cylindre, upon which is nailed a good thick piece of tanned shoe Leather, which will go so close to the Cylindre, that it will need to be very forcibly knocked and rammed in, if at any time it be taken out, which is therefore done, that it may the more exactly hinder the Air from insinuating itself betwixt it and the sides of the Cylindre whereon it is to move. To the midst of this former part of the Sucker is strongly fastened the other, namely a thick and narrow plate of Iron, (55) somewhat longer than the Cylindre, one of whose edges is smooth, but at the other edge it is indented (as I may so speak) with a row of teeth delineated in the Scheme, into whose intervals are to be fitted, the teeth of a small Iron nut, (〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉) (as Tradesmen call it) which is fastened by two staples (22) to the under side of the formerly mentioned transverse board (222) on which the Cylindre rests, and is turned to and fro by the third piece of this Pump, namely, the handle or manubrium, (7) of which the Figure gives a sufficient description. The fourth and last part of this Cylindre, is the Valve, (R) consisting of a hole bored through at the top of the Cylindre, a little tapering towards the cavity; into which hole is ground a tapering Peg of brass, to be thrust in, and taken out at pleasure. The Engine being thus described, it will be requisite to add, that something is wont to be done before it be set on work, for the more easy moving of the Sucker, and for the better exclusion of the outward Air: which when the Vessel gins to be exhausted, is much more difficult to be kept out then one would easily imagine. There must then be first poured in at the top of the Receiver a little salad oil, partly to fill up any small intervals that may happen to be betwixt the contiguous surfaces of the internal parts of the Stop-cock: And partly that it may be the more easy to turn the Key (S) backwards and forwards. Pretty store of oil must also be poured into the Cylindre, both that the Sucker may slip up and down in it the more smoothly and freely, and that the Air might be the better hindered from getting in between them: And for the like reasons, a little oil is to be used also about the Valve. Upon which occasion, it would not be omitted (for it is strange) that oftentimes, when neither the pouring in of water, nor even of oil alone, proved capable to make the Sucker move easily enough in the Cylinder; a mixture of both those Liquors would readily (sometimes even to admiration) perform the desired effect. And lastly, the brass cover of the Receiver, being put into the brass ring formerly described, that no Air may get between them, it will be very requisite to plaster over very carefully the upper edges of both, with the plaster formerly mentioned, or some other as close, which is to be spread upon the edges with a hot Iron; that being melted, it may run into and fill up all the crannies, or other little cavities, at which the Air might otherwise get entrance. All things being thus fitted, and the lower shank (O) of the stop-cock being put into the upper Orifice of the Cylinder (&), into which it was exactly ground; the Experimenter is first, by turning the handle, to force the Sucker to the top of the Cylinder, that there may be no Air left in the upper part of it▪ Than shutting the Valve with the Plug, and turning the other way, he is to draw down the Sucker to the bottom of the Cylinder; by which motion of the Sucker, the Air that was formerly in the Cylinder being thrust out, and none being permitted to succeed in its room, 'tis manifest that the cavity of the Cylinder must be empty, in reference to the Air: So that if thereupon the Key of the Stop-cock be so turned, as that through the perforation of it, a free passage be opened betwixt the Cylinder and the Receiver, part of the Air formerly contained in the Receiver, will nimbly descend into the Cylinder. And this Air, being by the turning back of the Key hindered from the returning into the Receiver, may, by the opening of the Valve, and forcing up of the Sucker to the top of the Cylinder again, be driven out into the open Air. And thus by the repetition of the motion of the Sucker upward and downward, and by opportunely turning the Key, and stopping the Valve, as occasion requires, more or less Air may be sucked out of the Receiver, according to the exigency of the Experiment, and the intention of him that makes it. Your Lordship will, perhaps, think that I have been unnecessarily prolix in this first part of my Discourse: But if you had seen how many unexpected difficulties we found to keep out the external Air, even for a little while, when some considerable part of the internal had been sucked out; You would peradventure allow that I might have set down more circumstances than I have, without setting down any, whose knowledge, he that shall try the Experiment may not have need of. Which is so true, that, before we proceed any further, I cannot think it unseasonable to advertise Your Lordship, that there are two chief sorts of Experiments, which we designed in our Engine to make trial of: The one, such as may be quickly dispatched, and therefore may be tried in our Engine, though it leak a little; because the Air may be faster drawn out, by nimbly plying the Pump, than it can get in at undiscerned leaks; I say at undiscerned leaks, because such as are big enough to be discovered can scarce be uneasy to be stopped. The other sort of Experiments consists of those that require not only that the internal Air be drawn out of the Receiver, but that it be likewise for a long time kept out of it▪ Such are the preservation of Animal and other Bodies therein, the germination and growth of Vegetables, and other trials of several sorts, which it is apparent cannot be well made unless the external Air can, for a competent while, be excluded: Since even at a very small leak there may enough get in, to make the Vacuum soon lose that name; by which I here declare once for all, that I understand not a space wherein there is no body at all, but such as is either altogether, or almost totally void of Air. Now this distinction of Experiments I thought fit to premise to the ensuing Narratives, because upon trial, we found it so exceeding (and scarce imaginable) difficult a matter, to keep out the Air from getting at all in at any imperceptible hole or flaw whatsoever, in a Vessel immediately surrounded with the compressed Atmosphere, that in spite of all our care and diligence, we never were able totally to exhaust the Receiver, or keep it when it was almost empty, any considerable time, from leaking more or less: although (as we have lately intimated) by unwearyed quickness in plying the Pump, the internal Air can be much faster drawn out then the external can get in, till the Receiver come to be almost quite empty. And that's enough to enable men to discover hitherto unobserved Phaenomena of Nature. The Experiments therefore of the first sort, will, I fear, prove the only ones wherewith my Avocations will allow me to entertain Your Lordship in this Letter. For till your further Commands shall engage me to undertake, by God's permission, such an Employment, and more leisure shall better fit me for it, I know not whether I shall be in a condition to try what may be done, to enable me to give you some account of the other sort of Experiments also. Experiment 1. TO proceed now to the Phaenomena, exhibited to us by the Engine above described; I hold it not unfit to begin with what does constantly and regularly offer itself to our observation, as depending upon the Fabric of the Engine itself, and not upon the nature of this or that particular Experiment which 'tis employed to try. First, Then upon the drawing down of the Sucker, (the Valve being shut) the Cylindrical space, deserted by the Sucker, is left devoid of Air; and therefore, upon the turning of the Key, the Air contained in the Receiver rushes into the emptied Cylinder, till the Air in both those Vessels be brought to about an equal measure of dilatation. And therefore, upon shutting the Receiver by returning the Key, if you open the Valve, and force up the Sucker again, you will find, that after this first exsuction you will drive out almost a whole Cylinder full of Air: But at the following exsuctions, you will draw less and less of Air out of the Receiver into the Cylinder, because that there will still remain less and less Air in the Receiver itself; and consequently, the Particles of the remaining Air, having more room to extend themselves in, will less press out one another. This you will easily perceive, by finding, that you still force less and less Air out of the Cylinder; so that when the Receiver is almost exhausted, you may force up the Sucker almost to the top of the Cylinder, before you will need to unstop the Valve to let out any Air: And if at such time, the Valve being shut, you let go the handle of the Pump, you will find the Sucker forcibly carried up to the top of the Cylinder, by the protrusion of the external Air; which, being much less rarified than that within the Cylinder, must have a more forcible pressure upon the Sucker, than the internal is able to resist: And by this means you may know how far you have emptied the Receiver. And to this we may add, on this occasion, that constantly upon the turning of the Key to let out the Air from the Receiver, into the emptied Cylinder, there is immediately produced a considerably brisk noise, especially whilst there is any plenty of Air in the Receiver. For the more easy understanding of the Experiments tryable by our Engine, I thought it not superfluous, nor unseasonable in the recital of this first of them, to insinuate that notion by which it seems likely that most, if not all, of them will prove explicable. Your Lordship will easily suppose, that the Notion I speak of is, That there is a Spring, or Elastical power in the Air we live in. By which 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 or Spring of the Air; that which I mean is this: That our Air either consists of, or at least abounds with, parts of such a nature, that in case they be bend or compressed by the weight of the incumbent part of the Atmosphere, or by any other Body, they do endeavour, as much as in them lies, to free themselves from that pressure, by bearing against the contiguous Bodies that keep them bend; and, assoon as those Bodies are removed or reduced to give them way, by presently unbending and stretching out themselves, either quite, or so far forth as the contiguous Bodies that resist them will permit, and thereby expanding the whole parcel of Air, these elastical Bodies compose. This Notion may perhaps be somewhat further explained, by conceiving the Air near the Earth to be such a heap of little Bodies, lying one upon another, as may be resembled to a Fleece of Wool. For this (to omit other likenesses betwixt them) consists of many slender and flexible Hairs; each of which, may indeed, like a little Spring, be easily bend or rolled up; but will also, like a Spring, be still endeavouring to stretch itself out again. For though both these Hairs, and the Aerial Corpuscles to which we liken them, do easily yield to external pressures; yet each of them (by virtue of its structure) is endowed with a Power or Principle of self-Dilatation; by virtue whereof, though the hairs may by a Man's hand be bend and crowded closer together, and into a narrower room than suits best with the nature of the Body: Yet whilst the compression lasts, there is in the fleece they compose an endeavour outwards, whereby it continually thrusts against the hand that opposes its Expansion. And upon the removal of the external pressure, by opening the hand more or less, the compressed Wool does, as it were, spontaneously expand or display itself towards the recovery of its former more lose and free condition, till the Fleece have either regained its former Dimensions, or at least, approached them as near as the compressing hand (perchance not quite opened) will permit. This Power of self-Dilatation, is somewhat more conspicuous in a dry Sponge compressed, then in a Fleece of Wool. But yet we rather chose to employ the latter, on this occasion, because it is not like a Sponge, an entire Body, but a number of slender and flexible Bodies, loosely complicated, as the Air itself seems to be. There is yet another way to explicate the Spring of the Air, namely, by supposing with that most ingenious Gentleman, Monsieur Des Cartes, That the Air is nothing but a Congeries or heap of small and (for the most part) of flexible Particles; of several sizes, and of all kind of Figures which are raised by heat (especially that of the Sun) into that fluid and subtle Etherial Body that surrounds the Earth; and by the restless agitation of that Celestial Matter wherein those Particles swim, are so whirled round, that each Corpuscle endeavours to beat off all others from coming within the little Sphere requisite to its motion about its own Centre; and (in case any, by intruding into that Sphere shall oppose its free Rotation) to expel or drive it away: So that according to this Doctrine, it imports very little, whether the particles of the Air have the structure requisite to Springs, or be of any other form (how irregular soever) since their Elastical power is not made to depend upon their shape or structure, but upon the vehement agitation, and (as it were) brandishing motion, which they receive from the fluid Ether that swiftly flows between them, and whirling about each of them (independently from the rest) not only keeps those slender Aërial Bodies separated and stretched out (at least, as far as the Neighbouring ones will permit) which otherwise, by reason of their flexibleness and weight, would flag or curl; but also makes them hit against, and knock away each other, and consequently require more room, then that which if they were compressed, they would take up. By these two differing ways, my Lord, may the Spring of the Air be explicated. But though the former of them be that, which by reason of its seeming somewhat more easy, I shall for the most part make use of in the following Discourse: yet am I not willing to declare peremptorily for either of them, against the other. And indeed, though I have in another Treatise endeavoured to make it probable, that the returning of Elastical Bodies (if I may so call them) forcibly bend, to their former position, may be Mechanically explicated: Yet I must confess, that to determine whether the motion of Restitution in Bodies, proceed from this, That the parts of a Body of a peculiar Structure are put into motion by the bending of the spring, or from the endeavour of some subtle ambient Body, whose passage may be opposed or obstructed, or else it's pressure unequally resisted by reason of the new shape or magnitude, which the bending of a Spring may give the Pores of it: To determine this, I say, seems to me a matter of more difficulty, then at first sight one would easily imagine it. Wherefore I shall decline meddling with a subject, which is much more hard to be explicated, then necessary to be so, by him, whose business it is not, in this Letter, to assign the adequate cause of the Spring of the Air, but only to manifest, That the Air has a Spring, and to relate some of its effects. I know not whether I need annex that, though either of the abovementioned Hypotheses, and perhaps some others, may afford us an account plausible enough of the Air-spring; yet I doubt, whether any of them gives us a sufficient account of its Nature. And of this doubt, I might here mention some Reasons, but that, peradventure, I may (God permitting) have a fit occasion to say something of it elsewhere. And therefore I should now proceed to the next Experiment, but that I think it requisite, first, to suggest to your Lordship what comes into my thoughts, by way of Answer to a plausible Objection, which I foresee you may make against our proposed Doctrine, touching the Spring of the Air. For it may be alleged, that though the Air were granted to consist of Springy Particles (if I may so speak) yet thereby we could only give an account of the Dilatation of the Air in Wine-Guns and other pneumatical Engines wherein the Air has been compressed, and its Springs violently bend by an apparent external force; upon the removal of which, 'tis no wonder that the Air should, by the motion of restitution, expand itself till it have recovered its more natural dimensions: whereas in our above mentioned first Experiment, and in almost all others tryable in our Engine, it appears not that any compression of the Air preceded its spontaneous Dilatation or Expansion of itself. To remove this difficulty, I must desire Your Lordship to take notice, that of whatever nature the Air, very remote from the Earth, may be, and whatever the Schools may confidently teach to the contrary, yet we have divers Experiments to evince, that the Atmosphere we live in is not (otherwise then comparatively to more ponderous Bodies) light, but heavy: And did not their gravity hinder them, it appears not why the steams of the Terraqueous Globe, of which our Air in great part consists, should not rise much higher than the Refraction of the Sun, and other Stars give men ground to think, that the Atmosphere, even in the judgement of those Recent Astronomers, who seem willing to enlarge its bounds as much as they dare, does reach. But lest you should expect my seconding this Reason by Experience; and lest you should object, That most of the Experiments that have been proposed to prove the gravity of the Air, have been either barely proposed, or perhaps not accuratly tried; I am content, before I pass further, to mention here, That I found a dry lambs-bladder containing near about two thirds of a pint, and compressed by a packthread tied about it, to lose a grain and the eighth part of a grain of its former weight, by the recess of the Air upon my having pricked it: And this with a pair of Scales, which when the full Bladder and the correspondent weight were in it, would manifestly turn either way with the 32 part of a grain. And if it be further objected, That the Air in the Bladder was violently compressed by the Packthread and the sides of the Bladder, we might probably (to wave prolix answers) be furnished with a Reply, by setting down the differing weight of our Receiver, when emptied and when full of uncompressed Air, if we could here procure scales fit for so nice an experiment; since we are informed, that in the Germane Experiment, commended at the beginning of this Letter, the Ingenious Tryers of it found, That their Glass Vessel, of the capacity of 32 measures, was lighter when the Air had been drawn out of it, than before, by no less than one ounce and 1/10 that is, an ounce and very near a third: But of the gravity of the Air, we may elsewhere have occasion to make further mention. Taking it then for granted that the Air is not devoid of weight, it will not be uneasy to conceive, that that part of the Atmosphere wherein we live, being the lower part of it, the Corpuscles that compose it, are very much compressed by the weight of all those of the like nature that are directly over them, that is, of all the Particles of Air, that being piled up upon them, reach to the top of the Atmosphere. And though the height of this Atmosphere, according to the famous Kepler, and some others, scarce exceeds eight common miles; yet other eminent and later Astronomers, would promote the confines of the Atmosphere, to exceed six or seven times that number of miles. And the diligent and learned Riviolo makes it probable, that the Atmosphere may, at least in divers places, be at least 50 miles high. So that according to a moderate estimate of the thickness of the Atmosphere, we may well suppose, that a Column of Air, of many miles in height, leaning upon some springy Corpuscles of Air here below, may have weight enough to bend their little springs, and keep them bend: As, to resume our former comparison, if there were fleeces of Wool piled up to a mountainous height upon one another, the Hairs that compose the lowermost locks which support the rest, would, by the weight of all the Wool above them, be as well strongly compressed, as if a man should squeeze them together in his hands, or employ any such other moderate force to compress them. So that we need not wonder, that upon the taking off the incumbent Air from any parcel of the Atmosphere here below, the Corpuscles, whereof that undermost Air consists, should display themselves, and take up more room than before. And if it be objected, That in Water, the weight of the upper and of the lower part is the same: I answer, That besides that it may be well doubted whether the observation, by reason of the great difficulty have been exactly made, there is a manifest disparity betwixt the Air and Water: For I have not found, that upon an Experiment purposely made, (and in another Treatise Recorded) that Water will suffer any considerable compression; whereas we may observe in Windguns (to mention now no other Engines) that the Air will suffer itself to be crowded into a comparatively very little room; in so much, that a very diligent Examiner of the Phaenomena of Windguns would have us believe, that in one of them, by condensation, he reduced the Air into a space at least eight times narrower than it before possessed. And to this, if we add a noble Phaenomenon of the Experiment De Vacuo; these things put together, may for the present suffice to countenance our Doctrine. For that noble Experimenter, Monsieur Pascal (the Son) had the commendable Curiosity to cause the Torricellian Experiment to be tried at the foot, about the middle, and at the top of that high Mountain (in Auvergne, if I mistake not) commonly called Le Puy de Domme; whereby it was found, That the Mercury in the Tube fell down lower, about three inches, at the top of the Mountain then at the bottom. And a Learned Man a while since informed me, That a great Virtuoso, friend to us both, has, with not unlike success, tried the same Experiment in the lower and upper parts of a Mountain in the West of England: Of which, the reason seems manifestly enough to be this, That upon the tops of high Mountains, the Air which bears against the restagnant Quicksilver, is less pressed by the less ponderous incumbent Air; and consequently is not able totally to hinder the descent of so tall and heavy a Cylinder of Quicksilver, as at the bottom of such Mountains did but maintain an Aequilibrium with the incumbent Atmosphere. And if it be yet further Objected against what hath been proposed touching the compactness and pressure of the Inferior Air; That we find this very Air to yield readily to the motion of little Flies, and even to that of Feathers, and such other light and weak Bodies; which seems to argue, that the particles of our Air are not so compressed as we have represented them, especially, since by our former Experiment it appears, that the Air readily dilated itself downward, from the Receiver into the Pump, when 'tis plain, that it is not the incumbent Atmosphere, but only the subjacent Air in the brass Cylinder that has been removed: If this, I say, be objected, we may reply, That when a man squeezes a Fleece of Wool in his hand, he may feel that the Wool incessantly bears against his hand, as that which hinders the hairs it consists of, to recover their former and more natural extent. So each parcel of the Air about the Earth, does constantly endeavour to thrust away all those contiguous Bodies, whether Aërial or more gross, that keep them bend, and hinder the expansion of its parts, which will dilate themselves or fly abroad towards that part, whether upwards or downwards, where they find their attempted Dilatation of themselves less resisted by the neihgboring Bodies. Thus the Corpuscles of that Air we have been all this while speaking of, being unable, by reason of their weight, to ascend above the Convexity of the Atmosphere, and by reason of the resistance of the surface of the Earth and Water, to fall down lower, they are forced, by their own gravity and this resistance, to expand and diffuse themselves about the Terrestrial Globe; whereby it comes to pass, that they must as well press the contiguous Corpuscles of Air that on either side oppose their Dilatation, as they must press upon the surface of the Earth, and, as it were recoiling thence, endeavour to thrust away those upper particles of Air that lean upon them. And as for the easy yielding of the Air to the Bodies that move in it, if we consider that the Corpuscles whereof it consists, though of a springy nature, are yet so very small, as to make up (which 'tis manifest they do) a fluid Body, it will not be difficult to conceive, that in the Air, as in other Bodies that are fluid, the little Bodies it consists of are in an almost restless motion, whereby they become (as we have more fully discoursed in another Treatise) very much disposed to yield to other Bodies, In a Discourse touching fluidity and firmness. or easy to be displaced by them, and that the same Corpuscles are likewise so variously moved, as they are entire Corpuscles, that if some strive to push a Body placed among them towards the right hand (for instance) others, whose motion has an opposite determination, as strongly thrust the same Body towards the left; whereby neither of them proves able to move it out of its place, the pressure on all hands being reduced as it were to an Aequilibrium: so that the Corpuscles of the Air must be as well sometimes considered under the notion of little Springs, which remaining bend, are in their entire bulk transported from place to place; as under the notion of Springs displaying themselves, whose parts fly abroad whilst as to their entire bulk they scarce change place: As the two ends of a Bow, shot off, fly from one another, whereas the Bow itself may be held fast in the Archers hand; and that it is the equal pressure of the Air on all sides upon the Bodies that are in it, which causes the easy Session of its parts, may be argued from hence: That if by the help of our Engine the Air be but in great part, though not totally drawn away from one side of a Body without being drawn away from the other; he that shall think to move that Body too and fro, as easily as before, will find himself much mistaken. In verification of which we will, to divert your Lordship a little, mention here a Phaenomenon of our Engine, which even to divers ingenious persons has at first sight seemed very wonderful. THe thing that is wont to be admired, Experiment 2. and which may pass for our second Experiment is this, That if, when the Receiver is almost empty, a By-stander be desired to lift up the brass Key (formerly described as a stopple in the brass Cover) he will find it a very difficult thing to do so, if the Vessel be well exhausted; and even when but a moderate quantity of Air has been drawn out, he will, when he has lifted it up a little, so that it is somewhat lose from the sides of the lip or socket, which (with the help of a little oil) it exactly filled before, he will (I say) find it so difficult to be lifted up, that he will imagine there is some great weight fastened to the bottom of it. And if (as sometimes has been done for merriment) only a Bladder be tied to it, it is pleasant to see how men will marvel that so light a Body, filled at most but with Air, should so forcibly draw down their hand as if it were filled with some very ponderous thing: whereas the cause of this pretty Phaenomenon seems plainly enough to be only this, That the Air in the Receiver, being very much dilated, its Spring must be very much weakened, and consequently it can but faintly press up the lower end of the stopple, whereas the Spring of the external Air being no way debilitated, he that a little lifts up the stopple must with his hand support a pressure equal to the disproportion betwixt the force of the internal expanded Air, and that of the Atmosphere incumbent upon the upper part of the same key or stopple: And so men being unused to find any resistance, in lifting things up, from the free Air above them, they are forward to conclude that that which depresses their hands must needs be some weight, though they know not where placed, drawing beneath it. And that we have not mis-assigned the cause of this Phaenomenon seems evident enough by this; That as Air is suffered by little and little to get into the Receiver, the weight that a man fancies his hand supports is manifestly felt to decrease more and more, the internal Air by this recruit approaching more to an Aequilibrium with the external, till at length the Receiver growing again full of Air, the stopple may be lifted up without any difficulty at all. By several other of the Experiments afforded us by our Engine, the same notion of the great and equal pressure of the free Air upon the Bodies it environs, might be here manifested, but that we think it not so fit to anticipate such Experiments: And therefore shall rather employ a few lines to clear up a difficulty touching this matter, which we have observed to have troubled some even of the Philosophical and Mathematical Spectators of our Engine, who have wondered that we should talk of the Air tightly shut up in our Receiver, as if it were all one with the pressure of the Atmosphere; whereas the thick and close body of the Glass, wholly impervious to the Air, does manifestly keep the incumbent Pillar of the Atmosphere from pressing in the least upon the Air within the Glass, which it can not where come to touch. To elucidate a little this matter, let us consider, That if a man should take a fleece of Wool, and having first by compressing it in his hand reduced it into a narrower compass, should nimbly convey and shut it close up into a Box just fit for it, though the force of his hand would then no longer bend those numerous springy Body's that compose the Fleece, yet they would continue as strongly bend as before, because the Box they are enclosed in would as much resist their re-expanding of themselves, as did the hand that put them in. For thus we may conceive, that the Air being shut up, when its parts are bend by the whole weight of the incumbent Atmosphere, though that weight can no longer lean upon it, by reason it is kept off by the Glass, yet the Corpuscles of the Air within that Glass continue as forcibly bend as they were before their inclusion, because the sides of the Glass hinder them from displaying or stretching out themselves. And if it be objected that this is unlikely, because even Glass bubbles, such as are wont to be blown at the flame of a Lamp, exceeding thin and Hermetically sealed will not break; whereas it cannot be imagined that so thin a Prison of Glass could resist the Elastical force of all the included Air, if that Air were so compressed as we suppose. It may be easily replied, That the pressure of the inward Air against the Glass, is countervailed by the equal pressure of the outward against the same Glass. And we see in bubbles, that by reason of this an exceeding thin film of Water is often able, for a good while, to hinder the eruption of a pretty quantity of Air. And this may be also more conspicuous in those great Spherical bubbles that boys sometimes blow with Water, to which Soap has given a Tenacity. But that, if the pressure of the ambient Air were removed, the internal Air may be able to break thicker Glasses than those lately mentioned, will appear by some of the following Experiments; to which we shall therefore now hasten, having, I fear, been but too prolix in this Excursion, though we thought it not amiss to annex to our first Experiments some general Considerations touching the Spring of the Air, because (this Doctrine being yet a stranger to the Schools) not only we find not the thing itself to be much taken notice of; but of those few that have heard of it, the greater part have been forward to reject it, upon a mistaken Persuasion, that those Phaenomena are the effects of nature's abhorrency of a Vacuum, which seem to be more fitly ascribeable to the weight and Spring of the Air. Experiment 3. WE will now proceed to observe that though, by the help of the handle, the Sucker be easily drawn down to the bottom of the Cylinder; yet, without the help of that Leaver, there would be required to the same effect, a force or weight great enough to surmount the pressure of the whole Atmosphere: Since otherwise the Air would not be driven out of its place, when none is permitted to succeed into the place deserted by the Sucker. This seems evident, from the known Torricellian Experiment, in which, if the inverted Tube of Mercury be but 25 Digits high, or somewhat more, the Quicksilver will not fall but remain suspended in the Tube; because it cannot press the subjacent Mercury with so great a force, as does the incumbent Cylinder of the Air reaching thence to the top of the Atmosphere: Whereas, if the Cylinder of Mercury were three or four digits longer, it would overpower that of the external Air, and run out into the Vesseled Mercury, till the two Cylinders came to an Aequilibrium, and no further. Hence we need not wonder, that though the Sucker move easily enough up and down in the Cylinder by the help of the Manubrium; yet if the Manubrium be taken off, it will require a considerable strength to move it either way. Nor will it seem strange, that if, when the Valve and Stop-cock are well shut, you draw down the Sucker, and then let go the Manubrium; the Sucker will, as it were of itself, re-ascend to the top of the Cylinder, since the spring of the external Air finds nothing to resist its pressing up the Sucker. And for the same reason, when the Receiver is almost evacuated, though, having drawn down the Sucker, you open the way from the Receiver to the Cylinder, and then intercept that way again by returning the Key; the Sucker will, upon the letting go the Manubrium, be forcibly carried up almost to the top of the Cylinder: Because the Air within the Cylinder, being equally dilated and weakened with that of the Glass, is unable to withstand the pressure of the external Air, till it be driven into so little space, that there is an Aequilibrium betwixt its force and that of the Air without. And congruously hereunto we find, that in this case, the Sucker is drawn down with little less difficulty, then if the Cylinder, being devoid of Air, the Stop-cock were exactly shut: We might take notice of some other things, that depend upon the Fabric of our Engine itself; but to shun prolixity, we will, in this place, content ourselves to mention one of them, which seems to be of greater moment than the rest, and it is this; that when the Sucker has been impelled to the top of the Cylinder, and the Valve is so carefully stopped, that there is no Air left in the Cylinder above the Sucker: If then the Sucker be drawn to the lower part of the Cylinder, he that manages the Pump finds not any sensibly greater difficulty to depress the Sucker, when it is nearer the bottom of the Cylinder, than when it is much further off. Which circumstance we therefore think fit to take notice of, because an eminent Modern Naturalist hath taught, that, when the Air is sucked out of a Body, the violence wherewith it is wont to rush into it again, as soon as it is allowed to re-enter, proceeds mainly from this; That the pressure of the ambient Air is strengthened upon the accession of the Air sucked out; which, to make itself room, forces the neighbouring Air to a violent-subingression of its parts: which, if it were true, he that draws down the Sucker, would find the resistance of the external Air increased as he draws it lower, more of the displaced Air being thrust into it to compress it. But, by what has been discoursed upon the first Experiment, it seems more probable, that without any such strengthening of the pressure of the outward Air, the taking quite away or the debilitating of the resistance from within, may suffice to produce the effects under consideration. But this will perhaps be illustrated by some or other of our future Experiments, and therefore shall be no longer insisted on here. HAving thus taken notice of some of the constant Phaenomena of our Engine itself, Experiment 4. let us now proceed to the Experiments tryable in it. We took then a Lamb's Bladder large, well dried, and very limber, and leaving in it about half as much Air as it could contain, we caused the neck of it to be strongly tied, so that none of the included Air, though by pressure, could get out. This Bladder being conveyed into the Receiver, and the Cover luted on, the Pump was set a-work, and after two or three exsuctions of the ambient Air (whereby the Spring of that which remained in the Glass was weakened) the Imprisoned Air began to swell in the Bladder, and as more and more of the Air in the Receiver was, from time to time, drawn out; so did that in the Bladder more and more expand itself, and display the folds of the formerly flaccid Bladder: so that before we had exhausted the Receiver near so much as we could, the Bladder appeared as full and stretched, as if it had been blown up with a Quill. And that it may appear that this plumpness of the Bladder proceeded from the surmounting of the debilitated Spring of the ambient Air remaining in the Vessel, by the stronger Spring of the Air remaining in the Bladder; we Returned the Key of the Stop-cock, and by degrees allowed the external Air to return into the Receiver: Whereupon it happened, as was expected, that as the Air came in from without, the disturbed Air in the Bladder, was proportionably compressed into a narrower room, and the sides of the Bladder grew flaccid, till the Receiver having readmitted its wont quantity of Air, the Bladder appeared as full of wrinkles and cavities as before. This Experiment is much of the same nature with that which was some years ago said to be made by that eminent Geometrician Monsieur Roberval, with a Carp Bladder emptied and conveyed into a Tube, wherein the Experiment De Vacuo was afterwards tried, which ingenious Experiment of his justly deserves the thanks of those that have been, or shall be solicitous to discover the nature of the Air. But to return to our Experiment, we may take notice of this Circumstance in it, That after the Receiver has been in some measure emptied, the Bladder does, at each exsuction, swell much more conspicuously than it did at any of the first Exsuctions; insomuch that towards the end of the pumping, not only a great fold or cavity in the surface of the Bladder may be made, even by the stretching of the inward self-expanding Air: But we have sometimes seen, upon the turning of the Key to let the ambient Air pass out of the Receiver into the Cylinder, we have seen (I say) the Air in the Bladder suddenly expand itself so much and so briskly, that it manifestly lifted up some light Bodies that leaned upon it, and seemed to lift up the Bladder itself. Now because it has by very Learned Men been doubted whether the swelling of the Bladder may not have proceeded from the Dilatation of the included Air, but from the Texture of the Fibres, which, being wont to keep the Bladder extended when the Animal to whom it belonged was alive, may be supposed in our Experiment to have returned, like so many Springs to their wont extent, upon the removal of the Ambient Air that compressed and bend them: because this, I say, has been doubted, we thought fit to make this further trial. We let down into the Receiver with the forementioned Bladder two other much smaller, and of the same kind of Animal; the one of these was not tied up at the neck that there might be liberty left to the Air that was not squeezed out (which might amount to about a fifth part of what the Bladder held before) to pass out into the Receiver: The other had the sides of it stretched out and pressed together, almost into the form of a Cup, that they might intercept the less Air betwixt them, and then was strongly tied up at the neck: This done, and the Air being in some measure sucked of the Pneumatical Glass (if I may so call it) the Bladder, mentioned at the beginning of our Experiment, appeared extended every way to its full Dimensions; whereas neither of the two others did remarkably swell, and that whose neck was not tied seemed very little, if at all less wrinkled than when it was put in. We made likewise a strong Ligature about the middle of a long Bladder partly emptied, and upon the drawing the Air out of the Receiver, could observe no such swelling betwixt the Ligature and the Neck of the Bladder, which had been purposely left open, as betwixt the same Ligature and the bottom of the Bladder, whence the included Air could no way get out. But a further and sufficient manifestation whence the intumescence of the Bladder proceeds, may be deduced from the following Experiment. TO try then at once both what it was that expanded the Bladder, Experiment 5. and what a powerful Spring there is even in the Air we are wont to think uncompressed, we caused a Bladder dry, well tied and blown moderately full, to be hung in the Receiver by one end of a string, whose other end was fastened to the inside of the Cover: and upon drawing out the ambient Air, that pressed on the Bladder; the internal Air not finding the wont resistance, first swelled and distended the Bladder, and then broke it, with so wide and crooked a rent, as if it had been forcibly torn asunder with hands. After which a second Bladder being conveyed in, the Experiment was repeated with like success: And I suppose it will not be imagined that in this case the Bladder was broken by its own Fibres, rather than by the Imprisoned Air. And of this Experiment these two Phaenomena may be taken notice of: The one, that the Bladder at its breaking gave a great report, almost like a Craker: And the other, That the Air contained in the Bladder, had the power to break it with the mentioned Impetuosity, long before the ambient Air was, all or near all, drawn out of the Receiver. But, to verify what we say in another Discourse, where we show, That even true Experiments may, by reason of the easy mistake of some unheeded Circumstance, be unsuccessfully tried; we will Advertise, on this occasion, that we did oftentimes in vain try the breaking of Bladders, after the manner abovementioned: Of which the cause appeared to be this, That the Bladders we could not break, having been brought us ready blown from those that sold them, were grown dry before they came to our hands: whence it came to pass, that, if we afterwards tied them very hard, they were apt to fret and so become unserviceable; and if we tied them but moderately hard, their stiffness kept them from being closed so exactly, but that when the included Air had in the exhausted Receiver distended them as much as easily it could, it would in part get out between the little wrinkles of the Sphincter of t●e Neck: Whence also it usually happened, that, upon the letting in the Air from without, the Bladders appeared more flaccid and empty then before they were put in; whereas when the Bladders were brought us moist from the Butchers, we could, without injuring them, tie their necks so close, that none of the Air once blown in, could get out of them, but by violently breaking them. It will not be amiss on this occasion to point at something which may deserve a more deliberate Speculation than we can now afford it; namely that the Elastical Power of the s●me Quantity of Air may be as well Increased by the Agitation of the Aërial Particles (whether only moving them more swiftly and scattering them, or also extending or stretching them out, I determine not) within an every way enclosing and yet yielding Body; as Displayed by the withdrawing of the Air that pressed it without. For we found that a Bladder, but moderately filled with Air and strongly tied, being a while held near the Fire, not only grew exceeding turgid and hard, but afterwards, being approached nearer to the Fire, suddenly broke with so loud and vehement a noise, as stonyed those that were by, and made us, for a while after, almost deaf. Experiment 6. HAving thus seen that the Air has an Elastical Power, we were next desirous to know in some measure how far a parcel of Air might by this its own Spring be dilated. And though we were not provided of Instruments fit to measure the dilatation of the Air any thing accurately, yet because an imperfect measure of it was more desirable than none at all, we devised the following Method as very easily practicable. We took a limber Lamb's Bladder which was thoroughly wetted in fair Water, that the sides of it being squeezed 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 drachmas of Water) the Bladder being first so compressed, that all the included Air was only in the Glass, without being pressed there; then the Pump being set a-work after a few exsuctions, the Air in the little Viol began to dilate itself and produce a small Tumour in the Neck of the Bladder; and as the ambient Air was more and more drawn away, so the included Air penetrated further and further into the Bladder, and by degrees lifted up the sides and displayed its folds, till at length it seemed to have blown it up to its full extent: whereupon the external Air, being permitted to flow back into the Reciver, repulsed the Air that had filled 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 Drachmas and an half: Five Drachmas whereof were abovementioned to be the contents of the Bottle. So that in this Experiment, when the Air had most extended the Bladder, it possessed in all above nine times as much room as it did when it was put into the Receiver. And it would probably have much enlarged 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 appeared 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 further expansion of the Air, especially supposing the dilatation not to be restrained 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 abovementioned Bladder, which was much to narrow to allow the Air its utmost distension. We took then first a Cylindrical Pipe of Glass, whose bore was about a quarter of an Inch in Diameter: this Pipe was so bend and doubled, that, notwithstanding its being about two foot in length, it might have been shut up into a small Receiver, not a Foot high: But by misfortune it cracked in the cooling, whereby we were reduced to make use of one part which was strait and entire, but exceeded not six or seven Inches. This little Tube was open at one end; and at the other, where it was Hermetically sealed, had a small Glass bubble to receive the Air whose dilatation was to be measured. Along the side of this Tube was pasted a strait narrow piece of Parchment, divided into twenty six equal parts, marked with black Lines and Figures, that by them might be measured both the included Air and its dilatation. Afterwards we filled the Tube with Water almost to the top, and stopping the open end with a Finger, and inverting the Tube, the Air was permitted to ascend to the abovementioned 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 enabled 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 covered with Water about half an Inch high; we included both Glasses into a small and slender Receiver, and caused the Pump to be set a-work. The event was, That at the first exsuction of the Air there appeared not any expansion of the bubble, comparable to what appeared 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 itself much further: Wherefore we took out the little Tube, and found that besides the twenty six divisions formerly mentioned, 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 had taken up one and thirty times as much room as before, and yet seemed 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 itself to have possessed sixty and odd times its former room. These two Experiments are mentioned 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 happened 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 sealed at the slender end, was almost filled with Water; and after the above-related manner a bubble was conveyed 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 a-work, after some exsuctions, not only the Air manifestly appeared extended below the surface of the subjacent Water; but one of the Bystanders 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 observed how at the unperceived leaks of the Receiver the Air got in so fast, that it very quickly impelled up the Water to the top of the Tube, excepting a little space whereinto that bubble was repulsed, which had so lately possessed the whole Tube; this Air at the slender end appeared to be a Cylinder of ⅚ parts of an Inch in length; but when the Pipe was taken out and turned upside down, it appeared at the other end inferior in bulk to a Pea. These things being thus done we took (to make the Experiment the more exactly) a small pair of Scales, such as Goldsmith's use to weigh Gold Coin in; and weighing the Tube and Water in it, we found them to amount to one Ounce thirty Grains and an half: Then we poured in as much Water as served to fill up the Tube, wherein before we had left as much space unfilled up as was possessed by the bubble, and weighing again the Pipe and Water, we found the weight increased only by one Grain. Lastly, pouring out the Water, and carefully freeing the Pipe from it (which yet we could not perfectly do) we weighed the Glass alone, and found it to want two Drachmas and thirty two Grains of its former weight: So that the bubble of Air taking up the room but of one Grain in weight of Water, it appeared that the Air by its own 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 was so rarified, as to take up one hundred fifty two times as much room as it did before: though it were then compressed by nothing but the ordinary pressure of the contiguous Air. I know not whether it be requisite to take notice, that this Experiment was made indeed in a moist Night, but in a Room, in whose Chimney there was burning a good Fire, which did perhaps somewhat rarify the Air of which the bubble consisted. It has seemed almost incredible which is related by the Industrious Mersennus, That the Air by the violence of heat, though as great as our Vessels can support without fusion, can be so dilated as to take up seventy times as much room as before: Wherefore because we were willing to have a confirmation of so strange a Phaenomenon; we once more conveyed into the Tube a bubble of the bigness of the former, and prosecuting the Experiment as before with the same Water, we observed that the Air did manifestly stretch itself so far, as to appear several times a good way below the surface of the Water in the Viol, and that too with a surface very convex toward the bottom of the Pipe. Nay, the Pump being plied a little longer, the Air did manifestly reach to that place where the bottom of the Tube leaned upon the bottom of the Viol, and seemed to knock upon it and rebound from it: Which Circumstances we add, partly that the Phaenomenon we have been relating may not be imputed to the bare subsiding of the Water that filled the Tube, upon the taking off the pressure of the ambient Air. And partly also that it may appear that if our Experiments have not been as accurately made as with fit Instruments might perhaps be possible; yet the expansion of the Air is likely to be rather greater then lesser than we have made it: Since the Air was able to press away the Water at the bottom of the Pipe, though that were about two Inches below the surface of the Water that was then in the Viol, and would have been at least as high in the Pipe, if the Water had only subsided and not been depressed: So that it seems not unlikely that if the Experiment could be so made, as that the expansion of the Air might not be resisted by the Neighbouring Bodies, it would yet enlarge its bounds, and perhaps stretch itself to two hundred times its former bulk, if not more. However, what we have now tried will, I hope, suffice to hinder divers of the Phaenomena of our Engine from being disinherited: Since in that part of the Atmosphere we live in, that which we call the free Air (and presume to be so uncompressed) is crowded into so very small a part of that space, which if it were not hindered it would possess. We would gladly have tried also whether the Air at its greatest expansion could be further rarified by heat; but do what we could, our Receiver leaked too fast to let us give ourselves any satisfaction in that particular. Experiment 7. TO discover likewise by the means of that pressure of the Air, both the strength of Glass, and how much interest the Figure of a Body may have in its greater or lesser Resistance to the pressure of other bodies, we made these further trials. We caused to be blown with a Lamp ● round Glass bubble, capable of containing, by guess, about five Ounces of Water, with a slender neck about the bigness of a Swans Quill, and it was purposely blown very thin, as Viols made with Lamps are wont to be, that the thinness of the matter might keep the roundness of the Figure from making the Vessel too strong. Then having moderately emptied the Receiver, and taken it out of the Pump, we speedily applied to the Orifice of the bottom of it the Neck of the newly mentioned Glass, carefully stopping the Crannies with melted Plaster, that no Air might get in at them: And after turning the Key of the Stop-cock, we made a free passage for the Air to pass out of the bubble into the Receiver: which it did with great celerity, leaving the bubble as empty as the Receiver itself; as appeared to us by some Circumstances not now to be insisted on. Notwithstanding all which, the Vessel, continuing as entire as before, gave us cause to wonder that the bare Roundness of the Figure should enable a Glass, almost as thin as Paper, to resist so great a pressure as that of the whole incumbent Atmosphere. And having reiterated the Experiment, we found again that the pressure of the ambient Body, thrusting all the parts inwards, made them, by reason of their arched Figure, so support one another, that the Glass remained as whole as at first. Now that the Figure of the Glass is of great moment in this matter, may be evinced by this other Experiment. Experiment 8. WE took a Glass Helmet or Alembick (delineated by the seventh Figure) such as Chemists use in Distillations, and containing by conjecture between two and three Pints: The Rostrum or Nose of it marked with (c) was Hermetically closed; and at the top of it was a hole, into which was fitted and cemented one of the Shanks of a middlesized Stop-cock; so that the Glass being turned upside-down, the wide Orifice (which in common Glass-Helmets is the only one) was upwards; and to that wide Orifice was fitted a cast Cover of Lead, which was carefully cemented on to the Glass: Then the other Shank of the Stop-cock being with Cement likewise fastened into the upper part of the Pump, the exsuction of the Air was endeavoured. But it was not long before, the remaining Air being made much too weak to balance the pressure of the ambient Air, the Glass was not without a great noise cracked almost half round, along that part of it where it began to bend inwards: As if in the Figure the crack had been made according to the Line (ab); and upon an endeavour to pump out more of the Air, the crack once began, appeared to run on further; though the Glass where it was broken seemed to be by conjecture above ten, some thought above twenty times as thick as the bubble mentioned in the foregoing Experiment. This will perhaps make it seem strange, that having taken another Glass bubble blown at the same time, and like for aught we discerned for size, thickness and Figure to that thin one formerly mentioned; and having sealed it up Hermetically, and suspended it in the Receiver, the exsuction of the ambient Air did not enable the imprisoned Air to break, or in the least to crack the bubble; though the Experiment were laboriously tried, and that several times with bubbles of other sizes: But that perhaps the heat of the Candle or Lamp wherewith such Glasses are Hermetically sealed, (not to mention the warmth of his hands that sealed it) might so rarify the contained Air, as much to weaken its Spring, may seem probable by the following Experiments. Experiment 9 WE took a Glass Viol. able to hold three or four Ounces of Water, and of the thickness usual in Glasses of that size; into the Neck of this was put a moderately slender Pipe of Glass, which was carefully fastened with a mixture of equal parts of Pitch and Rosin to the Neck of the Viol, and which reached almost to the bottom of it, as the sixth Figure declares. This Viol being upon a particular design filled with Water, till that came up in it a pretty deal higher than the lower end of the Pipe, was put into one of our small Receivers, (containing between a Pint and a Quart) in such manner as that the Glass Pipe, passing through a hole made purposely for it in the Leaden-Cover of the Receiver, was for the most part of it without the Vessel, which being exactly closed, the Pump was set a-work: But at the very first exsuction, and before the Sucker was drawn to the bottom of the Cylinder, there flew out of the Viol a piece of Glass half as broad as the Palm of a Man's Hand, and it was thrown out with such violence, that hitting against the Neighbouring side of the Receiver, it not only dashed itself to pieces, but cracked the very Receiver in many places, with a great noise that much surprised all that were in the Room. But it seemed that in so little a Receiver, the Air about the Viol being suddenly drawn out, the Air Imprisoned in the Vessel, having on it the whole pressure of the Atmosphere (to which by the Pipe open at both ends, It and the Water were exposed) and not having on the other side the wont pressure of the Ambient Air to balance that other pressure, the resistance of the Glass was finally surmounted, and the Viol once beginning to break where it was weakest, the external Air might rush in with violence enough to throw the cracked parcel so forcibly against the Neighbouring side of the Receiver, as to break that too. And this may be presumed sufficient to verify what we delivered in that part of our Appendix to the first Experiment, where we mentioned the almost equal pressure of the Air on either side of a thin Glass Vessel, as the cause of its not being broken by the forcible Spring of the contained Air. But yet that it be not suspected that chance had an interest in so odd an Experiment as we have been Relating, we will add that for farther satisfaction we reiterated it in a round Glass containing by guess about six ounces of water: this viol we put into such a small Receiver as was lately mentioned, in such manner as that the bottom of it rested upon the lower part of the pneumatical Glass, and the Neck came out through the Leaden-Cover of the same at a hole made purposely for it. But being made circumspect by the foregoing mischance, we had put the viol into a Bladder, before we put it into the Receiver to hinder this last named Glass from being endangered by the breaking of the other. Then the pneumatical vessel being closed so that no way was left for the outward Air to get into it, but by breaking through the Viol, into whose cavity it had free access by the mouth of it, (which was purposely left open,) the Sucker being nimbly drawn down, the external Air immediately pressed forcibly as well upon the Leaden-Cover as the Viol; and the Cover happening to be in one place a little narrower than the edge of the Pneumatical Glass, was depressed, and thrust into it so violently by the incumbent Air, that getting a little within the tapering Lip of the Glass, it did like a kind of Wedge, thrust out that side where it was depressed, so as, though the Receiver was new, to split it. This accident being thus mentioned upon the by to confirm what we formerly said touching the fitness or unfitness of Glasses of some Figures to resist the pressure of the Atmosphere; We will proceed to relate the remaining part of the Experiment, namely, That having fitted on a wider Cover to the same Receiver, and closed both that and the crack with Cement, we prosecuted the Experiment in the manner above related, with this success: That upon the quick depressing of the Sucker, the external Air burst the Body of the Viol in above a hundred pieces, many of them exceeding small, and that with such violence that we found a wide rent, besides many holes, made in the Bladder itself. And to evince that these Phaenomena were the effects of a limited and even moderate force, and not of such an abhorrency of a Vacuum as that to avoid it, many have been pleased to think that Nature must, upon occasion, exercise an almost boundless power; we afterwards purposely tried this Experiment with several Glasses somewhat thicker than those Viols, and found the event to verify our conjecture, that it would not succeed: for the Glasses were taken out as entire as they were put in. And here, My Lord, I hold it not unfit, upon occasion of the mention that has been made of our having employed small Receivers, and one of them, notwithstanding its being cracked, to annex these two Advertisements. First then, besides the great Pneumatical Glass so often mentioned, and the proportionate Stop-cock, we thought fit to provide ourselves of some small Receivers blown of Crystalline Glass, of several Shapes, and furnished with smaller Stop-cocks purposely made; and this we did upon hopes that when we had surmounted the difficulties to be met with in Cementing the Glasses to the Stop-cocks, and the Pneumatical Vessels to the Pump so tightly as is requisite for our purpose, we should from the smallness of our Receivers receive a fourfold Advantage. The first, that by reason of the slenderness of the Vessels, and their being made of much purer and clearer metal, as the Glassmen speak, than the great Receiver, we might have a more perfect view of every thing happening within them. The next, that such small Vessels might be emptied with less labour and in much less time. The third, that this nimble exsuction of the ambient Air would make many changes in the Bodies shut up in these glasses more sudden and conspicuous then otherwise they would prove. And the last, that we should be able to draw and keep out the Air much more perfectly from such small Vessels then from our large Receiver. But though we were not much disappointed in the expectation of the three first advantages, yet we were in our hopes of the fourth. For besides the great difficulty we found in fitting together the Glasses, the Stop-cocks and the Covers; besides this I say, we found ourselves seldom able to draw, and keep out the Air so far as to make the remaining Air in these Receivers weaker than the remaining Air in our great Receiver. For though sometimes the Leaks of some of these little Receivers may be much either fewer or smaller than those of the larger Vessel; yet a little Air getting into one of these, wherein it had but little room to expand and display itself, might press as much upon all parts of the internal surface of the Vessel, and upon the included Bodies, as a greater quantity of Air in a Vessel in whose capacity it might find more room to expand itself. The other thing that we were to advertise, is, That 'tis not every small crack that can make such a Receiver as is of a roundish Figure altogether useless to our Experiment, in regard that upon the exsuction of the internal Air, the ambient Air on all sides pressing the Glass inwards or towards the middle, does consequently thrust the Lips of the crack closer, and so rather close then increase it. This I mention partly because Receivers fit for our turn are more easily cracked then procured, and therefore ought not to be unnecessarily thrown away as unserviceable: And partly because I think it becomes one that professes himself a faithful Relator of Experiments, not to conceal from Your Lordship, that after a few of the foregoing Experiments were made, there happened in the great Receiver a crack of about a Span long, beginning at the upper Orifice, and occasioned, as it seemed, by the excessive heat of too large an Iron that was employed to melt the Cement about that Orifice. But having laid upon this crack a broad Plaster, which in one of our Essays written some years since to your ingenious and hopeful Cousin jones, we extol for the mending of cracked Receivers, and other Chemical Glasses; and having afterwards thickly over-laid this Plaster with Diachylon, we neither could then, nor can yet perceive that the Vessel leaks sensibly at that crack. The Plaster was made of good quick Lime finely powdered, and nimbly ground with a Pestle in a Mortar, with a quantity (I know not how much precisely, not having those Essays in this place) of scrape of Cheese and a little fair Water, no more than is just necessary to bring the mixture to a somewhat soft Paste, which when the Ingredients are tightly incorporated, will have a strong and stinking smell: Then it must be immediately spread upon a Linen clothe three or four finger's breadth, and presently applied, lest it begin to harden. But if Your Lordship had seen how we mended with it Receivers even for the most subtle Chemical Spirits, You would scarce wonder at the service it has done in our Pneumatical Glass. Experiment 10. WE took a Tallow-Candle of such a size that eight of them make about a pound, and having in a very commodious Candlestick let it down into the Receiver, and so suspended it that the Flame burned almost in the middle of the Vessel, we did in some two minutes exactly close it up: and, upon Pumping very nimbly, we found that within little more than half a minute after the Flame went out, though the Snuff had been purposely left of that length we judged the most convenient for the lasting of the Flame. But the second time having put in the same Candle into the Receiver, (after it had by the blasts of a pair of Bellows been freed from Fumes) the Flame lasted about two minutes from the time the Pumper began to draw out the Air; upon the first exsuction whereof, the Flame seemed to contract itself in all its Dimensions. And these things were further observable, that after the two or three first exsuctions of the Air, the Flame (except at the very top) appeared exceeding blue, and that the Flame still receded more and more from the Tallow, till at length it appeared to possess only the very top of the Week, and there it went out. The same Candle being lighted again was shut into the Receiver, to try how it would last there without drawing forth the Air, and we found that it lasted much longer then formerly; and before it went out receded from the Tallow towards the the top of the Week, but not near so much as in the former Experiment. And having an intention to observe particularly what the motion of the smoke would be in these Experiments: We took notice that when the Air was not drawn out, there did upon the extinction of the Flame a considerable part of the Week remain kindled, which (probably by reason of the Circulation of the Air in the Vessel, occasioned by the heat) emitted a Steam, which ascended swiftly and directly upwards in a slender and uninterrupted Cylinder of smoke, till it came to the top, whence it manifestly recoiled by the sides to the lower part of the Vessel. Whereas when the Flame went out upon the exsuction of the Air one time (when the Flame retired very leisurely to the top) we perceived it not to be followed by any smoke at all. And at an other time the upper part of the Week remaining kindled after the extinction of the Flame, the slender steam of Fumes that did arise ascended but a very little way, and then after some uncertain motions this and that way, did, for the most part, soon fall downwards. Being desirous also to try whether there would be any difference as well in our Receiver as there is wont to be elsewhere betwixt Candles made of Wax and those made of Tallow, as to their duration; we took slender Tapers of white Wax, (commonly called Virgins Wax) that being found to burn with much less smoke then common yellow Wax: Six of these of like bigness, and each of them of about the thickness of a Swans Quill, we pressed together into one Candle: And having lighted all the Weeks, we let in the abovementioned Wax into the Receiver, and made what haste we could to close it up with Cement. But though in the mean while we left open the Valve of the Cylinder, the hole of the Stop-cock and that in the Cover of the Receiver, that some Air might get in to cherish the Flame and the smoke might have a vent; Yet for so great a Flame the Air sufficed not so much as till the Cover could be perfectly luted on: So that before we were quite ready to employ the Pump, the Candle was extinguished. Wherefore we took but one of the above mentioned Tapers, and having lighted it, closed it up in the Receiver, to try how long a small Flame with a proportionable smoke would continue in such a quantity of Air: But we found upon two several trials, that from the beginning of pumping, the flame went out in about a minute of an hour. It appeared indeed to us that the swinging of the Wire to and fro (in the Engine shaken by pumping) hastened the vanishing of the Flame, which seemed by that motion to be cast sometimes on one side of the Week and sometimes on the other: But though once we purposely refrained pumping after a very few exsuctions of the Air, that the Flame might not be agitated, yet it lasted not much longer than the newly mentioned time. And lastly, closing up the same Taper, lighted again, to discover how long it would last without drawing out of the Air, we found that it burned for a while vividly enough, but afterwards began to be lessened more and more in all its Dimensions. And we observed that the Flame did not, as before, retire itself by little and little towards the top, but towards the bottom of the Week (from which yet it did a little withdraw upwards just before it went out) so that the upper part of the Week appeared for a pretty while manifestly above the top of the Flame, which having lasted about five minutes, was succeeded by a directly ascending stream of Smoak. Experiment 11. THere was taken a Wire, which being bend almost in the form of a Screw, constituted such an Instrument to contain Coals and leave them every way accessible to the Air, as the tenth Figure declares; the breadth of this Vessel was no less than that it might with ease be conveyed into the Receiver: And having filled it to the height of about five Inches with throughly kindled Wood-coals, we let it down into the Glass; and speedily closing it, we caused the Pumper to ply his work, and observed that upon the very first exsuction of the Air (though perhaps not because of that only) the Fire in the Coals began to grow very dim, and though the agitation of the Vessel did make them swing up and down (which in the free Air would have retarted the extinction of the Fire) yet when we could no longer discern any redness at all in any of them, casting our eyes upon a Minute-Watch we kept by us on this occasion, we found that from the beginning of the Pumping (which might be about two minutes after the Coals had been put in glowing) to the total dis-appearing of the Fire, there had passed but three minutes. Whereupon, to try the Experiment a little further, we presently took out the Coals, in which it seems there had remained some little parcels of Fire, rather covered then totally quenched: For in the open Air the Coals began to be rekindled in several places, wherefore having by swinging them about in the Wire, throughly lighted them the second time, we let them down again into the Receiver, and closed it speedily as before; and then waiting till the Fire seemed totally extinct without meddling with the Pump, we found that from the time the Vessel was closed till that no Fire at all could be perceived there had passed about four minutes: Whereby it seemed to appear that the drawing away of the ambient Air made the Fire go out sooner than otherwise it would have done; though that part of the Air that we drew out left the more room for the stifling steams of the Coals to be received into. Lastly, Having taken out the Wire and put other Coals into it, we did, in the same Room where the Engine stood, let it hang quietly by a string in the open Air, to try how long the Fire would last without agitation when no Air was kept from it. And we found that the Fire began to go out first at the top and outsides of the Coals; but inwards and near the bottom the Fire continued visible for above half an hour, a great part of the Coals, especially those next the bottom, being burnt to ashes before the Fire went out. We caused likewise a piece of Iron to be forged, of the bigness of a middle sized Char-coal, and having made it red hot throughout▪ we caused it in the lately mentioned Wier, to be speedily conveyed and shut up into the Receiver, being desirous to try what would become of a glowing Body, by reason of its texture more vehemently hot then a burning Coal of the same bigness, & yet unlike to send forth such copious & stifling Fumes: But we could not observe any manifest change upon the exsuction of the Air. The Iron began indeed to lose its Fiery redness at the top, but that seemed to be because it was at the upper end somewhat more slender then at the lower: The redness, though it were in the day time, continued visible about four minutes; and then, before it did quite disappear, we turned the Key of the Stop-cock but could not discern any change of the Iron upon the rushing in of the Air. Yet some little remainders of Wax that stuck to the Wire, and were turned into Fumes by the heat of the neighbouring Iron, seemed to afford a more plentiful, or at least a much more free expanded smoke when the Air was sucked out, then afterwards; though allowance was made for the decreasing heat of the Iron. And lastly, notwithstanding a considerable exsuction of the ambient Air, though not by far so great a one as might have been made by the Engine; and notwithstanding the inconsiderable dissipation of the parts of the Iron, the surrounding sides of the Receiver were sensibly, and almost offensively heated by it; insomuch that a pretty while after the Iron was taken out, the sides of the Glass manifestly retained a warmth: which would not be unfit to be considered by a Person at more leisure than I am now. BEing willing to try after this something that would not cherish much Fire at once, Experiment 12. and would keep Fire much longer than a Coal. We took a piece of Match, such as Soldiers use, of the thickness of a Man's little Finger, or somewhat thicker; and this being well lighted at one end, was by a string suspended with that end downwards in the cavity of the Receiver which was immediately closed: And yet by that time it could well be so, the copious Fumes of the Match had near filled and darkened the Receiver. Wherefore, lest the Vessel should be endangered, the Pump was nimbly plied, and a great deal of Air and Smoke mixed together was drawn out, whereby the Receiver growing more clear, we could discern the Fire in the Match to burn more and more languidly: And notwithstanding that by the diligence used in Pumping, it seemed to have room enough allowed it to throw out Fumes; yet after no long time it ceased from being discernible either by its Light or its Smoke. And though by that we were invited to suppose it quite extinguished, yet we continued pumping a while, in prosecution of another Experiment we were trying at the same time: And this we did the more willingly because of a suspicion the Experiment about the Coals might easily suggest, and which the event declared not to have been altogether groundless. For upon the Admission of the external Air, the Fire, that seemed to have gone out a pretty while before, did presently revive; and being as it were refreshd 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 formerly. Experiment 13. A While after we let down into the Receiver together with a lighted piece of Match, a great Bladder well tied 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 supposed to Recoil upon the Fire, and so to stifle it. The event of our trial was, That at the beginning of our Pumping the Match appeared well lighted, though it had almost filled the Receiver with its plentiful Fumes: But by degrees it burned 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 appeared by this, That the longer we pumped, the lesser Air and Smoke came out of the Cylinder at the opening 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 ourselves of its expiration, we had darkened 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 man●f●sted 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 rekindled 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 recovered by the readmitted Air. Some Circumstances, besides those already mentioned, occurred 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 darkened to his eye that looked upon the light through it: and this darkness was much less when the Receiver was much less filled with Fumes: It was also instantaneous, and seemed to proceed from a sudden change of place and situation in the exhalations, upon the vent suddenly afforded them and the Air they were mixed with, out of the Receiver into the Cylinder. The next thing we observed was, a kind of Halo that appeared a good while about the Fire, and seemed 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 itself after the same manner (for aught we could discern) as it would have otherwise done: So that before the Fire or the Match was quite extinct, the Bladder appeared swelled 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 thereabouts) 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 filled that small Receiver, as for aught we discerned, to choke the Fire. And having again and again reiterated the Experiment, it seemed 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 pumped once or twice, we suddenly turned the Key, and thereby gave access to the excluded Air, which rushing violently in, as if it had been forced thorough a pair of Bellows, did both drive away the ashes, fill the Glass with fresh Air, and by blowing the almost extinguished Fire, re-kindled it, as appeared by the Matches beginning again to smoke, which before it had ceased 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 pumped out, and found that upon the exsuction of it, the Match quickly left smokeing, as it seemed, by reason of the absence of the Air; and yet if some urgent occasions had not hindered us, we would for greater security have tried, whether or no the Match rekindled as formerly, would smoke much longer, in case of no exsuction of the ambient Air. Experiment 14. TO try divers things at once, and particularly whether Fire, though we found it would not long last, might not yet be produced in our evacuated Receiver: We took a Pistol of about a Foot in length, and having firmly tied it to a stick almost as long as the Cavity of the Receiver, we very carefully primed it with well dried Gunpowder, and then cocking it, we tied to the Tricker one end of a string, whose other end was fastened to the Key formerly mentioned to belong to the Cover of our Receiver. This done, we conveyed the Pistol, together with the annexed Staff, into the Vessel: which being closed up, and emptied after the usual manner, we began to turn the Key in the Cover; and thereby shortening the string that reached from it to the Pistol, we pulled aside the Tricker, and observed, 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 wont violence upon the Steel, struck out of it as many and as conspicuous parts of Fire, as, for aught we could perceive, it would have done in the open Air. Repeating this Experiment divers times, we also observed whether or no there would appear any considerable Diversity in the Motion of the shining Sparks in a place where the remaining Air was so much rarified, but could not perceive but that they moved some of them upwards, as well as some of them downwards, and some of them side-ways, as they are wont to do, when upon such collisions they fly out in the open Air. We likewise caused a piece of Steel to be made of the form and bigness of the Flint, in whose place we put it, and then the Pistol being cocked and conveyed into the Receiver, the Trigger was pulled after the Air was drawn out: And though the place were purposely somewhat darkened, yet there appeared not upon the striking of the two Steels against each other the least spark of Fire: Nor did we expect any (having before in vain attempted to strike Fire this way in the open Air) though we thought fit to make the Experiment to undeceive those who fancy in rarified Air, I know not what strange disposition, to take Fire upon a much slighter occasion than this Experiment afforded. We have indeed found, that by the dextrous Collision of two hardened pieces of Steel, store of sparks may be struck out: But that was done with such vehement percussion of the edges of the two Steels, as could not well be compassed in our Receiver. But the chief thing we designed to do with our Pistol, was, To observe whether Gunpowder would take Fire in our emptied and closely stopped Glass? Whether the expansion of the Flame would be considerably varied by the absence of so much of the ambient Air as was drawn out of the Receiver? and whether the Flame would diffuse itself upward, as it is wont, notwithstanding it's not having about it the usual proportion of Air to force it up? And though most of our attempts to fire the Gunpowder in the Pan of the Pistol succeeded not, because we were fain to let it hang almost perpendicular in the Receiver; whereby the Powder was shaken down before the sparks could reach it; yet once the Experiment succeeded, and the kindled Powder seemed to make a more expanded Flame than it would have done in the open Air, but mounted upwards according to its wont; whether by reason of that little portion of Air, which in spite of our pumping remained in the Receiver, or for any other cause, we have not now the leisure to consider. But we must not forget, that upon the extinction of the Flame the Receiver appeared darkened with smoke, which seemed to move freely up and down, and upon the letting in the Air at the Stop-cock began to circulate much faster than before. We would have made more observations concerning this Flame, but that of two or three attempts we afterwards made to repeat the kindling of Powder, not any one succeeded; and we have not the leisure to dwell long upon one kind of Trials. Experiment. 15. TO these Experiments concerning Fire we added another, which, though it succeeded not, may perhaps without impertinency be recorded: partly because that (as we have in another Treatise amply declared) it is useful to recite what Experiments miscarry as well as what succeed. And partly also because it is very possible that what we endeavoured in vain, may be performed by Your Lordship, or some other Virtuoso that shall have slancker Vessels than we had, and more Sunny days than the present Winter allows us. We conveyed then into one of our small Receivers a piece of matter combustible, dry and black (experience declaring things of that colour to be most easily kindled) & carefully closing the Vessel we brought it to a Window at which the Sun, not very fare from the Meridian, shone in very freely: then drawing out the Air with speed united the Sunbeams with a burning Glass upon the combustible matter which began immediately to send forth a Smoke that quickly darkened the Receiver, but notwithstanding all our care and diligence the external Air got in so fast that after divers trials we were fain to leave off the Experiment in that Glass and induced to make trial of it in our great Receiver. Having then after some difficulty lodged the combustible matter in the cavity of this Vessel in such manner as that it was almost contiguous to that side thereof that was next the Sun, we did endeavour with a pretty large burning Glass to kindle it, but found, as we feared, That by reason of the thickness of the Glass, (which was also of a less pure and less Diaphanous matter then the other) the Sunbeams thrown in by the burning Glass, were in their passage so Dislocated and Scattered (not now to mention those many that being reflected, I could not pierce into the cavity of the Receiver) that we could not possibly unite enough of them to kindle the matter, nor so much as to make it sensibly smoke. Yet we hope that the seeing whether Bodies (other than Gunpowder) may be kindled, and what would happen to them when set on fire, in a place in great measure devoid of Air, may prove so Luciferous an Experiment, that when the Season is more favourable we shall, God permitting, make further trial of it, and acquaint Your Lordship with the Event, if it prove prosperous. In the mean time we shall pass on to other Experiments, assoon as we have advertised Your Lordship that we have forborn to make such Reflections upon the several Experiments we have set down concerning Fire, as the matter▪ would have easily enough afforded, and Your Lordship may perhaps have expected. But I made the less scruple to forbear the annexing of Speculations to these Recitals, because Carneades & Eleutherius have in some Dialogues concerning Heat and Flame, which were last year seen by some Friends, and may be, when you please, commanded by You, mentioned diver's of my Thoughts and Experiments concerning Fire. WE designed to try whether or no divers Magnetical Experiments would exhibit any unusual Phaenomena, Experiment 16. being made in our Evacuated Receiver instead of the open Air: But for want of leisure and conveniency to prosecute such Trials, we were induced to reserve the rest for an other time, and to content ourselves with making that which follows. We conveyed into the Receiver a little Pedestal of Wood, in the midst of which was perpendicularly erected a slender Iron, upon whose sharp point an excited Needle of Steel purposely made, and of about five Inches long, was so placed that hanging in an Aequilibrium it could move freely towards either hand. Then the Air being after the usual manner pumped out, we applied a Loadstone moderately vigorous to the outside of of the Glass, and found that it Attracted or Repelled the ends of the Needle, according to the Laws Magnetical, without any remarkable difference from what the same Loadstone would have done had none of the Air been drawn away from about the Needle, which when the Loadstone was removed, after some tremulous Vibrations to and fro, rested in a position wherein it looked North and South. Experiment 17. PRoceed we now to the mention of that Experiment, whereof the satisfactory trial was the principal Fruit I promised myself from our Engine. It being then sufficiently known, that, in the Experiment De Vacuo, the Quicksilver 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 Quicksilver falls no lower, be, that at that Altitude, the Mercurial Cylinder in the Tube, is an Aequilibrium with the Cylinder of Air, supposed to reach from the adjacent Mercury to the top of the Atmosphere: If this Experiment could be tried out of the Atmosphere, the Quicksilver 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 inferred (as easily I might) that, if the Experiment could be tried in our Engine, the Quicksilver 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 does (according to what hath above been taught) continue there as strongly compressed, as it did whilst all the incumbent Cylinder of the Atmosphere leaned immediately upon it; because the Glass, wherein it is penned up, hinders it to deliver itself, 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 allowed to try the Experiment beyond the Atmosphere. Wherefore (after having surmounted some little difficulties which occurred 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 sealed at one end, was, at the other, filled with Quicksilver, care being taken in the filling, that as few bubbles as was possible should be left in the Mercury: Then the Tube being stopped with the Finger and inverted, was opened, 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 filled with Quicksilver: 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 slipped 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 tightly 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, then if the interposed Glass Receiver did not hinder the immediate pressure of the ambient Atmosphere upon the enclosed Air; which hereby appears to bear up on the Mercury, rather by virtue of its spring, then 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 Quicksilver 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 stopped, we caused him that managed the Pump to pump again, and marked how low the Quicksilver fell at the second exsuction; but continuing this work, we were quickly hindered 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 thenceforward mark it no other ways then by the eye. And thus, continuing the labour of pumping for about a quarter of an hour, we found ourselves unable to bring the Quicksilver in the Tube totally to subside; because, when the Receiver was considerably emptied of its Air, and consequently that little that remained grown unable to resist the Irruption of the external, that Air would (in spite of whatever we could do) press in at some little Avenue or other; and though much could not thereat get in, yet a little was sufficient to counterbalance the pressure of so small a Cylinder of Quicksilver, as then remained in the Tube. Now (to satisfy ourselves further, that the falling of the Quicksilver in the Tube to a determinate height, proceeds 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 impel 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 Quicksilver was impelled up almost to its first height: I say almost, because it stopped near a quarter of an Inch beneath the Paper mark formerly mentioned; which we ascribed to this, That there was (as is usual in this Experiment) some little Particles of Air engaged among those of the Quicksilver; which Particles, upon the descent of the Quick silver, did manifestly 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, hindered the Quicksilver from regaining its first height. This Experiment was a few days after repeated in the presence of those excellent and deservedly Famous Mathematic 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 Quicksilver 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 indeed begin to fall, but continued afterwards to subside, though we did not continue pumping. Whence it appeared, that though the Diachylon that stopped the end of the Tube were so thick and strong, that the external Air could not press it in (as experience taught us that it would have done, if there had been but little of it) yet the subtler parts of it were able (though slowly) to insinuate themselves through the very body of the Plaster, which it seems was of so close a Texture, as that which we mentioned ourselves to have successfully made use of in the Experiment De Vacuo some years ago. So that now we begin to suspect, that perhaps one Reason, why we cannot perfectly pump out the Air, may be, that when the Vessel is almost empty, some of the subtler parts of the external Air may, by the pressure of the Atmosphere, be strained through the very body of the Diachylon into the Receiver. But this is only conjecture. Another Circumstance of our Experiment was this, That, if (when the Quicksilver in the Tube was fallen low) too much ingress were, at the hole of the Stop-cock, suddenly permitted to the external Air; it would rush in with that violence, and bear so forcibly▪ upon the surface of the subjacent Quicksilver, that it would impel it up into the Tube rudely enough to endanger the breaking of the Glass. We formerly mentioned, that the Quicksilver did not in its descent fall as much at a time after the two or three first exsuctions of the Air, as at the beginning: For, having marked its several Stages upon the Tube, we found, that at the first suck it descended an Inch and ●/8, and at the second an Inch and ⅛; and when the Vessel was almost emptied, it would scarce at one exsuction be drawn down above the breadth of a Barleycorn. And indeed we found it very difficult to measure in what proportion these decrements of the Mercurial Cylinder did proceed: partly because (as we have already intimated) the Quicksilver was soon drawn below the top of the Receiver; and partly because, upon its descent at each exsuction, it would immediately reascend a little upwards; either by reason of the leaking of the Vessel at some imperceptible hole or other, or by reason of the motion of Restitution in the Air, which, being somewhat compressed by the fall as well as we weight of the Quicksilver, would repel it a little upwards, and make it vibrate a little up and down, before they could reduce each other to such an Aequilibrium as both might rest in. But though we could not hitherto make observations accurate enough concerning the measures of the Quick-silver's descent, to reduce them into any Hypothesis, yet would we not discourage any from attempting it; since, if it could be reduced to a certainty, 'tis probable that the discovery would not be unuseful. And, to illustrate this matter a little more, we will add, That we made a shift to try the Experiment in one of our above mentioned small Receivers, not containing a Quart; but that (agreeably to what we formerly observed) we found it as difficult to bring this to be quite empty as to evacuate the greater; the least external Air that could get in (and we could not possibly keep it all perfectly out) sufficing in so small a Vessel to display a considerable pressure upon the surface of the Mercury, and thereby hinder that in the Tube from falling to a level with it. But this is remarkable, that having two or three times tried the Experiment in that small Vessel, upon the very first Cylinder of Air that was drawn out of the Receiver, the Mercury fell in the Tube 18 Inches and a half, and at another 19 Inches and a half. But, on this occasion, I hold it not unfit to give Your Lordship notice that I hoped, from the descent of the Quicksilver in the Tube upon the first suck, to derive this advantage: that I should thence be enabled to give a near guess at the proportion of force betwixt the pressure of the Air (according to its various states, as to Density and Rarefaction) and the gravity of Quicksilver, than hitherto has been done. For in our Experiment there are divers things given, that may be made use of towards such a discovery. For first we may know the capacity of the Receiver wherein the Experiment is made, since, by filling it with water, we may easily compute how many Quarts, or Measures of any other denomination, it contains of Air; which Air, when shut up in the Vessel, may be supposed to have a pressure equal to that of the Atmosphere; since it is able to keep the Quicksilver in the Tube from falling any lower than it did in the free and open Air. Next here is given us the capacity of the brass Cylinder emptied by the drawing down of the Sucker (its bore and height being mentioned in the description of our Pump) whereby we may come to know how much of the Air contained in the Receiver is drawn out at the first suck. And we may also easily define, either in weight or cubick measures the Cylinder of Quicksilver that answers to the Cylinder of Air lately mentioned (that Mercurial Cylinder being in our Engine computable by deducting from the entire altitude of that Cylinder of Quicksilver, the altitude at which it rests upon the first exsuction.) But though, if this Experiment were very watchfully tried in Vessels of several sizes, and the various descents of the Quicksilver compared among themselves, 'tis not improbable that some such thing as we hoped for may thereby be discovered. Yet because not only the solid contents of as much of the Glass-tube as remains within the concave surface of the Receiver, and (which is more difficult) the varying contents of the Vessel containing the Mercury, and of as much of the Mercury itself as is not in the Tube, must be deducted out of the capacity of the Receiver; but there must also an allowance be made for this, that the Cylinder that is emptied by the drawing down of the Sucker, and comes to be filled upon the letting of the Air out of the Receiver into it, is not so replenished with Air as the Receiver itself at first was: because there passes no more Air out of the Receiver into the Cylinder, than is requisite to reduce the Air in the cavity of the Cylinder, and in that of the Receiver to the same measure of dilatation: Because of these (I say) and some other difficulties that require more skill in Mathematics than I pretend to, and much more leisure than my present occasions would allow me, I was willing to refer the nicer consideration of this matter to some of our Learned and Accurate Mathematicians, thinking it enough for me to have given the Hint already suggested. For further confirmation of what hath been delivered, we likewise tried the Experiment in a Tube of less than two foot long: and, when there was so much Air drawn out of the Vessel, that the remaining Air was not able to counterbalance the Mercurial Cylinder, the Quicksilver in the Tube subsided so visibly, that (the Experiment being tried in the little Vessel lately mentioned) at the first suck it fell above a span, and was afterwards drawn lower and lower for a little while; and the external Air being let in upon it, impelled it up again almost to the top of the Tube: So little matters it how heavy or light the Cylinder of Quick silver to subside is, provided its gravity overpower the pressure of as much external Air as bears upon the surface of that Mercury into which it is to fall. Lastly we also observed, That if (when the Mercury in the Tube had been drawn down, and by an Ingress permitted to the external Air, impelled up again to its former height) there were some more Air thrust up by the help of the Pump into the Receiver, the Quicksilver in the Tube would ascend much above the wont height of 27 digits, and immediately upon the letting out of that Air would fall again to the height it rested at before. Your Lordship will here perhaps expect, that as those who have treated of the Torricellian Experiment, have for the most part maintained the Affirmative, or the Negative of that famous Question, Whether or no that Noble Experiment infer a Vacuum? so I should on this occasion interpose my Opinion touching that Controversy, or at least declare whether or no, in our Engine, the exsuction of the Air do prove the place deserted by the Air sucked out, to be truly empty, that is, devoid of all Corporeal Substance. But besides that, I have neither the leisure, nor the ability, to enter into a solemn Debate of so nice a Question; Your Lordship may, if you think it worth the trouble, in the Dialogues not long since referred to, find the Difficulties on both sides represented; which then made me yield but a very wavering assent to either of the parties contending about the Question: Nor dare I yet take upon me to determine so difficult a Controversy. For on the one side it appears, that notwithstanding the exsuction of the Air, our Receiver may not be destitute of all Bodies, since any thing placed in it, may be seen there; which would not be, if it were not pervious to those Beams of Light which rebounding from the seen Object to our eyes, affect us with the sense of it: And that either these Beams are Corporeal Emanations from some lucid body, or else at least the light they convey doth result from the brisk Motion of some subtle Matter, I could, if I mistake not, sufficiently manifest out of the Dialogues abovementioned, if I thought your Lordship could seriously imagine that Light could be conveyed without, at least, having (if I may so speak) a Body for its Vehicle. By the sixteenth Experiment, it also appears that the closeness of our Receiver hinders it not from admitting the Effluvia of the Loadstone; which makes it very probable that it also freely admits the Magnetical steams of the Earth; concerning which, we have in another Treatise endeavoured to manifest that numbers of them do always permeate our Air. But on the other side it may be said, That as for the subtle Matter which makes the Objects enclosed in our evacuated Receiver, visible, and the Magnetical Effluvia of the Earth that may be presumed to pass thorough it, though we should grant our Vessel not to be quite devoid of them, yet we cannot so reasonably affirm it to be replenished with them, as we may suppose, that if they were gathered together into one place without Intervals between them, they would fill but a small part of the whole Receiver. As in the thirteenth Experiment, a piece of Match was inconsiderable for its bulk, whilst its parts lay close together, that afterwards (when the Fire had scattered them into smoke) seemed to replenish all the Vessel. For (as elsewhere our Experiments have demonstrated) both Light and the Effluvia of the Loadstone, may be readily admitted into a Glass, Hermetically sealed, though before their Admission, as full of Air as hollow Bodies here below are wont to be, so that upon the exsuction of the Air, the large space deserted by it, may remain empty, notwithstanding the pretence of those subtle Corpuscles, by which Lucid and Magnetical Bodies produce their effects. And as for the Allegations above mentioned, they seem to prove but that the Receiver devoyed of Air, May be replenished with some such Etherial Matter, as some Modern Naturalists writ of; but not that it really is so. And indeed to me it yet seems, that as to those spaces which the Vacuists would have to be empty, because they are manifestly devoid of Air; and all grosser Bodies, the Plenists (if I may so call them) do not prove that such spaces are replenished with such a subtle Matter as they speak of, by any sensible effects, or operations of it (of which divers new Trials purposely made, have not yet shown me any) but only conclude that there must be such a Body, because there cannot be a Void. And the reason why there cannot be a Void, being by them taken, not from any Experiments, or Phaenomena of Nature, that clearly and particularly prove their Hypothesis, but from their notion of a Body, whose Nature, according to them, consisting only in extension (which indeed seems the property most essential to, because inseparable from a Body) to say a space devoid of Body, is to speak in the School-mens Phrase, a Contradiction in Adjecto: This reason, I say, being thus desumed, seems to make the Controversy about a Vacuum, rather a Metaphysical, than a Physiological Question; which therefore we shall here no longer debate, finding it very difficult either to satisfy Naturalists with this Cartesian Notion of a Body, or to manifest wherein it is erroneous, and substitute a better in its stead. But though we are unwilling to examine any further the Inferences wont to be made from the Torricellian Experiment, yet we think it not impertinent to present Your Lordship with a couple of Advertisements concerning it. First, then if in trying the Experiment here or elsewhere, you make use of the English measures that Mathematicians and Tradesmen are here wont to employ, You will, unless you be forewarned of it, be apt to suspect that those that have written of the Experiment have been mistaken. For whereas men are wont generally to talk of the Quick-silver's remaining suspended at the height of between six or seven and twenty Inches; we commonly observed, when divers years. since we first were solicitous about this Experiment, that the Quicksilver in the Tube rested at about 29 Inches & an half above the surface of the Restagnant Quicksilver in the Vessel, which did at first both amaze and perplex us, because though we held it not improbable that the difference of the grosser English Air, and that of Italy and France, might keep the Quicksilver from falling quite as low in this colder, as in those warmer Climates; yet we could not believe that that difference in the Air should alone be able to make so great a 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 overlooked 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 inferior 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 of●●n times upon the opening of the inverted Tube into the Vesselled Mercury, you may observe a bubble of Air to ascend from the bottom of the Tube through the subsiding Quicksilver 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 Quicksilver & 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-silvers 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 Linen cloaths dipped in Water, to the same part of the Tube, the Quicksilver 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 accuratly filling up a Tube of Mercury, we found that yet there remained store of inconspicuous bubbles, by inverting the Tube, letting the Quicksilver fall to its wont height; and by approaching (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 Quicksilver seemed, to our wonder, to boil. We further 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 Quicksilver 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 bend 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 Quicksilver, 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 useful and compendious way not to fill the Tube at first quite full 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 itself 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 Quicksilver more to fill up the Tube exactly. And lastly, as for those lesser and inconspicuous parcels of Air which cannot this way be gleaned up, You may endeavour before you invert the Tube, to free the Quicksilver from them by shaking the Tube, and gently knocking on the outside of it, after every little parcel of Quicksilver which you pour in; and afterwards, by forcing the small latitant bubbles of Air to disclose themselves and break, by employing 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 eighth, 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 then in long ones, where the Air having more room to expand it self, does 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 Virtuosos a 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. WE took a Glass Tube, Experiment 18. which, though it were not much above three Foot long, we made choice of because it was of a more then ordinarily even thickness. This we filled 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 opened the mouth of it beneath the surface of some other Quicksilver, that in the Tube fell down to the wont 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 depressed. Lastly, having put both the Tube and the Vessel it leaned on into a convenient Wooden Frame, to keep them from mischances: we placed that Frame in a Window within my Bedchamber, that I might both keep the Mercury from being stirred, and have opportunity to watch from time to time the Phaenomena it was to exhibit. For the better discovery of which, when the Quicksilver both in the Tube and subjacent Vessel was perfectly at rest, we took notice, by a mark made on the outside of the Glass, how high the included Liquor then reached. During several Weeks that the Tube was kept in that Window (which was very rarely opened) I had the opportunity to observe, that the Quicksilver did sometimes faintly imitate the Liquor of a Weatherglass, subsiding a little in warm, and rising a little in cold Wether, which we ascribed to the greater or lesser pressure of that little Air that remained at the top of the Tube, expanded or condensed by the heat or cold that affected the ambient Air. But that which I was chief careful to observe, was this, That oftentimes the Quicksilver did rise and fall in the Tube, and that very notably, without conforming itself to what is usual in Weather-glasses, whose Air is at the top, nay quite contrary thereunto: for sometimes I observed it in very cold weather (such as this Winter has already afforded us good store of) to fall down much lower than at other times, when by reason of the absence of both Frost, Snow, and sharp Winds, the Air was comparatively much warmer. And I further observed, That sometimes the Quicksilver would for some days together rest almost at the same height; and at other times again it would in the compass of the same day considerably vary its altitude, though there appeared no change either in the Air abroad, or in the temper of the Air within the Room (wherein was constantly kept a good Fire) nor in any thing else, to which either I, or some eminently Learned Men whom I then acquainted with the Experiment, could reasonably impute such a change: Especially considering that the space wherein the Mercury wandered up and down, within about five Weeks, amounted to full two Inches, of which we found by our several marks whereby we had taken notice of its several removes, that it had descended about ●/16 of an Inch from the place where it first settled, & the other Inch and ●/16 it had ascended. And it seems probable that the height of the Mercurial Cylinder would have varied yet more, if the Experiment had been made in the open Air and in a long Tube, where the Particles of the Imprisoned Air, by having more room to display themselves in, might not have had so strong a Spring to work upon the Quicksilver with. But for want both of time and of a competent quantity of Mercury (which was not to be procured where we than happened to be) we were unable to make any further trials: which therefore chief troubled us, because we would gladly have tried an ingenious Experiment which was suggested unto us by that excellent Mathematician Mr. Wren, who being invited to name any thing he would have us try touching the pressure of the Air, desired us to observe whether or no the Quicksilver in a long Tube would not a little vary its height according to the Tides, especially about the New and Full Moon, about which times Mariners observe those great Flow and Ebbs of the Sea, that they call the Spring-Tides. For he sagaciously and plausibly conjectured that such observations accurately made, would discover the truth or erroneousness of the Cartesian Hypothesis concerning the Ebbing and Flowing of the Sea: which Des Cartes ascribes to the greater pressure made upon the Air by the Moon, and the Intercurrent Ethereal Substance at certain times (of the Day, and of the Lunary Month) then at others. But in regard we found the Quicksilver in the Tube to move up and down so uncertainly, by reason, as it seems, of accidental mutation in the Air; I somewhat doubt whether we shall find the Altitude of the Quicksilver to vary as regularly as the Experiment is ingeniously proposed. The success we shall (God permitting us to make trial of it) acquaint Your Lordship with; and in the mean time take notice, that when we had occasion to take the Tube out of the Frame (after it had stayed there part of November and part of December) a good Fire being then in the room, because it was a Snowy day, we found the Quicksilver in the Tube to be above the upper surface of the subjacent Mercury 29 Inches three quarters. If Your Lordship should now ask me what are the true causes of this varying altitude of the Mercurial Cylinder; I should not undertake to answer so difficult a question, and should venture to say no more, then that among divers possible causes to which it may be ascribed, it would not be, perhaps, absurd to reckon these that follow. First then we may consider, that the Air in the upper part of the Tube is much more rarified, and therefore more weak than the external Air, as may appear by this among other things, That upon the inclining of the Tube the Quicksilver will readily ascend almost to the very top of it, and so take up eight or nine tenth parts, and perhaps more of that space which it deserted before: which would not happen if that whole space had been full of unrarified Air, since that (as trial may easily satisfy you) would not have suffered itself to be thrust into so narrow a room by so weak a pressure. So that although in our Tube when the included Air was heated, the Quicksilver was somewhat depressed: Yet there is this difference betwixt such a Tube and common Weather-Glasses, that in these the included and the ambient Air are in an Aequilibrium as to pressure, and the weight of the Water that keeps them separate is scarce considerable. Whereas in such a Tube as we are speaking of, the Air within is very much more dilated then that without▪ and 'tis not so much the spring or resistance of the included Air, as the weight of the Mercurial Cylinder itself that hinders the Quicksilver from ascending higher; for if we should suppose that deserted part of the Tube perfectly devoid of Air, yet would the Quicksilver rise but a little higher in it, and be far from filling it, in regard the outward Air would not be able to impel up such a weight much higher: whereas it may, by our former Experiments appear, that if all the Air in the upper part of a Weatherglass were away, the Water would be impelled up to the very top of it, though the Pipe were above thirty Foot long. We may next consider, that this rarified Air at the upper part of our Tube being exactly shut up betwixt the Glass and the Quicksilver, it was scarce subject to any discernible alterations, save those it received from heat and cold. And we may further consider that yet the external Air or Atmosphere is subject to many alterations, besides them that proceed from either of those Qualities. For the Experiment that occasioned this Discourse, seems to make it probable enough that there may be strange Ebb and Flow, 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 complained 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, relates, 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 & 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, occasioned 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 mentioned our having often observed 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 seemed clear, there would not seldom 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 Candles, 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 rarifying it. Nor will it very much import the main scope of our Discourse, whether it be supposed 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 thickened yet they rather diminish then increase its gravitation, in regard that the quickness of their ascent, not only 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 appeared that as when the Air in the Receiver was expanded more than ordinarily, the Quicksilver in the Tube did proportionably subside; so when the Air in the same Receiver was a little more than ordinarily compressed, it did impel up the Quicksilver in the Tube above the wont height of betwixt six and seven and twenty digits. And if to these things we annex, that for aught we can find by trials purposely made, the degree of rarity or density of the Air, shut up into our Receiver, does 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 faintly hinder the ascent of the Quicksilver, 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 Quicksilver in the Vessel, that in the Tube was impelled 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 Quicksilver: I rather say, that such alterations may be, then that they are the causes of our Phaenomenon, because I think it sufficient, if I have proposed conjectures not altogether irrational about a new Mystery of Nature, touching which, the chief thing I pretend to, is to give occasion to the Curious to inquire further into it then I have been yet able to do. Experiment 19 THe same Reason that moved 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, induced 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 Quicksilver: 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 sealed at one end, of about four foot in length, and not very slender: This at the open end we filled with common Water, and then stopped that end till we had inverted the Tube, and opened it beneath the surface of a quantity of the like Water, contained in a somewhat deep and slender Vessel. This Vessel, with the Tube in it, was let down into the Receiver, and the Receiver being closed up after the accustomed manner, the Pump was set a-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 continued topful of Water as when it was put in, it being requisite that a great part of the Air formerly contained in the Receiver, should be drawn out, to bring the remaining Air to an Aequilibrium with so short and light a Cylinder of Water. But when once the Water began to fall in the Tube, than each exsuction of Air made it descend a little lower, though nothing near so much as the Quicksilver at the beginning did in the Experiment formerly mentioned. Nor did there appear so much inequality in the spaces transmitted by the Water in its descent, as there did in those observed in the ●all of the Quicksilver, of which the cause will scarce seem abstruse to him that shall duly reflect upon what has been already delivered. And whereas we drew down the Quicksilver in the Tube so far as to bring it within an Inch of the surface of the other Quicksilver into which it was to fall; the lowest we were able to draw down the Water was, by our conjecture, to about a Foot or more above the surface of that in the Vessel; of which I know not whether it will be needful to assign so obvious a cause as that, though the little Air remaining in the Receiver could not hinder a Cylinder of above an Inch high of Quicksilver from subsiding; yet it might very well be able, by its pressure, to countervail the weight of a Cylinder of a Foot long or more, of a Liquor so much less ponderous than Quicksilver, as Water is. And in fine, to conclude our Experiment, when the Water was drawn down thus low, we found, that by letting in the outward Air, it might be immediately impelled up again to the higher parts of the Tube. We will add no more concerning this Experiment, save that having tried it in one of our small Receivers, we observed, That upon the first exsuction of the Air the Water did usually subside dive●s Inches, and at the second (exsuction) fall down much lower, subsiding sometimes near two Foot; as also that upon the letting in of the Air from without, the Water was impelled up with very great celerity. THat the Air has a notable Elastical power (whencesoever that proceeds) we have, Experiment 20. I suppose, abundantly evinced, and it gins to be acknowledged by the eminentest Modern Naturalists. But whether or no there be in Water so much as a languid one, seems hitherto to have been scarce considered, nor has been yet, for aught I know, determined either way by any Writer, which invited us to make the following Experiment. There was taken a great Glass-bubble, with a long neck; (such as Chemists are wont to call a Philosophical Egg) which being filled with common Water till the Liquor reached about a span above the bubble, and a piece of Paper being there pasted on, was put unstopped into the Receiver, and then the Air was sucked out after the wont manner. The event was this, That a considerable part of the Air, penned up in the Receiver, was drawn out before we discerned any expansion of the Water; but, continuing the labour of pumping, the Water manifestly began to ascend in the stem of the Glass, and divers bubbles loosening themselves from the lower parts of the Vessel, made their way through the Body of the Water, to the top of it, and there broke into the Receiver: And after the Water once appeared to swell, then at each time the Stop-cock was turned to let out the air from the Receiver into the Pump, the Water in the Neck of the Glass did suddenly rise about the breadth of a Barleycorn in the Neck of the Glass, and so attained, by degrees, to a considerable height above the mark formerly mentioned. And at length (to make the expansion of the Water more evident) the outward Air was suddenly let in, and the Water immediately subsided and deserted all the space it had newly gained in the Glass. And, on this occasion, it will not perhaps be amiss to acquaint Your Lordship here (though we have already mentioned it in another Paper, to another purpose) with another Expedient that we made use of two or three years ago, to try whether or no Water had a Spring in it. About that time then, That Great and Learned Promoter of Experimental Philosophy Dr. Wilkins, doing me the Honour to come himself, and bring some of his inquisitive Friends to my Lodging, we there had in readiness a round and hollow Vessel of Pewter, great enough to contain two pounds of Water, and exactly close every where, but at one little hole where it was to be filled; then partly by sucking out the Air, and partly by injecting Water with a Syringe, it was (not without some difficulty) filled up to the top; and that hole being placed directly upwards, there was a little more Water leisurely forced in by the Syringe. Upon which, though the Vessel were permitted to rest, and the hole kept in its former posture, yet the compressed Water leisurely swelled above the Orifice of the hole, and divers drops ran over along the sides of the Vessel. After this, we caused a skilful Pewterer (who had made the Globe) to close it up in our presence with Soder so tightly, that none suspected there was any thing left in it besides Water. And lastly, the Vessel thus soldered up, was warily and often struck in divers places with a Wooden Mallet, and thereby was manifestly compressed, whereby the enclosed Water was crowded into less room than it had before: And thereupon when we took a Needle, and with it and the Mallet perforated the Vessel, and drew out the Needle again; the Water (but in a very slender Stream) was suddenly thrown after it into the Air, to the height of two or three Feet. As for the other Phaenomena of this Experiment, since they belong not to our present purpose, and are partly mentioned in another of our Papers, we shall, instead of recording them here, give this Advertisement: That as evidently as this Experiment, and that made in our Receiver, seem to prove a power in the Water to expand and restore itself after compression; yet for a reason to be met with ere long, I judged it not safe to infer that Conclusion from these Premises, till I had made some of the following trials, to the mention of which I will therefore hasten. TO discover whether the Expansion of the Water really proceeded from an Elastical power in the parts of the Water itself, Experiment 21. we thought it requisite to try two things: The one, Whether or no the Atmosphere gravitates upon Bodies under Water; and the other, Whether in case it do gravitate, the Intumescence of the Water may not be ascribed to some substance subtler than itself, residing in it. In order to the satisfying myself about the first of these, I intended to let down into the Receiver a Vessel of Water, wherein should be immersed a very small oiled Bladder, almost devoid of Air, but strongly tied up at the Neck with a string, and detained a little under Water by such a weight fastened to that string, as should just be able to keep the Bladder from swimming, and no more. For I supposed, that if when all things were thus ordered, the Receiver were emptied, in case there were any such pressure of the Atmosphere upon Water, as I was inclined to believe, the Air within the Bladder, being upon the exsuction of the Air within the Receiver, freed from that pressure, and being pressed only by the small weight of the incumbent Water, would considerably expand itself; but whilst we were preparing Bladders for this Experiment, there occurd an easy way for the making at once both the Discoveries I desired. We took then a Glass Viol., containing by guess a pound and some ounces of Water, this we filled 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 no Water get out of it, otherwise then through the Pipe; and then the Pipe being warily filled, about half way up to the top, with more Water, and a mark being pasted over against 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 wont manner tightly closed 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 discovered themselves. After a little while longer, the Water still swelling, there appeared 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, stayed there awhile and then broke; but the Pump being nimbly plied, the expansion of the Water so increased, that quickly, getting up to the top of the Pipe some drops of it began to run down along the outside of it, which obliged us to forbear pumping awhile, 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 at 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 appeared to be of the size of the smaller sort of Peas; and of these we reckoned 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 spite of all our pains and industry, some undiscerned Leak or other in the Receiver hindered us from being able to empty it altogether) we thought fit to desist for that time. After trial 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 mentioned, 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 pumped out of the Receiver, the rising bubbles ascended so very slowly in the Pipe, that their Progress was scarce discernible; which seemed 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 these bubbles should be of any considerable bulk, since 'tis 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, 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 emptied, 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 further observed, That whereas in the bubbles that first appeared in the Pipe, the ascending Air did, as in other common bubbles, make its way upwards, by dividing the Water through which it passed, in those bubbles that appeared 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 now 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, & 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 relapsed to their former inconspicuousness. All these things laid together seemed sufficiently to confirm that, which the consideration of the thing itself would easily enough persuade, namely, That the Air, and such like Bodies being under Water, may be pressed upon as well by the Atmosphere, as by the weight of the incumbent Water itself. Hence likewise we may verify what we observed 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 endowed with an Elastical power of expanding itself, since thereby it appears that the Intumescence produced by that Experiment, may (at least in great part) be ascribed to the numerous little bubbles which are wont to be produced in Water, from which the pressure of the Atmosphere is in great measure taken off. So apt are we to be misled, even by Experiments themselves, into Mistakes, when either we consider not that most Effects may proceed from various Causes, or mind only those Circumstances of our Experiment, which seem to comply with our preconceived Hypothesis or Conjectures. And hence it seems also probable, that in the Pores or invisible little recesses of Water itself there lie commonly interspersed many parcels of either Air, or at least something Analogous thereunto, although so very small that they have not been hitherto so much as suspected to lurk there. But if it be demanded how it appears that there is interspersed through the Body of Water any substance thinner than itself, and why that which produced the bubbles above mentioned should not be resolutely said to be nothing else then a more active and spirituous part of the Water, we shall, in order to the Elucidation of this matter, subjoin to what was formerly delivered the following Experiment. WE recited in our nineteenth Experiment, Experiment 22. how by drawing most of the Air out of the Receiver, we made the Water subside by degrees in a Glass not four Foot long: We shall now add, that in the like Experiment made in such a Tube, or a greater, it may be observed, That when the Water gins to fall, there will appear store of bubbles fastened all along to the sides of the Glass; of which bubbles, by the agitation of the Vessel consequent upon pumping, there will arise good numbers to the top of the Water, and there break; and as the Cylinder of Water is brought to be lower and lower, so the bubbles will appear more numerous in that part of the Tube which the Water yet fills; and the nearer the surface of the Water, in its descent, approaches to these bubbles, the greater they will grow, because having the less weight and pressure upon them, the Expansion of that Air which makes them, can be the less resisted by the pressure of the incumbent Water and Air; as seems probable from hence, that upon the letting in a little external Air, those bubbles immediately shrink. It may indeed, as we lately intimated, be conjectured, that these bubbles proceed not so much from any Air pre-existent in the Water, and lurking in the Pores of it, as from the more subtle parts of the Water itself; which by the expansion allowed them upon the diminished pressure of the ambient Bodies may generate such bubbles. And indeed, I am not yet so well satisfied that bubbles may not (at least sometimes) have such an Origination: but that which makes me suspect that those in our trials contained real Air formerly latitant in the Pores of the Water, is this, That upon the inletting of the external Air, the Water was not again impelled to the very top of the Tube whence it began to fall, but was stopped in its ascent near an Inch beneath the top. And since, if the upper part of the Tube had been devoid of any other than such Ethereal matter as was subtle enough freely to penetrate the pores of the Glass, the external Air would have been able to impel the Water to the top of a Tube seven or eight times as long as ours was; The Phaenomenon under consideration seemed manifestly to argue that the many bubbles that broke at the top of the Water did contain a real Air, which, being collected into one place and hindered by the top of the Glass from receding, was able to withstand the pressure of the outward Air. As we see that if never so little Air remain in the Tube upon the making the Experiment De Vacuo with Quicksilver, no inclining of the Tube, though a long one, will enable a Man to impel the Mercury up to the very top, by reason (as we formerly noted) of the resistance of the included Air, which will not be compressed beyond a certain degree. But in order to a further Discovery what our bubbles were, we will, on this occasion, inform Your Lordship that we tried the XIXth Experiment in one of our small Receivers, and found, that upon the drawing down of the Water, so many bubbles disclosed themselves and broke into the upper part of the Tube, that having afterwards let in the external Air, the Water was not thereby impelled to the top of the Tube (three Foot in length) within a little more than half an Inch. And whether or no it were Air that possessed that space at the top of the Tube which was not filled with Water, we took this course to examine. We drew the second time the Air out of the Receiver, and found, that by reason of the body that possessed the top of the Tube, we were able not only to make the Water in the Tube fall to a level with the surface of the Water in the Vessel: But also (by plying the Pump a little longer) a great way beneath it: which since it could not well be ascribed to the bare subsiding of the Water by reason of its own weight, argued that the Water was depressed by the Air: which was confirmed by the Figure of the surface of the Water in the Tube, which was much more concave than that of Water in Tubes of that bigness uses to be. And this further trial (to add that upon the by) we made at the same time, That when the Water in the Pipe was drawn down almost as low as the Water without it, we observed, that (though we desisted from pumping) by the bare application of a hand moderately warm to the deserted part of the Tube, the remaining Water would be speedily and notably depressed. And having for a while held a kindled Coal to the outside of the Tube, (the Pump being still unemployed, because the Vessel chanced to hold extraordinarily well) the Air was by the heat so far expanded, that it quickly drove the Water to the bottom of the Tube, which was divers Inches beneath the surface of the ambient Water. Whereby it appears (by the same way by which we formerly measured the dilatation of the Air) that the Air, even when it is expanded to between 90 and 100 times, its extent will yet readily admit of a much further rarifaction by heat. I considered also that in case the Bubbles we have been speaking of, were produced by the parcels of Air latitant in the Water, that Air being now got together to the top of the Tube, though the Air were again drawn out of the Receiver, the taking off its pressure would not disclose bubbles as before; and accordingly, the Air being again pumped out, the Water in the Tube descended as formerly: but for a great while we scarce saw one bubble appear, only when the Receiver had been very much exhausted, and the Water was fallen very low, there appeared near the bottom of the Tube, certain little bubbles, which seemed to consist of such parcels of Air as had not, by reason of their smallness, got up to the top of the Water, with the more bulky and vigorous ones. And that which is not inconsiderable, is, That having, by letting in the Air, forced up the Water into the Tube, we could not perceive that it ascended nearer the top, though we permitted the Engine to remain unemployed for two or three Nights together, and watched whether the Water would swell up and fill the Tube. And on this occasion I remember, that having tried such an Experiment as this with Quicksilver instead of Water, in a Tube of about a Foot and a half long, wherein it might seem more hopeful to escape bubbles; yet upon the drawing down the Quicksilver as low as we could, and letting in the external Air upon it, we found that some lurking particles of Air were got up to the top of the Tube, and hindered the Quicksilver from being forced up again so high. And though the Quicksilver were by this means brought to appear a very close and lovely Metalline Cylinder, not interrupted by interspersed bubbles as before; yet having caused the Air to be again drawn out of the Receiver, I could perceive several little bubbles to disclose themselves, fastened to the inside of the Tube, near the bottom of it; and having purposely watched one or two of the chiefest, I had the pleasure to observe, that though they grew bigger and bigger as the surface of the Mercurial Cylinder fell nearer and nearer to them, so as that at length they swelled into a conspicuous bulk; yet upon the wary letting in the Air upon them, they did not break, but presently shrunk up into a littleness that rendered them inconspicuous. Whence it seems very probable, if not certain, that even in the closest and most ponderous Liquors, and therefore much more in Water, there may lurk undiscernible parcels of Air, capable, upon the removal of the pressure of the ambient Air (though but in part) and that of the Liquor wherein it lurks, to produce conspicuous bubbles. And consequently, if it seem inconvenient to admit an Elastical power in the Water, it may be said that the swelling of the compressed Water in the Pewter Vessel lately mentioned, and the springing up of the Water at the hole made by the Needle, were not the effects of any internal Elater of the Water, but of the spring of the many little particles of Air dispersed through that Water, and acting upon it in their sudden recovering themselves to a greater extent, then that to which a violent compression had reduced them. But though, from all these particulars, it seems manifest that the bubbles we have been all this while treating of, were produced by such a substance as may be properly enough called Air; yet till we shall have had the opportunity of making some further trials concerning the nature of the Air, we shall not resolutely determine whether or no Air be a Primogenial Body (if I may so speak) that cannot now be generated or turned either into Water or any other Body. Yet in the mean while (because it is an important Question, and if rightly determined, may much conduce to the knowledge of the nature of the Air) We think it not unfit to make a brief mention of some of the particulars which at present occur to our thoughts in favour of either part of the Question. First then, divers Naturalists esteem the Air (as well as other Elements) to be ingenerable and incorruptible. And reasons plausible enough may be drawn to countenance this Opinion from the consideration of that permanency that ought to belong to the corporeal Principles of other Bodies. Next, Experience may be pleaded to the same purpose, for I have read of some who have in vain attempted to turn Air into Water, or Water into Air. The diligent Schottus tells us, Schottus Mech●●: hydrau●icopne●mat: Part 3. Cla●●. 1. That amongst the other rarities to be met with in that great Repository of them, the Musaeum Kercherianum, there is a round Glass with a tapering Neck near half full (as one may guests by the Scheme he annexes) of ordinary Spring-water, which having been Hermetically shut up there by Clavius the famous Geometrician, The included water is to this day preserved, not only clear and pure, as if it were but newly put in: But (as it seems) without (in the least) turning into Air, notwithstanding its having been kept there these fifty years: For he tells us, That the Water hath continued there all this while without any diminution. Nor does it appear in those Glasses, which for Chemical Experiments we usually close with Hermes his Seal (as they call it) that the included Air does, during its long Imprisonment, notwithstanding the alteration it receives from various degrees of heat, discernably alter its nature. Whereas we plainly perceive in our Digestions and Distillations, that though it may be rarified into invisible Vapours, yet it is not really changed into Air, but only divided by heat, and scattered into very minute parts, which meeting together in the Alembick or in the Receiver, do presently return into such Water as they constituted before. And we also see, that even Spirit of Wine, and other subtle and fugitive Spirits, though they easily fly into the Air, and mingle with it, do yet in the Glasses of Chemists easily lay aside the disguise of Air, and resume the devested form of Liquors. And so volatile Salts, as of Urine, Hartshorn, etc. though they will readily disperse themselves through the Air, and play up and down in the capacity of an Alembick or a Receiver: yet will they, after a while, fasten themselves to the insides of such Glasses in the form of Salts. Besides, since Air is confessedly endowed with an Elastical power that probably proceeds from its Texture, it appears not what it is that in such light alterations of Water, as are by many presumed capable of turning it into Air, can be reasonably supposed so to contrive the Particles of Water, as to give them, and that permanently, the structure requisite to a Spring. I add the word, Permanently, because the newly mentioned observations seem to argue the Corpuscles of Air to be irreducible into Water, whereas the Aqueous Particles may perhaps for a while be so vehemently agitated, as to press almost like Springs upon other Bodies; yet upon the ceasing of the agitation, they quickly, by relapsing into Water, disclose themselves to have been nothing else whilst they counterfeited the Air. Lastly, The Experiment formerly made in our Engine with a piece of Match, seems to evince, that even those light and subtle Fumes (for the most part not aqueous neither) into which the Fire itself shatters dry Bodies, have no such Spring in them as the Air, since they were unable to hinder or repress the expansion of the Air included in the Bladder they surrounded. Natural & Mo●al Hist. of the Indies, Lib. 3. C. 9 I remember indeed that the Learned josephus Acosta, in his History of the West Indies, tells us, That he saw in those parts some Grates of Iron so rusted and consumed by the Air, that the Metal being pressed between the Fingers, dissolved (to use his words) to powder, as if it had been Hay or parched Straw. And I remember too, Geogr. Gen●●al. Lib. 1. c. 19 that the accurate Varenius tells us, That in the Islands commonly called Azores, the Air (and Wind) is so sharp, that in a short time it frets not only Iron Plates, but the very Tiles upon the Roofs of Houses, and reduces them to dust. And I have elsewhere mentioned some recent Observations of this kind. But it may be said, That the abovementioned Authors ascribe the recited effects chief to the Winds, and that however the corrosion of the Iron and the Tiles may proceed not from the Air itself, or any of its genuine parts, but from some ●aline Corpuscles dispersed through the Air, and driven by the Winds against the Bodies it is presumed to fret. And that such volatile Salts may copiously ascend into the Air, and yet retain their Nature, as doth the more fixed Salt in the Sea Water, the sublimations of Salarmoniack may sufficiently evince. Not to mention that I have shown some Friends a secret kind of saline Substance incomparably subtler than Salarmoniack, which did not only easily enough ascend itself, but carried up with it (and that in a very great proportion) the solid and ponderous Body even of uncalcined Gold in the form of subtle exhalations, which did afterwards fasten themselves to the upper parts of the Vessels, and yet manifest themselves to continue Gold. We remember also, that to try whether Water could be turned into Air, we once took an Aeolipile, into which we had before conveyed some Water, and placing it upon kindled Coals when the heat forced out a vehement stream of aqueous Vapours; we tied about the neck of it, that of a Bladder, which we had before emptied of Air; and finding the Aeolipile after a while to blow up the Bladder, we carefully tied it again that the included substance might not get away. Then slipping it off from the Aeolipile we conveyed it into our Receiver, to try whether or no that which in part distended the Bladder would appear by its Spring to be true Air: whereby we found that upon the exsuction of the ambient Air, the included substance expanded itself and the Bladder to a very much greater bulk than it was of before. And for further satisfaction, having again taken out the Bladder, we suffered it to remain tied up till next morning, to try whether time, and the coldness of the night, would make the contained substance relapse into Water: But the next Morning we found it little less tumid than before. I remember, I say, that I once made this Experiment; but I might say in answer to it, that the chief reason of my mentioning it, is, To let Your Lordship see how requisite it is to be circumspect and considerate, when we are to make and to build upon nice Experiments. For though I may seem to have used sufficient caution, yet afterward considering with myself that the Aeolipile I had employed was a very large one, and that it required much more care than one that has not tried it would imagine, to drive out all the Air from a large Aeolipile, I easily suspected that the distension of the Bladder in our pneumatical Vessel, might proceed not from the Watery steams that came out at the narrow mouth of the Aeolipile, and had very much wetted the Bladder, but from the rarified Air which in that sort of Vessels is wont for a good while together to come out with the rarified Water: and accordingly having reiterated the Experiment I found it very difficult (by reason of the shrinking of the Bladders (upon their being heated) and of other impediments) to make it so accurately as to deduce from it, that Water may be rarified into true Air. Against the four other abovementioned Considerations, we cannot spend time to frame Objections, but must forth with proceed to the mention of those things that seem to argue that Air (at least such as produced our bubbles) maybe generated of Water and other Bodies. First then we have found by Experience that a vapid Air, or Water rarified into vapour, may at least for a while emulate the elastical power of that which is generally acknowledged to be true Air. For if you take a good Aeolipile, with a moderately strong and slender Neck, and filling it with Water, lay it upon quick Coals, you may after a while observe so great a pressure by some of the parts contained in the Aeolipile upon others, that the Water will sometimes be thrown up into the Air above three or four Foot high; and if you then take the Aeolipile almost red hot from off the Fire, you may perceive that the Water will for a longer time than one would easily imagine continue to be spouted out in a violent Stream. And if there remains but little Water in the Aeolipile when 'tis taken very hot from the Fire, immersing the Neck of it into cold Water, you will find, that after it gins to suck in some Water, there will be made from time to time store of large bubbles in that Water whereinto the neck was plunged. Which bubbles seem manifestly to proceed from hence, that for a while the heat in the Aeolipile continues strong enough to rarify part of the Water that is sucked in, and expel it in the form of Vapours through the Water incumbent on the Pipe. If also when the Aeolipile is almost full of water, and therefore can contain but little Air; you hold a Coal or Brand in that stream of Vapours that issues out of the narrow mouth of it, you will find this vapid or rorid Air, (if I may so call it) to blow the Fire very strongly and with a roaring noise. And that it be not said that 'tis by the external Air which the aqueous steams drive before them, and not by the Steams themselves, that the Blast is made and the Flame excited; it has been observed, that by approaching the Coal or Brand almost to the mouth of the Aeolipile, the wind appeared more vehement than if the Body to be kindled were held some Inches off. But in regard the elastical power of the Stream, issuing out of an Aeolipile, seems manifestly due to the heat that expands and agitates the aqueous Particles whereof that Stream consists, and that such rapid winds seem to be but water scattered into little parts and set a moving; since we find, that holding a Knife, or any solid, smooth and close Body against the stream that issues out of the Aeolipile, the vapours condensing upon it, will presently cover it with water: It will be very pertinent to subjoin a notable Experiment that I remember I have met with in the description given us by the Industrious Kircher, of several Musical Engines. And (though it may seem somewhat prolix) we will recite what he delivers in his own words, which are these. 〈…〉 & 〈◊〉: lib. 9 p. 309. Cum eodem tempore quo haec scripsi summi Pont: Innocentii X mi mandato organi hydraulici in horto Quirinali constituendi cur a mihi commendata esset; Aeoliam cameram insigni sane successu construi jussimus, eâ quae sequitur ratione. Erat longitudo sive altitudo camerae AH 5 Pedum, Latitudine 3 fear ex lateribus constructa; in medio duo tenebat Diaphragmata CD & EJ in modum cribri pluribus for aminibus pertusa. Paulo infra canalis G aquam advehens inserebatur in H eidem epistomium parabat exitum. Aqua itáque per canalem G maximo impetu ruen● vehementissimum ventum mox intus excitabat; qui ventus nimia humiditate imbutus, ut purior exiret sicciorque, Diaphragmata illa in cribri modum pertusa, ordinata sunt. Intra haec enim aquae vehemens agitatio rupta fractaque aerem puriorem per A canalem subtilioremque emittebat: Verum cum postea inventum sit acrē plus aequo humidum interioribus Organi meatibus maximum detrimentum infer: Hinc ut aer aquosus siccissimam consistentiam acquireret, ordinavimus canalem plumbeum QR in helicem contortum vasi S aliquantulum capaciori in modum Urnae efformato, inser●um. Intra urnam enim plumbeam & canalem tortuosum illisus aer humidus, ita ab omni aquositate defaecabatur, ut ex furno in Organum derivatus dici potuerit. Urna S canalis tortuosus QR ultimum orificium Q inseritur anemothecae organi. Et hunc modum organis hydraulicis omnium aptissimum reperi. Debet autem camera illa situari in loco quantum fieri potest sicciori ita ut longo canali aqua intra eam derivetur ne locus humiditate sua Organis officiat. Thus far the Ingenious Kircherus, whom I the rather cite, because although I have been informed of divers Ventiducts (as they call them) by very knowing Travellers that have observed them: Yet this relation of our Author being very punctual, and delivered upon his own particular Experience, has, I confess, made me wish I had had the good fortune when I was at Rome, to take notice of these Organs; or that I had now the opportunity of examining of such an Experiment. For if upon a strict inquiry I should find that the breath that blows the Organs does not really upon the ceasing of its unusual agitation by little and little relapse into water, I should strongly suspect that 'tis possible for Water to be easily turned into Air. I remember indeed, that we have formerly taught that there lurks an interspersed Air in the pores of ordinary Water, which may possibly be struck out by the breaking of the Water in its fall into the Aeolian Chamber, (as he calls it.) But in regard the Scheme seems to represent that Chamber as closely shut, and thereby forbids us to suppose that any Air is carried into it. but what is latitant in the Water, it will scarce seem probable to him who remembers how small a proportion of Air, that appeared to be when its rarification seized, which was concealed in the Water we freed from bubbles in our Receiver, that so little Air as is commonly dispersed through Water, should be able, in so little Water as was requisite for so small a room, to make so vehement a Wind as our Author here tells us of. I have sometime therefore suspected, that in this case the Wind may be produced by small particles of the water itself, forcibly expelled out of the Chamber into the Organs. And to the Objection to which I foresaw this guess to be liable, namely, That, no heat intervening, there appeared nothing that should raise the Water into exhalations and give them an impulse. I thought it might be said that motion alone, if vehement enough, may, without sensible heat, suffice to break Water into very minute parts, and make them ascend upwards, if they can not where else more easily continue their agitation. For I remember, that Travelling betwixt Lions and Geneva, I saw, not very far out of the Way, a place where the River of Rhone coming suddenly to be streighten'd betwixt two Rocks, so near each other, that a Man may (if my Memory fail me not) stand astride upon both at once: that rapid Stream dashing with great impetuosity against its Rocky Boundaries, does break part of its Water into such minute Corpuscles, and put them into such a motion, that Passengers observe at a good distance off, as it were a Mist arising from that place, and ascending a good way up into the Air. Such, I say, was my suspicion touching the Wind we have been considering, but it seems something odd that aqueous Vapours should, like a dry Wind, pass through so long and tortuous a Pipe of Lead, as that described by our Author, since we see in the Heads of Stills, and the Necks of Aeolipiles, how quickly such vapours are even by a very little cold recondensed into Water. But to this also something may be speciously replied; wherefore contenting myself to have mentioned our Author's Experiment as a plausible, though not demonstrative proof, that Water may be transmuted into Air. We will pass on to mention in the third place another Experiment, which we tried in order to the same enquiry. We took a clear Glass bubble (capable of containing by guess about three Ounces of Water) with a Neck somewhat long and wide, of a Cylindrical form; this we filled with Oil of Vitriol and fair water, of each almost a like quantity, and casting in half a dozen small Iron Nails, we stopped the mouth of the Glass (which was topful of Liquor) with a flat piece of Diapalma provided for the purpose, that accommodating itself to the surface of the water, the Air might be tightly excluded: and speedily inverting the Viol, we put the Neck of it into a small wide-mouthed Glass that stood ready with more of the same Liquor in it, to receive it. As soon as the neck had reached the bottom of the Liquor it was dipped into, there appeared at the upper part (which was before the bottom) of the Viol a bubble, of about the bigness of a Pea, which seemed rather to consist of small and recent bubbles, produced by the action of the dissolving Liquor upon the Iron, than any parcel of the external Air that might be suspected to have got in upon the inversion of the Glass, especially since we gave time to those little Particles of Air which were carried down with the Nails into the Liquor to fly up again. But whence this first bubble was produced, is not so material to our Experiment, in regard it was so small: For soon after we perceived the bubbles produced by the action of the Menstruum, upon the Metal ascending copiously to the bubble already named, and breaking into it, did soon exceedingly increase it, and by degrees depress the water lower and lower, till at length the substance contained in these bubbles possessed the whole cavity of the Glass Viol., and almost of its Neck too, reaching much lower in the Neck than the surface of the ambient Liquor, wherewith the open-mouthed Glass was by this means almost replenished. And because it might be suspected that the depression of the Liquor might proceed from the agitation whereinto the exhaling and imprisoned steams were put, by that heat which is wont to result from that action of corrosive salts upon Metals, we suffered both the Viol and the openmouth Glass to remain as they were, in a Window, for three or four days and nights together; but looking upon them several times during that while, as well as at the expiration of it, the whole cavity of the Glass bubble, and most of its Neck, seemed to be possessed by Air, since by its spring it was able for so long to hinder the expelled and ambient Liquor from regaining its former place. And it was remarkable, that just before we took the Glass bubble out of the other Glass, upon the application of a warm hand to the convex part of the bubble; the Imprisoned substance readily dilated itself like Air, and broke through the Liquor in divers bubbles, succeeding one another. Having also another time tried the like Experiment with a small Viol, and with Nails dissolved in Aquafortis, we found nothing incongruous to what we have now delivered. And this Circumstance we observed, that the newly generated steams did not only possess almost all the whole cavity of the Glass, but divers times without the assistance of the heat of my hand, broke away in large bubbles through the ambient Liquor into the open Air: So that these Experiments with corrosive Liquors, seemed manifestly enough to prove, though not that Air may be generated out of the Water, yet that in general air may be generated anew. Lastly, to the foregoing Arguments from Experience we might easily subjoin the Authority of Aristotle, and of (his followers) the Schools who are known to have taught, that Air and Water being Symbolising Elements (in the quality of moisture) are easily transmutable into one another. But we shall rather to the foregoing Argument add this, drawn from Reason, That if, as Leucippus, Democritus, Epicurus and others, followed by divers modern Naturalists, have taught, the difference of Bodies proceeds but from the various Magnitudes, Figures, Motions, and Textures of the small parts they consist of, (all the qualities that make them differ, being deducible from thence) there appears no reason why the minute parts of Water, and other Bodies, may not be so agitated or connected as to deserve the name of Air. For if we allow the Cartesian Hypothesis, according to which, as we noted at the beginning of this Letter, the Air may consist of any terrene or aqueous Corpuscles, provided they be kept swimming in the interfluent Celestial Matter; it is obvious that Air may be as often generated, as Terrestrial Particles minute enough to be carried up and down, by the Celestial Matter ascend into the Atmosphere. And if we will have the Air to be a congeries of little slender Springs, it seems not impossible, though it be difficult, that the small parts of divers Bodies may by a lucky concourse of causes be so connected as to constitute such little Springs, since (as we note in another Treatise) Water in the Plants it nourishes is usually contrived into Springy Bodies, and even the bare altered position and connexion of the parts of a Body may suffice to give it a Spring that it had not before, as may be seen in a thin and flexible Plate of Silver; unto which, by some strokes of a Hammer, you may give a Spring, and by only heating it read hot you may make it again flexible as before. These, My Lord, are some of the Considerations at present occurring to my thoughts, by which it may be made probable that Air may be generated anew. And though it be not impossible to propose Objections against these, as well as against what has been represented in favour of the contrary Doctrine; yet having already almost tired myself, and I fear more than almost tired Your Lordship with so troublesome an Enquiry after the Nature of bubbles, I shall willingly leave Your Lordship to judge of the Arguments alleged on either side, and I should scarce have ventured to entertain You so long concerning such empty things as the Bubbles, which have occasioned all this Discourse, but that I am willing to invite You to take notice with me of the obscurity of things, or the dimness of our created Intellects (which yet of late too many so far presume upon, as either to Deny or Censure the Almighty and Omniscient Creator himself) and to learn hence this Lesson, That there are very many Things in Nature that we disdainfully overlook as obvious or despicable, each of which would exercise our Understandings▪ if not pose them too, if we would but attentively enough consider it, and not superficially contemplate, but attempt satisfactorily to explicate the nature of it. Experiment 23. SInce the writing of the twenty one and twenty second Experiments (and notwithstanding all that hath been on their occasion delivered concerning bubbles) we made some further trials in prosecution of the same inquiry whereto they were designed. We chose then, amongst those Glasses which Chemists are wont to call Philosophical Eggs, one that containing about nine Ounces of Water, had a Neck of half an Inch in Diameter at the top, and as we guest, almost an Inch at the bottom; which breadth we pitched upon for a reason that will by and by appear: then filling it with common Water to the height of about a Foot and a half, so that the upper part remained empty, we shut it into the Receiver, and watched what would follow upon pumping, which proved that a great part of the Air being drawn out, the bubbles began to discover themselves at the bottom and sides of the Glass▪ and increasing, as the Air was more and more drawn away, they did from time to time ascend copiously enough to the top of the Water, and there quickly break: but by reason that the wideness of the Glass allowed them free passage through the Water, they did not appear as in the former Experiments to make it swell: The Water scarce ever rising at all above the mark affixed to its upper surface when it was put in, and upon the return permitted to the outward Air, and consequently the shrinking in of the remaining bubbles, the Water seemed to have lost of its first extent, by the avolation of the formerly interspersed Air. Being willing likewise to try whether distilled Water were by having been divided into minute parts, and then reunited, more or less disposed to expand itself then Water not distilled: We took out of our Laboratory some carefully distilled Rain-water, and put about two Ounces of it into a round Glass bubble with a very small Neck (not exceeding the sixth part of an Inch in Diameter) which we filled half way to the top, and then conveyed it into the Receiver; the issue was, That though we drew out more than ordinary, yet there appeared not the least intumescence of the Water, nor any ascending bubbles. But suspecting that either the small quantity of the water or the Figure of the Vessel might have an interest in this odd Phaenomenon, we took the lately mentioned Philosophical Egg, and another not much differing from it; the former we filled up with distilled Rain-water to the old mark, and into the latter we put a long Cylinder or Rod of solid Glass to straighten the cavity of the Neck by almost filling it up; and then pouring some distilled Water into that also, till it reached within some Finger's breadth of the top, the Eggs were let down into the Receiver. In this Experiment the Air was so far drawn forth before there appeared any bubble in either of the Glasses, that the disparity betwixt this and common water was manifest enough. But at length, when the Air was almost quite pumped out, the bubbles began to disclose themselves, and to increase as the pressure of the Air in the Receiver decreased. But whereas in the first mentioned Philosophical Egg the bubbles were very small, and never able to swell the Water, that we took notice of, at all above the mark: In the other, whose Neck, as we lately said, was straightened, and their passage obstructed, great numbers of them, and bigger, fastened themselves to the lower end of the Glass rammer (if we may so call it) and gathered in such numbers between that and the sides of the Neck, that the Water swelled about a Finger's breadth above the mark, though upon the admitting of the external Air it relapsed to the former mark, or rather fell somewhat below it. And although thereupon in the first named Vessel all the bubbles presently disappeared, yet in the other we observed, that divers remained fastened to the lower part of the Glass rammer, and continued there somewhat to our wonder, for above an hour after, but contracted in their Dimensions. Moreover, having suffered the Glasses to remain above twenty four hours in the Receiver, we afterwards repeated the Experiment, to try what change the exsuction of the external Air would produce in the Water, after the internal and latitant Air had (as is above recited) in great measure got away in bubbles, and whether or no the Water would by standing re-admit any new particles of Air in the room of those that had forsaken it. But though we exhausted the Receiver very diligently, yet we scarce saw a bubble in either of the Glasses; notwithstanding which, we perceived the Water to rise about the breadth of a Barleycorn, or more, in the Neck of that Glass wherein the solid Cylinder had been put; The Liquor in the other Glass not sensibly swelling. And lastly, upon the letting in of the Air, the Water in the straightened Neck soon subsided to the mark above which it had swollen, which whether it ought to be ascribed to the same small expansion of the parts of the Water itself, or to the rarifaction of some yet latitant Air broken into such small particles, as to escape our observation, seems not easily determinable, without such further trials, as would perhaps prove tedious to be recited as well as to be made, though I was content to set down those already mentioned, that it might appear how requisite it is in nice Experiments to consider variety of Circumstances. AFter having thus discovered what operation the exsuction of the ambient Air had upon Water, Experiment 24. we thought good to try also what changes would happen in other Liquors upon the like taking off the pressure of the external Air. We took ●●en a Glass Egg, somewhat bigger than a Turkey Egg, which had a long Neck or Stem of about a ⅓ part of an Inch in Diameter; and filling it up with Salad Oil until it reached above half way to the top of the Neck, we enclosed it in the Receiver together with common Water in a resembling Vessel, that we might the better compare together the operation of the exsuction of the Air upon those two Liquors. The Pump being set a-work there began to appear bubbles in the Oil much sooner than in the Water, and afterwards they also ascended much more copiously in the former Liquor than the latter: Nay, and when by having quite tired the Pumper, and almost our own patience, we gave over, the bubbles rise almost (if not altogether) in as great numbers as ever, insomuch as none of the various Liquors we tried either before or since, seemed to abound more with Aerial Particles than did this Oil. In which it was further remarkable, that between the time it was set into the Receiver, and that at which we could get ready to Pump, it subsided notably (by guess about half an Inch) below the mark it reached before it was put in. After this expressed Oil, we made try●● of a distilled one, and for that purpose made choice of the common Oil or Spirit (for in the Shops where it is sold, the same Liquor is promiscuously called by either name) of Turpentine; because 'twas only of that Chemical Oil, we had a sufficient quantity: which, being put into a small Glass bubble with a slender Neck, so as to fill it to about two Inches from the top, did, upon the evacuating of the Receiver, present us with great store of bubbles; most of which rising from the bottom, expanded themselves exceedingly in their ascent, and made the Liquor in the Neck to swell so much by degrees, that at length it divers times ran over at the top: by which means, we were hindered from being able to discern upon the letting in of the Air, how much the subsidence of the Oil below the first mark was due to the recess of the bubbles. Having likewise a mind to try whether as strong a solution of Salt of Tartar in fair Water as could be made (we having then no Oil of Tartar per deliquium at hand) though it be accounted, Quicksilver excepted, the heaviest of Liquors would afford us any bubbles; we put in a Glass Egg full of it at the same time, with other Liquors, and found that they did long yield store of bubbles before any discovered themselves in the Liquor of Tartar; and having pursued the Experiment, it appeared, That of all the Liquors we made trial of, this afforded the fewest and the smallest Bubbles. Spirit of Vinager being tried after the same manner, exhibited a moderate number of bubbles, but scarce any thing else worth the mentioning. Nor could we in red Wine, tried in a Glass Egg, take notice of any thing very observable. For though upon the exsuction of the Air the bubbles ascended in this Liquor, as it were in shoals, and shifted places among themselves in their ascent; yet the Intumescence of the whole bulk of the Liquor was scarce at all sensible, the bubbles most commonly breaking very soon after their arrival at the top, where during their stay, they composed a kind of shallow froth, which alone appeared higher in the Neck of the Glass, than was the Wine when it was first let down. Neither yet did Milk, conveyed into our Pneumatical Vessel, present us with any thing memorable, save that (as it seemed by reason of some unctuousness of the Liquor) the bubbles not easily breaking at the top, and thrusting up one another made the intumescence appear much greater than that of common Water. We likewise conveyed Hens Eggs into the Receiver, but, after the exsuction of the Air, took them out whole again. That which invited us to put them in, was, That (as perhaps we mention in other Papers) we had among other Experiments of cold, made Eggs burst, by freezing them within doors with Snow and Salt: The Ice, into which the aqueous parts of the Egg were turned by the cold, so distending (probably by reason of the numerous bubbles wont to be observable in Ice) the outward parts of the Egg, that it usually cracked the shell, though the inner Membrane that involved the several Liquors of the Egg, because it would stretch and yield, remained unbroken. And hereupon we imagined that in our Engine it might appear whether or no there were any considerable Spring, either in any of the Liquors, or in any other more spirituous substance included in the Egg. We took also some Spirit of Urine, carelessly enough deflegmed, and put it into the same Glass (first carefully scoured and cleansed) wherein we had put the oil-olive above mentioned: We took also another Glass, differing from a Glass Egg, only in that its bottom was flat, and filled it up to about 2/5 of the Neck (which was wider than that of the Egg) with rectified Spirit of Wine. We took also another Glass Egg, and having filled it with common Water till it reached to the middle of the Neck, we poured to it of the same Spirit of Wine, till it reached about an Inch higher. These three Glasses having marks set on them, over against the edges of the contained Liquors were put into the Receiver, and that beginning to be evacuated, the bubbles in all the three Liquors began to appear. The mixture of the Spirit of Wine and Water disclosed a great store of bubbles, especially towards the top; but scarce afforded us any thing worth remembering. The Spirit of Urine appeared to swell near an Inch and an half above the mark; and besides that, sent forth store of bubbles, which made a kind of froth at the upper part of it. And above that spume there appeared eight or ten great bubbles one above another, in a very decent order, each of them constituting, as it were, a Cylinder of about half an Inch high, and as broad as the internal cavity of the Neck: So that all the upper part of the Neck (for these bubbles reached to the top) seemed to be divided into almost equal parts, by certain Diaphragmes, consisting of the coats of the bubbles, whose edges appeared like so many Rings suspended one above another. In the Spirit of Wine there did arise a great multitude of bubbles, even till weariness did make us give over the Experiment. And in these bubbles two or three things were remarkable; as first, That they ascended with a very notable celerity: Next, That being arrived at the top, they made no stay there, and yet, notwithstanding the great thinness and spirituousness of the Liquor, did, before they broke, lift up the upper surface of it, and for a moment or two form thereof a thin film or skin which appeared protuberant above the rest of the superficies like a small Hemisphere. Thirdly, That they ascended strait up, whereas those produced at the lower part of the Vessel, containing the mixture of the Water and Spirit of Wine, ascended with a wavering or wriggling motion, whereby they described an indented Line. Lastly, It was observable in the Spirit of Wine (and we took notice of the like in the Oil of Turpentine lately mentioned) that not only the bubbles seemed to rise from certain determinate places at the bottom of the Glass, but that in their ascension they kept an almost equal distance from each other, and followed one another in a certain order, whereby they seemed part of small Bracelets, consisting of equally little incontiguous Beads: the lower end of each Bracelet, being as it were, fastened to a certain po●nt at the bottom of the Glass. The Air being sparingly let into the Receiver, the great bubbles formerly mentioned as incumbent upon one another, in that Glass that contained the Spirit of Urine, were by orderly degrees lessened, till at length they wholly subsided, notwithstanding the recess of so many bubbles as broke on the top of the Spirit of Urine, during all the time of the Experiment; yet it scarcely appeared at all to be sunk below the mark: Nor did the mixture of Spirit of Wine and Water considerably subside. But that is nothing to what we observed in the Spirit of Wine, for not only it conspicuously expanded itself in the Neck of the Vessel that contained it, notwithstanding the largeness of it; and that the bubbles were about to break at the top of it almost assoon as they arrived there: but upon the readmission of the external Air, the Spirit of Wine retained its newly acquired expansion. And though we let it alone for near an hour together, in expectation that it might subside; yet when we took it out, we found it still swelled between a quarter and half an Inch above the mark; and although it was not easily imaginable how this Phaenomenon could proceed from any mistake in trying the Experiment, yet the strangeness of it invited me to repeat it with fresh Spirit of Wine; which, swelling in the Neck as formerly, I left all Night in the Receiver, allowing free access to the external Air at the Stop-cock, and the next day found it still expanded as before, save that it seemed a little lower: which decrement perhaps proceeded from the avolation of some of the fugitive parts of so volatile a Liquor. And for better satisfaction having taken out the Glass, and considered it in the open Air, and at a Window, I could not find that there was any remaining Bubbles that could occasion the persevering and admired expansion. BEing desirous to discover what difference there might be as to gravity and levity, Experiment 25. between Air expanded under Water, and itself before such expansion; we took two very small Viols, such as Chemical Essences (as they call them) are wont to be kept in, and of the size and shape expressed by the 8th Figure: into one of these we put so much of a certain ponderous Mercurial mixture (happening to be then at hand) that the mouth being stopped with a little soft Wax, the Glass would just sink in Water and no more; this we let fall to the bottom of a wide-mouthed Crystal Jar, filled with about half a pint of common Water, and into the same Vessel we sunk the other Essence Glass unstopped, with as much Water in it as was more than sufficient to make it subside. Both these sunk with their mouths downward, the former being about three quarters full of Air, the latter containing in it a bubble of Air that was guessed to be of the bigness of half a Pea: This done, the wide-mouthed Glass was let down into the Receiver, and the way of employing the Engine was carefully made use of. The success was, That having drawn out a pretty quantity of Air, the bubbles began to disclose themselves in the Water, as in the former Experiments; and though for a good while after the bubbles ascended in swarms from the lower parts of the Water, and hastily broke at the top; yet we prosecuted the Experiment so long without seeing any effect wrought upon the Essence Bottles, that we began to despair of seeing either of them rise, but continuing to ply the Pump, that little Glass, whose mouth was opened, came to the top of the Water, being, as it were, buoy up thither by a great number of bubbles that had fastened themselves to the sides of it; swimming thus with the mouth downward, we could easily perceive that the internal Air above mentioned had much delated itself, and thereby seemed to have contributed to the emerging of the Glass, which remained floating, notwithstanding the breaking and vanishing of most of the contiguous bubbles: being hereby encouraged to persist in pumping, we observed with some pleasure, that at each time we turned the Key, the Air in the little Glass did manifestly expand itself and thrust out the water, generally retaining a very protuberant surface where it was contiguous to the remaining Water. And when after divers exsuctions of the Air in the Receiver, that in the little Viol so dilated itself as to expel almost all the Water, it turned up its mouth towards the surface of the Water in the Jar, and there delivered a large bubble, and then relapsed into its former floating posture: And this Experiment taught us, among other things, that it was a work of more time and labour than we imagined, to exhaust our Engine as much as it may be exhausted: for although before the emerging of the small Viol, we did (as has been▪ touched already) think we had very considerably emptied the Receiver, because there seemed to come out but very little or almost no sensible Air at each exsuction into and out of the Cylinder; yet afterwards, at each drawing down the Sucker, the Air included in the Viol did manifestly dilate itself, so long, that it did no less than nine times turn its mouth upwards, and discharge a bubble by conjecture about the bigness of a Pea, after the manner newly recited. But as for that Viol which had the weight in it, it risen not at all. So that being not able by quick pumping to gain another bubble from the Air in the swimming Glass, which proceeded from some small leak in the Vessel, though it held in this Experiment more staunch than was usual, we thought fit to let in leisurely the Air from without, upon whose admission that within the Viol shrinking into a very narrow compass, the Glass did, as we expected, fall down to the bottom of the Jar. But being desirous before we proceeded to any new Experiment, to try once more whether the little Glass that had the weight in it might not also be raised. After we had suffered the Engine to remain closed as it was, for five or six hours, the Pump was again plied with so much obstinacy, that not only about the upper part of the Jar there appeared a good number of bubbles (but very much smaller than those we saw the first time) but afterwards there came from the bottom of the Jar, bubbles about the bigness of small Peas: which the Pump being still kept going, followed one another, to the number of forty, coming from the stopped Viol; whose mouth, it seems, had not been shut so strongly and closely, but that the included Air, dilating itself by its own spring, made itself some little passage betwixt the Wall and the Glass, and got away in these bubbles; after which, the unstopped Glass began to float again, the Air shut up in it being manifestly so dilated as to expel a good part of the Water, but not so much as to break quite thorough. And at length, when our expectation of it was almost tired out, the heavier of the two Viols began to come aloft, and immediately to subside again, which appeared to be occasioned by the Air within it, whose bulk and spring being weakened by the recess of the forty bubbles beforementioned, it was no longer able, as formerly, to break forcibly through the incumbent Water; but forming a bubble at the mouth of the Glass, boyed it up towards the top, and there getting away, left it to sink again till the pressure of the Air in the Receiver being further taken off, the Air in the Viol was permitted to expand itself further, and to create another bubble, by which it was again for a while carried up. And it was remarkable, that though after having emptied the Receiver as far as well we could, we ceased from pumping; yet the Vessel continuing more staunch than it was wont, this ascent and fall of the Viol was repeated to the ninth time; the included Air, by reason of the smallness of the vent at which it must pass out, being not able to get away otherwise then little by little; and consequently, in divers such parcels as were able to constitute bubbles, each of them big enough to raise the Viol and keep it aloft until the avolation of that bubble. Whereby it may appear, that the grand rule in hydrostatics, That a Body will swim in the Water, in case it be lighter than as much of that Water that equals it in bulk, will hold likewise when the pressure of the Atmosphere is in very great measure, if not when it is totally taken off from the Liquor and the Body: though it were worth enquiring what it is that so plentifully concurs to fill the bubbles made in our Experiment by the so much expanded Air, for to say with the old Peripatetic Schools, That the Air, in Rarefaction, may acquire a new extent, without the admission of any new substance, would be an account of the Phaenomenon very much out of date, and which, I suppose, our Modern Naturalists would neither give, nor acquiess in. I know not whether it may be requisite to add, that in this Experiment, as in the former, the outward Air being let in did soon precipitate the floating Viol. But I think it will not be amiss to note, that (congruously to what hath been above recorded of the vast expansion of the Air) the Water which in the heavier Viol succeeded in the room of those forty odd, if not fifty great bubbles of Air, which at several times got out of it, amounted but to a very inconsiderable bigness. Experiment 26. IT having been observed by those that have considered what belongs to Pendulums (a Speculation that may, in my poor judgement, be highly useful to the Naturalists) that their Vibrations are more slowly made, and that their motion lasts less in a thicker, then in a thinner Medium: We thought it not amiss to try if a Pendulum would swing faster, or continue swinging longer in our Receiver, in case of the exsuction of the Air, than otherwise. Wherefore we took a couple of round and polished Pendulums of Iron or Steel, of equal bigness, as near as we could get the Artificer to make them, and weighing each of them twenty Dragmes, wanting as many Grains. One of these we suspended in the cavity of the Receiver by a very slender silken string, of about seven Inches and a half in length from the cover of the Receiver to which it was fastened. Then (by inclining the Engine) we made the Pendulum swing too and ●ro in it, and described as long Arches as in the capacity of so brittle a Vessel we thought safe and convenient. And one of the Assistants telling the recursions of the other Pendulum hanging in the free Air, by a string of about the same length, we shortened and lengthened this other Pendulum, till it appeared to keep the same pace in its Vibrations, with that shut up in the Receiver. Then having carefully drawn away the Air, we did again set the Pendulum in the Receiver a vibrating; and giving the other Pendulum such a motion as made it describe an Arch, according to one's guess, equal to that of the included Pendulum; we reckoned, one of us, the Recursions of that Pendulum which was swinging within the Receiver; and another of us that which was moving in (that which one would think a much more resisting medium) the Air. But once, one of us reckoned near two and twenty Recursions of the included Pendulum, whilst the other reckoned but twenty of the Pendulum that vibrated without. And another time also, the former of these Pendula was reckoned to have made one and twenty Recursions, wherein the other made but twenty: Yet this Experiment seemed to teach us little, save that the difference betwixt the motion of such a Pendulum in the common Air, and in one exceedingly rarified, is scarce sensible in Vessels no bigger than our Receiver; especially since though during this Experiment it held very well, yet we could not suppose it to be altogether devoid of Air. We observed also, that when the Receiver was full of Air, the included Pendulum continued its Recursions about fifteen minutes (or a quarter of an hour) before it left off swinging; and that after the exsuction of the Air, the Vibration of the same Pendulum (being fresh put into motion) appeared not (by a minute's Watch) to last sensibly longer. So that the event of this Experiment being other than we expected, scarce afforded us any other satisfaction, then that of our not having omitted to try it. And whether in case the trial be made with a Pendulum much less disproportionate to the Air than Steel is, the event will much better answer expectation, experience may be consulted. THat the Air is the medium whereby sounds are conveyed to the Ear, Experiment 27. has been for many Ages, and is yet the common Doctrine of the Schools. But this Received Opinion has been of late opposed by some Philosophers upon the account of an Experiment made by the Industrious Kircher, and other Learned Men, who have (as they assure us) observed, That if a Bell, with a Steel Clapper, be so fastened to the inside of a Tube, that upon the making the Experiment De Vacuo with that Tube, the Bell remained suspended in the deserted space at the upper end of the Tube: And if also a vigorous Loadstone be applied on the outside of the Tube to the Bell, it will attract the Clapper, which upon the Removal of the Loadstone falling back, will strike against the opposite side of the Bell, and thereby produce a very audible sound, whence divers have concluded, That 'tis not the Air, but some more subtle Body that is the medium of sounds. But because we conceived that, to invalidate such a consequence from this ingenious Experiment (though the most luciferous, that could well be made without some such Engine as ours) some things might be speciously enough alleged; we thought fit to make a trial or two, in order to the Discovery of what the Air does in conveying of sounds, reserving divers other Experiments tryable in our Engine concerning sounds, till we can obtain more leisure to prosecute them. Conceiving it then the best way to make our trial with such a noise as might not be loud enough to make it difficult to discern slighter variations in it, but rather might be, both lasting, that we might take notice by what degrees it decreased; and so small, that it could not grow much weaker without becoming imperceptible. We took a Watch, whose Case we opened, that the contained Air might have free egress into that of the Receiver. And this Watch was suspended in the cavity of the Vessel only by a Packthread, as the unlikeliest thing to convey a sound to the top of the Receiver: And then closing up the Vessel with melted Plaster, we listen▪ d near the sides of it, and plainly enough heard the noise made by the balance. Those also of us, that watched for that Circumstance, observed, that the noise seemed to come directly in a strait Line from the Watch unto the Ear. And it was observable to this purpose, that we found a manifest disparity of noise, by holding our Ears near the sides of the Receiver, and near the Cover of it: which difference seemed to proceed from that of the Texture of the Glass, from the structure of the cover (and of the Cement) through which the sound was propagated from the Watch to the Ear. But let us prosecute our Experiment. The Pump after this being employed, it seemed that from time to time the sound grew fainter and fainter; so that when the Receiver was emptied as much as it used to be for the foregoing Experiments, neither we, nor some strangers that chanced to be then in the room, could, by applying our Ears to the very sides, hear any noise from within; though we could easily perceive that by the moving of the hand which marked the second minutes, and by that of the balance, that the Watch neither stood still, nor remarkably varied from its wont motion. And to satisfy our selus further that it was indeed the absence of the Air about the Watch that hindered us from hearing it, we let the external Air at the Stop-cock, and then though we turned the Key and stopped the Valve, yet we could plainly hear the noise made by the balance, though we held our Ears sometimes at two Foot distance from the outside of the Receiver. And this Experiment being reiterated in another place, succeeded after the like manner. Which seems to prove, that whether or no the Air be the only, it is at least, the principal medium of Sounds. And by the way it is very well worth noting, that in a Vessel so well closed as our Receiver, so weak a pulse as that of the balance of a Watch should propagate a motion to the Ear in a Phisically strait Line, notwithstanding the interposition of so close a Body as Glass, especially Glass of such thickness as that of our Receiver; since by this it seems that the air imprisoned in the Glass, must, by the motion of the balance, be made to beat against the concave part of the Receiver, strongly enough to make its convex part beat upon the contiguous Air, and so propagate the motion to the Listeners ears. I know this cannot but seem strange to those, who, with an eminent Modern Philosopher, will not allow that a Sound, made in the cavity of a Room, or other place so closed, that there is no intercourse betwixt the external and internal Air, can be heard by those without, unless the sounding Body do immediately strike against some part of the enclosing Body. But not having now time to handle Controversies, we shall only annex, That after the foregoing Experiment, we took a Bell of about two Inches in Diameter at the bottom, which was supported in the midst of the cavity of the Receiver by a bend stick, which by reason of its Spring pressed with its two ends against the opposite parts of the inside of the Vessel: in which, when it was closed up, we observed that the Bell seemed to sound more dead than it did when just before it sounded in the open Air. And yet, when afterwards we had as formerly emptied the Receiver, we could not discern any considerable change (for some said they observe▪ d a small one) in the loudness of the sound, whereby it seemed that though the Air be the principal medium of sound, yet either a more subtle matter may be also a medium of it, or else an ambient Body that contains but very few particles of Air, in comparison of those it is easily capable of, is sufficient for that purpose. And this, among other things, invited us to consider, whether in the abovementioned Experiment made with the Bell and the Loadstone, there might not in the deserted part of the Tube remain Air enough to produce a sound: since the Tubes for the Experiment De Vacuo (not to mention the usual thinness of the Glass) being seldom made greater than is requisite, a little Air might bear a not inconsiderable proportion to the deserted space. And that also, in the Experiment De Vacuo, as it is wont to be made, there is generally some little Air that gets in from without, or at least store of bubbles that arise from the Body of the Quicksilver, or other Liquor itself, Observations heedfully made have frequently informed us: And it may also appear, by what has been formerly delivered concerning the Torricellian Experiment. On the occasion of this Experiment concerning sounds, we may add in this place, That when we tried the Experiment formerly mentioned, of firing Gun powder with a Pistol in our evacuated Receiver, the noise made by the striking of the Flint against the Steel, was exceeding languid in comparison of what it would have been in the open Air. And on divers other occasions it appeared that the sounds created within our exhausted Glass, if they were not lost before they reached the Ear, seemed at least to arrive there very much weakened. We intended to try whether or no the Wire-string of an Instrument shut up into our Receiver, would, when the ambient Air was sucked out, at all tremble, if in another Instrument held close to it, but without the Receiver a string tuned (as Musicians speak, how properly I now examine not) to an Unison with it, were briskly touched, and set a Vibrating. This, I say, we purposed to try to see how the motion made in the Air without, would be propagated through the cavity of our evacuated Receiver. But when the Instrument wherewith the trial was to be made came to be employed, it proved too big to go into the Pneumatical Vessel, and we have not now the conveniency to have a fit made. We thought likewise to convey into the Receiver a long and slender pair of Bellows, made after the fashion of those usually employed to blow Organs, and furnished with a small Musical instead of an ordinary Pipe. For we hoped, that by means of a string fastened to the upper part of the Bellows, and to the movable stopple that makes a part of the Cover of our Receiver, we should, by frequently turning round that stopple, and the annexed string, after the manner already often recited, be able to lift up and distend the Bellows; and by the help of a competent weight fastened to the same upper part of the Bellows, we should likewise be able, at pleasure, to compress them: and by consequence, try whether that subtler matter than Air (which, according to those that deny a Vacuum, must be supposed to fill the exhausted Receiver) would be able to produce a sound in the Musical Pipe; or in a Pipe like that of ordinary Bellows, to beget a Wind capable to turn or set a moving some very light matter, either shaped like the Sails of a Windmill, or of some other convenient form, and exposed to its Orifice. This Experiment, I say, we thought to make, but have not yet actually made it for want of an Artificer to make us such a pair of Bellows as it requires. We had thoughts also of trying whether or no, as Sounds made by Bodies in our Receiver become much more languid than ordinary, by reason of the want of Air, so they would grow stronger, in case there were an unusual quantity of Air crowded and shut up in the same Vessel, which may be done (though not without some difficulty) by the help of the Pump, provided the Cover and Stopple be so firmly fastened (by binding and Cement, or otherwise) to the Glass; and to each other, that there be no danger of the condensed Airs blowing of either of them away, or its breaking through the junctures. These thoughts, My Lord, as I was saying, we entertained; but for want of leisure, as, of as good Receivers as ours, to substitute in its place, in case we should break it before we learned the skill of condencing the Air in it, we durst not put them in practice: Yet, on this occasion, give me leave to advertise Your Lordship once for all, That though for the reasons newly intimated, we have, Only in the seventeenth Experiment, taken notice, that by the help of our Engine the Air may be condensed as well as rarified; yet there are divers other of our Experiments, whose Phaenomena it were worth while to try to vary, by means of the compression of the Air. Experiment 28. WE taught, among divers other things, when we discoursed of our first Experiment, That the Air shut up in our Receiver, presseth as strongly upon the Bodies shut up with it, as if they were exposed to the pressure of the whole Atmosphere. That this was not inconsiderately propounded, we hope Your Lordship has gathered from divers of the things already recited: But yet perhaps it will not be amiss to subjoin, by way of further confirmation of the same truth, the following Experiment, which should have accompanied the 20th, but the Paper where in the one was written chanc▪ d not to be at hand, when the other was sent away. We conveyed into the Receiver a new Glass Viol., capable of holding about 6 or 7 ounces of Water, into which we had before put 2 or 3 Spoonfuls of that Liquor, and stopped it close with a fit Cork. The Pneumatical Vessel being emptied, there appeared not any change in the enclosed Water, the Air imprisoned with it, not having the force to blow out the stopple, which event, though it were no other than we expected, was differing from what we desired. For we would gladly have seen what change would have appeared in the Water upon the Bottles being suddenly unstopped, in a place where the ambient Body was so differing from our common Air. Wherefore we did again put in the Viol, but less strongly closed then formerly, though as strongly stopped as seemed requisite on ordinary occasions: But when the Air was pumped out of the Receiver, that within the Viol did quickly, as we expected, find or make itself little passages to get out at: as we argued, from this, That whereas when the Viol was put in the time before, the Water remained all the while perfectly free from bubbles; at this time the bottom of the Glass appeared all covered with them, and they, upon the regress of the excluded Air into the Receiver, did presently flag and shrink up. From these trials it seemed deducible enough, that whilst the Viol continued to be well stopped, the included Water did, from the Air, shut up with it, sustain a pressure equal to that of the Atmosphere; since till the Air could get out of the Glass, there appeared no bubbles in the Water, notwithstanding the want of pressure in the ambient Body. But to be sure to reach the chief end of our Experiment, we made use of this other expedient: We caused a convenient quantity of Water to be put, and Hermetically shut up into a Glass Egg, to whose long Neck (which was purposely made of an unequal thickness) was fastened to one end of a string, whose other end was tied to the Cover of our Receiver, after the manner elsewhere mentioned already: Then the Egg being conveyed into the Pneumatical Vessel, and that being evacuated, we did, by turning the brass Stopple formerly described amongst the parts of our Engine, so shorten the string as to break the Glass; whereby liberty being given to the Air imprisoned in the Egg, to pass into the capacity of the Receiver, the sudden recess of the Air made the bubbles in a trice appear so numerous, and ascend so swiftly in the Water, that their motion looked like that of a violent shower of Rain; save that the bubbles did not, like the drops of Rain, tend downwards, but upwards, which made me resemble this Phaenomenon to what I have seen happen in the dissolution of Seed-Pearl in some acid Menstruum, in which, if a good quantity of the little Pearls be cast whole, they will at first, if the Menstruum be sharp enough, be carried in swarms from the bottom to the top of the Liquor. We will add, that without sealing up the Glass, this Experiment may be tried in one of our smallest Receivers, for there the exsuction of the ambient Air may be performed so nimbly, that immediately the bubbles lurking in the Water are allowed to display themselves, and ascend in throngs; insomuch, as having in such a Receiver tried the Experiment with Wine (as a more spirituous Liquor) instead of Water, the Red-Wine appeared all covered, with a copious, but vanishing white Froth, almost as if a Vessel full of bottled drink had been unwarily opened. IT may not a little conduce to the clearer explication of divers Points in the Doctrine of Meteors, Experiment 29. and perhaps of some other Physiological difficulties, to discover what the Air does to the motion of those Steams or Exhalations that ascend into it, namely, Whether they mount upwards by virtue of any such positive levity (as some Peripatetics speak) acquired together with their Aërial nature, as inables them to pierce through part of the Atmosphere, and overcome its resistance. Or else, whether these steams being once raised above the Earth by their agitation, have their ascent and sustentation aloft, rather promoted then hindered by the Air: as the inferior parts of that, being thicker and heavier than the superior, the steams can more easily continue for a while their agitation upwards then downwards; And afterwards are by the same fluidity and thickness of the Air, carried to and fro in it, and kept from relapsing to the Earth, as in the Sea water the saline parts are kept from subsiding by those aqueous ones wherewith they are associated. We hoped to illustrate this matter, by observing the motion of the smoke, proceeding from kindled or flaming Bodies in our exhausted Receiver. But as we formerly noted, upon the exsuction of the Air, the smoking of those Bodies presently ceased. We had thoughts also of conveying into our Pneumatical Glass a ●ot Iron, with some Body easy to be dissipated into smoke set upon it, but considered, that neither was that way free from inconveniencies; especially this, that the hot Body would make the Imprisoned Air circulate within the Receiver, and consequently make it questionable whether the ascent of the steams would not be due to the new and acquired motion of the Air. Wherefore I bethought myself of another way to satisfy in some measure my curiosity, to wit, by means of a certain Liquor, which I called to mind that some years ago I had (for a design that belongs not to our present purpose) prepared; which, I suppose, I showed Your Lordship, and which had the luck to be taken notice of by divers very Ingenious and Famous Men. For this Liquor, though most of its Ingredients be Metals, and all of them ponderous enough, is yet of that nature, that whilst the Viol wherein it is kept is stopped (how slight a Cover soever) both the Liquor and the Glass are transparent; and so is that upper half of the Glass to which the Liquor reaches not. But assoon as ever the stopple is taken out, and full access is given to the external Air, both the inward part of the Cork, and the Liquor itself, do presently send upwards, and scatter abroad a fume as thick and white, as if there were a quantity of Alablaster-dust thrown up into the Air: And this smoking of the Liquor lasts till my unwillingness to waste it, invites me stop it again, and then the ascension of the fumes suddenly ceases, till the Viol be again unstopped. This fuming Liquor than I thought would much conduce to the discovery I desired to make, since it saved me the need of conveying any hot Body with it into the Receiver, and would not darken it with fumes before the time. Wherefore having tied to the Viol a great weight o● Lead, to keep it from being lifted up by the drawing out of the Cork; and having tied to the stopple one end of a string, of which the other end was made fast to the Cover of the Pneumatical Glass, the Liquor was carefully closed up after the wont manner, than the Air being diligently pumped out, the Viol was unstopped in the emptied Receiver: and though immediately, upon the drawing out of the Cork, there appeared to be as it were thrown up some white fumes, which seemed to proceed from the Air before imprisoned in the Viol, and diffusing itself suddenly into the capicity of the Receiver. Yet we afterward observed, as we expected, That the fumes did not mount and disperse themselves as they use to do in the open Air, but that, when by reason of the agitation of the Corpuscles of the Liquor, which could not continue their motion in so narrow a space as the Viol afforded them, and were therefore reduced to thrust one another out of it; when, I say, by these assistances the fumes were ascended to the lip of the Viol, they mounted no higher, but ran down along the outside of the Viol to the bottom of it; and thence along, a long and inclining piece of Lead, on which the Viol rested, like a little Stream (not very much bigger than a Swans Quill) whose nature it seemed to emulate so well, that it quitted not the Viol till it was come to the bottom of it, and then forsook it in such a manner as a stream of Water of the same bigness would have done. And this stream lasted a pretty while, and would probably have lasted longer, but that being loath to waste my Liquor, I let in at the Stop-cock a pretty deal of the external Air; notwithstanding which, finding after a while the stream did run afresh, though, as it seemed, not altogether so copious as before: I let as much more Air, as would, come in, and found (somewhat to my wonder) that though the stream formerly mentioned disappeared, yet there appeared not any white fumes to arise, either from the Cork, or out of the Viol itself, no not when the Cover was removed from the Receiver; though not only after a while there ascended white Fumes from the Receiver: but having forthwith taken out the Viol into the open Air, it emitted white exhalations as before; and having presently after unstopped it in an open Window, we found both it and the Cork immediately to send forth a yet much more plentiful smoke. Though it be now divers years since this Numerical Liquor was prepared, after the manner mentioned either by Carneiades or Eleutherius (for I do not well remember which) in those Dialogues concerning Heat and Flame that have above been mentioned. More Circumstances concerning these Fumes we might have observed, had we not been deterred by an Indisposition in point of health, from having much to do with steams of so dangerous a nature, as by that of the Ingredients of this Liquor these seem likely to be of. The Reflections that may be made upon this Experiment, we have not now the leisure to prosecute, and therefore shall content ourselves to recommend the several Circumstances of it to Your Lordship's serious consideration; and to take notice (en passant) that steams in an ambient Body, or a medium thinner than themselves, may both tend downwards, and otherwise emulate the nature of a Liquor; which I therefore point at, that it may appear the less strange, if we sometimes speak of the Atmosphere as of a kind of Liquor, in comparison of that more thin and subtle Celestial Matter that surrounds it. And though it might perchance suffice to have on this occasion intimated thus much; yet, lest this way of speaking of the Atmosphere should be thought too bold and extravagant, I am content to borrow an Experiment of the Discourse formerly mentioned (touching fluidity and firmness) and subjoin it here with alterations suitable to the contrivance of our Engine; and this the rather, because I hope it may conduce to the discovery of the nature of the Atmosphere: for which reason it might have been annexed to what has been noted either upon the first, or eighteenth Experiment, but that when they were written and sent away, it came not into my mind. The Experiment then as we tried in our Engine, was as follows. Experiment 30. WE took one of the small Receivers, often mentioned already, and into it we conveyed a piece of well lighted Match; and letting it remain there till it had filled the Receiver with smoke, we took it out and hastily closed again the Receiver, that the smoke might not get away. Then staying awhile to let these fumes leisurely subside, we found, as we expected, that after some time they settled themselves in the lower half of the Receiver, in a darkish Body, leaving the upper half of the Receiver transparent, and as to sight, full of nought but clear Air. Now to manifest that this smoke thus settled emulated a Liquor, we inclined the Engine that contained it, sometimes to one side, and sometimes to the other; and observed the smoke to keep its surface almost Horizontal, notwithstanding the stooping of the Vessel that held it, as Water or another Liquor would in the like case have done. And if by a quicker rocking of the Engine the smoke were more swiftly shaken, it would, like Water, either Vibrate to and fro from one side to the other of the Glass, or else have its surface manifestly curled with Waves, but preserve its self in an entire and distinct Body from the incumbent Air; and being permitted to rest awhile, would soon recover its former smooth and level superficies: If also the Key were turned and the Valve unstopped, so that there was a free, though but a narrow passage opened betwixt the external Air and the cavity of the Receiver, then would some of this smoke fall down, as it were, in a stream into the subjacent Cylinder, and a proportionate quantity of the outward Air, would manifestly ascend through it into the incumbent Air, much after the same manner as if you invert a Viol with a long Neck, and well filled with Red-Wine, into a Glass full of fair water, you shall see the Water and Wine by degrees mingle with one another; the one falling down as it were in little coloured streams, and the other ascending into its room in the like curled streams, sometimes preceded by round parcels of water, which, by reason of their transparency, look almost like bubbles. The other circumstances of this Experiment, belonging not all of them to our present purpose, we shall content ourselves with taking notice of one which seems the most important, and may illustrate and confirm some things formerly delivered. And it was, That if, when the superficies of our Smoke lay smooth and horizontal, a hot iron were held near the outside of the Receiver, the Neighbouring part of the included fumes (for the rest did not very much alter their former superficies) being rarified by the heat, would readily ascend in a large Pillar of smoke to the very top of the Receiver, yet without seeming to lose a distinct superficies, or to be confounded with Air; below which, upon the recess of the adventitious heat that by agitating it impelled it upward, it would again subside. All which being added to the late Experiment of the smoking Liquor, and to what may be from that which has been elsewhere said, gathered to the same purpose, will, I hope, keep it at least from appearing absurd: If since we see that there is so great an inequality in the density and weight of Liquors, that water is near 14 times thinner or lighter than Quicksilver of the same bulk, and well dephlegmed; Spirit of Wine yet much lighter than water; we venture to speak sometimes of the Atmosphere, as if it were a peculiar kind of thin and halituous Liquor (if I may so call it) much lighter than Spirit of Wine. To these things I know not whether it will be requisite to add, that as we lately took notice of conspicuous waves that appeared upon the superficies of our agitated smoke. So some such thing may not absurdly be conjectured to happen on the superficies of the Atmosphere, by those strange ruggednesses that appear (especially in the Spring and Fall, when exhalations and vapours are wont to ascend most plentifully) upon the Limb or Edge of the Rising and Setting Sun. I speak thus diffidently upon this occasion because I know that by the Fluctuation or Boiling of the Sun's own superficies divers eminent Mathematicians have plausibly enough (but how truly I leave your Lordship to Judge) endeavoured to give an Account of it. But if we will join with those that have ascribed of late this Phaenomenon to the Refraction the Sunbeams suffer in our vapid Air; we may, as hath been intimated, promote their Doctrine by deducing from it, that probably the surface Atmosphere is oftentimes (if not always) exceedingly curled or waved. And certainly it is somewhat wonderful as well as very pleasant to behold, how, to him that looks upon the setting Sun through a long & excellent Telescope, there will not only appear strange inequalities in the edge of it (insomuch that I have often seen it more indented than a Saw) but those inequalities will vanish in one place and presently appear in another, and seem perfectly to move like waves succeeding and destroying one another; save that their Motion oftentimes seems to be quickest as if in that vast sea they were carried on by a current, or at least by a tide. And this (as we else where note) appears to the eye not only when it looks directly through the telescope upon the sun; but also when a large and well defined image of the sun is by the same telescope brought into a room and cast upon a sheet of white paper. But to insist on this were to digress: and therefore I will proceed to experiments of another kind. IT has been admired by very ingenious Men, Experiment 31. that if the exquisitely polished surfaces of two flat pieces of marble be so congruous to each other that from their mutual application there will result an immediate contact, they will stick so fast together, that he that lifts up the uppermost, shall, if the undermost be not exceeding heavy, lift up that too, and sustain it aloft in the free air. A probable cause of this so close adhesion we have elsewhere endeavoured to deduce from the unequal pressure of the Air upon the undermost stone; For the lower superficies of that stone being freely exposed to the Air is pressed upon by it, whereas the uppermost surface, being contiguous to the superior stone, is thereby defended from the pressure of the Air which consequently pressing the lower stone against the upper, hinders it from falling, as we have elsewhere more fully declared. Upon these grounds we conjectured that in case we could procure two marbles exactly ground to one another; and in case we could also sufficiently evacuate our Receiver, the lower stone would, for want of the wont and sustaining pressure of the Air, fall from the upper. But the further trial of this Experiment we must, unless your Lordship think it worth Your making at Paris, put off till a fit opportunity. For where we now are, we cannot procure marbles so exactly ground, that they will sustain one another in the Air, above a minute or two, which is a ●uch shorter time than the emptying of our Receiver requires. We did indeed try to make our marbles stick close together by moistening their polished surfaces with rectified spirit of Wine, in regard that Liquor by its sudden avolation from marble, if poured thereon, without leaving it moist or less smooth, seemed unable to sustain them together after the manner of a glutinous body, and yet seemed sufficient to exclude and keep out the Air. But this we tried to little purpose, for having conveyed into the Receiver two black square marbles (the one of two inches and a third in length or breadth, and somewhat more than half an inch in thickness: The other of the same extent, but not much above half so thick) fastened together by the intervention of pure Spirit of Wine; and having suspended the thicker by a string from the cover, we found not that the exsuction of the ambient Air would separate them, though a weight amounting to four ounces were fastened to the lowermost marble to facilitate its falling off. I would gladly have the Experiment tried with marble so well polished as to need no Liquor whatsoever to make them cohere, and in a Vessel out of which the Air may be more perfectly drawn than it was out of ours. But in the mean time though we will not determine whether the Spirit of wine did contribute to the strong cohesion of these stones, otherwise than by keeping even the subtl'st parts of the Air from getting in between them, yet it seemed that the not falling down of the lowermost marble might without improbability be ascribed to the pressure of the Air remaining in the Receiver; which as we formerly noted having been able to keep a Cylinder of water of above a Foot in height from falling to the bottom of the Tube, may well enough be supposed capable of keeping so broad a flat Marble from descending. And though this may seem a strange proof of the strength of the spring of Air, even when rarified, yet it will scarce seem incredible to him that has observed how exceeding strong a cohesion may be made betwixt broad Bodies, only by their immediate touching one another. A notable instance of which, I have met with in this short Narrative of the Learned Zucchius. P. Nic. Zucchius apud Schot: part 1. M●●: Hydraulopne●●m. juveni (says: he) lacertorum suorum robur: jactanti proposita semel est lamina aerea, per ansam in medio extantem apprehensam elevanda è tabula marmorea, cui optime congruebat: qui primo tanquam rem ludicram puero committendam contempsit: tum instantibus amicis manum utrámque admovens, cum luctatus diu haerentem non removisset, excusavit impotentiam, objecta perigrini & potentissimi glutinis interpositione, quo fortissime copulante nequiret divelli; donec vidit ab alio per tabulam facilimè laminam deduci, & ad extrema productam, & actam in transversum inde deportari. But that we may learn from our own Engine, ●hat two Bodies, though they touch each other but in a small part of their surfaces, may be made to cohere very strongly, o●ely by this, That the Air presses much more forcibly upon the inferior superficies of the lowermost Body, then upon the upper surface of the same: We will hereunto annex the following Experiment, though out of the order wherein they were made. I remember I have, Experiment 32. in a Discourse concerning Fluidity and Firmness, made mention of my having, by the exsuction of the Air out of a Glass Vessel, made that Vessel take up, or suck up (to speak in the common Language) a Body weighing divers Ounces▪ but our Engine affording us the opportunity of making considerabler Experiments of that kind, We thought fit to make a further trial of the force of the Atmosphere's pressure upwards, a●●er the following manner. The Receiver having been tightly closed, as we have often taught already, and the Air being in a good measure drawn out of it, it was removed from off the Pump: and to the lower Branch of the Stop-cock, there was speedily applied a tapering Valve of brass, such as is described in the 9th fig: made fit to go with its narrower end into the cavity of the branch, and to fill the orifice of that cavity with its broader part. And that the Air might not get in at the little intervals, left here and there between the convex surface of the stopple and the internal edge of the branch, those intervals were stopped with a little Diachylon. And to the door, or, (if you please) that part of the Valve which was to move to and fro, and in this Experiment hung perpendicular to the Horizon, there was, at a button of brass belonging to the Valve fastened a broad scale wherein weights were to be put. This done the key of the Stop-cock was turned, and the external Air beating like a forcible stream upon the Valve to get in there, it did suddenly both shut the Valve and keep it shut so strongly, that we had time to cast in divers weights one after another into the Scale; till at length the weight overpowering the pressure of the Atmosphere, drew down the Valve by the strings that tied the Scale to it, and gave liberty to the outward Air to rush into the Receiver. Though another time, when the Valve had but little weight hanging at it, being, by I know not what accident, drawn down beneath its former place, it was by the impetuous current of the outward Air suddenly impelled up into it again, and kept there. But in the former Experiment it is remarkable, That though the Receiver were not well exhausted, and though it leaked whilst the rest of the Experiment was in prosecution, and though the Valve whereon the Cylinder of the Atmosphere could press, were not above an Inch and ● half in Diameter, yet the weight kept up by suction, or rather supported by the Air, namely the Valve, the Seal and what was cast into it, being sent to be weighed, amounted to about ten of our common Pounds, consisting of sixteen Ounces apiece: So that we doubted not but that, had the Experiment been made with favourable Circumstances, the Air endeavouring to press in at the Orifice of the Stop-cock, would have kept a very much greater weight from falling out of it; I say the Air, because we found, by trial purposely made, that neither the imperfect contact of the Valve and the Stop-cock, nor the Diachylon that was employed to fill up the little Crannies left betwixt them, were considerable in this Experiment; by which may among other things appear, that I did not without cause in the abovenamed Discourse touching Fluidity and Firmness, ascribe a great force, even to such Pillars of Air as may be supposed to begin at the top of the Atmosphere, and recoiling from the ground to terminate on the Bodies on which they press: since in the present Experiment such a weight was supported by so slender a Cylinder of Air, rebounding from the Earth to the Valve whereon ●t did bear. Experiment 33. BUt in regard we have not yet been able to empty so great a Vessel as our Receiver, so well as we can the Cylinder itself; our Pump alone may afford us a nobler instance of the force of the Air we live in, insomuch, that by help of this part of our Engine, we may give a pretty near guess at the strength of the Atmosphere, computed as a weight. And the way may be this; First, the Sucker being brought to move easily up and down the Cylinder, is to be impelled to the top of it: Then the Receiver must be taken off from the Pump, that the upper Orifice of the Cylinder remaining open, the Air may freely succeed the Sucker, and therefore readily yield to its motion downward. This done, there must be fastened to one of the Iron Teeth of the Sucker, such a weight as may just suffice to draw it to the bottom of the Cylinder. And having thus examined what weight is necessary to draw down the Sucker, when the Atmosphere makes no other than the ordinary resistance of the Air against its descent; the Sucker must be again forced to the top of the Cylinder, whose upper Orifice must now be exactly closed; and then (the first weight remaining) we easily may, by hanging a Scale to the above-metioned Iron (that makes part of the Sucker) cast in known weights so long, till in spite of the reluctancy of the Atmostphere the Sucker be drawn down. For to these weights in the Scale, that of the Scale itself being added, the sum will give us the weight of a Column of Air, equal in Diameter to the Sucker, or to the cavity of the Cylinder; and in length to the height of the Atmosphere. According to this method we did, since the writing of the last Experiment, attempt to measure the pressure of the Atmosphere, but found it more difficult than we expected, to perform it with any accurateness; for though by the help of the Manubrium the Sucker moved up and down with so much ease, that one would have thought that both its convex surface, and the concave one of the Cylinder were tightly smooth, & as it were slippery; yet when the Sucker came to be moved only with a dead weight or pressure (that was not (like the force of him that pumped) intended as occasion required) we found that the little rufnesses, or other inequalities, and perhaps too, the unequal pressure of the Leather against the cavity of the Cylinder, were able now and then to put a stop to the descent or ascent of the Sucker, though a very little external help would easily surmount that impedi●ment; and then the Sucker would, for a while, continue its formerly interrupted motion, though that assistance were withdrawn. But this discouragement did not deter us from prosecuting our Experiment, and endeavouring, by a careful trial, to make it as instructive as we could. We found then that a Leaden Weight, of 28 pounds (each consisting of sixteen Ounces) being fastened to one of the teeth of the Sucker, drew it down slowly enough; when the upper Orifice of the Cylinder was left open, though by the help of Oil and Water, and by the frequent moving the Sucker up and down with the Manubrium, its motion in the Cylinder had been before purposely facilitated. This done, the upper Orifice of the Cylinder was very carefully and closely stopped, the Valve being likewise shut with its wont Stopple well oiled, after the Sucker had been again impelled up to the top of the Cylinder. Then to the precedent twenty eight pound, we added a hundred and twelve pounds more; which forcing down the Sucker, though but leisurely, we took off the twenty eight pound weight; and being unable to procure just such weights as we would have had, we hung on, instead of it, one of fourteen pound, but found that, with the rest, unable to carry down the Sucker. And to satisfy ourselves, and the Spectators, that it was the resistance of the ambient Air that hindered the descent of so great a weight, after that we had tried that upon unstopping the Valve, and thereby opening an access to the external Air, the Sucker would be immediately drawn down: After this, I say, we made this further Experiment, That having by a Man's strength forcibly depressed the Sucker to the bottom of the Cylinder, and then fastened weights to the abovenamed Iron that makes part of that Sucker, the pressure of the external Air finding little or nothing in the cavity of the evacuated Cylinder to resist it, did presently begin to impel the Sucker, with the weights that clogged it, towards the upper part of the Cylinder, till some such accidental Impediment as we formerly mentioned, checked its course; and when that rub, which easily might be, was taken out of the way, it would continue its ascent to the top, to the no small wonder of those Bystanders, that could not comprehend how such a weight could ascend, as it were, of itself; that is, without any visible force, or so much as Suction to lift it up. And indeed it is very considerable, that though possibly there might remain some particles of Air in the Cylinder, after the drawing down of the Sucker; yet the pressure of a Cylinder of the Atmosphere, somewhat less than three Inches in Diameter (for, as it was said in the description of our Engine, the cavity of the Cylinder was no broader) was able, uncompressed, not only to sustain, but even to drive up a weight of an hundred and odd pounds: for besides the weight of the whole Sucker itself, which amounts to some pounds, the weights annexed to it made up a hundred and three pounds, besides an Iron Bar, that by conjecture weighed two pounds more; and yet all these together fall somewhat short of the weight which we lately mentioned, the resistance of the Air to have held suspended in the cavity of the Cylinder. And though (as hath been already acknowledged) we cannot, peradventure, obtain by the recited means so exact an account as were to be wished, of what we would discover: Yet, if it serve us to ground Conjectures more approaching to the Truth, than we have hitherto met with, I hope it will be considered (which a famous Poet judiciously says) Est quodd●m prodire tenus, si non datur ultra. Peradventure it will not be impertinent to annex to the other Circumstances that have been already set down concerning this Experiment, That it was made in Winter, in Wether neither Frosty nor Rainy, about the change of the Moon, and at a place whose latitude is near about 51d and a half: For perhaps the force or pressure of the Air may vary, according to the Seasons of the Year, the temperature of the Wether, the elevation of ●he Pole, or the phases of the Moon; 〈◊〉, or even any of them seeming capable to alter either the height or consistence of the incumbent Atmosphere: And therefore it would not be amiss if this Experiment were carefully tried at several times and places, with variety of Circumstances. It might also be tried with Cylin●ers of several Diameters, tightly fitted with Suckers, that we might know what proportion several Pillars of the Atmosphere bear, to the Weights they are able to sustain or lift up; and consequently, whether the increase or decrement of the resistance of the ambient Air, can be reduced to any regular proportion to the Diameters of the Suckers: These, and divers other such things which may be tried with this Cylinder, might most of them be more exactly tried by the Torricellian Experiment, if we could get Tubes so accurately blown and drawn, that the Cavity were perfectly Cylindrical. To dwell upon all the several Reflections, that a speculative Wit might make upon this and the foregoing Experiment, (I mean the thirty third and thirty second) would require almost a Volume; whereas our occasions will scarce allow us time to touch upon three or four of the chief Inferences that seem deducible from them, and therefore we shall content ourselves to point at those few. And first, as many other Phaenomena of our Engine, so especially, the two lately mentioned Experiments, seem very much to call in question the received Opinion of the Nature or Cause of Suction. For 'tis true indeed, that when men suck, they commonly use some manifest endeavour by a peculiar motion of their Mouths, Chests, and some other conspiring parts, to convey to them the body to be sucked in. And hence perhaps they have taken occasion, to think that in all Suction there must be some Endeavour or motion in the sucking to attract the sucked Body. But in our last Experiment it appears not at 〈◊〉 how the upper part of the emptied Cylinder that remains moveless all the 〈◊〉, or any part of it, does at all endeavour to draw to it the depressed Sucker and the annexed weights. And yet those that behold the ascension of the Sucker, without seriously considering the cause of it, do readily conclude it to be raised by something that powerfully Sucks or attracts it, though they see not what that may be or where it lurks. So that it seems not absolutely necessary to Suction, that there 〈◊〉 Body, which is said to suck, an 〈◊〉 or motion in order thereunto, but rather that Suction may be at least for the most part reduced to Pulsion, and its effects ascribed to such a pressure of the neighbouring air upon those Bodies (whther aërial, or of other Natures) that are contiguous to the Body that is said to attract them, as is stronger than that Substance which possesses the cavity of that sucking Body is able to resist. To object here, that it was some particles of Air remaining in the emptied Cylinder that attracted this weight to obviate a Vacuum, will scarce be satisfactory; unless it can be clearly made out by what little hooks, or other grappling Instruments, the internal Air could take hold of the Sucker; how so little of it obtained the force to lift up so great a weight; and why also, upon the letting in of a little more Air into one of our evacuated Vessels, the attraction is, instead of being strengthened, much weakened, though, if there were danger of a Vacuum before, it would remain, notwithstanding this ingress of a little Air. For that still there remained in the capacity of the exhausted Cylinder store of little rooms, or spaces empty or devoid of Air, may appear by the great violence wherewith the air rushes in, if any way be opened to it. And that 'tis not so much the decrement of the Vacuum within the cavity of the vessel that debilitates the attraction, as the spring of the included air (whose presence makes the decrement) that does it by resisting the pressure of the external Air, seems probable, partly from the Disability of vacuities, whether greater or lesser, to resist the pressure of the Air; and partly by some of the Phaenomena of our Experiments, and particularly by this Circumstance of the three and Thirtieth, that the Sucker was by the pressure of the Ambient Air impelled upwards, with its weight hanging at it, not only when it was at the bottom of the Cylinder, and consequently left a great Vacuum in the cavity of it; but when the Sucker had been already impeled almost to the top of the Cylinder, and consequently, when the Vacuum that remained was become very little in comparison of that which preceded the beginning of the Sucker's ascension. In the next place, these Experiments may teach us, what to judge of the vulgar Axiom received for so many Ages as an undoubted Truth in the Peripatetic Schools; That Nature abhors and flies a Vacuum, and that to such a degree, that no humane power (to go no higher) is able to make one in the Universe; wherein Heaven and Earth would change places, and all its other Bodies rather act contrary to their own Nature, than suffer it. For, if by a Vacuum we will understand a place perfectly devoid of all corporeal Substance, it may be indeed then, as we formerly noted, be plausibly enough maintained, that there is no such thing in the world; but that the generality of the Plenists, (especially till of late years some of them grew more wary) did not take a Vacuum in so strict ● Sense, may appear by the Experiments formerly, and even to this Day employed by the Deniers of a Vacuum, to prove it impossible that there can be any made. For when they allege (for Instance) that when a man sucks Water through a long Pipe, that heavy Liquor, contrary to its Nature, ascends into the Sucker's mouth, only, to fill up that room made by the Dilatation of his Breast and Lungs, which otherwise will in part be empty. And when they tell us, that the reason why if a long Pipe exactly closed at one end be filled top-ful of Water, and then inverted, no Liquor will fall out of the open Orifice; Or, to use a more familiar Example, when they teach, that the cause why in a Gardener's watering Pot shaped conically, or like a Sugar-Loaf filled with Water, no Liquor falls down through the numerous holes at the bottom, whilst the Gardener keeps his Thumb upon the Orifice of the little hole at the top; and no longer, must be that if in the case proposed the Water should descend, the Air being unable to succeed it, there would be left at the upper and deserted part of the Vessel a Vacuum, that would be avoided if the hole at the top were opened. When (I say) they allege such Experiments, the Tendency of them seems plainly to import, that they mean, by a Vacuum, any space here below that is not filled with a visible body, or at least with Air, though it be not quite devoyed of all Body whatsoever. For why should Nature, out of her detestation of a Vacuum, make Bodies act contrary to their own Tendency, that a place may be filled with Air, if its being so were not necessary to the avoiding of a Vacuum. Taking then a Vacuum in this vulgar and obvious sense, the common opinion about it seems liable to several Exceptions, whereof some of the chief are suggested to us by our Engine. It will not easily then be intelligibly made out, how hatred or aversation, which is a passion of the Soul, can either for a Vacuum, or any other object, be supposed to be in Water, or such like inanimate Body, which cannot be presumed to know when a Vacuum would ensue; if they did not bestir themselves to prevent it, nor to be so generous as to act contrary to what is most conducive to their own particular preservation for the public good of the Universe. As much then of intelligible and probable Truth, as is contained in this Metaphorical Expression, seems to amount but to this; That by the Wise Author of Nature (who is justly said to have made all things in number, weight, and measure,) the Universe, and the parts of it, are so contrived, that it is as hard to make a Vacuum in it, as if they studiously conspired to prevent it. And how far this itself may be granted, deserves to be further considered. For in the next place, our Experiments seem to teach, that the supposed Aversation of Nature to a Vacuum is but accidental, or in consequence partly of the Weight and Fluidity, or, at least, Fluxility of the Bodies here below; and partly, and perhaps principally, of the Spring of the air, whose restless endeavour to expand itself every way, makes it either rush in itself, or compel the interposed bodies into all spaces, where it finds no greater resistance than it can furmount. And that in those motions which are made ob fugam Vacui (as the common phrase is) bodies acts without such generosity & Consideration, as is wont to be ascribed to them, is apparent enough in our 32d Experiment, where the torrent of Air, that seemed to strive to get into the Emptied Receiver, did plainly prevent its own Design, by so impelling the Valve, as to make it shut the only Orifice the Air was to get in at. And if afterwards either Nature, or the internal Air, had a design the external Air should be attracted, they seemed to prosecute very unwisely by continuing to suck the Valve so strongly, when they found that by that Suction the Valve itself could not be drawn in: Whereas by forbearing to suck, the Valve would by its own weight have fallen down, and suffered the excluded Air to return freely, and to fill again the exhausted Vessel. And this minds me to take notice of another deficiency, pointed at by our Experiments in the common Doctrine of those Plen●sts we reason with; for many of those unusual motions in Bodies, that are said to be made to escape a Vacuum, seem rather made to fill it. For why, to instance in our newly mentioned Experiment, assoon as the Valve was depressed by the weight we hung at it, should the Air so impetuously and copiously rush into the cavity of the Receiver; it there were before no vacant room there to receive it? and if there were, than all the while the Valve kept out the Air, those l●tle spaces in the Receiver, which the corpuscles of that Air afterwards filled, may be concluded to have remained empty. So that the seeming violence, employed by Nature on the occasion of the evacuating of the Vessel, seems to have come too late to hinder the making of Vacuities in the Receiver, and only to have, assoon as we permitted, filled up with Air those that were already made. And as for the Care of the Public Good of the Universe ascribed to dead and stupid Bodies, we shall only demand, why in our 19th Experiment, upon the Exsuction of the ambient Air, the Water deserted the upper half of the Glass-Tube; and did not ascend to fill it up, till the external Air was let in upon it: whereas by its easy and sudden regaining that upper part of the Tube, it appeared both that there was there much space devoid of Air, and that the Water might with small or no resistance have ascended into it, if it could have done so without the impulsion of the readmitted Air; which, it seems, was necessary to mind the Water of its formerly neglected Duty to the Universe. Nay, for aught appears, even when the excluded Air, assoon as 'twas permitted, rushed violently into our exhausted Receiver, that flowing in of the Air proceeded rather from the determinate Force of the Spring of the neighbouring Air, then from any endeavour to fill up, much less to prevent vacuity's. For though when as much Air as will, is gotten into our Receiver our present Opponents take it for granted that it is full of Air; yet if it be remembered that when we made our 17th Experiment we crowded in more Air to our Rece●●er than it usually holds; and if we also consider (which is much more) the Air of the same consistence with that in our Receiver may in windguns, as is known, and as we have tried, be compressed at least into half its wont room (I say at least, because some affirm, that the Air may be thrust into an 8th, or a yet smaller part of its ordinary extent) it seems necessary to admit either a notion of condensation & rarefaction that is not intelligible, or that in the capacity of our Receiver when presumed to be full of Air, there yet remained as much of space as was taken up by all the aërial corpuscles unpossessed by the Air. Which seems plainly, to infer that the Air that rushed into our emptied vessel did not do it precisely to fill up the Vacuities of it, since it left so many unfilled, but rather was thrust in by the pressure of the contiguous Air; which as it could not, but be always ready to expand itself, where it found least resistance, so was it unable to fill the Receiver any more, then until the Air within was reduced to the same measure of Compactness with that without. We may also from our two already often mentioned Experiments further deduce, that, (since Nature's hatred of a Vacuum is but Metaphorical and Accidental, being but a consequence or result of the pressure of the Air and of the Gravity, and partly also of the Fluxility of some other bodies) The power she makes use of to hinder a Vacuum, is not (as we have elsewhere also noted) any such boundless thing as men have been pleased to imagine. And the reason, why in the former Experiments, mentioned in favour of the Plenists, Bodies seem to forget their own Natures to shun a Vacuum, seems to be but this; That in the alleged cases the weight of that Water that was either kept from falling or impelled up, was not great enough to surmount the pressure of the contiguous Air; which, if it had been, the Water would have subsided, though no Air could have succeeded. For not to repeat that Experiment of Monsieur Paschal (formerly mentioned to have been tried in a Glass exceeding 32 Foot) wherein the inverted Pipe being long enough to contain a competent weight of Water, that Liquor freely ran out at the lower Orifice: Not to mention this (I say) we saw in our nineteenth Experiment, that when the pressure of the ambient Air was sufficiently weakened, the Water would ●all out apace at the Orifice even of a short Pipe, though the Air could not succeed into the room deserted by it. And it were not amiss if trial were made on the tops of very high Mountains, to discover with what ease a Vacuum could be made near the confines of the Atmosphere, where the Air is probably but light in comparison of what it is here below. But our present (three and thirtieth) Experiment seems to manifest, not only that the power, exercised by Nature, to shun or replenish a Vacuum, is limited, but that it may be determined even to Pounds and Ounces: Insomuch that we might say, such a weight Nature will sustain or will lift up to resist a Vacuum in our Engine; but if an Ounce more be added to that weight, it will surmount Her so much magnified detestation of Vacuities. And thus, My Lord, our Experiments may not only answer those of the Plenists, but enable us to retort their Arguments against themselves: since, if that be true which they allege, that, when Water falls not down according to its nature, in a Body wherein no Air can succeed to fill up the place it must leave, the suspension of the Liquor is made Ne detur Vacuum, (as they speak) it will follow, that if the Water can be brought to subside in such a case, that deserted space may be deemed empty, according to their own Doctrine; especially, since Nature (as they would persuade us) bestirs herself so mightily to keep it from being deserted. I hope I shall not need to remind Your Lordship, that I have all this while been speaking of a Vacuum, not in the strict and Philosophical sense, but in that more obvious and familiar one that has been formerly declared. And therefore I shall now proceed to observe in the last place, that our 33d Experiment affords us a notable proof of the unheeded strength of that pressure which is sustained by the Corpuscles of what we call the free Air, and presume to be uncompressed. For, as fluid and yielding a Body as it is, our Experiment teaches us, That even in our Climate, and without any other compression then what is (at least here below) Natural, or (to speak more properly) ordinary to it, it bears so strongly upon the Bodies whereunto it is contiguous, that a Cylinder of this free Air, not exceeding three Inches in Diameter is able to raise and carry up a weight, amounting to between sixteen and seventeen hundred Ounces. I said, even in our Climate, Aere frigido existente ta●dius moventur Automata quam 〈◊〉 ca●ido, adeo quidem ut Automaton quod Bel●●e i● No●a Zembla agent●s in aedibus 〈…〉, omnino 〈…〉. Varenius Geo: Genevat lib. 111. Propo: 7. pag. 648. because that is temperate enough; and as far as my observations assist me to conjecture, the Air in many other more Northern Countries may be much thicker, and able to support a greater weight: which is not to be doubted of, if there be no mistake in what is Recorded concerning the Hollanders, that were forced by the Ice to Winter in Nova Zembla, namely, That they found there so condensed an Air, that they could not make their Clock go, even by a very great addition to the weights that were wont to move it. I suppose Your Lordship will readily take notice, that I might very easily have discoursed much more fully and accuratly than I have done, against the common opinion touching Suction, and touching nature's hatred of a Vacuum. But I was willing to keep myself to those considerations touching these matters, that might be verified by our Engine itself, especially, since, as I said at first, it would take up too much time to insist particularly upon all the Reflections that may be made even upon our two last Experiments. And therefore, passing to the next, I shall leave it to your Lordship to consider how far these trials of ours will either confirm or disfavor the new Doctrine of several eminent Naturalists, who teach, That in all motion there is necessarily a Circle of Bodies, as they speak, moving together; and whether the Circles in such motion be an Accidental or Consequential thing or no. Experiment 34. 'tIs a known thing to those that are convesant in the hydrostatics, That two Bodies which in the Air are of equal weight, but of unequal bulk, as Gold, for instance and Iron, being afterwards weighed in Water, will lose their Aequilibrium upon the change of the ambient Body, so that the Gold will sink lower than the Iron; which, by reason of its greater bulk, has more Water to lift or displace, that it may sink. By Analogy to this Experiment, it seemed probable, that if two weights did in our Engine balance each other, when the Glass was full of Air; upon the exsuction of a great part of that Air, so notable a change in the consistence of the ambient Body, would make them lose their Aequilibrium. But being desirous at the same time to make a trial, for a certain Design that needs not here be mentioned, we took for one of our weights a dry Bladder, strongly tied at the Neck, and about half filled with Air (that being a weight both flight, and that would expand itself in the evacuated Glass) and fastening that to one part of our formerly mentioned exact balance (which turns with the 32d part of a Grain) we put a Metalline counterpoise into the opposite Scale; and so the two weights being brought to an Aequilibrium, the balance was conveyed into the Receiver, and suspended from the Cover of it. But before we proceed further, we must note, That presently after the laying on of the Cover, the Bladder appeared to preponderate, whereupon the Scales being taken out, and reduced very near to an Aequilibrium, yet so, that a little advantage remained on that side to which the Metalline weight belonged; they were again let down into the Receiver, which was presently made fast with Plaster, and a hot Iron: Soon after which, before the Pump was employed, the Bladder seemed again a little to preponderate. Afterwards the Air in the Glass being begun to be drawn out, the Bladder began (according to the formerly mentioned Observations) to expand itself, and manifestly to outweigh the opposite weight, drawing down the Scale to which it was fastened very much beneath the other, especially when the Air had swelled it to its full extent. This done, we very leisurely let in the external Air; and observed, that upon the flagging of the Bladder, the Scale whereto it was fastened, not only by degrees returned to an Aequilibrium with the other, but at length was a little outweighed by it. But because we suspected there might have intervened some unheeded Circumstance in this last part of the Experiment, we would not presently take out the Scales, nor meddle with the Cover, but leaving things as they were, we perceived, that after a little while the Bladder began again to preponderate, and by degrees to sink lower and lower for divers hours; wherefore, leaving the Vessel closed up all night, we repaired to it next Morning, and found the Bladder fallen yet lower. As if the very substance of it, had imbibed some of the moisture wherewith the Air (the Season being very rainy) did then abound: As Lute-strings, which are made likewise of the Membranous parts of Guts, strongly wreathed, are known to swell so much, oftentimes as to break in rainy and wet weather. Which conjecture is the more to be regarded, because congruously unto it one of the company having a little warmed the Bladder, found it then lighter than the opposite weight. But this must be looked upon as a bare conjecture, till we can gain time to make further trials about it. In the mean while we shall add, that without removing the Scales or the Cover of the Receiver, we again caused the A●r to be drawn out (the weather contiing very moist) but found not any manifest alteration in the balance; whether because the Aequilibrium was too far lost to let a small change appear, we determine not. But to make the Experiment with a Body less apt to be altered by the temperature of the Air, than was the Bladder; we brought the Scales again to an Aequilibrium with two weights, whereof the one was of Lead, the other of Cork. And having evacuated the Receiver, we observed, that both upon the exsuction, and after the return of the Air, the Cork did manifestly preponderate, and much more a while after the Air had been let in again, then whilst it was kept out. Wherefore, in the room of the Cork, we substituted a piece of Char-coal, as less likely to imbibe any moisture from the Air, but the event proved much the same with that newly related: So that this Experiment seems more liable to Casualties then any, excepting one we have made in our Engine. And as it is difficult to prevent them, so it seems not very easy to discover the causes of them, whereof we shall therefore at present forbear mentioning our Conjectures. Experiment 35. SOme Learned Mathematicians have of late ingeniously endeavoured to reduce Filters to Siphons'; but still the true cause of the ascension of Water, and other Liquors, both in Siphons' and in Filtration, needing (for aught we have yet found) a clearer Discovery and Explication, we were desirous to try whether or no the pressure of the Air might reasonably be supposed to have either the principal, or at least a considerable Interest in the raising of those Liquors. But because we found that we could not yet so evacuate our Receiver, but that the remaining Air, though but little in comparison of the exhausted, would be able to impel the the Water to a greater height than is usual in ordinary Filtrations: we resolved, instead of a List of Cotton, or the like Filtre, to make use of a Siphon of Glass, delineated in the third Figure, consisting of three pieces, two strait, and the third crooked to join them together; whose Junctures were diligently closed, that no Air might find entrance at them. One of the Legs of this Siphon was (as it should be) somewhat longer than the other, and was pervious at the bottom of it only, by a hole almost as slender as a hair, that the Water might but very leisurely drop out of it, lest it should all run out before the Experiment were completed. The other and shorter Leg of the Siphon was quite open at the end, and of the same wideness with the rest of the Pipe, whose bore was about ●/4 of an Inch. The whole Siphon made up of these several pieces put together, was designed to be about a Foot and a half long; that the remaining Air, when the Vessel was exhausted after the wont manner, might not be able to impel the Water to the top of the Siphon; which being inverted, was filled with Water, and of which the Shorter leg being let down two or three Inches deep into a Glass Vessel full of Water, and the upper parts of it being fastened to the inside of the Cover of the Receiver, we proceeded to close first, and then to empty the Vessel. The effect of the trial was this, that till a pretty quantity of Air had been drawn out, the Water dropped freely out at the lower end of the lower leg of the Siphon, as if the Experiment had been performed in the free Air. But afterwards, the Bubbles (as had been apprehended) began to disclose themselves in the Water, and ascending to the top of the Siphon, embodied themselves there into one, which was augmented little by little by the rising of other bubbles that from time to time broke into it, but much more by its own dilatation, which increased proportionably to the exsuction that was made of the Air out of the Receiver. So that at length the Water in the shorter Leg of the Siphon was reduced partly by the extraction of the ambient Air, and partly by the expansion of the great Bubble at the upper part of the Siphon, to be but about a Foot high, if so much; whereby it came to pass, that the course of the Water in the Siphon was interrupted, and that which remained in the longer Leg of it, continued suspended there without dropping any longer. But upon the turning of the Stop-cock, the outward Air (being let into the Receiver) got into the Siphon by the little hole at which the Water formerly dropped out; and traversing all the incumbent Cylinder of Water, in the form of Bubbles, joined itself with that Air that before possessed the top of the Siphon. To prevent the inconveniences arising from these Bubbles, two Glass Pipes, like the former, were so placed, as to terminate together in the midst of the Belly of a Glass Viol., into whose Neck they were carefully fastened with Cement; and then both the Viols and the Pipes being (which was not done without difficulty) totally filled with Water, the Siphon described in the fifth Figure, was placed with its shorter Leg in the Glass of Water, as formerly; and the Experiment being prosecuted after the same manner, much more Air then formerly was drawn out, before the Bubbles disclosing themselves in the Water were able to disturb the Experiment; because that in the capacity of the Viol there was room enough for them to stretch themselves, without depressing the Water below the ends of the Pipes; and, during this time, the Water continued to drop out of the propending Leg of the Siphon. But at length the Receiver being very much empty●d, the passage of the Water through the Siphon ceased, the upper ends of the Pipes beginning to appear a little above the remaining Water in the Viol, whose dilated Air appeared likewise to press down the Water in the Pipes, and fill the upper part of them. And hereby the continuity of the Water, and so the Experiment itself being interrupted, we were invited to let in the Air again, which, according to its various proportions of pressure to that of the Air in the Viol and the Pipes, did for a good while exhibit a pleasing variety of Phaenomena, which we have not now the leisure to recite. And though upon the whole matter there seemed little or no cause to doubt, but that, if the Bubbles had not disturbed the Experiment, it would manifestly enough have appeared that the course of Water through Siphons' depends upon the pressure of the Air: yet we resolved, at our next leisure and conveniency, to try the Experiment again, with a quantity of Water before freed from Bubbles by the help of the same Engine. This occasion I have had to take notice of Siphons', puts me in mind of an odd kind of Siphon that I caused to be made a pretty while ago, and which has been since, by an Ingenious Man of Your acquaintance, communicated to divers others. The occasion was this, An eminent Mathematician told me one day, that some inquisitive French Men (whose Names I know not) had observed, That, in case one end of a slender and perforated Pipe of Glass be dipped in Water, the Liquor will ascend to some height in the Pipe, though held perpendicular to the plain of the Water. And, to satisfy me that he misrelated not the Experiment, he soon after brought two or three small Pipes of Glass, which gave me the opportunity of trying it: though I had the less reason to distrust it, because I remember I had often in the long and slender Pipes of some Wether Glasses, which I had caused to be made after a somewhat peculiar fashion, taken notice of the like ascension of the Liquor, though (presuming it might be casual) I had made but little reflection upon it. But after this trial, beginning to suppose, that though the Water in these Pipes that were brought me, rise not above a quarter of an Inch, (if near so high) yet, i● the Pipes were made slender enough, the Water might rise to a very much greater height; I caused several of them to be, by a dexterous Hand, drawn out at the flame of a Lamp, in one of which that was almost incredibly slender, we found that the Water ascended (as it were of itself) five Inches by measure, to the no small wonder of some famous Mathematicians, who were Spectators of some of these Experiments. And this height the Water reached to, though the Pipe were held in as erected a posture as we could: For if it were inclined, the Water would fill a greater part of it, though not rise higher in it. And we also found, that when the inside of the Pipe was wetted beforehand, the Water would rise much better than otherways: But we caused not all our slender Pipes to be made strait, but some of them crooked, like Siphons': And having immersed the shorter Leg of one of these into a Glass that held some fair Water, we found, as we expected, that the Water arising to the top of the Siphon, though that were high enough, did of itself run down the longer Leg, and continue running like an ordinary Siphon. The cause of this ascension of the Water, appeared to all that were present so difficult, that I must not stay to enumerate the various Conjectures that were made at it, much less to examine them; especially, having nothing but bare Conjectures to substitute in the room of those I do not approve. We tried indeed, by conveying a very slender Pipe and a small Vessel of Water into our Engine, whether or no the Exsuction of the ambient Air would assist us to find the cause of the ascension we have been speaking of: But though we employed red Wine instead of Water, yet we could scarce certainly perceive thorough so much Glass, as was interposed betwixt our Eyes and the Liquor, what happened in a Pipe so slender, that the redness of the Wine was scarce sensible in it. But as far as we could discern, there happened no great alteration to the Liquor▪ which seemed the less strange, because the Spring of that Air that might depress the Water in the Pipe, was equally debilitated with that which remained to press upon the surface of the Water in the little Glass. Wherefore, in favour of his Ingenious Conjecture who ascribed the Phaenomenon, under consideration to the greater pressure made upon the Water by the Air without the Pipe, then by that within it, (where so much of the Water (consisting perhaps of Corpuscles more pliant to the internal surfaces of the Air) was contiguous to the sides) it was shown, that in case the little Glass Vessel that held the Water, of which a part ascended into the slender Pipe, were so closed, that a Man might with his mouth suck the Air out of it, the Water would immediately subside in the small Pipe. And this would indeed infer, that it ascended before only by the pressure of the incumbent Air: But that it may (how justly I know not) be objected, that peradventure this would not happen, in case the upper end of the Pipe were in a Vacuum: And that 'tis very probable the Water may subside, not because the pressure of the internal Air is taken off by Exsuction, but by reason of the Spring of the external Air, which impels the Water it finds in its way to the Cavity deserted by the other Air, and would as well impel the same Water upwards, as make it subside, if it were not for the accidental posture of the Glasses. However, having not now leisure to examine any further this Matter, I shall only mind Your Lordship, that if You will prosecute this Speculation, it will be pertinent to find out likewise, Why the surface of Water (as is manifest in Pipes) uses to be concave, being depressed in the middle, and higher on every side? and Why in Quicksilver on the contrary, not only the surface is wont to be very convex, or swelling, in the middle; but if you dip the end of a slender Pipe in it, the surface of the Liquor (as 'tis called) will be lower within the Pipe, then without▪ Which Phaenomena, whether, and how far, they may be deduced from the Figure of the Mercurial Corpuscles, and the Shape of the Springy Particles of the Air, I willingly leave to be considered. Experiment 36. SEveral ways we have met with proposed, partly by the excellent Galileo, and partly by other ingenious Writers, to manifest that the Air is not devoid of weight; some of these, require the previous absence of the Air to be weighed; and others, the violent condensation of it. But if we could lift a pair of Scales above the Atmosphere, or place them in a Vacuum, we might there weigh a parcel of Air itself, as here we do other Bodies in the Air, because it would there be heavier than that which surrounds it, as are grosser Bodies we commonly weigh, than the medium or ambient Air. Wherefore, though we have above declined to affirm, that our Receiver, when emptied, deserves the name of a true Vacuum, and though we cannot yet perfectly free it from Air itself, yet we thought fit to try how far the Air would manifest its gravity in so thin a medium, as we could make in our Receiver, by evacuating it. We caused then to be blown at the Flame of a Lamp, a Glass-bubble of about the bigness of a small Hen-egge, and of an Oval form, save that at one end there was drawn out an exceeding slender Pipe, that the Bubble might be sealed up, with as little rarifaction as might be, of the Air included in the great or oval Cavity of it. This Glass being sealed, was fastened to one of the Scales of the exact pair of Balances formerly mentioned; and being counterpoised with a weight of Lead, was conveyed into the Receiver, and closed up in it. The Beam appearing to continue Horizontal, the Pump was set a-work, and there scarce passed above two or three Exsuctions of the Air, before the Balance lost its Aequilibrium, and began to incline to that side on which the Bubble was; which, as the Air was further and further drawn out, did manifestly more and more preponderate, till he that pumped began to grow weary of his Employment: after which the air being leisurely let in again, the scales by degrees returned to their former Aequilibrium. After that we took them out, and casting into that scale to which the lead belonged three quarters of a grain, we conveyed the balance into the Receiver, which being closed up, and exhausted as before, we observed, that as the air was drawn out more and more, so the glass bubble came nearer and nearer to an Aequilibrium with the other weight, till at length the beam was drawn to hang horizontal; which (as we had found by another trial) we could not bring it to do, when a quarter of a Grain more was added to the scale, to which the lead belonged: though it seemed questionless, that if we could have perfectly emptied the Receiver of the contained air, that included in the bubble would have weighed above a grain, notwithstanding its having been probably somewhat Rarified by the flame by the help of which, the bubble was sealed up. Let us add, that on the regress of the excluded air, the Lead, and the weight cast into the same scale, did again very much preponderate. We likewise conveyed into the Receiver, the same bubble, opened at the end of the slender pipe above mentioned, but having drawn out the air, after the accustomed manner, we found not as before, the bubble to outweigh the opposite lead, so that by the help of our Engine, we can weigh the Air, as we weigh other Bodies, in its natural or ordinary consistence, without at all condensing it: Nay, which is remarkable, having conveyed a Lamb's 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 itself, as to distend the Bladder so, as to seem ready to break it; yet this rarified 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 trials concerning the weight of the Air; namely, That having once caused the Pump to be somewhat obstinately plied, to discover the better what may be expected from the thinness of the medium in this Experiment; the Imprisoned Air broke its brittle Prison, and throwing the greatest part of it against the side of the Receiver, dashed it against that th●ck Glass into a multitude of pieces. Which Accident I mention, partly that it may confirm what we delivered in our Reflections, upon the first Experiment, where we considered what would probably be done by the Spring of the Air Imprisoned in such Glasses, in case the balancing 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) proved so impervious to the Air, that it could not get away through the Pores, but was forced to break the glass in pieces to free itself; 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 happened 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 persuade 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 courser sort of Glass, (which the Tradesmen 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 increased, that when we came back to the Furnace we found the Spirituous and Saline Corpuscles poured 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 fly in pieces, then fit to be touched. Yet, being curious to observe the effects of a Distillation, prosecuted with so intense and unusual degree of heat, we ventured to come near, and observed, among other things, that on the outside of the Receiver, at a great distance from the juncture, there was settled 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 Oil, 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 suspicion, and therefore called 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 considered, the subtle parts of the distilled matter being violently agitated, by the excessive heat had passed through the Pores of the Glass, widened by the same heat. But this having never happened 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 loser Texture of that particular parcel of Glass the Receiver was made of (for Experience has 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, opened the Pores of the Glass; then to imagine that such a substance as Air, should be able to permeate the Body of Glass contrary to the testimony of a thousand Chemical 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 rarified Air. And on this occasion we will annex an Experiment, which has 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 itself, 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 forced 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 than was this: I took a fair Glass Siphon, the lower end o● 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 ordered that a little Bubble of Air was intercepted in the slenderest part of the Siphon, betwixt the little hole newly mentioned, and the incumbent Water, upon which, it came to pass, that the Air being not to be forced through so narrow a passage, by so light a Cylinder of Water, though amounting to the length of divers Inches, as leaned upon it, hindered the further 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 continued 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 Man's Finger, is yet towards one end so slender, as to terminate in a hole almost as small as a Horsehair; and if you fill this Pipe with Water, you will find that Liquor to drop down freely enough thorough the slender Extreme: 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 'tis 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, then 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 thorough the Pores of a Lamb's Bladder, yet Particles of Water will, as we have long since observed, and as may be easily tried, by very closely tying a little Alcalizate Salt (we used 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 thorough the Pores of the Bladder Water enough to dissolve the Salt into a Liquor. But I see I am slipped 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 o● Bodies, than the more flexible Particles of Water; or whether it may more probabiy be ascribed to some other Cause. Nor will I stay to consider how far we may hence be assisted to guess at the cause of the ascension of Water in the slender Pipes and Siphons' formerly mentioned, but will return to our Bubble; and take notice, That we thought fit also to endeavour 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 answered 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 what 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 occurred 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 itself 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 imprisoned; whereas Air penned 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 Loadstone) relates, P: Nicol: Cab: lib: 4. Met●o●▪ Aristot: That he saw a Marble Pillar (so vast, that three men together with displayed arms could not embrace it, and that 1000 Yoke of Oxen drawing it several ways with all their strength, could not have torn it asunder) 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 Fire, so rarified 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 itself. I remember I have taken notice that probably the reason why the included Air did not break the hermetically sealed Bubbles that remained entire in our emptied Receiver, was, That the Air, being somewhat rarefied by the Flame employed to close the Glass, its Spring, upon the recess of the heat, grew weaker than before. But though we reject not that guess, yet it will not in the present case serve the turn, because that much smaller Glass bubbles exactly closed, will, by the included Air (though agitated but 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 does 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 chief 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 ascribed 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 trials (though not made in our Engine) have taught us, concerning what we would have discovered by the newly mentioned 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 suffered leisurely to cool was again weighed together with the wax that stopped it, and was found to weigh (by reason of the additional weight of the wax) six ounces, six drachmas, 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 drachmas, and 50. grains. So that the Aeolipile freed as fare as our fire could free it, from its Air, weighed less than itself 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 the 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 rarify the Air in our Aeolipile (though made red hot almost all over, and so immediately plunged into cold water) to half that degree which he mentions, namely to 70. times it's natural extent, unless it were that the Aeolipile he employed was able to sustain a more vehement heat then ours (which yet we kept in so great an one, that once the solder melting, it fell asunder into the two Hemispheres it consists of.) The forementioned way of weighing the Air by the help of an Aeolipile, seems somewhat more exact than that which Mersennus used, In that in ours the Aeolipile was not weighed, till it was cold; whereas in his, being weighed red hot, it is subject to lose of its substance in the cooling, for (as we have elsewhere noted on another occasion) Copper heated red hot is wont in the cooling to throw off little thin scales in such plenty, that having purposely watched a Copper Aeolipile during its refrigeration, we have seen the place round about it almost covered with those little scales it had every way scattered: which, however they amount not to much, ought not to be over-looked, when 'tis so light a body as Air, that is to be weighed. We will not examine, whether the Aeolipile in cooling may not receive some little increment of weight, either from the vapid or faline Steames that wander up and down in the Air: But we will rather mention, that (for the greater exactness) we employed to weigh our Aeolipile, both when filled only with Air and when replenished with Water, a pair of scales that would turn (as they speak) with the fourth part of a grain. As to the proportion of weight betwixt Air and Water, some learned men have attempted it by ways so unaccurate that they seem to have much mistaken it. For (not to mention the improbable accounts of Kepler and others.) The learned and diligent Ricciolus, having purposely endeavoured to investigate this proportion by means of a thin bladder, estimates the weight of the Air to that of the Water to be as one to ten thousand, or thereabouts. And indeed I remember that having formerly, on a certain occasion, weighed a large bladder full of Air, and found it when the Air was all squeezed out, to have contained fourteen grains of Air. I found the same bladder afterwards filled with water to contain very near 14. pound of that liquor: according to which account, the proportion of Air to Water was almost as a grain to a pound, that is, as one to above 7600. To this we may add, that on the other side, Galileo himself using another, but an unaccurate way too, defined the Air to be in weight to Water, but as one to 4. hundred. But the way formerly proposed of weighing the Air by an Aeolipile, seems by great odds more exact; and (as fare as we could guess) seemed to agree well enough with the experiment made in our Receiver. Wherefore it will be best to trust our Aeolipile in the enquiry we are about, and according to our observations the water it contained amounting to one and twenty ounces and an half, and as much Air as was requisite to fill it weighing eleven grains, the proportion in gravity of Air to Water of the same bulk will be as one to 938. And though we could not fill the Aeolipile with water, so exactly as we would, yet in regard we could not either as perfectly as we would, drive the Air out of it by heat; we think the proportion may well enough hold: but those that are delighted with round numbers (as the phrase is) will not be much mistaken if they reckon water to be near a thousand times heavier than Air. And (for further proof that we have made the proportion betwixt these two bodies rather greater then lesser than indeed it is; and also to confirm our former observation of the weight of the Air) we will add, That, having another time put some Water into the Aeolipile before we set it on the fire, that the copious vapours of the rarefied liquor might the better drive out the Air, we found, upon trial carefully made, that when the Aeolipile was refrigerated, and the included vapours were by the cold turned again into water (which could not have happened to the Air, that the preceding Steams expelled) the Air, when it was let in, increased the weight of the Aeolipile as much as before, namely, Eleven Grains; though there were already in it twelve Drachmas and a half, besides a couple of Grains of Water, which remained of that we had formerly put into it to drive out the Air. Mersennus indeed tells us, that by his account Air is in weight to Water, as 1 to 1356. And adds, that we may, without any danger, believe that the gravity of Water to that of Air of a like bulk, is not less than of 1300 to 1. And consequently, that the quantity of Air to a quantity of Water equiponderant thereto, is as 1300 to 1. But why we should relinquish our own carefully repeated trials, I see not. Yet I am unwilling to reject those of so accurate and useful a Writer: And therefore shall propose a way of reconciling our differing Observations, by presenting, that the discrepance between them may probably arise from the differing consistence of the Air at London and at Paris: For our Air being more cold and moist, then that which Your Lordship now breathes, may be supposed also to be a fourth or fifth part more heavy. I leave it to be considered, whether it be of any moment that our Observations were made in the midst of Winter, whereas his were perhaps made in some warmer time of the Year. But I think it were not amiss that, by the method formerly proposed, the gravity of the Air were observed both in several Countries, and in the same Country, in the several Seasons of the Year and differing Temperatures of the Wether. And I would give something of value to know the weight of such an Aeolipile as ours full of air in the midst of Winter in Nova Zembla, if that be true which we formerly took notice of, namely, That the Hollanders, who Wintered there, found that Air so thick that their Clock would not go. If Your Lordship should now ask me, if I could not by the help of these, and our other Observations, decide the Controversies of our Modern Mathematicians about the height of the Air or Atmosphere, by determining how high it doth indeed reach: I should answer, That though it seems easy enough to show that divers Famous and Applauded Writers have been mistaken in assigning the height of the Atmosphere: Yet it seems very difficult precisely to define of what height it is. And because we have hitherto but lightly touched upon a matter of such importance, we presume it will not be thought impertinent, upon this occasion, to annex something towards the Elucidation of it. What we have already tried and newly set down, allows us to take it for granted, that (at least about London) the proportion of gravity betwixt Water and Air, of equal bulk, is as of a thousand to one. The next thing therefore that we are to inquire after, in order to our present design, is the difference in weight betwixt Water and Quicksilver: And though this hath been defined already by the Illustrious Verulam, and some other inquisitive Persons, that have compared the weight of several Bodies, and cast their Observations into Tables, yet we shall not scruple to annex our own trials about it: Partly, because we find Authors considerably to dis-agree; partly, because we used exacter Scales, and a somewhat more wary method than others seem to have done: And partly also, because having prosecuted our inquiry by two or three several ways; the small difference between the events may assure us that we were not much mistaken. We took then a Glass Pipe, of the form of an inverted Siphon, whose shape is delineated in the sixteenth Figure: And pouring into it a quantity of Quick silver, we held it so, that the superficies of the Liquor, both in the longer and shorter leg, lay in a Horizontal Line, denoted in the Scheme by the pricked Line OF; then pouring Water into the longer Leg of the Siphon, till that was almost filled, we observed the surface of the Quicksilver in that leg to be, by the weight of the Water, depressed, as from E to B; and in the shorter leg, to be as much impelled upward as from F to G: Whereupon having formerly stuck marks, as well at the point B, as at the opposite point D, we measured both the distance DC to have the height of the Cylinder of Quicksilver, which was raised above the Point D (level with the surface of the Quicksilver in the other leg) by the weight of the Water, and the distance BASILIUS which gave us the height of the Cylinder of Water. So that the distance D C amounting to 2 ●●/●● Inches, and the height of the Water amounting 30 45/5● Inches; and the whole numbers on both sides, which the annexed Fractions being reduced to improper Fractions of the same denomination, the proportion appeared to be (the denominators being left out as equal on both sides) as 121 to 1665; or by reduction, as one to 13 ●●/●●. Besides this unusual way of determining the gravity of some things, we measured the proportion betwixt Quicksilver and Water, by the help of so exact a balance, as loses its Aequilibrium by the hundredth part of a Grain. But because there is wont to be committed an oversight in weighing Quicksilver and Water, especially if the Orifice of the Vessel wherein they are put be any thing wide, in regard that men heed not that the surface of Water in Vessels will be concave, but that of Quicksilver, notably convex or protuberant: To avoid this usual oversight (I say) we made use of a glass bubble, blown very thin at the Flame of a Lamp, that it might not be too heavy for the Balance, and terminating in a very slender neck, wherein the concavity or convexity of a Liquor could not be considerable: This Glass weighing 23 1/● Grains, we filled almost with Quicksilver, and fastening a mark over against the middle of the protuberant Superficies as near as our Eyes could judge, we found that the Quicksilver alone weighed 299 ●/3● Grains: Then the Quicksilver being poured out, and the same Glass being filled as full of common Water, we found the Liquor to weigh 21 7/8 Grains. Whereby it appeared that the weight of Water to Quicksilver, is as one to 13 ●9/2●: Though our Illustrious Verulam (questionless not for want of Judgement or Care, but of exact Instruments) makes the proportion betwixt those two Liquors to be greater than of 1 to 17. And to add, that upon the by, since Quicksilver and well rectified Spirit of Wine, are (how justly I say not) accounted, the one the heaviest, and the other the lightest of Liquors; we thought to fill in the same Glass, and with the same Scales to observe the difference betwixt them, which we found to be as of 1 to 16 64●/●0●4; whereby it appeared, That the difference betwixt Spirit of Wine, that may be made to burn all away, (such as was ours) and common Water, is as betwixt 1 and 1 ●●/●●● We might here take occasion to admire, that though Water (as appeared by the Experiment formerly mentioned of the Pewter Vessel) seems not capable of ●ny considerable condensation, and seems not to have interspersed in it any store of Air; yet Quicksilver, of no greater bulk than Water, should weigh near fourteen times as much. But having only pointed at this as a thing worthy of consideration, we will proceed in our inquiry after the height of the Atmosphere: And to avoid the trouble of Fractions, we will assume that Quicksilver is fourteen times as heavy as Water, since it wants so little of being so. Wherefore having now given us the proportion of Air to Water, and Water to Quicksilver, it will be very easy to find the proportion betwixt Air and Quicksilver, in case we will suppose the Atmosphere to be uniformly of such a consistence as the Air we weighed here below. For since our Engine hath sufficiently manifested that 'tis the Aequilibrium with the external Air, that in the Torricellian Experiment keeps the Quicksilver from subsiding; And since, by our accurate Experiment formerly mentioned, it appears that a Cylinder of Mercury, able to balance a Cylinder of the whole Atmosphere, amounted to near about thirty Inches; and since, consequently we may assume the proportion of Quicksilver to Air to be as fourteen thousand to one; it will follow, that a Cylinder of Air, capable to maintain an Aequilibrium, with a Mercurial Cylinder of two Foot and an half in height, must amount to 35000 Feet of our English Measure; and consequently (reckoning five Foot to a Geometrical Pace, and one thousand such Paces to a Mile) to seven full Miles. But this (as we lately intimated) proceeds upon the supposition, that the Air is every where of the same consistence that we found it near the surface of the Earth; but that cannot with any safety be concluded, not only for the reason I find to have been taken notice of by the Ancients, and thus expressed in Seneca: Omnis Aër (says he) quo propior est terris hoc crassior; Senec: Nat: quest: lib. 4. cap. 10. quemadmodum in aqua & in omni humore faex ima est, ita in Aëre spississima quaeque desidunt; but much more, because the springy Texture of the Aërial Corpuscles, makes them capable of a very great compression, which the weight of the incumbent part of the Atmosphere is very sufficient to give those that be undermost and near the surface of the Earth. And if we recall to mind those former Experiments, whereby we have manifested, That Air, much rarefied without heat, may easily admit a further rarefaction from heat; and that the Air, even without being expanded by heat, is capable of being rarefied to above one hundred and fifty times the extent it usually possesses here below; How can it be demonstrated that the Atmosphere may not, for aught we know, or at least for aught can be determined by our Statical and Mechanical Experiments, rise to the height of Five and twenty Germane Leagues, if not of some hundred of common Miles? And this conjecture itself may appear very injurious to the height whereunto Exhalations may ascend, Ricciol: Alma: Nov: Tom: 2. lib. 10 sect. 6. prop. 50. Ex magnan: lib. 1. Perspective horary prop: 38. if we will allow that there was no mistake in that strange Observation made at Tolous in a clear Night in August, by the diligent Mathematician Emanuel Magnan, and thus Recorded by Ricciolus, (for I have not at hand the Authors own Book) Vidit (says he) ab hor a undecima post meridiem usque ad mediam noctem Lunâ infra horizontem posit â, nubeculam quandam lucidam prope Meridianum fere usque ad Zenith diffusam quae consideratis omnibus non poterat nisi à sole illuminari; ideoque altior esse debuit tota umbra terrae. Addit (continues Ricciolus) simile quid evenisse Michaeli Angelo Riccio apud Sabinos versanti nempe viro in Mathesi eruditissimo. Various Observations made at the feet, tops, and interjacent parts of high Mountains, might perchance somewhat assist us to make an estimate in what proportion, if in any certain one, the higher Air is thicker than the lower, and guess at the dis-form consistence, as to laxity and compactness of the Air at several distances from us. And if the difficulties about the refractions of the Celestial Lights, were satisfactorily determined, that might also much conduce to the placing due limits to the Atmosphere (whose Dimensions those Observations about Refractions seem hitherto much to contract.) But for the present we dare not pronounce any thing peremptorily con●cerning the height of it, but leave it to further inquiry: contenting ourselves to have manifested the mistake of divers eminent Modern Writers, who will not allow the Atmosphere to exceed above two or three Miles in height (as the Famous Kepler will not the Aër refractivus) and to have rendered a reason why in the mention we made in the Notes upon the first Experiment, touching the height of the Atmosphere, we scrupled not to speak of it, as if it might be many Miles high. WE will now proceed to recite a Phaenomenon, Experiment 37. which, though made amongst the first, we thought fit not to mention till after many others, that we might have the opportunity to observe as many Circumstances of it as we could, and so present Your Lordship at once, most of what we at several times have taken notice of concerning so odd a Phaenomenon. Our Engine had not been long finished, when, at the first leisure we could steal from our occasions to make trial of it, we caused the Air to be pumped out of the Receiver; and whilst I was busied in entertaining a Learned Friend that just than came to visit me, an Ingenious By-stander, thought he perceived some new kind of Light in the Receiver, of which giving me hastily notice, my Friend and I presently observed, that when the Sucker was drawn down, immediately upon the turning of the Key, there appeared a kind of Light in the Receiver, almost like a faint flash of Lightning in the Daytime, and almost as suddenly did it appear and vanish. Having, not without some amazement, observed divers of these Apparitions of Light, we took notice that the Day was clear, the hour about ten in the Morning, that the only Window in the Room faced the North; and also, that by interposing a Cloak, or any opacous Body between the Receiver and the Window, though the rest of the Room were sufficiently enlightened, yet the flashes did not appear as before, unless the opacous Body were removed. But not being able on all these Circumstances to ground any firm Conjecture at the cause of this surprising Phaenomenon, as soon as Night was come, we made the Room very dark; and plying the Pump as in the Morning, we could not, though we often tried, find, upon the turning of the Key, so much as the least glimmering of Light; whence we inferred, that the flash appearing in the Receiver, did not proceed from any new Light generated there, but from some reflections of the light of the Sun, or other Luminous Bodies placed without it; though whence that Reflection should proceed, it posed us to conjecture. Wherefore the next Morning, hoping to inform ourselves better, we went about to repeat the Experiment, but though we could as well as formerly exhaust the Receiver, though the place wherein we made the trial was the very same; and though other Circumstances were resembling, yet we could not discover the least appearance of Light all that Day, nor on divers others on which trial was again fruitlessly made; nor can we to this very time be sure a Day before hand that these Flashes will be to be seen in our great Receiver. Nay, having once found the Engine in a good humour (if I may so speak) to show this trick, and sent notice of it to our Learned Friend Doctor Wallis, who expressed a great desire to see this Phaenomenon, though he were not then above a Bow-shoot off, and made haste to satisfy his Curiosity; yet by that time he was come, the thing he came for was no longer to be seen; so that having vainly endeavoured to exhibit again the Phaenomenon in his presence, I began to apprehend what he might think of me, when unexpectedly the Engine presented us a flash, and after that a second, and as many more, as sufficed to satisfy him that we might very well confidently relate, that we have ourselves seen this Phaenomenon, though not confidently promise to show it others. And this unsuccessfulness whereto our Experiment is liable, being such, that by all our watchfulness and trials, we could never reduce it to any certain Rules or Observations; since in all constitutions of the Wether, times of the Day, etc. it will sometimes answer, and sometimes dis-appoint our Expectations; We are much discouraged from venturing to frame an Hypothesis to give an account of it: which if the Experiment did constantly succeed, might the more hopefully be attempted; by the help of the following Phaenomena laid together: some of them produced upon trials purposely made to examine the validity of the conjectures, other trials had suggested. First then we observed, that the Apparition of Light may be made as well by Candle-light, as by Daylight; and in whatever position the Candle be held, in reference to the Receiver, as on this or that hand of it, above it, beneath it, or any other way, provided the Beams of Light be not hindered from falling upon the Vessel. Next, we noted that the flash appears immediately upon the turning of the Key, to let the Air out of the Receiver into the emptied Cylinder, in so much that I remember not that when at any time in our great Receiver, the Stop-cock was opened before the Cylinder was exhausted (whereby it came to pass that the Air did rather descend, then rush into the Cylinder) the often mentioned flash appeared to our eyes. Yet, we further observed, that when instead of the great Receiver we made use of a small Glass, not containing above a pound and a half of Water, the Phaenomenon might be exhibited though the Stop-cock were open, provided the Sucker were drawn nimbly down. We noted too, that when we began to empty the Receiver, the appearances of Light were much more conspicuous then towards the latter end, when little Air at a time could pass out of the Receiver. We observed also, that when the Sucker had not been long before well Oiled, and instead of the great Receiver, the smaller Vessel abovementioned was employed; We observed, I say, that then, upon the opening of the Stop-cock, as the Air descended out of the Glass into the emptied Cylinder, so at the same time there ascended out of the Cylinder into the Vessel a certain Steam, which seemed to consist of very little Bubbles, or other minute Corpuscles thrown up from the Oil, rarefied by the attrition it suffered in the Cylinder. For at the same time that these Steams ascended into the Glass, some of the same kind manifestly issued out like a little Pillar of Smoke at the Orifice of the Valve, when that was occasionally opened. And these Steams frequently enough presenting themselves to our view, we found, by exposing the Glass to a clear Light, that they were wont to play up and down ●n it, and so by their whiteishness, to emulate in some measure the apparition of Light. For we likewise sometimes found, by watchful observation, that when the Flash was great, not only at the very instant the Receiver lost of its transparency, by appearing full of some kind of whitish substance; but that for some short time after the sides of the Glass continued somewhat opacous, and seemed to be darkened, as if some whitish Steam adhered to the inside of them. He that would render a Reason of the Phaenomenon, whereof all these are not all the Circumstances, must do two things; whereof the one is difficult, and the other little less than impossible: For he must give an Account not only whence the appearing whiteness proceeds, but wherefore that whiteness does sometimes appear and sometimes not. For our part, we freely confess ourselves at a loss about rendering a Reason of the less difficult part of the Problem: And though Your Lordship should even press us to declare what Conjecture it was, that the above-recited Circumstances suggested to us, we should propose the thoughts we then had, no otherwise then as bare Conjectures. In case then our Phaenomenon had constantly and uniformly appeared, we should have suspected it to have been produced after some such manner as follows. First, we observed that, though that which we saw in our Receiver seemed to be some kind of Light, yet it was indeed but a whiteness which did (as hath already been noted) opacate (as some speak) the inside of the Glass. Next we considered, that our common Air abounds with Particles or little Bodies, capable to reflect the Beams of Light. Of this we might easily give divers proofs, but we shall name but two: The one, that vulgar observation of the Motes that appear in Multitudes swimming up and down in the Air, when the Sunbeams shooting into a Room, or any other shady Place discover them, though otherwise the eye cannot distinguish them from the rest of the Air: The other proof we will take from what we (and no doubt very many others) have observed, touching the Illumination of the Air in the Night. And we particularly remember, that, being at some distance from London one Night, that the People, upon a very welcome Occasion, testified their Joy by numerous Bonfires; though, by reason of the Interposition of the Houses, we could not see the Fires themselves, yet we could plainly see the Air all enlightened over and near the City; which argued, that the lucid Beams shot upwards from the Fires, met in the Air with Corpuscles opacous enough to reflect them to our Eyes. A third thing that we considered, was, That white may be produced (without excluding other ways, or denying invisible Pores in the solidest Bodies) when the continuity of a Diaphanous Body happens to be interrupted by a great number of Surfaces, which, like so many little Looking-glasses, do confusedly represent a multitude of little and seemingly contiguous Images of the elucid Body. We shall not insist on the explanation of this, but refer You for it to what we have said in another Paper (touching Colours.) But the Instances that seem to prove it are obvious: For Water or whites of Eggs beaten to froth, do lose their transparency and appear white. And having out of one of our lesser Receivers carefully drawn out the Air, and so ordered it, that the hole by which the Water was to get in, was exceeding small, that the Liquor might be the more broken in its passage thorough it, we observed with pleasure, That, the Neck being held under Water, and the little hole newly mentioned being opened, the Water that rushed in was so broken, and acquired such a multitude of new Surfaces, that the Receiver seemed to be full rather of Milk than Water. We have likewise found out, That by heating a lump of Crystal to a certain degree, and quenching it in fair Water, it would be discontinued by such a multitude of Cracks, (which created new Surfaces within it) that though it would not fall asunder, but retain its former shape, yet it would lose its transparency, and appear white. Upon these Considerations, My Lord, and some others, it seemed not absurd to imagine, That upon the rushing of the Air out of the Receiver into the emptied Cylinder, the Air in the Receiver being suddenly and vehemently expanded, the Texture of it was as suddenly altered, and the parts made so to shift places (and perhaps some of them to change postures) as during their new and vehement Motion and their varied Situation, to disturb the wont continuity and so the Diaphaneity of the Air; which (as we have already noted) upon its ceasing to be a transparent Body, without the interposition of coloured things, must easily degenerate into white. Several things there were that made this Conjecture seem the less improbable. As first, That the whiteness always appeared greater when the Exsuction began to be made, whilst there was store of Air in the Receiver, then when the Air was in great part drawn out. And next, That, having exhausted the Receiver, and applied to the hole in the Stop-cock a large bubble of clear Glass, in such a manner, that we could at pleasure let the Air pass out at the small Glass into the great one, and easily fill the small one with Air again, We observed with pleasure, That upon the opening the passage betwixt the two Glasses, the Air in the smaller having so much room in the greater to receive it, the Dissilition of that Air was so great, that the small Viol seemed to be full of Milk; and this Experiment we repeated several times. To which we may add, That, having provided a small Receiver, whose upper Orifice was so narrow that I could stop it with my Thumb, I observed, that when upon the Exsuction of the Air the capacity of the Glass appeared white, if by a sudden removal of my Thumb I let in the outward Air, that whiteness would immediately vanish. And whereas it may be objected, That in the Instance formerly mentioned, Water turning from perspicuous to white, there intervenes the Air, which is a Body of a Heterogeneous nature, and must turn it into Bubbles to make it lose its transparency. We may borrow an Answer from an Experiment we deliver in another Treatise, where we teach how to make two very volatile Liquors, which being gently put together are clear as Rock-water, and yet will almost in a moment, without the sub-ingression of Air to turn them into Bubbles, so altar the disposition of their insensible parts, as to become a white and consistent Body. And this happens not as in the precipitation of Benjamin, and some other Resinous Bodies, which being dissolved in Spirit of Wine, may, by the effusion of fair Water, be turned into a seemingly Milky substance. For this whiteness belongs not to the whole Liquor, but to the Corpuscles of the dissolved Gum, which after a while subsiding leave the Liquor transparent, themselves only remaining white: Whereas in our case, 'tis from the varied texture of the whole formerly transparent fluid Body, and not from this or that part that this whiteness results: For the Body is white throughout, and will long continue so; and yet may, in process of time, without any addition, be totally reduced into a transparent Body as before. But besides the Conjecture insisted on all this while, we grounded another upon the following Observation, which was, That having conveyed some smoke into our Receiver placed against a Window, we observed, that upon the exsuction of the Air, the Corpuscles that were swimming ●n it, did manifestly enough make the Receiver seem more opacous at the very moment of the rushing out of the Air: For considering that the whiteness, whose cause we inquire of, did but sometimes appear, it seemed not impossible but that at such times the Air in the Receiver might abound with Particles, capable of reflecting the Light in the manner requisite to exhibit a white colour, by their being put into a certain unusual Motion. As may be in some measure illustrated by this, That the new motion of the freshly mentioned Fumes, made the inside of the Receiver appear somewhat darker than before: And partly by the nature of our formerly mentioned smoking Liquor, whose parts though they seemed transparent whilst they composed a Liquor, yet when the same Corpuscles, upon the unstopping of the Glass, were put into a new motion, and disposed after a new manner, they did opacate that part of the Air they moved in, and exhibited a greater whiteness then that which sometimes appears in our Pneumatical Vessel. Nor should we content ourselves with this single Instance, to manifest, That little Bodies, which being ranged after one manner, are Diaphanous and Colourless, may, by being barely agitated, dispersed, and consequently otherways ranged, exhibit a colour, if we were not unwilling to rob our Collection of Experiments concerning Colours. But, My Lord, I foresee You may make some Objections against our proposed guess, which perhaps I shall scarce be able to answer, especially, if You insist upon having me render a Reason why our Phaenomenon appears not constantly. I might indeed answer, that probably it would do so, if instead of our great Receiver we use such a small Viol as we have lately mentioned, wherein the Dissilition of the Air being much greater, is like to be the more conspicuous: Since I remember not that we ever made our trial with such small Vessels, without finding the expected whiteness to appear. But it would remain to be explicated, why in our great Receiver the Phaenomenon should sometimes be seen, and oftentimes not appear. And though that Conjecture which we last made should not be rejected, yet if we were further pressed to assign a reason why the Air should abound with such Particles, as we there suppose, more at one time then another, we are not yet provided of any better Answer, than this general one, That the Air about us, and much more that within the Receiver, may be much altered by such causes as few are ware of: For, not to repeat those probable Arguments of this Assertion which we have occasionally mentioned here and there in the former part of this Epistle, we will here set down two or three Instances to verify the same Proposition. First, I find that the Learned josephus Acosta, joseph: Acosta: ●at: & Mo●: Hyst: of the Indles, l●b. 3. cap. 9 among other Judicious Observations he made in America, hath this concerning the Effects of some Winds; There are (says he) Winds which naturally trouble the Water of the Sea, and make it green, and black; others, clear as Crystal. Next, we have observed, That though we conveyed into the Receiver our Scales, and the Pendula formerly mentioned, clean and bright; yet after the Receiver had been emptied, and the Air let in again, the gloss or lustre both of the one, and of the other, appeared tarnished by a beginning rust. And in the last place, we will subjoin an Observation we made some Years ago, which hath been heard of by divers Ingenious Men, and seen by some of them: We had, with pure Spirit of Wine, drawn a Tincture out of a certain Concrete which uses to be reckoned among Mineral Bodies; And this Tincture being very pure and transparent, we did, because we put a great value upon it, put into a Crystal Viol. which we carefully stopped, and locked up in a Press among some other things that we specially prized. This Liquor being a Chemical Rarity, and besides, very defecate and of a pleasing Golden Colour; we had often occasion to look upon it, and so to take notice, that one time it seemed to be very much troubled, and not clear as it was wont to be: Whereupon we imagined, that though it would be something strange, yet it was not impossible that some Precipitation of the Mineral Corpuscles was then happening, and that thence the Liquor was opacated; but, finding after some days that though the expected Precipitation had not been made, yet the Liquor, retaining its former vivid Colour, was grown clear again as before; we somewhat wondered at it, and locking it up again in the same Press, we resolved to observe, both whether the like changes would again appear in our Tincture; and whether in case they should appear, they would be ascribable to the alterations of the Wether. But though, during the greatest part of a Winter and a Spring, we took pleasure to observe, how the Liquor would often grow turbid, and after a while clear again: Yet we could not find that these Mutations depended upon any that were manifest in the Air, which would be often dark and clouded, when the Tincture was clear and transparent; as on the other side, in clear Wether the Liquor would appear sometimes troubled, and more opacous. So that being unable to give an account of these odd changes in our Tincture (which we suppose we have not yet lost, though we know not whether it have lost its fickle Nature) either by those of the Air, or any thing else that occurred to our thoughts; we could not but suspect that there may be in divers Bodies, as it were Spontaneous Mutations, that is, such changes as depend not upon manifest Causes. But, My Lord, what has been all this while said concerning our Phaenomenon, is offered to You, not as containing a satisfactory Account of it, but to assist You to give Yourself one. WE took a Glass Vessel, Experiment 38. open at the top, and into it we put a mixture of Snow and common Salt (such a mixture as we have in another Treatise largely discoursed of) and into the midst of this mixture we set a Glass, of a Cylindrical form, closely stopped at the lower end with Plaster, and open at the upper, at which we filled it with common Water. These things being let down into the Receiver, and the Pump being set a-work, the Snow began to melt somewhat faster than we expected; whether upon the account of the Exsuction of the Air, or because there was but little of the Snow, or whether for any other Reason, it appeared doubtful. But however, by that time the Receiver had been considerably exhausted, which was done in less than ¼ of an hour, we perceived the Water near the bottom of the Glass Cylinder to Frieze, and the Ice by a little longer stay, seemed to increase, and to rise somewhat higher than the surface of the surrounding Liquor, whereinto almost all the Snow and Salt were resolved. The Glass being taken out, it appeared that the Ice was as thick as the inside of the Glass it filled, though into that I could put my Thumb. The upper surface of the Ice was very concave, which whether it were due to any unheeded accident, or to the exsuction of the Air, we leave to be determined by further trial. And lastly, the Ice held against the Light, appeared not destitute of Bubbles, though some Bystanders thought they were fewer than would have been found if the Water had been frozen in the open Air. The like Experiment we tried also another time in one of our small Receivers, with not unlike success. And on this occasion, My Lord, give me leave to propose a Problem, which shall be this: Whence proceeds that strange force that we may sometimes observe in frozen Water, to break the Bodies that Imprison it; though hard and solid? That there is such a force in Water exposed to Congelation, may be gathered not only from what may be often observed in Winter, of the bursting of Glasses too close stopped; filled with Water or aqueous Liquors, but by Instances as much more considerable as less obvious. For I remember, that an Ingenious Stone-cutter not long since complained to me, That sometimes, through the negligence of Servants, the Rain being suffered to soak into Marble Stones, the supervening violent Frosts would burst the Stones, to the Professors no small damage. And I remember another Tradesman, in whose House I had Lodgings, was last Winter complaining, that even Implements made of Bell-metal, being carelessly exposed to the wet, have been broken and spoiled by the Water, which, having gotten into the little Cavities and Crannies of the Metal, was there afterwards frozen and expanded into Ice. And to these Relations, In l●b. 4. 〈…〉. we can add one of the formerly mentioned Cabaeus', whereby they not only may be confirmed, but are surpassed: For he tells us, That he saw a huge Vessel of exceeding hard Marble, split asunder by congealed Water, whose Rarefaction, says our Author, proved so vehement, that the hardness of the Stone yielded to it; and so a Vessel was broken, which would not have been so by 100 Yoke of Oxen drawing it several ways. I know, My Lord, that to solve this Problem, it will be said, That Congelation does not (as is commonly, but erroneously presumed) reduce water into less room than it possessed before, but rather makes it take up more. And I have elsewhere proved by particular Experiments, That whether or no Ice may be truly said to be Water rarefied (for that seems questionable) it may be said to take up more room than the Water did before Glaciation. But though we grant that freezing makes Water swell, yet, how Cold (which in Weather-Glasses manifestly condences the Air) should expand either the Water, or the intercepted Air so forcibly, as to perform such things as we have newly related, will yet remain a Problem. Experiment 39 WE took an Oval Glass, clear and (lest it should break) pretty strong, with a short Neck at the obtuser end; through this Neck, we thrust almost to the bottom, a Pipe of Glass, which was closely Cemented to the newly mentioned Neck, the upper part of which Pipe, was drawn in some places more slender than a Crow's Quill, that the changes of the Air in that Glass Egg might be the more conspicuous; Then there was conveyed into the Glass five or six Spoonfuls of Water, part of which, by blowing Air into the Egg, was raised into the abovementioned slender part of the Pipe, so that the Water was interposed between the external Air, and that included in the Egg. This Weatherglass (delineated in the fourteenth Figure) was so placed, and closed up in the cavity of one of our small Receivers, that only the slender part of the Pipe, to the height of four or five Inches, passing thorough a hole in the Cover, remained exposed to the open Air. The Pump being set a work, upon the Exsuction of the Air, the Water in the Pipe descended about a quarter of an Inch, and this upon two or three reiterated trials; which seemed sufficiently to argue that there was no heat produced in the Receiver upon the Exsuction of the Air: For even a little heat would probably have been discovered by that Weatherglass, since upon the bare application of my hand to the outside of the Receiver, the warmth having after some time been communicated or propagated through both the Glasses, and the interval betwixt them to the Imprisoned Air, did so rarify that, as to enable it, by pressing upon the subjacent Water, to impel that in the Pipe very many times as far as it had fallen downwards upon the Exsuction of the Air. Yet shall not we conclude, that in the cavity of the Receiver the cold was greater after the Exsuction of the Air then before. For if it be demanded what then could cause the forementioned subsiding of the Water? it may be answered, That probably it was the reaching of the Glass Egg, which, upon the Exsuction of the ambient Air, was unable to resist altogether as much as formerly the pressure of the included Air, and of the Atmosphere, which▪ by the intervension of the Water, pressed upon its concave surface: Which seemed probable, as well by what was above delivered, in the Experiment about the breaking of the Glass by the force of the Atmosphere; as by this notable. Circumstance (which we divers times observed) That when by drawing the Air out of the Receiver, the Water in the Pipe was subsided, upon the readmission of the external Air to press against the convex surface of the Egg, the Water was presently reimpelled to its former height: Which would perhaps appear less strange to Your Lordship, if You had yet seen what we have heretofore taught in another Treatise concerning the Spring that may be discovered in Glass, as rigid and ●●●lexible a Body as it is generally esteemed. And in the mean while it may se●ve the turn to cause a Glass Egg to be blown exceeding thin, and then, having broken it, try how far you can by degrees bend some narrow parts of it; and how readily, upon the removal of what kept it bend, it will restore itself to its former state or posture. But to return to our Experiment, From thence it seems probable, either that there succeeds no Body in the room of the Air drawn out of our Receiver, or that it is not every Matter that is subtle enough readily to pass through the Pores of Glass, that is always agitated enough to produce Heat where ever it is plentifully found. So that if no Vacuum be to be admitted, this Experiment seems to invite us to allow a great disparity, either as to bulk, or as to agitation, or as to both, betwixt some parts of the Etherial Substance, and those that are wont here below to produce Heat and Fire. We tried also what Operation the drawing out of the Air would have upon Camphire, that being a Body, which, though not a Liquor, consists of such Volatile or Fugitive parts, that without any greater agitation then that of the open Air itself, they will copiously fly away. But we found not that even this lose Body was sensibly altered by the Exsuction of the ambient Air. Experiment 40. IT may seem well worth trying, whether or no in our exhausted Glass the want of an ambient Body, of the wont thicness of Air, would disable even light and little Animals, as Bees, and other winged Infects, to fly. But though we easily foresaw how difficult it would be to make such an Experiment; yet not to omit our endeavours, we procured a large Flesh-fly, which we conveyed into a small Receiver. We also another time shut into a great Receiver a Humming Bee, that appeared strong and lively, though we had rather have made the trial with a Butterfly, if the cold Season would have permitted us to find any. * Since the writing of this XLth Experiment, we procured a white Butterfly, and enclosed it in one of our smaller Receivers, where, though at first he fluttered up and down, yet presently, upon the exsuction of the Air, he fell down as in a ●woo●, retaining no other mot●on then some little trembling of the wings. The Fly, after some Exsuctions of the Air, dropped down from the side of the Glass whereon she was walking: But, that the Experiment with the Bee m●ght be the more instructive, we conveyed in with her a bun●●e of Flowers, which remained suspended by a string near the upper part of the Receiver: And having provoked the Bee, we excited her to fly up and down the capacity of the Vessel, till at length, as we desired, she lighted upon the Flowers; whereupon we presently began to draw out the Air, and observed, That though for some time the Bee seemed to take no notice of it, yet within awhile after she did not fly, but fall down from the Flowers, without appearing to make any use of her Wings to help herself▪ But whether this fall of the Bee, and the other Insect, proceeded from the mediums being too thin for them to fl●e in, or barely from the weakness, and as it were swooning of the Animals themselves▪ you will easily gather from the following Experiment. Experiment 41. TO satisfy ourselves in some measure, about the account upon which Respiration is so necessary to the Animals, that Nature hath furnished with Lungs, we took (being then unable to procure any other lively Bird, small enough to be put into the Receiver) a Lark, one of whose Wings had been broken by a shot, of a Man that we had sent to provide us some Birds for our Experiment; but notwithstanding this hurt, the Lark was very lively, and did, being put into the Receiver, divers times spring up in it to a good height. The Vessel being hastily, but carefully closed, the Pump was diligently plied, and the Bird for a while appeared lively enough; but upon a greater Exsuction of the Air, she began manifestly to droop and appear sick, and very soon after was taken with as violent and irregular Convulsions, as are wont to be observed in Poultry, when their heads are wrung off: For the Bird threw herself over and over two or three times, and died with her Breast upward, her Head downwards, and her Neck awry. And though upon the appearing of these Convulsions, we turned the Stop-cock, and let in the Air upon her, yet it came too late; whereupon, casting our eyes upon one of those accurate Dial's that go with a Pendulum, and were of late ingeniously invented by the Noble and Learned Hugenius, we found that the whole Tragedy had been concluded within ten Minutes of an hour, part of which time had been employed in cementing the Cover to the Receiver. Soon after we got a Hen-sparrow, which being caught with Birdlime was not at all hurt; when we put her into the Receiver, almost to the top of which she would briskly raise herself, the Experiment being tried with this Bird, as it was with the former, she seemed to be dead within seven minutes, one of which were employed in cementing on the Cover: But upon the speedy turning of the Key, the fresh Air flowing in, began slowly to revive her, so that after some pant she opened her eyes, and regained her feet, and in about a ¼ of an hour, after threatened to make an escape at the top of the Glass, which had been unstopped to let in the fresh Air upon her: But the Receiver being closed the second time, she was killed with violent Convulsions, within five Minutes from the beginning of the Pumping. A while after we put in a Mouse, newly taken, in such a Trap as had rather affrighted then hurt him; whilst he was leaping up very high in the Receiver, we fastened the Cover to it, expecting that an Animal used to live in narrow holes with very little fresh Air, would endure the want of it better than the lately mentioned Birds: But though, for a while after the Pump was set a-work, he continued leaping up as before; yet ' 'ttwas not long ere he began to appear sick and giddy, and to stagger, after which he fell down as dead, but without such violent Convulsions as the Birds died with. Whereupon, hastily turning the Key, we let in some fresh Air upon him, by which he recovered, after a while, his senses and his feet, but seemed to continue weak and sick: But at length, growing able to skip as formerly, the Pump was plied again for eight minutes, about the middle of which space, if not before, a very little Air by a mischance got in at the Stop-cock; and about two minutes after that, the Mouse divers times leaped up lively enough, though after about two minutes more he fell down quite dead, yet with Convulsions far milder than those wherewith the two Birds expired. This alacrity so little before his death, and his not dying sooner then at the end of the eighth minute, seemed ascribable to the Air (how little soever) that slipped into the Receiver. For the first time, those Convulsions (that, if they had not been suddenly remedied, had immediately dispatched him) seized on him in six minutes after the Pump began to be set a-work. These Experiments seemed the more strange, in regard, that during a great part of those few minutes the Engine could but considerably rarefie the Air (and that too, but by degrees) and at the end of them there remained in the Receiver no inconsiderable quantity; as may appear by what we have formerly said of our not being able to draw down Water in a Tube, within much less than a Foot of the bottom: with which we likewise considered, that by the exsuction of the Air and interspersed Vapours, there was left in the Receiver a space some▪ hundreds of times exceeding the bigness of the Animal, to receive the fuliginous Steams, from which, expiration discharges the Lungs; and, which in the other cases hitherto known, may be suspected, for want of room, to stifle those Animals that are closely penned up in too narrow Receptacles. I forgot to mention, that having caused these three Creatures to be opened, I could, in such small Bodies, discover little of what we sought for, and what we might possibly have found in larger Animals; for though the Lungs of the Birds appeared very red, and as it were inflamed, yet that colour being usual enough in the Lungs of such winged Creatures, deserves not so much our notice, as it does, That in almost all the destructive Experiments made in our Engine, the Animals appeared to die with violently Convulsive Motions: From which, whether Physicians can gather any thing towards the Discovery of the Nature of Convulsive Distempers, I leave to them to consider. Having proceeded thus far, though (as we have partly intimated already) there appeared not much cause to doubt, but that the death of the forementioned Animals proceeded rather from the want of Air, then that the Air was over-clogged by the steams of their Bodies, tightly penned up in the Glass; yet I, that love not to believe any thing upon Conjectures, when by a not over-difficult Experiment I can try whether it be True or no, thought it the safest way to obviate Objections, and remove Scruples, by shutting up another Mouse as close as I could in the Receiver, wherein it lived above three quarters of an hour; and might probably have done so much longer, had not a Virtuoso of quality, who in the mean while chanced to make me a Visit, desired to see whether or no the Mouse could be killed by the exsuction of the ambient Air, whereupon we thought fit to open, for a little while, an intercourse betwixt the Air in the Receiver, and that without it, that the Mouse might thereby (if it were needful for him) be refreshed, and yet we did this without uncementing the Cover at the top, that it might not be objected, that perhaps the Vessel was more closely stopped for the exsuction of the Air then before. The Experiment had this event, that after the Mouse had lived ten Minutes, (which we ascribed to this, that the Pump, for want of having been lately Oiled, could move but slowly, and could not by him that managed it, be made to work as nimbly as it was wont) at the end of that time he died with Convulsive Fits, wherein he made two or three bounds into the Air, before he fell down dead. Nor was I content with this, but for Your Lordships further satisfaction, and my own, I caused a Mouse, that was very hungry, to be shut in all Night, with a Bed of Paper for him to rest upon: And to be sure that the Receiver was well closed, I caused some Air to be drawn out of it, whereby, perceiving that there was no sensible leak, I presently readmitted the Air at the Stop-cock, left the want of it should harm the little Animal; and then I caused the Engine to be kept all Night by the Fire side, to keep him from being destroyed by the immoderate cold of the Frosty Night. And this care succeeded so well, that the next Morning I found that the Mouse not only was alive, but had devoured a good part of the Cheese that had been put in with him. And having thus kept him alive full twelve hours, or better, we did, by sucking out part of the Air, bring him to droop, and to appear swelled; and by letting in the Air again, we soon reduced him to his former liveliness. A Digression containing some Doubts touching Respiration. I Fear Your Lordship will now expect, that to these Experiments I should add my Reflections on them, and attempt, by their assistance, to resolve the Difficulties that occur about Respiration; since at the beginning I acknowledged a further Enquiry into the Nature of that, to have been my Design in the related Trials. But I have yet, because of the inconvenient Season of the Year, made so few Experiments, and have been so little satisfied by those I have been able to make, that they have hitherto made Respiration appear to me rather a more, than a less Mysterious thing, than it did before. But yet, since they have furnished me with some such new Considerations, concerning the use of the Air, as confirms me in my Diffidence of the Truth of what is commonly believed touching that matter; That I may not appear sullen or lazy, I am content not to decline employing a few hours in setting down my Doubts, i● presenting Your Lordship some Hints, and in considering whether the Trials made in our Engine, will at least assist us to discover wherein the Deficiency lies that needs to be supplied. And this, My Lord, being all my present Design, I suppose You will not expect that (as if You knew not, or had forgotten what Anatomists are wont to teach) I should entertain You with a needless Discourse of the Organs of Respiration, and the variety of their Structure in several Animals; though if it were necessary, and had not been performed by others, I should think, Gale●us de usu, Part: lib: 3. with Galen, that by treating of the Fabrics of living Bodies, I might compose Hymns to the wise Author of Nature, who, in the excellent contrivance of the Lungs, and other parts of (those admirable Engines) Animals, manifests himself to be indeed what the Eloquent Prophet most justly speaks him, Wonderful in Council, Isa. 28.29. and excellent in working. Nor shall we any further meddle with those Controversies so much agitated among the Moderns, namely, Whether the motion of the Lungs in Respiration be their own, or but consequent to the motion of the Thorax, Diaphragme, and (as some Learned Men would have it) the Abdomen; And, Whence it is that the Air swells the Lungs in Inspiration, any further than they may receive light from our Engine: But that it may appear what kind of service it is that may be expected from it on this occasion, we must premise a few Words to show wherein the strength of the Objection we are to answer, lies: In favour then of those that would have the Lungs rather passive then active in the business of Respiration, it may against the common opinion be alleged, That as the Lungs being destitute of Muscles and of Fibres, are unfit to dilate themselves, so it appears, that without the motion of the Thorax they would not be filled with Air. Since as our Learned Friend Dr. Highmore has well (and congruously, to what ourselves have purposely tried) observed, if a live Dog have a great wound made in his Chest, the Lobes of the Lungs on that side of the Mediastinum will subside and lie still; the Thorax and the Lobes on the other side of the Mediastinum, continuing their former motion. And if suddenly at once the Muscles of the Chest be on both sides dissected, upon the Ingress of the Air, the whole Lungs, though untouched, will remain moveless, at least, as to any expansion or contraction of their substance. To which we may add the Observation of the diligent Bartholinus, who affirms the like of the Diaphragme also, namely, That it being wounded, the Lungs will fall together, and the Respiration cease, which my Experiments oppose not, provided the Wound be any thing great. And indeed the Diaphragme seems the principal Instrument of ordinary and gentle Respiration, although to restrained Respiration (if I may so call it) the intercostal Muscles, and perhaps some others may be allowed eminently to concur. But the chief of the Controversies formerly pointed at, is not yet decided, namely, what it is that conveys the Air into the Lungs. For when, to counterbalance all that has been alleged, those that plead for the Lungs, demand what it is that should bring the Air into the Lungs, if themselves do not attract it, their Antagonists disagree about the Reply. For when to this question some of the best Modern Philosophers answer, that by the dilatation of the Chest the contiguous Air is thrust away, and that pressing upon the next Air to it, and so onwards, the Propulsion is continued till the Air be driven into the Lungs, and so dilate them: When this (I say) is answered, it is Objected even by Bartholine himself, as a convincing Reply, that, according to this Doctrine, a Man could not fetch his Breath from a great Vessel full of Air, with a slender Neck, because, that when his Mouth covers the Orifice of the Neck, the dilatation of his Thorax could not propel the Air in the Vessel into his Lungs, by reason of its being separated by the enclosing Vessel from the ambient Air; and yet, say they, Experience witnesses that out of such a Vessel a Man may suck Air. But of this difficulty our Engine furnishes us with an easy Solution, since many of the former Experiments have manifested, That in the case proposed, there needs not be made any (though 'tis true that in ordinary Respiration there is wont to be made some) propulsion of the Air by the swelling Thorax or Abdomen into the Lungs; since upon the bare Dilatation of the Thorax, the Spring of that internal Air, or halituous substance that is wont to possess as much of the Cavity of the Chest as the Lungs fill not up, being much weakened, the external and contiguous Air must necessarily press in at the open Windpipe into the Lungs, as finding there less resistance than any where else about it. And hence (by the way) we may derive a new assistance to judge of that famous Controversy disputed among Naturalists and Physicians, ever since Galens time, some maintaining that the Chest, with the contained Lungs, may be resembled to a pair of Bellows, which comes therefore to be filled because it was dilated: And others pleading to have the comparison made to a Bladder, which is therefore dilated because it is filled. For as to the Thorax, it seems evident from what has been lately said, that it, like a pair of Bellows, happens to be partly filled with Air, but because it was dilated: But as for the Lungs themselves, who want Fibres to distend them, they may fitly enough be compared to a Bladder; since they are dilated by being filled namely, by that Air which rushes into them upon the dilatation of the Chest, in whose increased Cavity it finds (as we freshly noted) less resistance to its Spring than elsewhere. And this brings into my mind that strange Observation of Nicolaus Fontanus, a Physician at Amsterdam, Fontanus apud Bartholin: lib. 2. cap. 9 who testifies, That in a Boy of the same Town, four years old, there was found, instead of Lungs, a certain Membranous Bladder; which being filled with Wind, and furnished with little Veins, had its origination from the Windpipe itself; which being supposed true, how well it will agree with most of the Opinions touching Respiration, I leave to be considered. And thus may the grand Objection of Bartholine, and others, be answered: But I leave to Anatomists to consider what is to be said to some Observations that seem to contradict those Anatomical Experiments already mentioned: Such was particularly that which I remember I have read in Sennertus (from the observation of his Farther-in-law Schato) of a Melancholy Student, who having stabbed himself, and pierced the Diaphragme in the thinner or tendonous part (called by many the Nervous Circle) lived seven Months after he had so wounded himself, though after his death (preceded by violent Vomitings) the Wound (perchance dilated by those strainings) appeared so great, that the whole Stomach was found to have got in by it into the left side of the Thorax. And such also was the accident that happened to a Noble Man, whom I remember I have seen, and who is yet alive, in whose Chest there has, for these many years, remained a hole so great, that the motion of his Heart may be perceived by it. These (I say) and some other Observations, I shall now forbear to insist on, because I hold it not unfit, before we come to consider the use of Respiration, that we acquaint Your Lordship with an Ingenious Conjecture, that was made at the cause of the hasty death of the Animals our Engine killed: namely, That it was not the want of Air that destroyed them, but the Pressure of the innate Air in the cavity of the Chest; as if the Spring of this Air being no longer counterballanced by the ambient Air, was thereby become so strong, that it kept the Thorax forcibly distended, and hindered its wont contraction; and so compressed the Lungs and their Vessels, as to obstruct the Circulation of the Blood. And this Conjecture, as it is specious enough, so I might have admitted it for true, but that I considered, that (not to mention that one, especially of the Animals killed in our Engine, seemed manifestly for a pretty while, and not long before he died, to move his Thorax, as if he exercised Respiration) the diligent Wallaeus relates, That he divers times observed, in the Dissection of live Bodies, that the Membrane that invests the Lungs, had Pores in it as big as the larger sort of Peas, which agrees with the Observations of Chirurgeons and Physicians, viz. That matter collected in the Thorax, has penetrated into the Lungs, and been discharged by coughing. And I remember too, that most of the Animals we killed in our Engine were Birds, of whose Lungs Harvey somewhere informs us, That he observed them very manifestly to open at their Extremities into the Abdomen. And by such Perforations we may well suppose the passage free betwixt the external Air and that in the Abdomen: But 〈◊〉 Conjecture may be further 〈◊〉 Besides, to show that the Anim●●● 〈◊〉 died in our Glasses, need not be 〈◊〉 to have been killed by the want of Air, we foresee another Argument that we must deal so ingeniously with Your Lordship, as not to conceal. You very well know, that besides the generality of the Schools, there are many new Philosophers who, though they descent from the old Peripatetics in other things, do, as they, deny the possibility of a Vacuum; and hold, that those spaces which are devoid of Air, and other grosser Bodies, are all of them exactly replenished with a certain Etherial Matter, so thin and subtle, that it can freely permeate the Pores of the compactedst and closest Bodies, and even of Glass itself. Now some of those Naturalists that are of this persuasion may object, That the Animals that died in our Receivers, did so, not so much for lack of Air, as by reason that the Air that was pumped out was necessarily succeeded by an Etherial Substance; which consisting of parts vehemently agitated, and so very small, as without resistance to pass in and out through the very Pores of Glass; it may well be supposed, that a considerable quantity of this restless and subtle Matter, meeting together in the Receiver, with the excessive heat of it, may be quickly able to destroy a little Animal, or at least, make the Air too intemperately hot to be fit for Respiration. But though this be a Difficulty not so easily to be resolved without the assistance of our Engine, yet I suppose we have already answered the Objection by our 38th and 39th Experiments; which though we made partly for other purposes, yet we premised them only to clear up the difficulty proposed. Another suspicion we should have entertained concerning the death of our Animals, namely, That upon the sudden removal of the wont pressure of the ambient Air, the warm Blood of those Animals was brought to an Effervescence or Ebullition, or at least so vehemently expanded, as to disturb the Circulation of the Blood, and so disorder the whole Oeconomy of the Body. (This (I say) I should have had some suspicion of) but that Animals of a hot Constitution are not the sole ones that cannot in our exhausted Engine exercise the Function of Life. But I must not now dwell upon matters of this nature, because I think it high time to proceed to the consideration of the principal subject of our Engine, namely, The use of Respiration; or rather, The use of the Air in Respiration. For whereas of the divers uses of it mentioned by Anatomists the most, such as the Production and Modulation of the Voice by the Elision of the Air, the Larynx etc. the expulsion of Excrements by Coughing, the conveying in of Odours by Inspiration, and some others, rather convenient for the well being of an Animal, then absolutely necessary to his Life: Whereas (I say) the other uses are such as we have said, The great Hypocrates himself gives this notable Testimony to the use of the Air, as to Animals endowed with Lungs, Mortalibus (says he) hic (spiritus) tum vitae, tum morborum aegrotis causa est. Tantáque corporibus omnibus spiritûs inest necessitas, ut siquidem aliis omnibus & cibis & potionibus, quis abstineat, duos tamen aut tres, vel plures dies possit vitam ducere: At si quis spiritus in corpus vias intercipiat, vel exiguâ diei parte, homini pereundum sit; Ad●o necessarius est usus spiritûs in corpore. Ad haec quoque, quum omnibus aliis actionibus homines qu●escant, quod mutationibus innumeris vita sit exposita, ab hâc tamen solá actione nunquam desistant animantia, quin aut spiritum adducant, aut reddant. But touching the account upon which the Inspiration and Expiration of Air (both which are comprehended in 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 Respiration) is so necessary to Life, both Naturalists and Physicians do so disagree, that it will be very difficult either to reconcile their Opinions, or determine their Controversies. For first, Many there are who think the chief (if not sole) use of Respiration to be the Cooling and tempering of that Heat in the Heart and Blood, which otherwise would be immoderate: And this Opinion, not only seems to be most received amongst Scholastic Writers, but divers of the new Philosophers, Cartesians, and others, admitted with some variation; teaching, That the Air is necessary, by its coldness, to condense the Blood that passes out of the right Ventricle of the Heart into the Lungs, that thereby it may obtain such a consistence, as is requisite to make it fit Fuel for the vital Fire or Flame, in the left Ventricle of the heart. And this Opinion seems favoured by this, That Fishes, and other cold Creatures, whose Hearts have but one cavity, are also unprovided of Lungs, and by some other considerations. But though it need not be denied, that the inspired Air may sometimes be of use by refrigerating the Heart; yet (against the Opinion that makes this Refrigeration, the most genuine and constant use of the Air) it may be Objected, That divers cold Creatures (some of which, as particularly Frogs, live in the Water) have yet need of Respiration, which seems not likely to be needed for Refrigeration by them that are destitute of any sensible heat, and besides, live in the cold Water: That even decrepit old Men, whose natural heat is made very languid, and almost extinguished by reason of age, have yet a necessity of frequent Respiration: That a temperate Air is fittest for the generality of breathing Creatures; and as an Air too hot, so also an Air too cold, may be inconvenient for them (especially, if they be troubled with an immoderate degree of the same Quality which is predominant in the Air:) That in some Diseases the natural heat is so weakened, that in case the use of Respiration were to cool, it would be more hurtful than beneficial to breath; and the suspending of the Respiration, may supply the place of those very hot Medicines that are wont to be employed in such Distempers: That Nature might much better have given the Heart but a moderate heat, than such an excessive one, as needs to be perpetually cooled, to keep it from growing destructive; which the gentle, and not the burning heat of an Animals Heart, seems not intense enough so indispensably to require. These, and other Objections, might be opposed, and pressed against the recited Opinion: But we shall not insist on them, but only add to them, That it appears not by our foregoing Experiments (I mean the 38th and 39th) that in our exhausted Receiver, where yet Animals die so suddenly for want of Respiration, the ambient Body is sensibly hotter than the common Air. Other Learned Men there are, who will have the very substance of the Air to get in by the Vessels of the Lungs, to the left Ventricle of the Heart, not only to temper its heat, but to provide for the generation of Spirits. And these allege for themselves the Authority of the Ancients, among whom Hypocrates seems manifestly to favour their Opinion; and both Aristotle and Galen do sometimes (for methinks they speak doubtfully enough) appear inclinable to it. But for aught ever I could see in Dissections, it is very difficult to make out, how the Air is conveyed into the left Ventricle of the Heart, especially the Systole and Diastole of the Heart and Lungs, being very far from being Synchronical: Besides, that the Spirits seeming to be but the most subtle and unctuous Particles of the Blood, appear to be of a very differing Nature from that of the lean and incombustible Corpuscles of Air. Other Objections against this Opinion have been proposed, and pressed by that excellent Anatomist, and my Industrious Friend, Dr. Highmore, to whom I shall therefore refer you. Another Opinion there is touching Respiration, which makes the genuine use of it to be Ventilation (not of the Heart, but) of the Blood, in its passage thorough the Lungs; in which passage, it is disburdened of those Excrementitious Steams, proceeding, for the most part, from the superfluous Serosities of the Blood, (we may add) and of the Chyle too, which (by those new Conduits of late very happily detected by the famous Pecquet) hath been newly mixed with it in the Heart.) And this Opinion is that of the Industrious Moebius, and is said to have been that of that excellent Philosopher Gassendus; and hath been in part an Opinion almost vulgar: But this Hypothesis may be explicated two ways: For first, The necessity of the Air in Respiration, may be supposed to proceed from hence; That as a Flame cannot long burn in a narrow and close place, because the Fuliginous Steams it uncessantly throws out, cannot be long received into the ambient Body; which after a while growing too full of them, to admit any more, stifles the flame, so that the vital Fire in the Heart requires an ambient Body, of a yielding nature, to receive into it the superfluous Serosities and other Recrements of the Blood, whose seasonable Expulsion is requisite to depurate the Mass of Blood, and make it fit both to Circulate, and to maintain the vital heat residing in the Heart. The other way of explicating the above mentioned Hypothesis, is, by supposing, that the Air does not only, as a Receptacle, admit into its Pores the Excrementitious vapours of the Blood, when they are expelled through the Windpipe, but does also convey them out of the Lungs, in regard that the inspired Air, reaching to all the ends of the Aspera Arteria, does there associate itself with the Exhalations of the circulating Blood, and when 'tis exploded, carries them away with itself, as we see that winds speedily dry up the surfaces of wet Bodies, not to say any thing of what we formerly observed touching our Liquor, whose fumes were strangely elevated upon the Ingress of the Air. Now of these two ways of explicating the use of Respiration, our Engine affords us this Objection against the first; That upon the Exsuction of the Air, the Animals die a great deal sooner than if it were left in the Vessel; though by that Exsuction the ambient space is left much more free to receive the steams that are either breathed out of the Lungs of the Animal, or discharged by insensible Transpiration through the Pores of his Skin. But if the Hypothesis proposed, be taken in the other sense, it seems congruous enough to that grand observation, which partly the Phaenomena of our Engine, and partly the relations of Travellers, have suggested to us, namely, That there is a certain consistence of Air requisite to Respiration; so that if it be too thick, and already overcharged with vapours, it will be unfit to unite with, and carry off those of the Blood, as Water will dissolve, and associate to itself but a certain proportion of saline Corpuscles; and if it be too thin or rarefied, the number or size of the Aërial Particles is too small to be able to assume and carry off the halituous Excrements of the Blood, in such plenty as is requisite. Now that Air too much thickened (and as it were clogged) with Steams, is unfit for Respiration, may appear by what is wont to happen in the Lead-Mines of Devonshire, (and, for aught I know, in those too of other Countries, though I have seen Mines where no such thing was complained of) for I have been informed by more than one credible Person (and particularly by an Ingenious Man, that has often, for curiosity, digged in those Mines, and been employed about them) that there often rises Damps, as retaining the German Word by which they call them) which does so thicken the Air, that unless the Workmen speedily make signs to them that are above, they would (which also sometimes happens) be presently stifled for want of Breath; and though their Companions do make haste to draw them up, yet frequently, by that time they come to the free Air, they are, as it were, in a swoon, and are a good while before they come to themselves again. And that this swooning seems not to proceed from any Arsenical or Poisonous Exhalation contained in the Damp; as from its overmuch condensing the Air, seems probable from hence; That the same Damps oftentimes leisurely extinguish the flames of their Candles or Lamps; and from hence also that it appears (by many Relations of Authentical Authors) that in those Cellars where great store of new Wine is set to work, men have been suffocated by the too great plenty of the steams exhaling from the Must, and too much thickening the Air: as may be gathered from the custom that is now used in some hot Countries, where those that have occasion to go into such Cellars, carry with them a quantity of well kindled Coals, which they hold near their Faces; whereby it comes to pass, that the Fire discussing the Fumes, and rarefying the Air reduces the ambient Body to a consistence fit for Respiration. We will add (by way of confirmation) the following Experiment: In such a small Receiver, as those wherein we killed divers Birds, we carefully closed up one, who, though for a quarter of an hour he seemed not much prejudiced by the closeness of his Prison, afterwards began first to pant very vehemently, and keep his Bill very open, and then to appear very sick; and last of all, after some long and violent strainings, to cast up some little matter out of his Stomach: which he did several times, till growing so sick, that he staggered and gasped, as being just ready to die; we perceived, that within about three quarters of an hour from the time that he was put in, he had so thickened and tainted the Air with the Steams of his Body, that it was become altogether unfit for the use of Respiration: Which he will not much wonder at, who has taken notice in Sanctorius his Statica Medicina, how much that part of our Aliments, which goes off by insensible Transpiration, exceeds in weight all the visible and grosser Excrements both solid and liquid. That (on the other side) an Air too much dilated is not serviceable for the ends of Respiration, the hasty death of the Animal we killed in our exhausted Receiver, seems sufficiently to manifest. And it may not irrationally be doubted, whether or no, if a Man were raised to the very top of the Atmosphere, he would be able to live many minutes, and would not quickly die for want of such Air as we are wont to breath here below. And that this Conjecture may not appear extravagant, I shall on this occasion subjoin a memorable Relation that I have met with in the Learned josephus Acosta, who tells us, That when he himself past the high Mountains of Peru, (which they call Pariaecaca) to which, he says, That the Alps themselves seemed to them but as ordinary Houses, in regard of high Towers, he and his Companions were surprised with such extreme Pangs of Straining and Vomiting, (not without casting up Blood too) and with so violent a Distemper, that he concludes he should undoubtedly have died, but that this lasted not above three or four hours, before they came into a more convenient and natural temperature of Air: To which our Learned Author adds an Inference, which being the principal thing I designed in mentioning, the Narrative I shall set down in his own Words: I therefore (says he) persuade myself, That the Element of the Air is there so subtle and delicate, as it is not proportionable with the breathing of Man, which requires a more gross and temperate Air; and I believe it is the cause that doth so much alter the Stomach, and trouble all the Disposition. Thus far our Author, whose Words I mention, that we may guess by what happens somewhat near the Confines of the Atmosphere (though propably far from the surface of it) what would happen beyond the Atmosphere. That which some of those that treat of the height of Mountains, relate out of Aristotle, namely, That those that ascend to the top of the Mountain Olympus, could not keep themselves alive, without carrying with them wet Sponges, by whose assistance they could respire in that Air, otherwise too thin for Respiration: (That Relation (I say) concerning this Mountain) would much confirm what has been newly recited out of Acosta, if we had sufficient reason to believe it: But, I confess, I am very diffident of the truth of it; partly because when I passed the Alps, I took notice of no notible change betwixt the consistence of the Air at the top and at the bottom of the Mountain; partly because of a very punctual relation made by an English Gentleman, of his ascension on to the top of the Pike of Tenariff (which is by great odds higher than Olympus) I find no mention of any such difficulty of breathing; and partly also because the same Author tells us out of Aristotle, That upon the top of Olympus there is no motion of the Air, insomuch, that Letters traced upon the dust, have been, after many years, found legible, and not discomposed; whereas that Inquisitive Busbequius (who was Ambassador from the Germane to the Turkish Emperor) in one of his Eloquent Epistles, Epist. 3. tells us, upon his own knowledge, That Olympus may be seen from Constantinople, blanched with perpetual Snow; which seems to argue, That the top of that, as well as of divers other tall Hills, is not above that Region of the Air wherein Meteors are form. Though otherwise, in that memorable Narrative which David Fraelichius, Fraelichius apud Varen: Geogra: Gener: lib. 1. cap. 19 made of his ascent to the top of the prodigiously high Hungarian Mountain Carpathus: he tells us, That when, having passed through very thick Clouds, he came to the very top of the Hill, he found the Air so calm and subtle, that not a hair of his head moved, whereas in the Lower Stages of the Mountain he felt a vehement Wind. But this might well be casual, as was his, having a clear Air where he was, though there were Clouds, not only beneath him, but above him. But (though what has been hitherto discoursed, incline us to look upon the Ventilation and Depuration of the Blood, as one of the principal and constant uses of Respiration; yet) methinks it may be suspected that the Air does something more than barely help to carry off what is thrown out of the Blood in its passage through the Lungs, from the right Ventricle of the Heart to the left. For we see, in Phlegmatic Constitutions and Diseases, that the Blood will circulate tolerably well, notwithstanding its being excessively serous: And in Asthmatical Persons, we often see, that though the Lungs be very much stuffed with tough Phlegm, yet the Patient may live some Months, if not some Years. So that it seems scarce probable, that either the want of throwing out the superfluous Serum of the Blood for a few Moment's, or the detaining it, during so short a while, in the Lungs, should be able to kill a perfectly sound and lively Animal: I say, for a few moments, because, that having divers times tried the Experiment of kill Birds in a small Receiver, we commonly found, that within half a minute of an hour, or thereabouts, the Bird would be surprised by mortal Convulsions, and within about a minute more would be stark dead, beyond the Recovery of the Air, though never so hastily let in. Which sort of Experiments seem so strange, that we were obliged to make it several times, which gained it the Advantage of having Persons of differing Qualities, Professions and Sexes, (as not only Ladies and Lords, but Doctors and Mathematicians) to witness it. And to satisfy Your Lordship, that it was not the narrowness of the Vessel, but the sudden Exsuction of the Air that dispatched these Creatures so soon; we will add, That we once enclosed one of these Birds in one of these small Receivers, where, for a while, he was so little sensible of his Imprisonment, that he eat very cheerfully certain Seeds that we conveyed in with him, and not only lived ten minutes, but had probably lived much longer, had not a great Person, that was Spectator of some of these Experiments, rescued him from the prosecution of the Trial. Another Bird being within about half a minute, cast into violent Convulsions, and reduced into a sprawling condition, upon the Exsuction of the Air, by the pity of some Fair Lady's (related to Your Lordship) who made me hastily let in some Air at the Stop-cock, the gasping Animal was presently recovered, and in a condition to enjoy the benefit of the Lady's Compassion. And another time also, being resolved not to be interrupted in our Experiment, we did, at night, shut up a Bird in one of our small Receivers, and observed, that for a good while he so little felt the alteration of the Air, that he fell asleep with his head under his wing; and though he afterwards awaked sick, yet he continued upon his legs between forty minutes and three quarters of an hour; after which, seeming ready to expire, we took him out, and soon found him able to make use of the liberty we gave him for a compensation of his sufferings. If to the foregoing Instances of the sudden destruction of Animals, by the removal of the ambient Air, we should now annex some, that we think fit to reserve till anon; perhaps Your Lordship would suspect, with me, that there is some use of the Air, which we do not yet so well understand, that makes it so continually needful to the Life of Animals. Paracelsus indeed tells us, That as the Stomach concocts Meat, and makes part of it useful to the Body, rejecting the other part, so the Lungs consume part of the Air, and proscribes the rest. So that according to our Hermetick Philosopher (as his followers would have him styled) it seems we may suppose, that there is in the Air a little vital Quintessence (if I may so call it) which serves to the refreshment and restauration of our vital Spirits, for which use the grosser and incomparably greater part of the Air being unserviceable, it need not seem strange that an Animal stands in need of almost incessantly drawing in fresh Air. But though this Opinion is not (as of some of the same Author) absurd, yet besides that, it should not be barely asserted, but explicated and proved; and besides that, some Objections may be framed against it, out of what has been already argued against the Transmutation of Air into vital Spirits: Besides these things, it seems not probable, that the bare want of the Generation of the wont quantity of vital Spirits, for less than one minute, should within that time be able to kill a lively Animal, without the help of any external violence at all. But yet, on occasion of this Opinion of Paracelsus, perhaps it will not be impertinent, if before I proceed, I acquaint Your Lordship with a Conceit of that deservedly Famous Mechanician and Chemist, Cornelius Drebell, who among other strange things that he performed, is affirmed (by more than a few credible Persons) to have contrived for the late Learned King james, a Vessel to go under Water; of which, trial was made in the Thames, with admired success, the Vessel carrying twelve Rowers, besides Passengers; one of which is yet alive, and related it to an excellent Mathematician that informed me of it. Now that for which I mention this Story, is, That having had the curiosity and opportunity to make particular Inquiries among the Relations of Drebell, and especially of an Ingenious Physician that married his daughter, concerning the grounds upon which he conceived it feasible to make men unaccustomed to continue so long under water without suffocation, or (as the lastly mentioned Person that went in the vessel affirms) without inconvenience. I was answered, that Drebell conceived, that 'tis not the whole body of the Air, but a certain Quintessence (as Chemists speak) or spirituous part of it, that makes it fit for respiration, which being spent, the remaining grosser body, or carcase (if I may so call it) of the Air, is unable to cherish the vital flame residing in the heart: So that (for aught I could gather) besides the Mechanical contrivance of his vessel he had a Chemical liquor, which he accounted the chief Secret of his submarine Navigation. For when from time to time he perceived, that the finer and purer part of the Air was consumed, or over clogged by the respiration, and steames of those that went in his ship, he would, by unstopping a vessel full of this liquor, speedily restore to the troubled Air such a proportion of Vital parts, as would make it again, for a good while, fit for Respiration, whether by dissipating, or precipitating the grosser Exhalations, or by some other intelligible way, I must not now stay to examine. Contenting myself to add, that having had the opportunity to do some service to those of his Relations, that were most Intimate with him, and having made it my business to learn what this strange Liquor might be, they constantly affirmed that Drebell would never disclose the Liquor unto any, nor so much as tell the matter whereof he made it, to above one Person, who himself assured me that it was. This account of Drebell's performance, I mention, not that I any further assent to his opinion than I have already intimated, but because the man, and the Invention being extraordinary, I suppose Your Lordship will not be displeased to know the utmost I could learn about it; especially not having found it mentioned by any Writer. Wherefore I have been sometimes inclined to favourable thoughts of their opinion, who would have the Air necessary to ventilate, and cherish the vital flame, which they do suppose to be continually burning in the heart. For we see, that in our Engine the flame of a Lamp will last almost as little after the Exsuction on of the Air, as the life of an Animal: Nay I remember, that though I devised a more promising way, to make a fire last in our exhausted Receiver, yet it would not succeed: We took a hard body made in the form of a Clove, but twice as long, and proportionably thick, this body being made of such a Composition, that if it be kindled at the upper end, it will most certainly burn away to the very bottom, much better than a Match; we conveyed it divers times kindled at the upper end, into one of our small Receivers, but still found, that though presently upon the Exsuction of the Air, it would leave smoking, and seem quite gone out, and again begin to smoke as soon as the Air was let in upon it; yet if the Air were kept out but four or five minutes, the fire would be totally, and irrevocably extinguished. To which we will add, that though we conveyed into a great Receiver, a small lamp with rectified spirit of Wine, that being so pure as not to smut the Cotton week, or so much as a piece of white Paper held over it; yet we could not by divers trials make the flame last a couple of minutes after the Air was begun to be drawn out. But though our Engine thus shows us a new kind of resemblance betwixt fire and life: yet the opinion we have last mentioned is not free from Difficulties. For though in the hearts of many Animall's Blood be a warm liquor, and in some even a hot one; yet it is not easy to conceive either how the Air (in substance) can get thither, or how, in case it could, it were able to increase the heat. Since, however, the Air may increase the heat of a coal by blowing off the ashes, and making the active Corpuscles pierce further into the kindled body, and shatter it the more, yet we see hot liquors have their heat allayed, and not augmented, by having Air blown on them. And whereas some Eminent Naturalists think it not inconvenient, to make the heat residing in the heart to be a true flame, provided they add, that 'tis such a temperate, and almost insensible fire, as the flame of spirit of Wine, which will long burn upon fine white Linen or Paper without consuming either: give me leave to wish that they had been more curious to make differing trials with that liquor. For (as we observe in another Treatise) the reason why a Linen cloth, dipped in common Spirit of Wine, is not burnt by the flame of it, is because the Phlegm of the Liquor defends the Cloth. And the Flame of Spirit of Wine is so far from being too weak to burn a piece of Paper, or of Linen, that I have used it in Lamps to distil Liquors out of tall Cucurbits, and found that the Spirit burned away indeed much faster than Salad Oil, but gave at least as great a heat: Nay, I have, for curiosity sake, melted crude Gold, and that readily enough, with the bare Flame of pure Spirit of Wine. But not to press this any further, we will, on this occasion, venture to subjoin an odd Observation, which may perhaps invite to a further Enquiry into the Opinion we have for Discourse sake opposed. Our English Democritus, Dr. Harvey, proposes this difficult and noble Problem to Anatomists, Why a faetus, even out of the Womb, if involved in the secundines, may live a good while without a Respiration; but in case after having once begun to breath, its respiration be stopped, it will presently die. We are far from pretending to solve so hard a Problem, but this we tried in relation to it; We took a Bitch that was said to be almost ready to whelp, and having caused her to be hanged, we presently opened her Abdomen, and found four Puppies in her Womb; one of these we took out, and having freed him from the Teguments th●● involved him, and from the Liquor he swum in, we observed that he quickly opened his Mouth very wide, moved his Tongue, and exercised Respiration; then we opened both his Abdomen and his Chest, and cut asunder the Diaphragme, notwithstanding which, he seemed often to endeavour Respiring, and moved in a notable manner, both the Intercostal Muscles, part of the Diaphragme, the Mouth and the Tongue: But that which we mention this Puppy for, was this, That being desirous to try whether the other young ones that had not yet breathed at all, would long survive this or no; we took them also out of the Womb, and having opened them, found none of them so much alive, as to have any perceptible motion in his heart, whereas the heart of that Puppy which had once enjoyed the benefit of Respiration, continued beating so long, that we ourselves observed the Auricle to beat, after five or six hours; and a Servant that stayed up and watched it after we were gone to Bed, affirmed, That he saw the Pulsation continue about two hours longer. I shall leave it to others to make Reflections upon this Observation, compared with Dr. Harvey's Problem. It is much doubted, whether Fishes breath under Water, and we shall not take upon us, as yet, to determine the Question either way, because we have not yet been able to procure little Fishes alive to make Experiments upon: That such as are not Setaceous (for such manifestly breath) have not Respiration, properly so called, such as is exercised by four footed Beasts, and Birds, may be argued from their having but one cavity in their Hearts, & from their want of Lungs, whence they are observed to be Mute; unless we say, what is not altogether absurd, That their Gills seem somewhat Analogous (as to their use) to Lungs. But that on the other side, Air is necessary to the Lives even of Fishes, and that therefore 'tis probable they have some obscure kind of Respiration, seems manifest by two or three Observations and Experiments, mentioned by divers Authors, who tell us, That Fishes soon die in Ponds and Glasses quite filled with Water; if the one be so frozen over, and the other so closely stopped, that the Fishes cannot enjoy the benefit of the Air, if we allow them to be true. But because these Relations are not wont to be delivered by Writers upon their own Knowledge; as I shall not reject them, so I dare not build upon them, till I have opportunity to examine them by experience. In the mean time, we will add, That our Engine has taught us two things that may illustrate the matter in hand: The one, That there is wont to lurk in Water, many little parcels of interspersed Air, whereof it seems not impossible that Fishes may make some use, either by separating it when they strain the Water thorough their Gills, or by some other way: The other, what may be collected from the following Experiment. We took a large Eel (being able to procure no other Fish alive) and removing it out of the Vessel of Water, wherein it was brought us, into our great Receiver, we caused the Air to be pumped out; and observed, That the Eel, after some motion to and fro in the Glass, seemed somewhat discomposed; and that when we had prosecuted the Exsuction of the Air somewhat obstinately, she turned up her Belly, as dying Fishes are wont to do, and from thenceforward lay altogether moveless, just as if she were stark dead; and though I did not think her so, yet the continuing in that Posture, even after the Cover of the Receiver was taken off (whereby the Air was let in) I shoul● have been of the Opinion of the By standers, if the Diffidence I am wont to exercise in trying Experiments (especially such as are not usual) had not invited me to take the Fish out of the Receiver, upon which she showed herself, by her vivid motions, as much alive as before. But that is most strange which we observed of a great, g●ay, House Snail (as they call it) which being closed up in one of our small Receivers, did not only, not fall down from the side of the Glass, upon the drawing-out of the Air (For that may be ascribed to the tenacity of the Liquor wherewith S●●il, use to stick themselves, even to the smoothest Bodies) but was not so much as deprived of progressive motion by the recess of the Air: Though except this Snail, we never put any living Creature into our Receiver, whom it did not either kill, or at least reduce to seem ready to die. But as we shall not here examine what interest the glutinous, and uneasily dissipable Nature of the Juices of Snails, may have on this event; so whether this escape of our Eel be to be ascribed to the particular and vivacious Nature of this sort of Fishes; or to this, That the Air is not indeed necessary to the life of Fishes; or finally to this, That though these Animals need some Air, yet they need so little, that that which could not be drawn out of the Receiver, might (at least for a while) suffice them, we will not now determine. Nor are we at leisure to examine that Paradox of Hypocrates, which some Learned Physicians have of late revived, namely, That the Foetus respires in the Womb: For on the one side it seems very difficult to conceive, how Air should traverse the Body of the Mother, and the Teguments of the Child: And since Nature has, in newborn Babes, contrived peculiar and temporary Vessels, that the Blood may circulate thorough other Passages, than it is wont to do in the same Individuals when they come to have the free use of their Lungs, it seems unlikely, th●t Infants in the Womb do properly respire. But then since our Experiments have manifested, That almost all kind of Liquors do, as well as Water, abound with interspersed Corpuscles of Air, it seems not altogether absurd to say; That when the Foetus is grown big, he may (especially the upper part of the involving Amnios, being destitute of Liquor, and filled only with an halituous Substance) exercise some obscure Respiration, especially, since 'tis not (as many wise Men think it) a Fable, That Children have been heard to cry in the Mother's Womb. For though it happens exceeding rarely, yet sometimes it has been observed. And I know a young Lady, whose Friends, when she was some Years since with Child, complained to me, That she was several times much frighted with the Cries of her Infant, which, till I disabused Her, She and Her Friends looked upon as Portentous. And such Observations are the more credible, because not only Housewives, but more judicious Persons, mention it, as no very unfrequent thing to hear the Chick Pip or Cry in the Egg, before the Shell be broken. But this I mention but as a probable, not a cogent Argument, till I can discover whether an Elision of an halituous Substance, though no true Air, may not at the top of the Larynx produce a Sound, since I find that the Blade of a Knife, held in several postures in the stream of Vapours (or rarified Water) that issu's out of an Aeolipile, will afford various and very audible Sounds. I had thoughts of conveying into our Receiver young ones, ripped out of the womb of their Dams, with their involving Coats entire, but could not procure them. And I have also had thoughts of trying whether it be not practicable, to make a Receiver, though not all of glass, yet with little glass windows, so placed, that one may freely look into it, capacious enough to hold a Man, who may observe several things, both touching Respiration, and divers other matters; and, who in case of fainting, may, by giving a sign of his weakness, be immediately relieved by having air let in upon him. And it seems not impossible, but that by accustomance, some Men may bring themselves to support the want of Air a pretty while, since we see that divers will live so much longer than other Men under Water: that those that dive for Pearls in the West Indies are said to be able to stay a whole hour under water. And Cardan tells us of one Colanus a Diver in Sicily, who was able to continue (if Cardan neither mistake, Cardan. de Subtilitat. lib. 11. nor impose upon us) three or four times as long. Not to mind Your Lordship, that You have Yourself often seen in England, a corpulent Man, who is wont to descend to the bottom of the Thames, and bring out of the deep holes at the bottom of the banks, large fishes alive in his hands. lib 3. c. 15. And Acosta tells us, he saw in Peru the like manner of fishing, but more difficult, practised by the Indians. I made mention of some Men, and of Accustomance: because there are but very few, who, though they use themselves to it by degrees, are fit to support, for many Minutes, the want of Air. Insomuch that an ingenious Man of my acquaintance, who is very famous for the useful skill of drawing Goods, and even Ordnance out of sunk Ships, being asked by me, how long he was able to continue at the depth of 50. or 60. feet under water, without the use of Respiration, confessed to me, that he cannot continue above two minutes of an hour, without resorting to the Air, which he carries down with him in a certain Engine (whereof I can show your Lordship a Description.) Another thing I also learned of him by enquiry, that was not despicable: For ask him, whether he found any use of chawing little sponges dipped in oil in his Mouth, when he was perfectly under water, and at a distance from his Engine, he told me, that by the help of these sponges he could much longer support the want of his wont Respiration, than he was able to do without them. The true cause of which would perhaps, if discovered, teach us some thing pertinent to the Problem touching the Respiration of Fishes But the necessity of Air to the most part of Animals unaccustomed to the want of it, may best be judged of by the following Experiments, which we tried in our Engine, to discover whether Infects themselves have not, either Respiration, or some other use of the Air equivalent thereunto. We took then an humble-bee, one of those common flies that are called flesh flies, and one of those hairy worms that resemble caterpillars, and are wont to be called Palmerwormes: These three we conveyed into one of our small Receivers, and observed to the great wonder of the Beholders, that not only the Bee, and the Fly fell down, and lay with their bellies upwards; but the worm itself seemed to be suddenly struck dead: all of them being reduced to lie without motion, or any other discernible sign of life, within somewhat less (if we mistake not) than one minute of an hour. And this, notwithstanding the smallness of the Animals in proportion to the capacity of the vessels: which circumstance we the rather mention, because we found that the vessel was not free from leaks. And to satisfy the Spectators, that 'twas the absence of the Air that caused this great and sudden change: we had no sooner readmitted the Air at the stopcock, than all the three Infects began to show signs of life, and little by little to recover. But when we had again drawn out the Air, their motions presently ceased, & they fell down seemingly dead as before, continuing moveless, as long as, by continuing to pump, the vessel was kept exhausted. This invited us thankfully to reflect upon the wise goodness of the Creator, who by giving the Air a spring, has made it so very difficult, as men find it, to exclude a thing so necessary to Animals: and it gave us also occasion to suspect that if Infects have no lungs, nor any part analogous thereunto, the ambient Air affects them, and relieves them at the Pores of their Skin, it not being irrational to extend to these Creatures that of Hypocrates; who says, That a Living Body is throughout perspirable; or to use his expression, 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉, disposed to admit and part with what is Spirituous: Which may be somewhat Illustrated by what we have elsewhere noted▪ That the moister parts of the Air readily insinuate themselves into, and recede from the pores of the Beards of wild Oats, and those of divers other wild Plants; which almost continually wreath and unwreath themselves according to, even, the light variations of the temperature of the ambient Air. This Circumstance of our Experiment we particularly took notice of, that when at any time, upon the Ingress of the Air, the Bee began to recover, the first sign of Life she gave, was a vehement panting, which appeared near the Ta●l: Which we therefore mention, because we have observed the like in Bees drowned in Water, when they first come to be revived by a convenient heat: As if the Air were in the one case as proper to set the Spirits and Alimental Juice a moving, as heat is in the other; and this may perchance deserve a further consideration. We may add, That we scarce ever saw any thing that seemed so much as this Experiment, to manifest, That even living Creatures (Man always excepted) are a kind of curious Engines, framed and contrived by nature (or rather the Author of it) much more skilfully than our gross Tools and unperfect Wits can reach to. For in our present Instance we see Animals, vivid and perfectly sound, deprived immediately of motion, and any discernible signs of life, and reduced to a condition that differs from death, but in that it is not absolutely irrecoverable. This (I say) we see performed without any, so much as the least external violence offered to the Engine; unless it be such as is offered to a Windmill, when the Wind ceasing to blow on the Sails, all the several parts remain moveless and useless, till a new Breath put them into motion again. And this was further very notable in this Experiment; That whereas 'tis known, that Bees and Flies will not only walk, but fly for a great while, after their heads are off; and sometimes one half of the Body will, for divers hours, walk up and down, when it is severed from the other: Yet, upon the Exsuction of the Air, not only the progressive motion of the whole Body, but the very motions of the Limbs do forthwith cease; as if the presence of the Air were more necessary to these Animals, than the presence of their own Heads. But it seems, that in these Infects, that fluid Body (whether it bea Juice or Flame) wherein Life chief resides, is nothing near so easily dissipable, as in perfect Animals. For where, as we have above recited, that the Birds we conveyed into our small Receiver were within two minutes brought to be past Recovery, we were unable (though by tiring him that pumped) to kill our Infects by the exsuction of the Air: For though, as long as the Pump was kept moving, they continued immovable, yet when we desisted from pumping, the Air that pressed in at the unperceived Leaks, did (though slowly) restore them to the free exercise of the functions of Life. But, My Lord, I grow troublesome, and therefore shall pass on to other Experiments: Yet without despairing of your pardon for having entertained you so long about the use of Respiration, because it is a subject of that difficulty to be explained, and yet of that importance to humane Life, that I shall not regret the trouble my Experiments have cost me, if they be found in any degree serviceable to the purposes to which they were designed. And though I despair not but that hereafter our Engine may furnish us with divers Phaenomena useful to Illustrate the Doctrine of Respiration; yet having not, as yet, had the opportunity to make the other trials, of various kinds, that I judge requisite for my Information: I must confess to Your Lordship, that in what I have hitherto said, I pretend not so much to establish, or overthrow this or that Hypothesis, as to lay together divers of the Particulars that occurred to me, in order to a future inquiry. I say, divers of the Particulars, because I could add many others, but that I want time, and fear that I shall need Your Lordship's pardon, for having been so prolix in Writing; and that of Physicians (which perhaps I shall more easily obtain) for having invaded Anatomy, a Discipline which they challenge to themselves, and indeed have been the almost sole Improvers of. Without denying then that the inspired and expired Air may be sometimes very useful, by condensing and cooling the Blood that passes through the Lungs; I hold that the depuration of the Blood in that passage, is not only one of the ordinary, but one of the principal uses of Respiration. But I am apt also to suspect, that the Air does something else in Respiration, which has not yet been sufficiently explained; and therefore, till I have examined the matter more deliberately, I shall not scruple to answer the Questions that may be asked me touching the genuine use of Respiration, in the excellent Words employed by the acute St. Austin, to one that asked him hard Questions: Mallem quidem (says he) corum que à me quaesivisti, habere scientiam quam ignorantiam: sed quia id nondum potui, magis eligo cautam ignorantiam confiteri, quam falsam scientiam profiteri. HAving (partly upon the consideration of some of the foregoing Experiments, Experiment 42. and partly upon grounds not now to be insisted on) entertained a suspicion, that the action of Corrosive Liquors in the dissolving of Bodies, may be considerably varied by the gravitation or pressure of the incumbent Air, and the removal of it; I thought fit to examine my Conjecture by the following Experiment. I took whole pieces of red Coral, and cast them into as much Spirit of vinegar, as sufficed to swim above an Inch over them: These substances I made choice of, that the Ebullition upon the Solution might not be too great, and that the operation might last the longer. Having then put about half-a-score Sprigs of Coral, together with the Menstruum, into a somewhat long necked Viol, whereof they seemed scarce to fill a third part, we conveyed that Viol into one of our small Pneumatical Glasses, containing by guess about a Quart of Water; and having fastened on the Cover, after the accustomed manner, we suffered the Liquor to remain unmoved awhile, to observe whether the Menstruum would work upon the Coral otherwise then before. But finding there did only arise, as formerly, a pretty number of small Bubbles, that made no sensible froth upon the surface of the distilled vinegar, there were made two or three Exsuctions of the Air; upon which, there emerged from the Coral such a multitude of Bubbles, as made the whole Body of the Menstruum appear white; and soon after, a Froth, as big as all the rest of the Liquor, was seen to swim upon it: And the Menstruum plainly appeared to boil in the Glass, like a seething Pot. And though, if we desisted but one minute from pumping, the decrement of the Froth and Ebullition, upon the getting in of a little Air at some leak or other, seemed to argue, that the removal of the the pressure of the external Air was the cause, or, at least, the occasion of this effervescence: Yet to evince this the more clearly, we turned the Key, and let in the external Air at the Stop-cock; immediately upon whose entrance the Froth vanished, and so many of the Bubbles within the body of the Liquor disappeared, that it lost its whiteness, & grew transparent again: The Menstruum also working as languidly upon the coral, as it did before they were put into the Receiver: But when we had again drawn out the Air, first the whiteness re-appeared, than the ebulition was renewed, which, the pumping being a while longer & nimbly pursued, grew so great, that for 3 or 4 times one after another, when ever the Air was let out of the Receiver into the emptied Cylinder; the frothy liquor overflowed the glass, & ran down by the sides of it: And yet, upon the readmitting of the excluded air, the boiling Liquor grew immediately as calm and as transparent as at first: as if indeed the operation of it, upon the Coral, had been facilitated by the exsuction of the incumbent air, which on its recess, left it more easy for the more active parts of the liquor to show themselves such, than it was whilst the wont pressure of the Air continued unremoved. It may indeed be suspected, that those vast & numerous Bubbles proceeded, not from the action of the Menstruum upon the Coral, but from the sudden emersion of those many little parcels of air that (as we formerly observed) are wont to be dispersed in liquors, without excluding Spirit of Vinegar; but having had this suspicion before we tried the Experiment, we conveyed our distilled vinegar alone into the Receiver, and kept it awhile there, to free it from its Bubbles (which were but very small) before ever we put the Coral into it. It may be suspected likewise, that the agitation of the Liquor, necessary following upon the shaking of the Glass, by pumping, might occasion the recited Ebullition, but upon trial made, there appeared not any notable change in the liquor, or its operation, though the containing Vessel were shaken, provided no Air were sucked out of it. The former Experiment was another time tried in another small Receiver, with Coral grossly powdered, and the success was very much alike, scarce differing in any thing, but that the Coral being reduced to smaller parts, upon the ebullition of the liquor, so many little lumps of Coral would be carried & Buoy up by the emerging Bubbles, as sometimes to darken the Viol; though the same Coralline Corpuscles would be let fall again upon the letting in of the Air. Something also we tried in our great Receiver, concerning the solution of Metals in Aqua fortis, and other Corrosive Liquors; but partly the stink, and partly some accidents, kept us from observing any thing peculiar & remarkable about those Solutions. One thing we must not omit, that when the Spirit of vinegar was boiling upon the Coral, we took off the Cover of the Receiver, and took out the Viol, but could not find, that notwithstanding so very late an Ebullition, the Liquor had any heat great enough to be at all sensible to our hands. Experiment 43. WE will now subjoin an Experiment, which, if the former did not lessen, the wonder of it would probably appear very strange to Your Lordship, as it did to the first Spectators of it. The Experiment was this: We caused Water to be boiled a pretty while, that by the heat it might be freed from the latitant Air, so often already taken notice of in common Water: Then almost filling with it a Glass Viol., capable of containing near four Ounces of that Liquor; we conveyed it, whilst the Water was yet hot, into one of our small Receivers (big enough to hold about a pound of Water) and having luted on the Cover, we caused the Air to be drawn out: Upon the two first Exsuctions, there scarce appeared any change in the Liquor, nor was there any notable alteration made by the third; but at the fourth, and afterwards, the Water appeared to boil in the Viol, as if it had stood over a very quick Fire; for the Bubbles were much greater than are usually found upon the Ebullition of very much more Water than was contained in our Viol. And this Effervescence was so great in the upper part of the Water, that the Liquor boiling over the top of the Neck a pretty deal of it ran down into the Receiver, and sometimes continued (though more languidly) boiling there. Prosecuting this Experiment, we observed, that sometimes, after the first Ebullition, we were reduced to make divers Exsuctions of the Air, before the Liquor would be brought to boil again. But at other times, as often as the Key was turned to let the Air pass from the Receiver into the Pump, the Effervescence would begin afresh, though the Pump were plied for a pretty while together; which seemed to argue, that the boiling of the Water proceeded from hence, That upon the withdrawing the pressure of the incumbent Air, either the Fiery Corpuscles, or rather the Vapours agitated by the heat in the Water (which last, what we have formerly noted touching the rarefied Water of an Aeolipile, manifest to be capable of an Elastical Power) were permitted to expand themselves mightily in the evacuated Receiver; and did, in their tumultuous Dilatio, lift up (as the Air is wont to do) the uppermost part of the Water, and turning it into Bubbles, made the Water appear boiling. This conjecture was further confirmed by these additional Circumstances: First, The Effervescence was confined to the upper part of the Water, the lower remaining quiet, unless the Liquor were but shallow. Next, although sometimes (as is already noted) the Ebullition began again, after it had ceased a pretty while, which seemed to infer, That some concurrent cause (whatever that were) did a little Modify the operation of heat; yet, when the water in the Viol could by no pumping be brought to boil any more, the selfsame Water, being in the very same Viol warmed again, and reconveyed into the Pneumatical Glass, was quickly brought to boil afresh, and that vehemently and long enough; not to mention, that a new parcel, taken out of the same parcel of the boiled Water with the former, and put in cold, could by no pumping be brought to the least show of Effervescence. Besides, having tried this Experiment in hot Salad Oil, being a much more tenacious Liquor, and requiring a stronger heat to make it boil, could not be brought to an Effervescence in our Reciver; whereas the Chemical Oil of Turpentine, being thinner and more volatile, was presently made to boil up, till it reached four or five times its former height in the Viol, in whose bottom it lay, and continued boiling till it was almost reduced to be but lukewarm. Wine also being a more thin and spirituous Liquor than Water, being conveyed in hot instead of the Oil, did, as I remember, at the very first Exsuction begin to boil so vehemently, that, in a short time that the Pump was kept moving, four parts of five, by our guess, boiled over out of the Viol, though it had a pretty long Neck. On which occasion we will add, that even the Water itself, near one half, would sometimes boil over into the Receiver before it became lukewarm. And it was also remarkable, that once, when the Air had been drawn out, the Liquor did, upon a single Exsuction, boil so long with prodigiously vast Bubbles, that the Effervescence lasted almost as long as was requisite for the rehearsing of a Pater Noster. Now the Experiment having been tried more than once, and found to succeed as to the main, seems much to countenance the conjecture we made at the beginning of this Letter, where we told your Lordship, That perhaps the pressure of the Air might have an interest in more Phaenomena then men have hitherto thought. For as we had not then made this Experiment, so now we have made it, it seems to teach, That the Air, by its stronger or weaker pressure, may very much Modify (as the Schoolmen speak) divers of the Operations of that vehement and tumultuous Agitation of the small parts of Bodies, wherein the nature of heat seems chief, if not solely, to consist. Insomuch that if a heated Body were conveyed above the Atmosphere, 'tis probable that the heat may have a differing operation, as to the power of dissipating the parts of it, from what it has here below. To conclude, This Experiment might have been further prosecuted, but our want of leisure makes us content ourselves to add at present; That perhaps it would not be lost labour if this were tried, not only with other Liquors, but with variety of heated, and especially soft or melted Bodies: But in such cases the Receiver ought to be so shaped, as is most proper to preserve the Cement wherewith the Cover must be fastened on, from being melted by the heat of the included Matter; the inconvenience to be hereby avoided, having befallen us in the use of a Receiver too shallow, though otherwise capacious enough. The Conclusion. BEing come thus far, My Dear Lord, not without thoughts of proceeding further: The unwelcome Importunity of my Occasions becomes so prevalent, that it quite hinders, for the present, my designed Progress; and reduces me, not only to reserve for another opportunity that kind of Experiments, which, at some distance from the beginning of this Letter, I called (as Your Lordship may remember) Experiments of the second sort; but to leave unessayed some of the first sort, which I might try in the Engine, as it now is, were it not that my Avocations are grown so urgent, for my remove from the place where the Engine was set up, that I am put to write Your Lordship this Excuse, Weary, and in an Inn which I take in my way to my Dearrest Brother Cork: Who being at length arrived in England, after I h●ve for divers Years been deprived of His Company, and wished for it as long; what ever my other occasions may be, my first Business must be to wait on Him and Your Excellent Mother; in whose grateful Company I may hope to forget a while those public calamities that distress this too deservedly unhappy Nation. Since that is endeared to me, both by their personal Merit; by the near Relation which Nature gives me to Him, Affinity to Her, and Friendship to both; and also by their many Favours, especially that of my owing them My Lord of Dungarvan. But I suffer myself to be transported too fare with these delightful thoughts; To return therefore to our Engine. Though I find this Letter is beyond my expectation swelled, not only into a Book, but almost into a Volume; yet the Experiments already mentioned in it, are so fare from comprising all those that may be tried by the help of our Engine, that I have not yet been able to try all those, which, presently occurring to my thoughts, upon my first seeing the working of it, I Caused to be set down in a Catalogue within less than half an hour. But I doubt I have but too much cause to apprehend that the Affairs, and other things I complain of, have made it needful for me to Apologise, as well for the things I have set down, as for those I am necessitated to omit. For as partial as men use to be to the children of their own Brains, as well as to those of their Loins, I must not deny that the foregoing Trials are not altogether free from such unaccuratenesses, nor the recital of them from such imperfections, as I myself can now discern, and could perhaps partly mend, if I had the leisure to repeat the Experiments, with the Circumstances that have since offered themselves to my thoughts, as things that might have been worth Observation or Enquiry. But the truth is, that I was reduced to make these Experiments, when my Thoughts had things that more concerned me to employ them, and the same avocations made me set them down, for the most part, assoon as I had made them, and in the same order, and that so fast that I had not over-frequently the opportunity to mind any more than the bare Truth of what I set down; without allowing it any of those Advantages that Method, Style, and decent Embellishments, are wont to conferee on the Composures they are employed do adorn. But, my Lord, though to invite and encourage You and your learned Friends at Paris, to make a further use of this Engine than I have yet been able to do, I am thus free to acknowledge the imperfections of the foregoing Letter: yet if some Intelligent Persons mistake not, by what has been done, such as it is, there is a way opened, whereby Sagacious Wits will be assisted to make such further Discoveries in some points of Natural Philosophy, as are yet scarce dreamed of. And I am the more desirous to engage You to that Employment, because I am apt to think, that if the Making and Writing of such Experiments shall cost You as much trouble as they have me, You will be inclined to Excuse me; and if the Discoveries give You as much pleasure as they gave me, You will (perhaps) be invited to thank me. However, I think (my Lord) I may justly pretend, that the things I have set down have been faithfully Recorded, though not elaborately Written; and I suppose my former Papers may have long since satisfied You, that though many devise Experiments better that Your Servant, none perhaps has related them more carefully and more truly: And particularly of These; sometimes one, sometimes another hath been performed in the presence of Persons, divers of them eminent for their Writings, and all for their Learning. Wherefore hav●ng in the foregoing Narratives made it my business to ennoble them with the chief Requisites of H●storicall Composures, Candour, and Truth, I cannot despair that You will either Excuse their Imperfections, or at least Forgive them: Especially considering, that this unpolished Letter is as well a Production of Your Lordship's Commands and my Obedience, as a Testimony of my Desire to make others beholden to my Lord of Dungarvan, by the same way by which I endeavour to express myself Bec●n's-fi●ld this 20●h. of December, 1659. His Lordship's Most obedient Servant, and Most affectionate Uncle, ROBERT boil. ERRATA. Pag. 4. line. 8. deal that. 10.11. d. within and without. 12.3. out at the. 18.25. devoid. 18. 〈…〉 27.11. air's spring. 28.27. refraction●. 31.1. 〈◊〉 32.5. de that. 34.16. it bent. 46.22. 〈…〉 4●. 21. made even, by. 48.6. not from. 69.19. 〈◊〉 73.26. cloth of. 76.26. wax candle. 102.23 〈◊〉 10●. 6. we united. 104.1. d. l. 106.21. in an. 106.24. 〈◊〉 i●. 115.16. an other tryll. 150.22. time, after. 152.9. it, is. 116.26., how ever, 172.15. EF. 173.9. 〈◊〉 S—. Canalis tortuosi (QR) ultimum orificium Z. 174.18. raresaction. 182.9. twenty first. 184 6. 〈…〉 194.19. wo●t to. 128: 11. of the Atmosphere. 235 16. 〈…〉 246.27. d. be. 247.19. admit it. 257. in margin. 〈◊〉 general. 270.24. the glass. 277.24. a degree. 290.8. 〈◊〉 neither as. 294.27. F to C. 294. vlt. 30 45/54 299.24. Tolouse. 1300.15. difforme. 309.27. Lucid. 321.10. possessor's. 356.16. Pariacaca. 358.3. 〈…〉 ●●8. 26. Froelichius. 362.14. proscribe. 362.26. as some of