TRACTS Written By the Honourable Robert boil, CONTAINING  
New EXPERIMENTS, touching the Relation betwixt Flame and Air. And about EXPLOSIONS.  
An HYDROSTATICAL Discourse occasioned by some Objections of Dr. Henry More against some Explications of New Experiments made by the Author of these Tracts: To which is annexed, An Hydrostatical Letter dilucidating an Experiment about a Way of Weighing Water in Water.  


New Experiments,  
Of the Positive or Relative Levity of Bodies under Water.  
Of the Air's Spring on Bodies under Water.  
About the Differing Pressure of Heavy Solids and Fluids.    
LONDON, Printed for Richard Davis, Bookseller in Oxon MDCLXXII.   

Advertisement to the Book-binder.  
SOme of these Tracts having been misplaced in the printing, the Book-binder is desired to take care of placing the several Tracts in the order, as they stand in the Title-page; as also to observe, in the binding, the Advertisement given p. 131. immediately following after the Experiments about the Relation betwixt Air and the Flamma vitalis of Animals.   

NEW Experiments, Touching the Relation betwixt Flame & Air: And particularly betwixt AIR, and the Flamma Vitalis of Animals.  
To which are annexed  
Two Attempts; the one, to produce Living Creatures in Vacuo Boyliano; the other made upon Gnats in the same Vacuum.   

THE PUBLISHER TO THE READER.  
IT will, 'tis presumed, be altogether needless to preface any thing by way of commendation to the following Tracts; they will certainly commend themselves by their own worth to the Intelligent and Attentive Reader, who might have seen them sooner if the Press had not detained them longer than was expected; since, to the Publisher's knowledge, they were ready in the Year 1671. except the Hydrostatical Discourse and the Explication of the Author's Experiment of Weighing Water in Water, the former of which was finished in the beginning of this Year 1672; though the latter could not be so till near the end of the same Year, viz. the month of February English stile, because the Book of Mr. George Sinclair's hydrostatics, in which it is excepted against, came not, I think, before that time to London, I am sure not to the view of the Honourable Author. Farewell.   

NEW EXPERIMENTS Touching the Relation betwixt Flame and Air, Sent in a Letter To the Learned Publisher of the Philosophical Transactions.  
SIR,  
YOu may have observed as well as I, that since the publishing of the Experiments I sent you, touching Respiration, divers of our Learned men have spent both Thoughts and Discourses in enquiring and disputing, Whether there reside in the heart of Animals, such a fine and kindled, but mild, Substance, as they call a Vital Flame, to whose preservation, as to that of other flames, the Air, (especially as 'tis taken in, and expelled again by Respiration) is necessary. This among other considerations makes me think it seasonable (though many avocations make it inconvenient) to complete the performance of the Promise I made you, by adding to the Experiments about Respiration, which your commands have already obtained of me, those scattered Notes, that I have been able to pick up about the Relation betwixt Flame and Air: And though, I confess, they are very much inferior in number to the Trials about Respiration; and that in making them it was not so much my Design to complete an entire and distinct Tract, though but a small one, of such Experiments, as to gratify my own curiosity in the examining of a Paradox or two I had been writing about Flame; yet the nobleness of the Question now under debate, and their pertinenoy to it, will possibly keep them, as few as they are, from being useless. And that also they may be the better kept from being unwelcome, I have chosen to make myself a Relater of matters of fact, without engaging with either of the Litigant parties in a Controversy, wherein I am the less tempted to be partial, because I have not formerly declared my opinion about it, and at present, I see, on either side, Persons for whom I have no small respect and kindness.  
And now, Sir, that you may not expect in the following Papers such a number and variety of Experiments as I might perhaps be able to present you with, on some more tractable subject; I shall briefly mention to you some of the chief difficulties I met with in the making of these; which I do the rather, that, if you and your ingenious friends have a mind to prosecute such Trials, you may not be surprised with the difficulties I have met with; but provide at least against those fore-seen ones, by which you will scarce fail to be encountered.  
I shall then inform you, that the ensuing experiments were rendered uneasy and troublesome to me by this; that some of them could not be conveniently done at all seasons of the year, nor in any season in all weathers; but must be made not only in the day time, but in Sunshine days. You will easily guess, that I speak of those experiments, that are to be made by the help of a Burning-glass, casting the reflected or refracted beams of the Sun upon the combustible matter placed in the exhausted Receiver: For, by reason of the interposition of so thick a Glass, whereby many of the incident beams of Light are reflected, and others inconveniently refracted; there is ordinarily requisite a clear day, and a competent height of the Sun above the Horizon; and sometimes also a convenient time of the year; to bring such experiments, as we were speaking of, to a fair Trial. Not to take notice, that in such attempts there usually intervene circumstantial difficulties, not so easy to be fore-seen: And it not being Summer when I had occasion to make the following Experiments, I could make but very few with the Sunbeams; besides that there are divers others which are not that way to be made so conveniently, if at all, as by the help of the Fire.  
But though the Trials of this second sort had their conveniencies, in regard they might be made in any weather, and as well by night, as day; yet they were not unattended with peculiar inconveniencies: some of which you will easily discern by the mention of them, that was necessary to be made in some of the relations themselves. And, besides more particular and emergent difficulties, there was this in general, that rendered these Experiments troublesome; that, whether I made them in larger Receivers, or in small, or in middle-sized ones, each of these cases had its inconveniencies: For, very large Receivers, besides that 'twas very toilsome and tedious to empty them of Air, required so much time for the exhaustion, that too frequently, by that time the Operator had done pumping, the included Iron, or other heated body, was grown too cold to perform the desired effect: And if the Receiver were not considerably large, than the red-hot Iron, or other included body that was to burn the combustible matter, would much endanger the breaking of the overheated Glass, and not afford room enough for some Phaenomena to be fairly exhibited in; and besides create another difficulty, to which we found middle-sized Receivers also obnoxious: For, several times when the Experiment required an intense heat within the Receiver, than (especially if some casual obstacle hindered the quick exhaustion) the heat of the ignited Iron, or some such other included body, would so melt or soften the Cement, that fastened the Receiver to the Engine, that, when the Glass was brought to be well exhausted, and sometimes also before, the external air would by its pressure and fluidity squeeze or thrust in somewhere or other the yielding Cement, and thereby cause in the Instrument a leak, that would much incommodate us, if not reduce us to begin the Experiment again, in so much that for some trials we were fain to provide a Cement on purpose: the least fusible, that we used on other occasions, being yet found too fusible on these.  
Nor were those, I have already mentioned, the only difficulties and impediments I met with in making experiments about Flame and Air; but I shall not here trouble you with them in this place, where it may suffice for me to have mentioned those that are of a more general nature, and are like the most frequently to occur.  
But though I declined to name any other to you, than the foregoing difficulties in making the following Experiments; yet I must not omit to take notice of one that may occur to you about judging of them. For, in those trials that require to have an ignited Iron or any such thing included in the Receiver, it would usually happen, that so much heat would rarify the Air shut up in the Mercurial Gage, and consequently enable it to depress the Mercury, that lies under it, far beneath the mark it would have stayed at upon the mere account of so much ambient Air pumped out: This would happen, I say, before the heated Receiver was well exhausted; so that, if one be not ware of this, 'twill be obvious, by looking on the Gage, to conclude the Receiver to be well emptied, before it really is so. And therefore the safest way in these cases is, to continue to pump (without trusting to the ordinary marks) till you see that the Mercury will be no further depressed in the sealed leg of the Gage; though otherwise, by concurring signs, one that is versed in those trials may well enough judge when he needs to pump no longer.  
But perhaps you will here demand, whether by our Engine we can competently withdraw the Air out of a Receiver; or whether at least that may not be much better done by the help of Quicksilver, after the manner of the Torricellian Experiment, in regard that ponderous liquor frees the glass, it deserts, from all the Air at once, and exactly hinders the regress of it.  
In answer whereunto, I hope you do not expect, that I should contend for a favourabler judgement of the Engine, I employ, than the Virtuosos (as well Foreign as English) have been pleased to pass on it already: And therefore, to tell you freely my thoughts, about the main part of the proposed Question, I shall readily avow to you, that I think, there may be experiments (such as some of those where the included body need be but small, and where the being suddenly produced is chief desired in the effect,) wherein, by the help of Quicksilver, the exhaustion of the Air may be dispatched with greater celerity, and consequently make the effect be more conspicuous, than, by our ordinary way of trying, it would be in our Engine; since the fall of the Mercury does, as the objection intimates, produce a Vacuum (in our sense of that word) very nimbly, whereby the Expansion of the Air is presently effected, and the Aereal particles, harboured in the pores of any body placed in this deserted cavity, will thereby have opportunity more suddenly to expand themselves. But, on the other side, I might answer in general, that when I have particular occasions to dispatch the exhaustion of the Air, I can very much hasten it, by barely lessening, as I have several times done, the capacity of the Receiver; insomuch that I have sometimes employed so small an one, that in half a minute, or much less, after it was fitted on, we could considerably exhaust it, and thereby produce Phaenomena exceeding conspicuous. And as to the Experiments of this little Tract in particular, it may be said, that, not to mention the troublesomeness, and other inconveniencies of needing to employ such an unwieldy weight of Mercury, you will easily find, by the Phaenomena of divers of the ensuing trials, that most of them cannot be with any conveniency, and some of them not at all, made in the Torricellian tubes. As for the ground of the Objection, that the Air cannot be so well drawn out by our way, as by the subsiding of the Mercury; though you may think that very clear, yet one, that were very jealous of the Reputation of the instrument I employ, may perhaps reasonably enough question it. For, the Vacuum, that is produced in the Torricellian Experiment, as 'tis made all at once, so 'tis made once for all; and therefore if there were any Aereal particles lurking in the Mercury (as there will be pretty store, if the quantity of that liquor be great enough to make a considerable Vacuum; which if it be not, it will be too small for very many of our trials;) they will remain in the deserted cavity at the top of the Glass, and, by their expansion there, much hinder the full operation of an ambient Vacuum upon the bodies placed in it. Besides that almost all such bodies, if they be dry, will be so incongruous to Mercury (which scarce sticks to any consistent bodies but metals,) that probably there will be no small number of aereal corpuscles intercepted between the Mercury and those surfaces, to which it does not closely adhere: which airy corpuscles, when the subsiding Mercury deserts them, will be left to increase the number of those, that, (as we were saying) will emerge from the Mercury; from which, as also from the pores of the included bodies, will perhaps arise divers new ones from time to time for a pretty while after. And in case the Vacuum be made by a Cylinder of two or three and thirty foot of water, (as for some experiments, that have been tried in France and Italy, hath been done) the emersion of bubbles may last a long time, as may be gathered from some observations of mine elsewhere related.  
On the contrary, in our Engine, though when the Receivers are not very small, they are more slowly emptied; yet in recompense, we may continue the pumping out of the Air as long, and renew it in the same Experiment as often as we think fit: So that, if we perceive, that, after the first exhaustion of the Glass, there happen any aereal particles to extricate themselves successively out of the included body, we can, by resuming the Pump from time to time, whenever need requires, free the Vacuum from these also; which, in some cases, I have found to be longer and more copiously emitted by the included bodies, than any thing but jealous trials could have convinced me of. And to confirm what I have been saying by something Historical, I shall add; That though the excellent Florentine Academians are thought to have prosecuted the Experiments about the Vacuum made with Mercury the furthest of any; yet some eminent members of that Illustrious Society were pleased to confess to me, that they never were able by the help of Mercury, to bring a Glass-buble, sealed up with Air in it, to burst of itself by the withdrawing of the external Air; which yet I have often done with the Engine I employ, and convinced them, that I could do so by doing it in their presence.  
You will, perhaps, think it somewhat strange, to find, that I set down some of the following Narratives in such a way, as does not express me solicitous to ascribe and vindicate to the Air so absolute and equal a necessity to the production and conservation of all Flames, as divers Learned men have concluded from my former Experiments. But I, that am content to be kind to the Air, but not partial, shall not scruple to declare to you, that, as much as some may think me beholden to the Air for any discoveries of itself, it may have vouchsafed me; yet, I think, a natural, as well as a civil Historian, does, in his accounts of matters of fact, own more to Truth than to Gratitude itself. And though, wherever the Air can challenge a clear, or at least a probable interest in a Phaenomenon, I am not only disposed, but glad to do it right; yet I would not easily assert to it a larger Jurisdiction than I find Nature to have assigned it; especially since (without partiality) that, I presume, may be shown to be very large and considerable, and perhaps to reach to many things, wherewith men seem not to have yet taken notice that it hath any thing to do at all.  
What hath been hitherto said, will not, I hope, seem impertinent or useless, whenever you shall fall upon the actual making of such Experiments as you are about to read. But I fear, that to add any thing more, (which were not difficult for me to do to the preliminary part of this small Tract) would make it too disproportionate to the historical; From which I shall therefore no longer detain you.   

THE FIRST TITLE.  
OF THE DIFFICULTY OF PRODUCING FLAME WITHOUT AIR.   

THE FIRST TITLE. Of the Difficulty of Producing FLAME without AIR.  

EXPERIMENT I. A way of kindling Brimstone in vacuo Boyliano unsuccessfully tried.  
WE took a small earthen melting Pot, of an almost Cylindrical figure, and well glazed (when it was first baked) by the heat; and into this we put a small cylinder of Iron of about an inch in thickness, and half as much more in Diameter, made red hot in the fire; and having hastily pumped out the Air, to prevent the breaking of the Glass; when this vessel seemed to be well emptied, we let down, by a turning key, a piece of Paper, wherein was put a convenient quantity of flower of Brimstone, under which the iron had been carefully placed; so that, being let down, it might fall upon the heated metal, which as soon as it came to do, that vehement heat did, as we expected, presently destroy the contiguous paper; whence the included Sulphur fell immediately upon the iron, whose upper part was a little concave, that it might contain the flowers when melted. But all the heat of the iron, though it made the Paper and Sulphur smoke, would not actually kindle either of them that we could perceive.   

EXPER. II. An ineffectual attempt to kindle Sulphur in our Vacuum another way.  
ANother way I thought of to examine the inflammability of Sulphur without Air; which, though it may prove somewhat hazardous to put it in practice, I resolved to try, and did so after the following manner:  
Into a Glass-buble of a convenient size, and furnished with a neck fit for our purpose, we put a little flower of Brimstone (as likely to be more pure and inflammable than common Sulphur;) and having exhausted the Glass, and secured it against the return of the Air, we laid it upon burning coals, where it did not take fire, but rise all to the opposite part of the glass, in the form of a fine powder; and that part being turned downward and laid on coals, the Brimstone, without kindling, risen again in the form of an expanded substance, which (being removed from the fire) was, for the most part, transparent, not unlike a yellow varnish.   

ADVERTISEMENT.  
THough these unsuccessful attempts to kindle Sulphur in our exhausted Receivers, were made more discouraging by some more, that were made another way; yet judging that last way to be rational enough, we persisted somewhat obstinately in our endeavours, and conjecturing that there might be some unperceived difference between Minerals, that do all of them pass, and are sold for common Sulphur, I made trial, according to the way hereafter to be mentioned, with another parcel of brimstone, which differed not so much from the former, as to make it worth while to set down a description of it, that probably would not be useful.  
But in this place, it may suffice to have given a general intimation of the possibility of the thing. The proof of it you will meet with under the third Title, when I come to tell you what use I endeavoured to make of our sulphureous Flames.   

EXPER. III. Showing the efficacy of Air in the production of Flame, without any actually flaming or burning body.  
HAving hitherto examined by the presence of the Air, what interest it has in kindling of Flame; it will not be impertinent to add an Experiment or two, that we tried to show the same interest of the Air by the effects of its admission into our Vacuum. For I thought, it might reasonably be supposed, that if such dispositions were introduced into a body, as that there should not appear any thing wanting to turn it into Flame but the presence of the Air, an actual accension of that body might be produced by the admitted Air, without the intervention of any actual Flame, or Fire, or even heated substance; the warrantableness of which supposition may be judged by the two following Experiments.  
When we had made the Experiment, ere long to be related in its due place, (viz. Title II. Exper. the 2d) to examine the presumption we had, that even when the Iron was not hot enough to keep the melted Brimstone in such a heat, as was requisite to make it burn without Air, or with very little, it would yet be hot enough to kindle the Sulphur, if the Air had access to it: To examine this (I say) we made two or three several Trials, and found by them, that if some little while after the flame was extinguished, the Receiver were removed, the Sulphur would presently take fire again, and flame as vigorously as before. But I thought it might without absurdity be doubted, whether or no the agency of the Air in the production of the flame might not be somewhat less than these trials would persuade; because that, by taking off the Receiver, the Sulphur was not only exposed to fresh Air, but also advantaged with a free scope for the avolation of those fumes, which in a close Vessel might be presumed to have been unfriendly to the Flame.  
How far this doubt may, and how far it should, be admitted, we may be assisted to discern by the subjoined experiment, though made in great part for another purpose; which you will perceive by the beginning of the Memorial I made of it, that runs thus.   

EXPER. IU. A differing Experiment to the same purpose with the former.  
HAving a mind to try, at how great a degree of rarefaction of the Air it was possible to make Sulphur flame by the assistance of an adventitious heat, we caused such an experiment as the above mentioned to be reiterated, and the pumping to be continued for some time after the flame of the melted flowers of Brimstone appeared to be quite extinguished, and the Receiver was judged by those that managed the Pump (and that upon probable signs) to be very well exhausted. Then, without stirring the Receiver, we let in at the stop-cock very warily a little Air, upon which we could perceive, though not a constant flame, yet divers little flashes, as it were, which disclosed themselves by their blue colour to be sulphureous flames; and yet the Air that had sufficed to re-kindle the Sulphur, was so little, that two exsuctions more drew it out again, and quite deprived us of the mentioned flashes. And when a little Air was cautiously let in again at the stop-cock, the like flashes began again to appear, which upon two exuctions more did again quite vanish, though, upon the letting in a little fresh Air the third time, they did once more reappear.  
Whether and how far such experiments as these may conduce to explicate what is related of Fires suddenly appearing in long undisclosed Vaults or Caves to those that first broke into them, I may perchance elsewhere consider; but shall not here inquire, especially being not yet fully satisfied of the truth of the matter of fact.   

EXPER. V About an endeavour to fire Gunpowder in vacuo with the Sunbeams.  
Whatever hath been hitherto delivered, will not, I presume, make it unreasonable to inquire, whether, what interest soever the Air appears to have in the production of those flames that are to last for some time, there may not easily be produced a momentany flame or flash without any assistance from the Air. Wherefore I employed some endeavours to discover, whether there were the same need of Air to the going off of Gunpowder, as to the inflammation of other bodies. And though my first attempt of this nature being unprosperous, it was concluded by the Learned of the bystanders, that I should never be able to make a successful one to kindle Gunpowder in an exhausted Receiver; yet this did not hinder me from prosecuting a design, for whose feasibility I considered, that it might be alleged à priori (as they use to speak) that Brimstone, which is one of the ingredients of Gunpowder, appears by several trials to be sometimes capable of accension in our Vacuum, and therefore probably may kindle the rest. But how far the firing of Powder, without the help of Air, is possible, will be best judged by the experiments you will meet with under the third Title: And how far 'tis more difficult to be kindled in our exhausted Receivers, than in the open air (which is an inquiry proper for this place) may be guessed by the subjoined trial; which, though it were made many years since (in the year 1660.) before we had devised the Mercurial Gage, to examine how well the Receiver was exhausted, I shall yet afford it a room in this place, because 'twas made in Summer by the help of a Burning-glass, which I could not employ to purpose in the winter-season, wherein the two following Trials were made.  
To give you then some account of that part of the Experiment, which concerns our present inquiry, I will subjoin a transcript of what I find registered about it; which is to this purpose, and almost in these words: That, having conveniently placed three or four grains of Gunpowder in the cavity of our Receiver, and having carefully drawn out the Air, we cast the Sunbeams, united by a good Burning-glass, upon the powder, and kept them there a pretty while to little purpose; till at length the Powder, instead of taking fire, smoking only, and melting like a metal; those Spectators, that were of another opinion than I was yet convinced of, would have me leave off. The further event of such trials more fully prosecuted you will find under the third Title: All that will be pertinent to be here added being, that the newly recited experiment was not the single one, we made about that time, that discovered a great indisposition even in Gunpowder to be fired in our Vacuum.   

EXPER. VI An attempt to fire Gunpowder in vacuo, by means of a hot Iron.  
WE took (by weight) what we judged a convenient quantity of Gunpowder, that was extraordinarily strong and well made, and having in our Receiver, that was capable of holding about 16 pound of water, placed the formerly mentioned Iron first heated red-hot, when the Air appeared by the Mercurial Gage to have been diligently pumped out, we let down, by help of the turning Key, a small piece of thin Paper, wherein the Powder had been put, till we saw it reached the plate, by whose heat we hoped the Paper would be destroyed, and the Powder made to go off. But though both the one and the other had been purposely well dried near the fire, before they were put into the Receiver; the desired explosion of the Powder did not ensue. Yet there appeared upon the iron-plate a pretty broad blue flame, like that of brimstone (whence 'twas judged to be the Sulphureous ingredient of the Gunpowder that was kindled) which lasted so very long as we could not but wonder at it. But at length the Powder not going off, and the still decaying heat of the iron forbidding us to wait any longer, we thought fit to take off the Receiver, & found (as we expected) that the Paper contiguous to the Iron, was, in part, destroyed by its heat; but most of the grains of the Powder seemed not altered, and were found disposed enough to be fired, notwithstanding the consumption of the brimstone, that had burned away.   

APPENDIX.  
TO confirm the foregoing Experiment, by showing how great a disposition to take fire there may be in Gunpowder, that yet would not do so without Air, I shall subjoin this observation:  
Having reiterated the newly mentioned Experiment after the like manner, and with the same Receiver, and Iron-plate, as formerly, we did not find any explosion to be made for so long a time, that, thinking it in vain to wait any farther, we let in the Air, which might perhaps, by help of the remaining heat of the iron, procure the operation we at first desired. The event was; that after nothing had ensued for a good while, and we scarce thought, that such a thing would happen; the Powder suddenly went off with a great flash, and so shook the Receiver that was yet standing on the Engine, as to endanger the throwing of it down. Which circumstance I mention, to give you a caution that may prove useful, in case you try in close vessels experiments with Gunpowder; since if they be not warily managed, they may sometimes (as I have had occasion to observe) prove dangerous enough; which will be the better discerned, if I add, that the Powder, that had this operation on a Receiver (large enough to contain two Gallons of liquor) was weighed before it was put in, and amounted but to one grain, (though a greater quantity might perhaps have been well enough ventured upon, if it had been but common Gunpowder.)   

EXPER. VII. Reciting another way, whereby the firing of Gunpowder in vacuo Boyliano was attempted.  
TO diversify our ways of examining the indisposedness of Gunpowder to be fired in our Vacuum, we thought fit to add to the foregoing Trials that which followeth:  
Into a pretty large and strong Glass-buble, we put a few small corns of Gunpowder, and having carefully exhausted it, and secured it against the return of the Air, we put it upon a pretty quantity of Live-coals superficially covered with Ashes: By whose heat the sulphureous ingredient of the Powder was in part kindled, and burned blue for a pretty while, and with a flame considerably great (in proportion to the Powder;) upon whose ceasing, the Powder, which, when all was done, did not take fire, appeared to have sent up, besides the flame, a pretty deal of sulphureous sublimate, that stuck to the upper part of the Glass, and being held against a Candle, we caused to be brought in, (for the Experiment had been purposely made in a dark place) it exhibited divers vivid colours like those of the Rainbow.   

EXPER. VIII. About a trial made to fire Gunpowder in our Vacuum by the help of Sparks.  
THough, in the fourteenth of the long since published Physicomechanical Experiments, there is recited a trial made about kindling of Gunpowder with a Pistol; yet I shall not forbear to subjoin the ensuing account, partly because the Receiver we then employed, being about four times, if I mis-remember not, as big as that we last made use of, 'twas very difficult to exhaust the one so well as the other; and partly because we wanted some accommodations, with which we since furnished ourselves, and (having not then devised the Mercurial Gage we employed in the making this last Experiment) we could not then judge so well, as we since could, of the degrees to which the Receiver was emptied. And therefore, when in the Relation of that fourteenth trial there is mention made of one attempt that did succeed, among divers that did not; there is towards the close an intimation given, That in spite of the great Rarefaction that had been made in the Air, there might yet be some little portion of it remaining in the Receiver. I proceed then to the promised Relation, which I find thus set down:  
To prosecute the design of the foregoing Experiment by a way somewhat differing from those hitherto mentioned; we made, though not without difficulty, the ensuing trial; one of whose scopes you will find intimated at the close of the Relation.  
We took a small and very short Pistol, and having well fastened it with strings to a great weight, that was placed upon the iron-plate of our Engine, we drew up the cock, and primed the pan with dry Powder; then over both the weight and Pistol we whelmed a Receiver, capable of containing two Gallons of liquor, and having carefully cemented it on, we caused the Air to be diligently pumped out; having before put in a Mercurial Gage to help us to discern when it was exhausted. Lastly, ordering the Pump to be plied in the mean while, for fear some Air should steal in, before the trial was completed, we did, by the motion of the turning key, shorten a string that was tied both to it and the trigger of the Pistol, by which means we did as much as we could towards the firing of the powder in the pan; but though the pan were made to fly open, yet the powder did not go off: whereupon letting in the Air, and cocking the Pistol again without taking it off the weight it was tied to before, we drew out a little Air, to be sure that the Receiver was closely cemented on, (which care we took in reference to another Experiment;) and then letting in the Air at the top of the Receiver, and stopping it in with the turning key, we did, by the help of that key, draw aside the trigger again; whereupon, though there had been no new Powder put into the Pan, nor any left in it, but only some little that remained after the late trial; yet that little readily took fire and flashed in the pan; which made it the more probable, that in the former trial sparks of fire had been struck out by the collision of the Flint and Steel: which was the more credible, because in an other trial, made the same hour in the same exhausted Receiver, two of the assistants plainly saw a spark or two fly out upon the falling of the Cock, though I, that chanced to stand in an inconvenient place, did not then perceive it. But afterwards, having caused the Experiment for my fuller satisfaction to be repeated, I freed myself from need of trusting others eyes: So that it appears, that, notwithstanding the great indisposition of Gunpowder itself to be reduced into flame in our Vacuum; yet even solid matter is not uncapable of being ignited there, if it be put into a motion sufficiently vehement.  
If this Experiment had not been so very troublesome to make, I should have been invited to reiterate it, because a not contemptible scruple may be prevented, if the trial can be made to succeed, in regard that the going off of the whole Gunpowder, by the falling of a spark or two only upon two or three of its grains, would argue, that the accension of the rest was made by the propagation of flame from the kindled grains to the rest; so small a portion of ignited and suddenly vanishing matter, as is to be found in a spark or two, being not likely to be able in so very short a time to impart a Vehement, or so much as a Sensible, heat, to the whole aggregate of grains, or at least a great part of them, as the focus of a Burning-glass, held long enough upon them to make them melt, may well be supposed to do.   

EXPER. IX. Two ways of making Aurum fulminans go off in our exhausted Receiver.  
BEcause 'tis wont to be supposed (how justly I here dispute not,) that Aurum Fulminans, as the Chemists call it, is much of the nature of Gunpowder, though by vast odds stronger than it; I thought it not unfit to make trial, whether it could be made to go off in our exhausted Receiver; and accordingly, about the time that the other Experiment of firing Gunpowder by the Sunbeams was made, we also made trial of this; and that, as I remember, in the same Receiver, and with the same Burning-glass. The event was; that, though the Air had been pumped out, the concentrated beams of the Sun made the Aurum fulminans go off, and violently scatter about the cavity of the Receiver a yellowish dust or powder, which other trials in the free Air made us look upon as particles of the Gold, that was the main ingredient of this odd composition.  
This Experiment we reiterated a good while after in another place, and with other vessels, and yet with the like success.  
But in regard these trials being made by the united Sunbeams, 'twas unavoidable that our eyes would be beforehand affected with the vivid impressions of so glaring a light; it seemed not safe to determine, by the bare going off, or shattering of the Aurum fulminans, whether or no it afforded any flame or light upon its explosion: For, as we could not be sure of the affirmative, because our eyes could not discern any momentany flame or flash; so it seemed not safe to conclude the negative: since, though there had been such a flame, yet, if it had not been strong, it would not have been sensible to our eyes, whilst preaffected by a powerful Light. Wherefore we resolved to make this trial in the night with an Iron heated, but not candent, (that its light might not eclipse that which the powder might afford;) and having, after the manner already often recited, exhausted a pretty large Receiver, and let down by a string half a quarter of a grain (by weight) of good Aurum fulminans of our own preparing, loosely tied in a little piece of thin paper, (which paper, former trials to another purpose kept us from fearing that no hotter an iron, than ours than was, would kindle,) we found, as we expected, that after the powder had lain long enough upon the iron to be throughly heated, it went off all together, and, as the bystanders affirmed, with a flash: but my face being accidentally turned to remove a Light that I feared might disturb us, I could not see the flash myself, and therefore caused the Experiment to be made once more, to ground my narrative upon my own observation: which quickly assured me, that the Luminous flash, produced upon the explosion, was not only sensible, but considerable.    

THE SECOND TITLE.  
OF THE DIFFICULTY OF PRESERVING FLAME WITHOUT AIR.   

Of the Difficulty of Preserving Flame without Air.  
SInce it is generally, and in most cases justly, esteemed to be more easy to preserve Flame in a body that is already actually kindled, than to produce it there at first; we thought fit to try, whether at least bodies already burning might not be kept in that state without the concurrence of Air. And though in some of our formerly published Physicomechanical experiments it happened, that actual Flame would scarce last a minute or two in our large Pneumatical Receiver; yet because it seemed not improbable, that Mineral bodies once kindled might afford a vigorous and very durable flame; we thought fit to devise and make the following trials: Whence probably we might receive some new informations about the Diversities, and some other Phaenomena of Flame, and the various degrees, wherein the Air is necessary or helpful to them.  

EXPER. I. Reciting an attempt to preserve the flame of Brimstone without Air.  
WE put upon a thick metalline place a convenient quantity of flowers of Sulphur; and having kindled them in the Air, we nimbly conveyed them into a Receiver, and made haste to pump out some of the included Air, partly for other reasons, and partly that the cavity of the Receiver might be the sooner freed from smoke, which would, if plentiful, both injure the flame, and hinder our sight. As soon as the Pump began to be plied, or presently after, the flame appeared to be sensibly decayed, and continued to be lessened at every exsuction of the Air; and in effect, it expired before the Air was quite drawn out. Nor did it, upon the early removal of the Receiver, do any more than afford, for a very little while, somewhat more of smoke in the open Air, than it appeared to do before.  
The reiteration of this Experiment, presently after, afforded us nothing new, worth mentioning in this place.   

EXPER. II. Relating a Trial about the Duration of the flame of Sulphur in vacuo Boyliano.  
TO vary a little the foregoing Experiment, and try to save some moments of time, which on these occasions is to be husbanded with the utmost care; having provided a Cylinder of iron, larger than the former, that it might by its bulk, being once heated, both contribute to the accension of the Sulphur, and to the lasting of its flame, we made a trial, that I find registered to this effect:  
We took a pretty big lump of Brimstone, and tied it to the turning-key; and having got what else was necessary in a readiness, we caused the iron-plate to be hastily brought red-hot from the fire, and put upon a Pedestal, that the flame might be the more conspicuous; and, having nimbly cemented on the Receiver, we speedily let down the suspended Brimstone till it rested upon the red-hot iron, by which being kindled, it sent up a great flame with copious fumes, which hindered us not from plying the Pump, till we had, as we conjectured, emptied the Receiver; which we could not do without withdrawing together with the Air much sulphureous smoke (that was offensive enough both to the eyes and nostrils.) But notwithstanding this pumping out of the Air, though the flame did seem gradually to be somewhat impaired; yet it manifestly continued burning much longer, than by the short duration of other flames in our Receivers (when diligence is used to withdraw the Air from them) one could have expected. And especially one time, (for the experiment was made more than once) the flame lasted till the Receiver was judged to be well exhausted; and some thought it did so survive the exhaustion, that it went not out so much for want of Air, as Fuel; the Brimstone appearing, when we took off the Receiver, either to have been consumed by the fire that fed on it, or to have casually run off from the Iron, whose heat had kept it constantly melted.  
☞ In case you should have a mind to prosecute Experiments of the nature of this and the precedent, it may not prove useless, if I intimate to you the following Advertisements. 1. For the red-hot iron above mentioned we thought it not amiss to provide, instead of the melting-pot employed in the first experiment, a Pedestal (if I may so call it) made of a lump of dried Tobacco-pipe-clay, that the vehement heat of the iron might neither fill the Receiver with the smoke of what it leaned on, nor injure the Engine, if it should rest immediately upon that: And this Pedestal should be so placed, that the iron may be as far, as you can, from the sides of the Receiver, which else the excessive heat would endanger.  
2. To the abovementioned concave iron, that was to receive the Brimstone, we did for some occasions cause to be fitted a thick convex piece of iron, shaped almost like a flattish Button; which was not to be used constantly, but upon occasion, that, being laid red-hot over the melted Brimstone, it might increase the heat, and keep the flame from having so broad a superficies, whereby it would consume its fuel too fast.  
3. We sometimes thought it expedient, for the clearer discerning of what should happen in the Receiver, to make the experiment by night, and remove the Candles when we were just about to pump, presuming that the flame would be conspicuous enough by its own light; as indeed we found it to be, though its Light were but dim, considering the greatness of the flame; whose colour, though it did not quite lose its wont blewishness, seemed yet to have received a great and somewhat odd alteration.  
4. There is one great inconvenience, scarce avoidable in this Experiment, viz. that the fumes ascending very copiously, do quickly much darken the Receiver, and (if the trial be long continued) line it with a kind of flower of Brimstone, which obscures it much more (and therefore aught to be carefully wiped away whensoever the Receiver is taken off;) upon which account you will not, I presume, wonder, if you shall find the Phaenomena of these Experiments not always to be the very same with what you meet with in this paper: since, as 'tis very possible that we may not have been able to observe things so accurately by reason of the newly mentioned fumes and flowers; so 'tis not impossible, that the difference (if there shall be any) of other men's Observations from ours should proceed from the same cause.  
Before we pass from this second Experiment, it will not be amiss to take notice, that though the flames of Brimstone may be allowed to be somewhat more durable than the flames of Vegetables are wont to be; yet 'tis not safe to conclude, that 'twas merely upon the account of their native vigour, that the flames above mentioned lasted so long in our Receiver.  
For we seemed to observe, that there was requisite a very intense heat of the Iron to make the Sulphur capable of flaming on it, when any considerable proportion of Air was withdrawn. For which reason it seems expedient, according to what I lately intimated, that the Iron, that is to keep it melted, be of a good thickness, that it may the longer retain a competent heat; and we thought, it contributed to the successfullest trials we made, that in them we used, besides the concave iron, the convex one mentioned in the second Note.   

EXPER. III. Of the lasting of the flame of a Metalline substance in the same Vacuum.  
THose Sulphurs that Chemists call Metalline, being supposed by many to be of a much more fixed nature than common Sulphur, and it being indeed probable enough, that in them good store of very minute particles are crowded together, I thought fit to try, whether a body, wherein a vulgar Chemist would think the Sulphur of a metal to be the main ingredient, would afford in our Vacuum, a more vigorous or lasting flame than that of common Sulphur. And though I will not here trouble you with my particular scruples about the Chemist's doctrine concerning metalline Sulphurs, nor with the grounds on which I devised the following inflammable solution of Mars, (for I do not now give it a more determinate name) which some Chemists will not perhaps dislike; I shall here annex the ensuing transcript of the Trial itself.  
Having provided a saline Spirit, which by an uncommon way of preparation was made exceeding sharp and piercing, we put into a vial, capable of containing three or four ounces of water, a convenient quantity of filings of Steel, which were not such as are commonly sold in shops to Chemists and Apothecaries, (those being usually not free enough from rust;) but such as I had a while before caused to be purposely filled off from a piece of good steel. This metalline powder being moistened in the viol with a little of the menstruum, was afterwards drenched with more; whereupon the mixture grew very hot, and belched up copious and stinking fumes; which whether they consisted altogether of the vol tile sulphur of the Mars, or of metalline steams participating of a sulphureous nature, and joined with the saline exhalations of the menstruum, is not necessary to be here discussed. But whencesoever this stinking smoke proceeded, so inflammable it was, that upon the approach of a lighted candle to it, it would readily enough take fire, and burn with a bluish and somewhat greenish flame at the mouth of the viol for a good while together; and that, though with little light, yet with more strength than one would easily suspect.  
This flaming Viol therefore we conveyed into a Receiver, which he, who used to manage the Pump, affirmed that about six exsuctions would exhaust. And the Receiver being well cemented on, upon the first suck the flame suddenly appeared four or five times as great as before; which I ascribed to this, That, upon the withdrawing of the Air, and consequently the weakening of its pressure, great store of bubbles were produced in the menstruum, which breaking could not but supply the neck of the Viol with store of inflammable steams, which (as we thought) took not fire without some noise; upon the second exsuction of the Air the flame blazed out as before, and so it likewise did upon the third exsuction, but after that it went out; nor could we re-kindle any fire by hastily removing the Receiver; only we found, that there remained such a disposition in the smoke to inflammability, that holding a lighted candle to it, a flame was quickly rekindled.   

EXPER. IU. Of the Duration of the Flame of Spirit of Wine impregnated with a metal in the Exhausted Receiver.  
BEcause it may, upon grounds not improbable, be thought, that well-dephlegmed Spirit of Wine being a pure Aethereal liquor, which does not, like combustible Sulphurs (whether vulgar or metalline) emit any visible smoke to stifle the flame (into which it may in the free air be totally resolved;) if this spirituous and thus qualified liquor could be duly associated with a metalline body, the resulting flame might be more than ordinarily vigorous and durable; I resolved to make an Experiment of this sort, and having by a way, that I deliver in another paper, [in a Paradox about the Fuel of Flames] so united highly rectified spirit of Wine with a prepared metal, that they would both afford a conspicuously tincted Flame; we put this mixture into a small Glass-lamp, made on purpose, and furnished with a very slender wieke, which the mixture would not burn whilst there was liquor enough to imbibe it well; and putting this lighted Lamp into a convenient place of a Receiver that was not small, since it was able to contain about two gallons or sixteen pound of water, we made haste to cement on the glass to the Engine, and yet found not in two or three several trials, that, after the Pump began to be moved, so little a quantity of tincted flame in that capacious Glass lasted much (if at all) more than half a minute of an hour (estimated by a minute watch.)  
And, because the Receiver, we then made use of, seemed to me, by reason of its size and some accommodations that belong to it, proper enough to be employed about other trials, concerning the relation between Flame and Air; I thought fit to try with the same small Lamp and liquor, what other Phaenomena of that kind would be afforded by letting Air in and out, according to the various exigencies of my particular aims.  
But not having then, nor in some time after, the leisure and opportunity of setting down things circumstantially, I contented myself to take those short Notes (of the Principal things) whereof I now subjoin the transcript.  
When the flame began to decay, the turning key being now and then drawn almost out, the tincted flame lasted once a minute and a half, and another time longer.  
The turning key being taken out in the beginning, the flame lasted two minutes or better.  
A Pipe bedded in the cement at the bottom of the Glass, and having at each end an open orifice almost of the bigness of that filled by the turning key, which key was then removed from the top; the tincted spirit seemed to burn very conveniently, as if the flame would have burned very long, if we would have permitted it so to do.  
The orifice at the top being stopped with the turning key, though the Pipe were left open at the bottom, it plainly in a short time seemed much to decay and ready to expire; whereupon I caused one to blow constantly, yet but very gently, in at the pipe with a pair of bellows, and by this means, though we did not keep the flame vigorous, yet we kept it alive for above four minutes; and then observing it to be manifestly stronger than it was when we began to refresh it with the Bellows, we ceased from blowing, and found, that though the Glass-pipe was still left open, yet within about one minute the flame was quite extinguished.   

EXPER. V Of the Conservation of Flame under water.  
THe better to examine the necessity of Air to Flame, I thought fit not only to make the several Trials mentioned in this Paper, whether it would live in a medium much thinner than Air; but also to try, whether it would be able to continue in a medium many hundred times thicker than Air, namely in Water.  
I doubted not but many would think this both an easy and a needless Inquiry, since eminent Writers, both Ancient and Modern, tell us without scruple, that Naptha and Camphire will burn under Water; but I had never the good fortune to be able to make them do so; and may be allowed to doubt, whether these Writers; notwithstanding their confidence, deliver what they affirm upon Experience, not bare Tradition. And though in celebrated Authors I have met with divers Receipts of making Compositions that will not only burn under water, but be kindled by it; yet I have found those, I had occasion to consider, to be so lamely or so darkly (and some of them I fear so falsely) set down, that by the following composition, how slight soever it may seem, I have been able to do more than with things they speak very promisingly of; since, though 'twill not be kindled by water, yet being once kindled it will continue to burn under water.  
And that there might be no suspicion, that whilst the mixture continued under water, it did only as it were vehemently ferment, or suffer a violent agitation of its parts without having them kindled, till in their ascending they were actually fired by the contact of the air, incumbent on the surface of the water; To obviate this suspicion (I say) we were careful to try the Experiment, not only in other Vessels, but in a large Glass, the transparency of whose sides, as well as that of the contained water, would permit us to see for a while the burning of our composition, which was sometimes with a weight detained, and sometimes with a Forceps held, till 'twas consumed, a good way under the surface of the Water.  
The way of making the Experiment is this: We took of Gunpowder three ounces, of well  Charcoal one drachm, of good Sulphur or flower of Brimstone a little less than half a drachm, of choice Salt-petre near a drachm and half: Which Ingredients being well reduced to powder, and diligently mingled without any liquor; either a large Goose-quill, whose feathery part was cut off, or a piece of a Tobacco-pipe of two or three inches long, and well stopped at one end, had its cavity well filled with this mixture, (instead of which, beaten Gunpowder alone might serve, if it did not operate too violently, or waste too soon:) For the kindling whereof, the open orifice of the Quill or Pipe was carefully stopped with a convenient quantity of the same mixture, made up with as little Chemical Oil or Water, as would bring it to a fit consistence. This Wildfire was kindled in the Air, and the Quill or Pipe, together with a weight, to which 'twas tied to keep it from ascending, was slowly let down to a convenient depth under water, where it would continue to burn, as appeared by the great smoke it emitted, and other signs, as it did in the air; because the shape of the Quill or Pipe kept the dry mixture from being accessible to the water (that would have disordered and spoiled it) at any other part than the upper Orifice; and there the stream of kindled matter issued out with such violence, as did incessantly beat off the neighbouring water, and kept it from entering into the cavity that contained the mixture, which therefore would continue burning till 'twas consumed.  
'Tis probable, that most men will conclude from this Experiment, that Air is not so absolutely necessary to the duration of Flame, as some other of our Trials seem to argue; and that there ought to be a difference made between ordinary Flames, and those that burn with an extraordinary vehemency. But my design being, as I long since intimated, rather to relate Trials than debate Hypotheses, I shall only add, that it may be pretended on the behalf of the opinion that this experiment seems to disprove, that, not to mention the Air that may lurk in the Pores of the Water, or that which may be intercepted between the little grains of Powder whereof the mixture consists, the Salt-petre itself may be supposed to be of such a texture, that in its very formation the corpuscles, that compose it, may intercept store of little aereal particles between the very minute solid ones which those Corpuscles are made up of. And this inexistence of the Air in Nitre may be probably argued from the great windiness of the flame that is produced upon the deflagration of Nitre. According to this surmise, though our mixture burns under water, yet it does not burn without air, being supplied with enough to serve the turn by the numerous eruptions of the aereal particles of the dissipated Nitre itself.  
On this occasion I remember, that in another Paper I relate, that for divers purposes, and among them to remove this suspicion, I successfully tried to reproduce Nitre in Vacuo Boyliano, that there might not be any Air, or at least any quantity worth heeding, intercepted between the convening particles, that by their coalitions made up the nitrous Corpuscles, which in favour of the necessity of Air to Flame may be pretended to be but so many little empty bubbles close stopped, whose moister parts may be the fire that kindles the nitre be exceedingly rarified, and in that estate emulate air, and violently burst their little prisons, and throw about the fragments of them with force, and in numbers enough to make their aggregate appear such a flame, as is wont to be made by unctuous and truly combustible Bodies; and yet this rarified substance, that thus shatters the nitrous particles, may really be no true and lasting air, but only vehemently agitated vapours, which presently, upon the cessation of the hear, return to liquor; as we see, that the vapours of an Aeolipile, that issue out after the aereal Particles have been expelled, though they make a great noise and a temporary wind near the hole they stream. out at, and would perhaps, if that hole were close stopped, break the Aeolipile; yet are not true and permanent Air, but at a small distance off the Instrument return into water.  
But though I could suggest other suspicions and conjectures about the inclusion of Air between the particles of Salt-petre; yet I forbear to mention them in a Writing designed to be chief Historical.   

EXPER. VI Relating an odd Phaenomenon about the Flame of a Metal in our Vacuum.  
TO the foregoing Experiments made on purpose, I shall add a Phaenomenon afforded us by chance, and yet not unworthy to accompany the rest.  
Whilst we were trying to kindle something in our exhausted Receiver, it happened by some accident or other, that the combustible substance, that was to be kindled, fell besides the iron, whereby our intended trial was defeated. But whilst we were considering what was to be done on this occasion, and had not yet let in the Air that had been pumped out, the lights also continuing yet removed; we were surprised to see something burn like a pale bluish Flame almost in the midst of the cavity of the Receiver, and at first suspected it to be some illusion of the eyes; but all the bystanders perceiving it alike, and observing that it grew very broad, we looked at it with great attention, and found it to last much longer, than, I remember, I have seen any flame do in an Exhausted Receiver. I should have suspected, it had proceeded from some Brimstone, sticking, without our heeding it, to some part of the iron, which we had formerly employed to kindle Sulphur in our Receiver, had it not been that, besides other things, I remembered, that we had just before kept it red-hot in the fire, and consequently must have burned away any little Brimstone, if there were any that adher'd to it: But though we much wondered, whence this our Flame proceeded, I would not let any thing be done that might hasten its extinction; and at length, when it expired of itself, we let in the Air, which had been till then kept out, and perceived upon the concave part of the iron (which we judged to be the place where the flame had appeared) a piece of melted metal, which we concluded had been fastened to the string, that the fuel we designed to kindle had been tied to, in order to the letting it down the more easily: And this made us conceive, that the string happening to be burned by the excessive heat of the iron, the piece of metal fell into the cavity of it, and, by the same heat, the more combustible part, which the Chemists call the Sulphur, was melted and kept on fire, and continued burning so long as we have related. The piece of metal was judged to be Lead, but having not formerly observed such a disposition in that metal to be inflamed, I considered it attentively, and perceived, that 'twas some Fragment, that the Operator had chanced to light on, of a mixture of Lead and Tin that I had (a while before, for an Experiment not at all belonging to our present subject) caused to be colliquated in a certain proportion. Upon whose account it seems, the mixture of the ingredients had acquired such a new texture, as, whether by making the bodies open one another, or by what other means soever, fitted the mass to afford us the Phaenomenon above recited. And though I made an unsuccessful Trial with a mixture of Lead and Tin to produce such a flame upon the heated Iron in the open Air; yet the newly related experiment may suffice to argue, that there may be Flames of metalline Sulphurs (as the Chemists call them) that will be at least as easily produced without the concurrence of the Air, as that of common Sulphur, and continue to burn in our Vacuum longer than it.    

THE THIRD TITLE.  
Of the strangely Difficult PROPAGATION OF Actual Flame IN VACVO BOYLIANO.   

THE THIRD TITLE. Of the strangely difficult Propagation of Actual Flame in Vacuo Boyliano.  
I Have more than once observed, that some bodies (whereof I make particular mention in another Paper) though they will not be turned into Flame by very intense heats, and those of very differing kinds, are yet very readily kindled by an actual Flame. So that the Propagation of Flame to contiguous bodies, that, according to the hitherto observed and unquestioned course of things, must thereby in a moment, as it were, be actually inflamed, seems to be not only very easy, but almost infallible: And yet, that this propagation is not easy, or is perhaps scarce possible to be performed without the assisting presence of the Air, may be gathered from the next following Experiments: At whose titles though you will probably be surprised, in regard that by the two first Experiments of the first Title of this Tract it will scarce be expected, that Sulphur should be kindled in our Vacuum; yet I presume your wonder will cease, when I put you in mind, that I formerly took notice to you of my having sometimes met with such Sulphur, as would be kindled there; and 'twas, whilst that well-disposed parcel of Sulphur lasted, that I took the opportunity of making with the flame of it the Trials, to which I now proceed.  

EXPER. I. An ineffectual attempt to make Flame kindle Spunck in an Exhausted Receiver.  
HAving placed the often mentioned Cylindrical plate of iron, first brought to be red-hot, in a Receiver, capable of containing two Gallons of water; and having also diligently pumped out the Air, we kindled a little Sulphur upon the heated plate, and then a piece of dried Spunck, tied to a string, was, by the help of a turning key, let down to the Flame; and when the Experiment was finished, and the Spunck was taken out, we found it in divers places not manifestly altered so much as in colour; and in those parts, that had been most exposed to the Flame, it was turned to a substance very differing from ashes, being black and brittle as tinder, and, like it, exceedingly disposed to be kindled upon the touch of Fire.   

EXPER. II. An unprosperous attempt to make Flame kindle Camphire without the help of Air.  
AS a farther confirmation of the difficulty of propagating Flame in our Vacuum, we may annex the following Trials.  
Into the lately mentioned Receiver we conveyed the Cylindrical plate of iron, made use of in the former Experiment; and when the Air had been diligently pumped out, we did, by the help of the turning key, let down upon the hot iron a piece of such brimstone, as would, in spite of so disadvantageous a place, be kindled with that heat. A little above this Sulphur we had tied to the same string a piece of Camphire, that being a body exceedingly apt to take fire, if not (as it were) to draw it, at the flame of lighted Brimstone. But our Sulphur, melting with the heat of the iron Cylinder, dropped unluckily from the string 'twas fastened to before, and for the most part fell off. And as soon as it came to the ground, where it was distant from the vehement heat of the metal, the flame expired, and that part of the Sulphur, that happened to stick to the side of the iron, was inflamed by it: And I, that chanced to be then in an inconvenient posture for seeing the Camphire, could not, because of the smoke of the extinguished Brimstone, well discern what became of it. But my Amanuensis, that happened to be on the best side of the Receiver, affirmed, he plainly saw the Flame of the Brimstone reached the Camphire, without being able to make it flame. Which seemed the less to be doubted of, because the Camphire was by help of the turning Key let down low enough, and if it had afforded a flame, the difference of Colours betwixt that and the blue flame of Sulphur would have made it very easy for me to have distinguished them.  
Another trial I would have thoroughly made to kindle one piece of Sulphur in our Vacuum by the flame of another, tied a little lower in the same string, that it might first touch the heated iron, and be thereby set on fire; but, though we could find nothing that was visibly amiss in the kind of Sulphur we then used, yet we were not able even by a reiterated trial to make it take fire upon the iron, where nevertheless it melted and seemed a little to boil.  
A third Trial was not so unsuccessful; for having in the well-exhausted Receiver let down upon the very hot iron a match, made of a piece of Card dipped in Brimstone, the lower extreme of it was kindled by the contact of the hot iron. But though the sulphurated part of the match thus flamed away, yet the remaining part, which was a mere piece of Card, was not thereby turned into flame, nor in most places so much as sensibly scorched or blacked; though (as I remember) the match had been purposely dried beforehand to facilitate its inflammation.   

EXPER. III. A strange Experiment upon Gunpowder, showing, that though it were fired itself, yet would not fire the contiguous grains in Vacuo Boyliano.  
THe preceding Trials may suffice to manifest the difficulty of communicating Flame, without the help of Air, from one body to another, even when the bodies to be kindled are of a very inflammable nature. But because there is no propagation of Flame made in any bodies that we converse with here below, with any thing near such Celerity as in the contiguous grains of Gunpowder; a great heap whereof will, almost in the twinkling of an Eye, be turned into Flame by propagation from any one small kindled grain; nothing seemed fit to manifest how much Flame is beholden to Air, than if such an Experiment could be made, as might show, that, even amongst the contiguous grains of kindled Gunpowder, Flame would not be propagated without the help of Air. How far a trial of this nature may be made in our Engine, the following Narratives will best declare.  
We took some Paper, and laying it upon some convenient part of the plate of the Engine, we made upon it a train of dry Powder as long as the glass would well cover; then, carefully fastening on the Receiver with good Cement, we solicitously pumped out the Air; which done, we took a good Burning-glass, and about noon cast the Sunbeams through it upon the train of some Gunpowder: where, though the indisposition to accension was so great, that the powder did not only smoke but melt without going off, and the Operator (though versed in such Experiments) would not allow that it would signify any thing to continue the trial any longer; yet upon my being obstinate to prosecute it, he, being willing to follow the Experiment, rationally considered, that the Receiver, we had been hitherto fain to use, was so opacous as to resist the entrance of many of the beams that should have their operation upon the Powder: whereupon taking a finer glass that was lately come in, we laid by the former, and employed that, which, by reason of its transparency, so little weakened the beams of the Sun, that being according to my direction held obstinately upon the same parts of the train, they were able to fire several of them one after another. But though the Sun could thus kindle the Powder, yet it could not make the flame propagate, but only those parts that were melted did at length kindle and fly away, leaving the rest unalter'd, as I curiously observed, finding several little masses of colliquated matter in several places of the train, with the Powder unchanged in all the other parts of the same train that lay in a direct line; besides that some of the little colliquated masses were contiguous to the rest of the Powder, which appeared unchanged, and kindled readily, and flashed all away as soon as I caused the Burning-glass to be applied to it in the open Air.   

EXPER. IU. Reciting another Attempt to confirm the former.  
FOr further Confirmation of so odd an Experiment, I shall also add a short account of another made with Gunpowder in our Vacuum.  
To try on an occasion, that need not here be discoursed of, whether by the help of one of those little instruments that are now used at London to examine the strength of Powder, we could find any difference made by the absence and presence of the Air, in the resistance of the Instrument, or the effects of the Powder on it; we fastened it to a competently heavy and commodiously shaped weight of Lead, and when 'twas carefully filled and primed with Powder, we placed it in a Receiver of a convenient bigness, whence we pumped out the Air after the usual manner, and perhaps with more than usual diligence. But though at length, after the Powder had long resisted the beams of the Sun concentrated on it by a good double convex Burning-glass, it did, as I expected, take fire at the Touchhole, and fill the Receiver with smoke; yet this kindled Powder could not propagate the flame to that which was in the box, how contiguous soever the two parcels were to one another. And when the instrument was taken out into the Air, (by which it appeared how free the Touchhole was,) as soon as ever new-priming with the same sort of Powder was put to it, the whole very readily went off: And when, for further satisfaction, we caused the instrument to be new charged, and upon its taking fire only at the Touchhole in the exhausted Receiver, we ordered new-priming to be added without so much as taking the instrument out of the Receiver, though afterwards the Receiver was closed again, but without being exhausted of Air; the Powder, though closely shut up in the Glass, did readily go off, as well that which was in the box or cavity of the Powder-tryer, as that which lay on the outward part of the Instrument. And this trial, for the main, was repeated with the like success.   

EXPER. V Briefly mentioning two differing Trials with two differing Events, to kindle Gunpowder in our Vacuum.  
YOu will easily believe, that the event of the foregoing trials seemed strange enough to the ingenious persons, that I had desired to be present at them; and perhaps the attentive consideration of it may well enough suggest such odd suspicions and conjectures, as I have neither the leisure nor the boldness to discourse of in this place.  
But here I shall not dissemble my having, by a somewhat differing way, made a couple of trials, whereof though the first may confirm the great indisposition of Gunpowder to be kindled in our Vacuum, yet the second seems to look another way.  
The first is summarily set down in my Notes to this purpose. [A few small corns of Gunpowder, being included in a very small bubble freed from its Air, and secured against the return of it, or any other, and then applied warily to Coals covered with Ashes; did not go off nor burn, but afforded a little yellow powder that seemed to be Sulphur, and sublimed to the upper part of the glass.]  
The Latter's event I found in the same paper to have been thus registered. [But two larger Bubbles though strong, whereof one had the Air but in part, and the other carefully emptied; being provided each of them with a greater quantity of Powder (though scarce enough to promise such an effect) a while after they were put upon quick Coals, each of them was blown in pieces with a Report almost like that of a Musket; but, though this was done in a dark place, yet we did not perceive, whether or no there were any real flame produced.]  
The event of this Trial seems at first sight to contradict the inference, that probably you have drawn from the foregoing Experiments. But yet it may not be unworthy of our inquiry, whether this way of trial be as proper to give satisfaction to the curious, as that, made with the Sunbeams, was. And I leave it to be considered, whether or no it may not be doubted, whether the going off of the Gunpowder was caused by a successive, though extremely swift, propagation of real Flame, from the first kindled grains to the rest; or did not proceed from this, That the coals acting strongly at the same time on the whole Area or extent of the powder that was next to them, and this in the absence of the Air, each grain was in that case, as 'twere, a little Granado, and the heap of them being uniformly enough acted on by the fire, they were made to go off, as to sense, all at once, as if there had been but a contemporary Explosion made of them all together by the action of the external fire, rather than any true Accension made by the flaming grains of the unkindled ones. As I remember I have tried, that even in the open air one may, with a Burning-glass dextrously employed, make some part of a little parcel of Aurum fulminans go off, whilst the neighbouring parts of the same parcel, to which the focus does not extend with heat enough, will not be made to do so.    

NEW EXPERIMENTS About the Relation betwixt AIR AND THE FLAMMA VITALIS of Animals.  
(Sent to the same Person to whom the former Papers were addressed.)   

NEW EXPERIMENTS About the Relation betwixt Air, and the Flamma Vitalis of Animals.  
(Sent to the same Person to whom the former Papers were addressed.)  
THe xx. Experiments hitherto set down under the three foregoing Titles, by showing the Relation betwixt Air and Flame in general, may be serviceable to the Inquirers into the nature of the Vital Flame in particular. But yet having had occasion to make some trials, that more directly regard the requisiteness of Air to the Flamma Vitalis or Vital Principle of Animals; I shall now present you by themselves as many as I could light on, without being solicitous that they should be quite differing from each other; because in so new and nice a subject, the affinity that may be found between some, either in regard of the subjects exposed to trial, or in the manner of making it, may be useful, if not necessary, to confirm things by the resemblance of Events, or make us proceed cautiously and distinctly in pronouncing upon cases where the success was not uniform.  

EXPER. I. Where in the Durations of the Life of an Animal, and of the Flame of Spirit of Wine, included together in a close Vessel, were compared.  
WE took some highly rectified Spirit of Wine, and put about a spoonful of it into a small Glass-lamp, conveniently shaped and purposely blown with a very small orifice, at which we put in a little Cotton-wieke, which was but very slender.  
We also provided a tall Glass-Receiver, which was in length 18 inches, and contained above twenty pints of water. This Receiver, which was open at both ends, was at the upper orifice (which was not wide) covered with a Brass-plate, fastened on very close with good cement, for uses whose mention belongeth not to this place; and for the lower orifice, which was far the widest, we had provided a Brass-plate furnished with a competent quantity of the cement we employed to keep the Air out of the Pneumatical Engine; by means of which plate and cement we could sufficiently close the lower orifice (though a wide one) of our Receiver, and hinder the Air from getting in at it.  
These things being thus prepared, we took the small Glass-lamp above mentioned, and having lighted it, we placed both it and a small Bird (which was a Green-finch) upon the Brass-plate, and in a trice fastened it to the lower orifice of the Receiver, and then watched the event; which was, that within two minutes (as near as we could estimate by a good minute-watch) the flame, after having several times almost quite disappeared, was utterly extinguished; but the Bird, though for a while he seemed to close his eyes as though he were sick, appeared lively enough at the end of the third minute; at which time, being unwilling to wait any longer by reason of some avocations, I caused him to be taken out.  
After he had for a pretty while, by being kept in the free Air, recovered and refreshed himself, the former trial was repeated again, and at the end of the second minute the flame of the Lamp went out; but the Bird seemed not to be endangered by being kept there a while longer.  
After this, we put in together with the same Bird two lighted Lamps at once, (viz. the former and another like it) whose flames, according to expectation, lasted not one whole minute before they went out together. But the Bird appeared not to have been harmed, after having been kept five or six times as long before we took off the Receiver.  
In the tall Receiver  we included a Mouse, with a lighted Lamp filled with the Spirit of Wine; but before the Experiment was near finished, the Mouse, being at liberty within the Glass, made a shift to blow out the flame; which being revived without taking out either the Lamp or the Animal, the Spirit of Wine burned about a minute longer, during which time the Mouse appeared not to be grown sick, no more than it did afterwards, when for some minutes, after the extinction of the flame, he had been kept in the same close and infected Air.  
Afterwards we placed the same Mouse in another Receiver, which seemed to be by a third part less capacious than the former, and in it we also fixed a piece of slender Wax-candle, such as is wont to be made up in Rolls, (and employed to light Tobacco.) This Candle continued burning in this new Receiver but for one minute, during which time it emitted store of smoke; but this not hindering the Animal to appear lively enough, even after we had kept him much longer in that infected Air, the same Candle without being taken out was lighted again, but burned not so long as before; yet it sufficed to darken the Receiver, and therefore probably much to clog the included Air, in which nevertheless the Mouse being kept, by our guess, eight or ten minutes longer, he appeared, neither when he was taken out, nor a while before, to have received any considerable harm by his detention there.   

EXPER. II. Of the Duration of the Life of a Bird compared with the lasting of a burning Candle and Coal in our Vacuum.  
WE took a Green-finch and a piece of Candle of twelve to the pound, and included them in a 〈◊〉 capped Receiver, capable of 〈◊〉 about two Gallons or sixteen pound of water, which was very carefully cemented on to the Pump, that no Air might get in or out. In this Glass we suffered the Candle to burn till the flame expired, (which it did, in more than one Trial, within two minutes or somewhat less;) at which time the Bird seemed to be in no danger of sudden death; and, though kept a while longer in that clogged and smoky Air, appeared to be well enough when the Receiver was removed. Afterwards, we put the same Bird into the Receiver with a piece of a small wax Taper, whose flame though it lasted longer than the other, yet the Bird outlived it; and 'twas judged he would have done so, though the Flame had been much more durable. After this, we included the same Bird with the first-mentioned Candle in the Receiver, which we had caused to be often blown into with a pair of Bellows, to drive out the smoke and infected Air; and then beginning to pump out the Air, we found, that the Flame began more quickly to decay, and the Bird to be much more discomposed than in the former Experiments; but still the Animal outlived the Flame, though not without Convulsive motions. The Experiment we repeated with a piece of the forementioned Taper, and the same Bird, which, though cast into threatening symptoms upon the gradual withdrawing of the Air, outlived not only the Flame, but the smoke too that issued from the kindled Wieck; which circumstance was also observed in the preceding Trial.  
Lastly, having freed the Receiver from smoke, and supplied it with fresh air, we put in with the same Bird a piece of Charcoal of about two inches in length, and half an inch in breadth, which had been, just before 'twas put in, well blown with a pair of Bellows, that it might be freed from ashes, and thoroughly kindled; and made haste to pump out the air. This diligence was continued not only till none of the fire could be discerned by any of the Bystanders, but till, in our estimation, (which the event justified) it was irrecoverable by the admission of the outward air; which at its coming in found the Bird very sick indeed, but yet capable of a very quick Recovery. And this Experiment was, with the same Animal and Coal rekindled, tried over again with the same success.  
Whether this survival of Animals, not only to a flame that emits store of fuliginous steams, as in this trial; but to that which is made of so pure a fuel as Spirit of Wine, that affords not such steams (as in the former experiment;) Whether, I say, this survival proceed from this, That the Common flame and the Vital flame are maintained by distinct substances or parts of the Air; or that common Flame making a great waste of the Aereal substance, they both need to keep them alive, cannot so easily as the other find matter to prey upon, and so expires, whilst there yet remains enough to keep alive the more temperate Vital flame; or that both these causes, and perhaps some other, concur to the Phaenomenon, I leave to be considered.   

EXPER. III. Of what happened to the Light of Glowworms in the Exhausted Receiver.  
FOr the sake of those Learned men, that have thought the Light of Glowworms and other shining infects to be a kind of effulsion of the Biolychnium, or vital Flame, that nature has made more Luminous in these little Animals than in others; and which a very eminent Physician of the College of London affirms to have felt in a warm climate more than sensibly hot; I shall subjoin on this occasion some trials made on Glowworms, which else should be referred to those Experiments of mine about the Relation betwixt Air and Light, that you were formerly pleased to publish.  
We took two Glowworms, that shone vividly enough, especially one of them, whose Light appeared strong and tincted as if it had been transmitted through a blue Glass: These we laid upon a little plate, which we included in a small Receiver of finer glass than ordinary, that we might the better see what would happen: And having for the same purpose removed the Candles, that no other Light might obscure that of the Infects, we waited in the dark till that was conspicuous, and then ordered the Air to be begun to be pumped out; and, as we expected, upon the very first exsuction there began to be a very manifest diminution of the Light, which grew dimmer and dimmer, as the Air was more and more withdrawn, till at length it quite disappeared, though there were young Eyes among the assistants. This darkness having been suffered to continue a long while in the Receiver, we let in the Air again, whose presence (as we looked for) restored at least as much Light as its absence had deprived us of. This experiment was repeated with one more of those infects; and the event was, that they all three gradually lost their Light by the Exhaustion of the Receiver, and regained it (with some increase, as was judged) by the return of the Air. And in this Experiment we let in the Air by degrees, and with an interval or two, to observe, as we did, that, as the diminution of Light was greater and greater when the Air was more and more withdrawn, so the returning splendour was gradually increased as we pleased to let in more and more Air upon the worms.   

EXPER. IU. Containing a variation and improvement of the foregoing Trial.  
BUt here I foresaw, it might be suspected, that the disappearing of the Light in our Exhausted Receiver did not so much proceed from any real, though but temporary, extinction or eclipse of it, as from this, that the Glowworms having, as I have often observed, a power of drawing the luminous part into the opacous part of their body, they might, finding themselves prejudiced by the withdrawing of the Air, hid their Light from our Eyes, without losing it, till being again refreshed by the return of the Air, they might be invited to protrude it again into the transparent part of their tails. This scruple seeming grounded upon the nature of the thing, I thought it worth while to remove it by the help of another observation, that I long since made and have mentioned elsewhere about Glowworms. Which is this, that, if they be killed whi●t they are shining, their luminous matter may continue to shine for a good while after 'tis taken out of their bodies; and accordingly having put some of that, we took out of the forementioned infects, upon a little paper, and included it in the Receiver we employed, the Candles being removed, we perceived it to shine vividly enough before the Pump was set on work, and afterwards to grow dimmer and dimmer, as the Air was more and more drawn out, till at length it quite vanished; and it re-appeared immediately upon the Air's return. This experiment was reiterated twice more with the same success for the main. But we took notice, that the luminous matter, after the Air was let in, seemed to us not only to have regained its former degree of Light, but sensibly increased it, (as it once happened also in the Experiment made on the living worms;) which whether it was caused by any real change made by the recess and access of the Air in the matter itself, or by the greater accustomance of our Eyes to the darkness of the place, I dispute not; and shall only add this Phaenomenon of one of our trials, that having a mind to see, whether a very little proportion of returning Air would not suffice ●●●●store some little Light to the disappearing matter; it was 〈…〉 strange to observe, that so 〈…〉 a quantity of Air, as was 〈…〉 fore the Light was revived, 〈…〉 enough to make it become p●a●●ly 〈◊〉 sible though but dim: In 〈…〉 state it continued, till we thought ●it to let in more Air upon it. (Farther trials I could not make 〈◊〉 these Glowworms, having received them but that night out of the Country, and being the next morning to begin a journey.)   

EXPER. V Wherein the former Inquiry is farther prosecuted.  
AFter the lately mentioned Trials we made with the Glowworms, having procured two or three other of those infects, whereof one was judged to be as large as three ordinary ones, we found, when we had brought them out of the Country to London, that this great worm was dead, as far as we were able to judge, and finding him to retain a considerable degree of luminousness in the under part of his tail, we put him into the small Receiver formerly mentioned, to try, whether, after the death of the animal, the shining matter would retain its former properties; but at the first time the Air was pumped out after the usual manner, the light was not only not abolished, but continued vivid enough, and so it did, when the Air being let in and again withdrawn, the trial was made a second time. But being unwilling to abandon the Experiment till we tried it yet further, I caused the Receiver to be exhausted yet once or twice more, and at length I perceived, that the Light began to diminish, as the Air was withdrawn; and last of all it so disppeared that the bystanders could not see it, whereas upon the readmission of the Air the Light shone vividly as before, if not more bright. This Experiment was reiterated with the like success, and in both these times the like happened to the Light of the dead one and of a living one that we included with it, to be able to compare them together; though there were this disparity betwixt them, that the luminous part of the dead worm was much larger than that of the living, and the Light of the later appeared of a very greenish blue, whereas that of the former seemed to be of a white yellow.   

EXPER. VI Made to examine whether Animals be heavier dead than alive.  
'TIs a received Tradition, that bodies when dead are much heavier than the same were when alive; the matter of fact being taken for granted, some will perhaps ascribe the change to the utter inability of a dead body any way to assist those that endeavour to remove it. But, according to the general opinion, this difference proceeds from the total extinction or recess of the spirits vital and animal, which being supposed to be not only agile but light, lessened the weight of the body they enlivened; and Flame being conceived to be the lightest among bodies here below, 'tis not improbable that some will ascribe the Phaenomenon to the levity of the Flame, which by being diffused through the body of an Animal, and vivifying it, deserves the name of Vital. But I would not advise any to rely on this conceit, till they are duly satisfied of the truth of the matter of fact, which because I have not yet found that any has endeavoured to try, I shall on this occasion give you the following transcript of one of my Notes about Statical Experiments.  
A Mouse weighing about three drachms and a half, being put in one of the scales of a very nice balance, was counterpoised together with a string that was tied about his neck like a noose, and after a while by drawing the ends of it was there strangled. As soon as we judged him quite dead, we weighed him again, and though nothing was seen to fall from him; yet, contrary to the received Tradition, that Bodies are much heavier dead than alive, we found the weight to have lost about 7/16 of a grain; which probably proceeded from the avolation of divers subtle particles upon his violent and convulsive struggle with death. But this was no more than an Experiment of this kind, made some years ago, induced me to expect and foretell.  
Afterwards in a larger Balance, but a very good one, purposely made for nice Experiments, we took a very young Catlin, of between 10. and 11. ounces in weight, and caused him to be strangled on the same scale, wherein he had been put. But he could not be dispatched so soon as an ordinary full grown animal; so that by that time he was quite dead, we found him not only not to be grown heavier but lighter by four grains; which did not much surprise us, having elsewhere noted the life of so very young Creatures of that kind not to be easily destroyed for want of Respiration. And I remember, that, for trial's sake, another Catlin of the same Litter with this I have mentioned, being included in a Receiver, wherein another Animal of that size might probably have been dispatched in two or three minutes, by the pumping out of Air, was kept there somewhat above a quarter of an hour before he appeared to be quite dead.    

ADVERTISEMENT.  
THese two following Attempts falling into the hands of the Author after the preceding Experiments were printed, it was thought fit to annex them here for the affinity of the subject.  
Place this after Page 130.   

An ATTEMPT To produce Living Creatures in Vacuo Boyliano.  
IN reference to the Opinion of those Naturalists, that hold the Seeds of Living Creatures to be animated, and especially to the Hypothesis of those Learned men that assert the Flamma Vitalis lately mentioned; it may be an inquiry of moment, Whether or no in the Seminal Principles, or Rudiments of Animals, the manifest operations of Life may be excited without the concurrence of the Air, whose interest in the production and conservation of Flame may be gathered from the foregoing Experiments. For, it seems likely to prove no inconsiderable discovery in reference to the lately mentioned Hypothesis, if it be found, that the Principle of Life in Seminal rudiments needs, as well as other Flames, the concurrence of the Air to actuate it.  
I thought fit therefore, notwithstanding the great and almost insupeperable difficulties, which 'twas easy enough for me to foresee I should meet with, to attempt the hatching of Eggs in our Vacuum; but though I made some unsuccessful trials of this kind in order to a discovery about Respiration, (not here to speak of the attempts I made about the animation of putrid matter,) yet leaving the mention of them to its proper place, I shall only take notice in this what directly concerns the present inquiry. Considering then that pregnant females cannot be made to live and bring forth young in our exhausted Receiver, and that the Eggs of Birds and such greater animals do in this colder climate of ours require to be hatched by the incubation of the females (or other Birds;) I thought the fittest subjects, I could both make choice of and procure for the designed Experiments, would be the Eggs of Silkworms: For, having many years since tried several things about those Infects, and among others found, that their Eggs would be hatched, not only by the heat of ones body, though that be the usual way, but by the warmth of the Sun even here in England, if they be kept till the Spring be far enough advanced: Remembering this (I say) I got a good number of Silkworms Eggs; and having caused three conveniently shaped, but very small, Receivers, to be purposely made, that differed very little (and that accidentally) either in size or figure, we conveyed into each of them, together with a small stock of Mulberry-leaves, such a number of Eggs as we thought sufficient to make one morally secure, that at least some of them were prolific; this done, we carefully exhausted one of them, and secured it against the return of the Air; the two others we left full of Air: But having left in one, a little hole for the Air to come in and get out at, we stopped the other so close, as to hinder all intercourse between the included Air and the External. All things being thus pnepared, we exposed the Receivers to a South-window, where they might lie quiet, and where I either came, or sent to look on them from time to time; the spring being then so far advanced, that I supposed the heat of the Sun would be of itself sufficient to hatch them in no long time.  
As to the success of this trial, my not being able to find any register of the particular Phaenomena that occurred, keeps me from venturing to relate it very circumstantially; but this I remember in general, that both I and others took notice, that in the unexhausted Receivers there were divers Eggs hatched into little Infects that perforated their shells, and crept out of them; though afterwards for want of change of Food, or Air, or both, few or none of them proved long-lived. But though the Eggs in these Receivers began to afford us little animals in a few days; yet the Eggs in the exhausted Receiver did not, in many more, afford us any. And though I will not venture to say how long precisely we kept them in the same window, after some of the abovementioned Eggs were hatched; yet (if I much mistake not) 'twas (from first to last) about three or four times as long; and I remember, we kept them till it was thought to no purpose to wait any longer, and agreed in imputing the not hatching of the Eggs by the so long continued action of the Sun to the absence of the Air.  
What other Phaenomena occurred to us in making this Experiment, and another not unprosperous one upon the Eggs of Flies, you may expect, when I can light on my Notes about them, or have my memory refreshed by those that assisted at the making of them.  

An ATTEMPT Made upon Gnats in our Vacuum.  
I Elsewhere mention that it has been observed, by a couple of our Virtuosos (whom I there name,) and several times by Me, that (here in England) multitudes of Gnats are generated of little animals that live, for a part of the Summer, like Fishes in the water; and considering, that by these a very unusual passage is made from Swimming to Flying animals, I thought them very fit subjects, whereon to make the following Experiment.  
[Partly to try whether at least an animal already living and moving in our Vacuum may be able to attain the perfection due to it according to the course of Nature; and partly to examine, whether, in case he should attain it, at least the lighter sort of winged Infects may be able to fly in that place; and partly to discover, whether an animal, that had long lived in our Vacuum, would, when turned to a Fly, be able to continue alive without a Respiration, he had never been accustomed to, in its pristine form or state; we took divers of those little swimming Creatures, which, in Autumn, especially towards the end of it, are wont to be turned into Gnats, and having put a convenient number of them together in a fit quantity of Rain-water, wherein they had been found and kept, into a small Receiver, the Air was pumped out, and the vessel secured against its return, and then set aside in a place, where I could observe, that the day after some of these little animals were yet alive and swimming to and fro, not without minute bubbles adhering to them; but at the end of a day or two after that, I could not perceive any of them to survive their dead Companions, nor did any of them recover, when fresh Air was let in upon them. But though this Experiment were the best I was then able to make, yet I resolved, if God should vouchsafe me life and health, to repeat it the ensuing Autumn; that, wherein it was made, proving so cold and unseasonable, that a number of these little Creatures, put up with water into another small Receiver, died all within a few days, though none of the Air was exhausted; and several, that I kept in an ordinary Glass, that was divers times unstopped to give them fresh air, did yet perish at no ordinary rate. And I confess (as unkind as this trouble of mine may seem to the Air;) that the failing of this and some other Experiments of producing Animals in our exhausted Receivers was the more unwelcome to me, because I had and have still a great desire to see, if it be possible, what would happen to Animals, which had been produced in a place free from the pressure of the Atmosphere, as if they had been born in Epicurus' imaginary intermundane spaces, upon their coming to be suddenly surrounded with our heavy Air, and having their tenderly framed bodies exposed to its immediate pressure.    

NEW EXPERIMENTS ABOUT Explosions.  
(Annexed by way of Appendix to the former Papers.)   

NEW EXPERIMENTS ABOUT EXPLOSIONS.  
(Annexed by way of Appendix to the former Papers.)  
FOr as much as some of the Learned men, that are the grand Assertors of the Flamma Vitalis (whose opinion occasioned my presenting you the foregoing Experiments,) do also with the justly famous Doctor Willis explicate many of the motions of Animals, especially those performed in the Muscles, by the Explosions made of certain juices or fluid substances of the Body, when they come to mingle with each other: And for as much also as I do not remember, I have heard the Maintainers of this Hypothesis insist on other instances in favour of it, than the going off of Gunpowder; which being not a liquor but a consistent and brittle body, and requiring for its explosion either Actual Fire, or a far intenser heat than can be supposed natural in Men and other Animals; I was induced to suspect, they were not yet provided with better Examples; and therefore I presume, it will be looked upon as a thing neither useless, nor altogether impertinent, if, without offering to determine any thing about the truth of the opinion, I supply the embracers of it with two or three examples of Explosions made by the bare mingling of liquors; which I shall borrow from the elsewhere mentioned Notes, that I drew up some years ago, in order to the improvement of some parts of Physic.  

EXPER. I. Of an Explosion made with the Spirits of Nitre and Wine.  
WE took Spirit of Nitre, so strong, that the fumes made the upper part of the Glass, it was kept in, always reddish, and having put but one ounce of it into a bolt-head with a long neck, capable to contain, as we guessed, twelve or sixteen times as much, we caused an equal weight of Alkhool (or highly rectified Spirit of Wine) to be taken, and a little of it being put to the Spirit of Nitre, it presently made so strong and quick an expansion or explosion, that some of it flew out of the Glass and hit against the ceiling of the room, (where I saw the mark of it,) and falling upon his face that held the Glass, made him think (as he told me) that fire had fallen upon it, and made him run down the stairs like a mad man to quench the heat at the Pump. Wherefore bidding the Laborant proceed more warily, I ordered him to put into the Bolt-head but part of a spoonful of Spirit of Wine at a time; and yet at each of a pretty many affusions, that I stayed to see the effect of, there would be a great noise, as of an ebuilition, though no store of froth produced, and accompanied with so great a heat that I could not hold the Glass in my hand; and immediately there would issue out a copious and red smoke; to which when I caused a little Candle to be held, though at near half a foot distance from the top of the bolt-head, it would presently take fire, and burn at the top of the bolt-head like a flame at the upper end of a Candle, till I caused it to be blown out, that fresh Spirit of Wine might be poured in; which when it was all mingled with the other liquor, the heat and conflict caused.  
Divers other Phaenomena relating to this Experiment (by which I intended to make out more things than one,) belong not to our present subject, and are already set down in other Papers. But yet 'twill be pertinent to show in this place, that the noise and ebullition produced in this mixture is not unaccompanied with a briskly Expansive or an Explosive motion. To make then an Experiment to this purpose, and yet avoid the danger whereto the making of it unwarily might expose both the vessels and us; we put an ounce of such strong Spirit of Nitre, as is above mentioned, into a moderately large bolt-head furnished with a proportionable stem, over the orifice of which we strongly tied the neck of a thin Bladder, out of which most part of the Air had been expressed, and into which we had conveyed a small Viol, with a little highly rectified Spirit of Wine: Then this Viol, that before was closed with a cork, being unstopped without untying or taking off the Bladder, a small quantity, by guests not a quarter of a spoonful, of the Alcohol of Wine was made to run down into the Spirit of Nitre, where it presently produced a great heat and commotion, and blew up the Bladder as far as it would well stretch, filling also the stem and cavity of the Glass with very red sums, which presently after forced their way into the open Air, in which they continued for a good while to ascend in the form of an Orange-coloured smoke.   

EXPER. II. Of an Explosion made with Oil of Vitriol and Oil of Turpentine.  
IF I had at hand the Papers you have divers times heard me speak of about Heat, I could give you the particulars of some Trials about Explosion, that perhaps you would think more pertinent than despicable; but for want of those Papers I must content myself to tell you in general: That I remember, that I have more than once taken strong Oil of Vitriol and common Oil of Turpentine, and warily mixed them in a certain proportion by shaking them very well together; and that thereupon ensued (what I had reason to look for) so furious an agitation of the minute parts of the mixture, and so vehement or sudden Expansion or Explosion, as did not only seem strange to the Spectators, but would have proved dangerous too, if I had not taken care beforehand, that the Trials should be made in a place where there was room enough, and that even the Operator, that shook the vessel, should stand at a convenient distance from the mixture.   

EXPER. III. About an Explosion made by two Bodies actually Cold.  
I Remember not, that I found the Assertors of Explosions in Animals to have taken notice of a difficulty, which to me seems not uneasy to be observed, and yet very worthy to be cleared. For 'tis known, that Fishes, and those especially of the vaster sort, can move and act in the waters with a stupendious force; and yet it is affirmed by those that pretend to know it, that the Blood of most Fishes is still actually cold: And I remember, I found the blood even of those I dissected alive, to be so. From whence most men would argue, that even in the vast Sea-monsters, there can be made no Explosions, these being still effected by or accompanied with an intense degree of heat.  
'Twere incongruous to my design, to examine this difficulty as it directly regards the Explosions, said to be made in Animals: But speaking of Explosions in general, perhaps I might do the favourers of vital ones (if I may so term them) not unacceptable piece of service, by experimentally showing, that 'tis not impossible, though it seem very unlikely, that Explosions should be made upon the mixture of bodies, which, whilst they seem to put one another into a state of Effervescence, are really cold, nay colder than before their being mingled. Of these odd kind of mixtures, I remember I have in another 
* About the Preduction or Extrication of Air.  paper set down some Trials that I made to other purposes, as well with two liquors as with a liquor and a solid body; which later sort I there mention my having made by an improvement of an experiment of the excellent Florentine Virtuosos. And among those Trials I find one, whose pertinency to the matter in hand invites me to annex as much of it as is proper in this place.  
There were put two ounces of powdered Sal Armoniac into a pretty large Glass-tube Hermetically sealed at one end; into the same a slender Glass-pipe, furnished with two ounces of Oil of Vitriol, was so put, that, when we pleased, we could make the liquor run out into the larger Tube, which, after these things were done, was closed exactly, so that nothing might get in or out. My design was, that this instrument should be so warily inverted, that the Operator might get out of the way, and the Oil of Vitriol, falling slowly upon the Sal Armoniac, should, without producing any heat, produce an explosion not dangerous to the Bystanders. But whilst I was withdrawn to a neighbouring place to write a Letter, the Operator not staying for particular directions, rashly inverted the instrument without taking care to get away: whence it happened, that as soon as ever the contained liquor, being too plentifully poured out, came to work on the Shall Armoniac, wherewith it is wont to produce cold, there was so surprising and vehement an Expansion or Explosion made, that with a great noise, (which, as the Laborant affirmed, much exceeded the report of a Pistol,) the Glasses were broken into a multitude of pieces, many of which I saw presently after, and a pretty deal of the mixture was thrown up with violence against the Operators Doublet and his Hat, which it struck, off, and his face; especially about his eyes, where immediately were produced extremely painful tumours, which might also have been very dangerous, had I not come timely in, and (to add that upon the by) made him forthwith dissolve some Saccharum Saturni in fair water, and with a soft sponge keep it constantly moistened by very frequently renewed applications of the Liquor: By God's blessing upon which means, within an hour or two, the pain, that had been so raging, was taken away, and the fretting Oil of Vitriol was kept from so much as breaking the skin of the Tumours that it had made.  
The first part of the Relation of this trial might have been omitted, or at least shortened, unless I had designed to communicate unto you a way of doing what I do not know to have been attempted by others, namely to put bodies together when and by what degrees one pleases, after the Glass that contains them has been Hermetically sealed up; which Mechanical contrivance, especially as it may be varied, may be, as I have tried, usefully applied to more purposes than 'twere proper here to take notice of.  
But to conclude with a word or two touching the foregoing Experiment; I shall only add, That another time we made a like trial a safer way, by tying a Bladder so to the top of a Bolt-head, into which we had beforehand put the Sal Armoniac, that, by warily moving the Bladder, whence the Air had been expressed, we could make some of the Shall Armoniac, we had lodged in its folds, to fall upon the liquor, with which it presently made an Explosive mixture, that quickly blew up the Bladder.  
But these, Sir, are bare Conjectures, left to be, after a farther discussion, (if you think them worthy of it) determined by You, to whom as these Papers are addressed, so they are also submitted by the Writer of them,  
Who is Sir Your most, etc.    

AN HYDROSTATICAL Discourse Occasioned by The Objections of the Learned Dr. Henry More, AGAINST Some Explications of New Experiments made by Mr. boil;  
AND Now published by way of PREFACE to the Three ensuing Tracts.   

ADVERTISEMENT.  
THis Hydrostatical Discourse (distinguished by small letters for the Signature) is to be placed immediately before the Title, New Experiments of the Positive and Relative Levity of Bodies under Water.   

TO The Reader.  
WHen I determined to write this Polemical Discourse, I did not forget, that when I first ventured some of my trifles abroad into the world, my friends obtained from me a promise that, after I should have answered, the two first that should expressly write against me (which happened to be the Learned Linus and Mr. Hobbs,) to show that I was not altogether unacquainted with a way of defending Truths, I would afterwards write no Book in answer to any, that should come forth against mine; for, not only my friends, but I, thought it enough for a person that never was a Gown-man, to communicate freely his thoughts and Experiments to the Curious, without despairing, that those things, that should be evidently true, would be able to make their own way, and such as were very probable would meet with Patrons and Defenders, in so inquisitive an age as ours. And indeed I do not find, that either upon the account of my Writings, or Ingenious men's opinion of them, I have had much cause to repent the keeping of my promise, notwithstanding the Writings, that have impugned some of mine, but without much prejudice, that I know of, either to the proposed Truths, or the Proposer of them. And therefore I should not at all have entered upon a defence of what is attaqued of mine by the Learned Doctor More, if I had not supposed, that it would not require a Book, but might be dispatched in a Preface: For, having by me some little Tracts, that should, though the Doctor had never engaged me, have been imparted to the Public, and observing, that the new Experiments contained in one or other of them, would 〈◊〉 an easy application be brought to co●●●●● my formerly delivered explications of other Phaenomena, and enervate the Doctor's Objections against them, I thought I might without long troubling the Reader, or myself, defend what I looked upon as Truth, by answering some incidental passages of the Doctor's discourse, and referring the Reader, for the main points in Controversy between us, to those Experiments of the following Tracts, which clearly contain the grounds of deciding them. But yet this Consideration would not perhaps have engaged me to write the following Preface, if the Objections I was to answer had not been, by a Person of so much Fame, proposed, with so much confidence; and though with very great Civility to me, yet with such endeavours to make my Opinions appear not only untrue, but irrational and absurd, that I feared his discourse, if unanswered, might pass for unanswerable, especially among those Learned men, who, not being versed in hydrostatics, would be apt to take his Authority and his Confidence for cogent Arguments; and who (not observing how liberal some men are of titles to the Arguments that please them) would make a scruple of thinking, that what is with great solemnity delivered for a Demonstration in a Book of Metaphysics, can be other than a Metaphysical Demonstration. The Care therefore, that what I judge to be true, should not be made to pass for Absurd, which is a degree beyond what is merely Erroneous, by being so severely handled by a person of Doctor More's fame and Learning, induced me to begin the following Paper, which should have been shorter than now it is, but that I was persuaded to lengthen it beyond what was either necessary or designed, that I might, by the addition of some few thoughts and Experiments on the occasions that were suggested to me, endeavour to clear up and confirm some Hydrostatical Truths, that, I fear, are but by very few either assented to, or perhaps so much as understood, and so might make the Reader amends for the trouble I was forced to give him in a Dispute which I apprehended he might otherwise think himself but little concerned in. And he will, I hope, easily discern, that I have no mind to burden him in my Preface with things not pertinent to the scope of it, if he take notice, that both for his sake and the Learned Doctors, (whose Civility I would not leave unanswered) I have restrained myself to the Defensive part, forbearing to attaque any thing in his Enchiridium Metaphysicum, save the two Chapters wherein I was particularly invaded.  
But though I have declined the delivering my Opinion of the Doctor's Book; yet I dare not forbear owning my not being satisfied with that part of his Preface, which falls foul upon Monsieur des Cartes and his Philosophy. For though I have often wished, that Learned Gentleman had ascribed to the Divine Author of Nature a more particular and immediate efficiency and guidance in contriving the parts of the Universal Matter into that great Engine we call the World; and though I am still of Opinion, that he might have ascribed more than he has to the Supreme Cause in the first Origine and Production of things Corporeal, without the least injury to Truth, and without much, if any, prejudice to his own Philosophy; and though not confining myself to any Sect, I do not profess myself to be of the Cartesian: yet I cannot but have too much value for so great a wit as the founder of it, and too good an opinion of his sincerity in asserting the existence of a Deity, to approve so severe a Censure as the Doctor is pleased to give of him. For I have long thought, that in Tenets about Religion, though it be very just to charge the ill consequences of men's opinions upon the Opinions themselves; yet 'tis not just, or at least not charitable, to charge such Consequences upon the Persons, if we have no pregnant cause to think, they discern them, though they disclaim them. And since men have usually the fondness of Fathers for the Offspring of their own Brains, I see not, why Cartesius himself may not have overlooked the bad inferences, that may be drawn from his Principles, (if indeed they afford any such,) since divers Learned and not a few pious persons, and professed Divines of differing Churches, have so little perceived, that the things objected are consequent to such Principles, that they not only absolve them as harmless, but extol them as friendly and advantageous to natural Religion. And I see not, why so great and radiant a Truth, as that of the Existence of a God, that has been acknowledged by so many mere Philosophers, might not as well impress itself on so capable an intellect as that of Monsieur des Cartes, or that so piercing a wit may not really believe he had found out new Mediums to demonstrate it by. And since the Learned Gassendus, though an Ecclesiastic, had been able as well safely as largely to publish the irreligious Philosophy of Epicurus himself; it seems not likely, that so dextrous a wit as that of Monsieur des Cartes, could not have proposed his notions about the Mechanical Philosophy, without taking so mean a course to shelter himself from danger, as in the most important points that can fall under man's consideration to labour with great skill and industry to deceive abundance of ingenious men, many of which appeared to be Lovers of Truth, and divers of them Lovers of Him also. And I am the more averse from so harsh an opinion of a Gentleman, whose way of writing, even in his private Letters, tempts me very little to it, because I cannot think him an Atheist and an Hypocrite, without thinking him (what Doctor More has too much celebrated him) to call him a weak head, and almost as bad a Philosopher as a Man. For as far as I understand his Principles, some of the most important points of his Philosophy (which if it were needful I could name) are inter woven with the Truth of the Existence of a God, or do at least suppose it, and are not demonstrable without it. But I must not prevent the Cartesians, who, now he cannot do it for himself, I doubt not will Apologise for their Master; though looking upon him as a great Benefactor to, though not the first founder of the Mechanical Philosophy, I could not consent by a total silence, upon such an occasion, to become any way accessary to the blemishing of his Memory.   

AN HYDROSTATICAL DISCOURSE Occasioned by the Objections of the Learned Dr. Henry More, against some Explications of New Experiments made by Mr. boil; and now published by way of PREFACE to the Three ensuing Tracts.  
SIR,  
UPon the Advertisement you gave me yesternight, that I was particularly concerned in the Learned Doctor More's Enchiridium Metaphysicum, I this day turned over the leaves of one, which I have freshly received from the Reverend Author himself: And being assisted by the series of the Titles, I quickly lighted on that part of the Book, whose subject made me expect to find myself questioned there, as I presently found I was. For though that civil Adversary is pleased to omit my name, and, the farther to disguise it; employs instead of it a great and unmerited Encomium; yet by the Book he citys, and the Experiments against which he argues, 'tis very easily discoverable, that his objections are meant against me, who see yet no cause at all to be scrupulous to own my Name, and the Doctrine delivered in the passages he is pleased to oppose.  
I doubt not but you will presently desire to know, what I think of this much expected work; but when I have told you, that I have gained time to peruse only (and that but cursorily) the 12th. and 13th. Chapters, you will, I question not, excuse a person that does exceedingly want health, and yet wants not almost continual avocations; if I now content myself to give you my thoughts of that part of the newly mentioned Chapters, which properly relates to me; I say, that part of the Chapters, because there are others wherein I need not interess myself. For to omit other Paragraphs, the Doctor has in the former part of the 12th Chapter thought fit to separate from my explication of the Phaenomena in question betwixt us, that of the Learned Henricus Regius; and the later part of the same Chapter he employs in an ingenious dispute against those that would have the Aerial Particles act with perception and design, 
Sect. 16, 17.  and (as he speaks) pro re nata, which Opinion you will easily believe I neither was of, nor am like to adopt.  
It remains then, that setting aside those discourses of the 12th Chapter, wherein it is needless that I should make myself a party; I proceed to consider those Paragraphs, which will be easily guessed to be levelled at my Explications, and by which I must confess, I cannot at all be yet convinced of their being false ones. But in doing this, I shall not only in compliance with my present haste, but also to express my respect to the Learned Doctor, forbear to say any more, than what I shall judge requisite to answer the Objections, that directly concern my own Explications, without meddling, by way of Retaliation, with his Hypotheses or Opinions, or endeavouring to set any passages of his Writings at variance among themselves, or to take those little advantages, which are usually sought for by Disputants.  
I shall not trouble you, nor tyre myself with any Schemes, since the Doctor has taken the pains to insert those that are necessary for his purpose in his Book, and I have not my own at hand. Wherefore, not doubting that you have by you those Books of mine he refers to, and supposing that you will, whilst you are reading, have also his Book with the inserted Schemes before your eyes, I shall not spend time on any further Preamble, but immediately enter upon the consideration of the Objections I am to answer.  

THE FIRST SECTION.  

CHAP. I.  
THe first Explication of mine, that the Learned Doctor animadverts upon in his 12th Chapter, is, that which I give in the 33th of my Physicomechanical Experiments, touching the Spring and Weight of the Air; where I relate, that the Sucker in the Air-Pump of our Engine, having been forcibly depressed to the lower part of the Brass Cylinder, which yet was carefully closed at the top, so that the cavity of the Cylinder was empty of Air; this Sucker, I say, would in this case appear spontaneously to remount towards the top of the Cylinder, though it were clogged with a hundred pound weight to hinder its ascent. Which Phaenomenon I ascribed to this, that the Sucker being, by the withdrawing of the Air in the Cylinder, freed from the wont force of the springy Air that endeavoured to depress the internal part of it, was not enabled by the appendent weight to resist the pressure of an Atmospherical Cylinder equal in diameter to it, which, pressing against its lower or external surface, endeavoured to impel it up.  
Now the Doctor having in the two first Paragraphs made a Description of my Engine, (which I shall now pass over) does in the third teach us, that the Corporeal cause, if there be any, of the ascent of the Sucker, must be, either in the Sucker itself, or in the almost exhausted cavity of the Cylinder, or lastly in the external Air: Which premised, he does in the same third Section, and in the fourth, endeavour to prove at large, that the cause is to be derived neither from the one, nor from the other of the two first. And therefore I, that maintain neither of the Opinions he disputes against, shall leave those Paragraphs of his untouched. Nor shall I meddle with the fifth, sixth, and seventh, where he argues against the explications of some, that would solve the Phaenomenon upon some Cartesian grounds, and as well amply as particularly against the solution that he supposes would be given of it congruously to his own Sentiments by the Learned Regius. These Discourses, I say, of the Doctors I leave untouched; because 'tis at length in the eighth Paragraph, that he impugns that solution of the Phaenomenon, which he ascribes to me, whose Opinion he first delivers, though not just in the terms I would express it myself; yet I dare say very sincerely, and so near my sense, that I shall forthwith pass from the eighth Section to the beginning of the ninth, where he gins to propose his Objections, which he is pleased to usher in with a compliment to me, that I should be very vain if I looked upon as any thing more than a Compliment.  
To his first Objection, proposed in these words, 
* 139.  Primò enim, si haec solutio verè mechanica sit, quae tandem Causa verè mechanica assignari potest gravitationis singularum particularum, totiúsque atmosphaerae in suis locis? Nam quod materiam subtilem attinet, etc. I answer, that I did not in that Book intent to write a whole Systeme, or so much as the Elements of Natural Philosophy; but having sufficiently proved, that the Air, we live in, is not devoid of weight, and is endowed with an Elastical Power or springiness, I endeavoured by those two Principles to explain the Phaenomena exhibited in our Engine, and particularly that now under debate, without recourse to a Fuga Vacui, or the Anima Mundi, or any such unphysical Principle. And since such kind of Explications have been of late generally called Mechanical, in respect of their being grounded upon the Laws of the Mechanics; I, that do not use to contend about Names, suffer them quietly to be so: And to entitle my now examined Explication to be Mechanical, as far as I pretend, and in the usual sense of that expression, I am not obliged to treat of the cause of Gravity in general; since many Propositions of Archimedes, Stevinus, and those others that have written of Staticks, are confessed to be Mathematically or Mechanically demonstrated, though those Authors do not take upon them to assign the true cause of Gravity, but take it for granted, as a thing universally acknowledged, that there is such a quality in the Bodies they treat of. And if in each of the Scales of an ordinary and just Balance, a pound weight, for instance, be put; he that shall say, that the Scales hang still in Aequilibrium, because the equal weights counterpoise one another: and in case an ounce be put into one of the Scales, and not into the opposite; he that shall say that the loaded Scale is depressed, because 'tis urged by a greater weight than the other, will be thought to have given a Mechanical Explication of the Aequilibrium of the Scales, and their losing it; though he cannot give a true cause, why either of those Scales tends towards the Centre of the Earth. Since then the assigning of the true cause of Gravity is not required in the Staticks themselves, though one of the principal and most known of the Mechanical Disciplines; Why may not other Propositions and Accounts, that suppose Gravity in the Air, (nay prove it, though not à priori) be looked on as Mechanical?   

CHAP. II.  
THe next thing the Doctor opposes to my Explication, is a resolute Denial, that there is any such Gravitation, as I pretend, of Bodies, or their Particles, in their proper places. But because, for the proof of his negation, he refers us to the next Chapter, we shall hereafter have a fit place than this to consider it in.  
Thirdly, he tells us, we may justly doubt of the equal diffusion of the Springy power, or the Pressure of the Air every way. In what sense, in some cases, I admit of a small inaequality between the pressure of Fluids against differing parts of a surrounded body, I have 
* See the Hydrostatical Paradoxes, esp. cial Parad. 7.  elsewhere declared, and need not here discourse of; since in the case before us, and in the like, that Pressure is inconsiderable enough to be safely neglected. And whereas our Author thus argues, 
* p. 139.  Semotâ vi Elasticâ, particulae tamen Atmosphaerae deorfum tenderent. Est igitur depressio quaedam deorsum praeter vim Elasticam ipsi superaddita; sursum non item sed elastica sola, éstque suppar ratio in pressionious transversis & obliquis. I presume, he did not sufficiently consider our Hypothesis and the nature of the pressure of Fluid Bodies that have weight: For Water, to which no Springiness is ascribed, as there is to Air, but which acts by its weight and fluidity, is able upon the score of those Qualities to buoy up great Ships, that the ebbing Tide often leaves upon the strand.  
And whereas the Learned Examiner proposes a fourth Objection in these terms, 
* p. 139.  Quibus omnibus addas, difficile esse intellectu, si unius Cylindri Atmosphaerae pondus aequalis diametri cum Embolo reflectione in fundum Emboli derivetur, cur non quinque alii Cylindri Aeris qui circumstant Embolum in ejus fundum eodem modo simul agere possunt, ita ut vis sursum impellens Embolum sextuplo major sit quàm hactenus ab bujus opinionis fautoribus existim ita est. Quod si sit, tunc certe, siquo artificio fieri possit ut unius solius Cylindri actio in Embolum admitteretur, re iquorum quinque exclusa, & pari tamen facilitate Embolus ascenderet, manifestum indicium esset, ne unum quidem Cylindrum Atsmosphaerae agere in fundum Emboli, sed totam Hypothesin, ingeniosam tantummodo esse fictionem. I presume, Hydrostaticians will think, this might have been spared. For they will tell him, that there can no more of a fluid press directly upward against the Cylindrical Orifice of a Body immersed in that fluid, than a Cylinder of that fluid of the same diameter with the Orifice (the lateral pressures bearing against the lateral parts of the Cylinder.) And therefore if you invert, for instance, a Pipe open at both ends, and filled to a certain height with Oil, into common water; the Oil that is kept up by the pressure of the water upwards, will keep at the same height as to sense, whether the Vessel that contains the Water be broad or narrow, provided it be somewhat larger than the Orifice of the Pipe.  
And now, to invalidate yet further the precedent Objections, made by the Doctor, I shall add, that it need not be thought incredible, that the Atmosphere by its weight, or the Spring of the Air compressed by that weight, should be able to raise up fourscore or a hundred pound, hanging at the Sucker: Since I have 
* See Continuat. of New Exper. Physico-Mechan. Exp. 48. p. 165.  manifested two or three years ago by a clear and cogent Experiment, that a little air included in a Bladder will by its mere Spring be able to heave up a weight of a hundred Pound, and this without the help of any rarefaction by heat. By which Experiment may be also confirmed, what I delivered a while since about the endeavour of the Air, that is wont to be included in our brass Cylinder, by expanding itself to thrust away the Sucker (which, in regard of the structure of the Pump, it can do no otherwise than downwards,) with a depressing force, equivalent to the pressure upwards of the Atmosphere against the external part of the same Sucker.   

CHAP. III.  
BUt I shall not insist upon the foregoing Objections, because the Learned Doctor himself tells us, that their attempts may seem to be but light skirmishes in comparison of that which follows. Whereunto I shall therefore apply my attention.  
This grand Objection our Learned Adversary takes from the already often-mentioned ascent of the Sucker clogged with a hundred pound weight, and recommends by this introduction. 
* p. 140.  Etenim ex ipsis Phaenomeni visceribus robustissimum jam contra omnem mechanicam illius solutionem Argumentum eruo, & quod non solum contra vim aeris elasticam suprà dicto modo explicatam militat, sed etiam contra Cartesianum illum aeris conatum nixúmque, etc. Which premised, the Argument itself is thus proposed: 
p. 140.  Est enim (says he) juxta hujus experimenti Phaenomenon, vis illa aeris elastica (nixusque expansorius) major multo quàm quae fieri potest à rerum natura, quámque quotidianis illis Phaenomenis congruit. Nam si nixus hic elasticus tantam vim elasticam haberet ut plus centum pondo plumbum sursum possit propellere, omnes profecto rerum terrestrium compages tantâ violentiâ comprimerentur, ut nullae, nisi quae admodum firmiter compactae sint, tantae compressioni resistere possent, quin confringerentur, vel partium collisione ita contererentur ut brevi tempore perirent, etc.  
Though this Objection be specious enough, yet it presents me with no difficulty, that I was not well ware of; as I presume you will easily perceive by what you will meet with in the following Papers, especially that, which consists of Experiments and Considerations about the differing Pressures of Solids, Weights, and Ambient Fluids. The nature of which Pressure and its equality (as far as in our controversy 'tis needful to be supposed) will, I hope, satisfy you of the invalidity of the proposed objections; especially since the Doctrine it impugns, namely the Weight and Pressure of the Atmosphere, is not a bare Hypothesis, but a truth made out by divers Experiments, by which even professed Opposers of it have publicly acknowledged themselves to be convinced.   

CHAP. IU.  
IN the next Paragraph (which is the 11th.) the Learned Doctor adds a further Objection, wherein he supposes, that there is laid upon a wooden Scale, of the same diameter with the abovementioned Sucker, a lump of Butter of the same largeness with the Scale. Whence he argues, that if our Hypothesis take place, the Butter must be pressed against by two Cylinders of Air, the one pressing it upwards, the other downwards, and the pressure of them both amounting to two hundred pounds. But, says he, the Butter is not pressed at all, as appears by this, that no serous humour is squeezed out of it towards the edges, not so much as in those parts that lie parallel to the Horizon, whence the Conclusion seems easy to be deduced.  
But in the 12th Paragraph, the Doctor himself proposes a Solution, which he might easily foresee I would employ to invalidate his Argument; Namely, that the Air pressing, as well against the sides of the Butter, as against the top and bottom, hinders the Mass from horizontally extending itself. And whereas, by way of reply to this subterfuge, as 'tis called in the margin, he subjoins, 
* p. 142.  Cui respondeo, quòd tamen hoc nihil prohibet quo minùs in omnes partes horizontales exprimatur humor serosus & lacteus, si revera esset ulla hujusmodi pressura elastica qualis fingitur. The Reply is easy, that the pressure of the ambient Air, which is a fluid more subtle than Buttermilk, will as well hinder the starting out of that liquor as of the parts of the Butter itself: As he will easily grant, that attentively considers the nature of the thing, and remembers how Air keeps Water from running out at the little holes of a Gardeners Watering-pot closed at the top. What the Objector adds about the extrusion of what he calls a subtler Element (supposed to be harboured in the Butter) by the pressure of the Atmosphere, in case it had any, I think it would not be difficult to answer, if we considered, that a great and undeniable pressure applied to water does not sensibly condense it, or deprive it of its fluidity, because of the grossness and strength of its parts. But the Argument being but transiently mentioned by the Author, and grounded upon a Cartesian supposition that I never employed, I leave it to those that may think themselves concerned (which I am not) to make a solemn answer to.  
And whereas our Learned Examiner superadds, 
* p. 142.  Quod tametsi butyri massa in disci lignei speciem reducta, cujus margo centum vicibus areâ sit minor, interque duas laminas ligneas ejusdem formae ac latitudinis posita, filis sus● enderetur in aere tanquam in lance, ita ut pressura aeris elastica quà ab infra, quà desuper ducentis fere vicibus excessura sit pressionem in marginem butyri, butyrum tamen nihilo arctiùs comprimetur per vim aeris elasticam, nec aliter hîc afficietur quàm antea: He seems not to have sufficiently considered the Laws of the hydrostatics, according to which, supposing the pressure of the Atmosphere that he rejects, the Butter ought not to be deprived of its shape. For the pressure of the ambient Air, being equal on all sides, if we suppose the superficies of the Butter to be distinguished into a multitude of little equal portions, each of these, whether they be situated Horizontally, or on the edges, can be pressed against but by an Atmospherical Pillar equal to its Basis; and the Horizontal portions, if I may so call them, cannot be thrust out of place, without there be at the same time squeezed out some of the Lateral portions, which yet cannot be so displaced, because they also are with equal force pressed (inwards) by little aerial Pillars, whose Bases are contiguous to them, and bear against them. Which Answer, though of itself sufficient, may be much confirmed by the Instance, you will hereafter meet with, of a lump of Butter that kept its irregular shape, in spite of a great and manifest pressure of the water that surrounded it.  
And this Answer may suffice to disprove, what the Doctor annexes in the beginning of the 13th Paragraph, about the vast excess of Pressure, which the Air exercises upon the flat and Horizontal surfaces of the abovementioned lump of Butter, in comparison of the pressure the Marginal parts of its surface can be exposed to. What he adds, and illustrates with a Scheme, about the hands being assisted with the pressure of the Air, it concerns not me to answer. But whereas among the places where the Elastical power of the Air is understood not to reach, he reckons a Pail full of water, with a lump of butter put in it; he supposes that, which our hydrostatics will by no means allow, and which is disproved by several both of our former Experiments, and by those you will meet with in the following Papers. By which it appears, that the pressure of the Atmosphere is exercised, as indeed I do not see what should hinder it from being, even upon Bodies that are quite immersed under water; and by which, added to what has been hitherto discoursed in answer to the Learned Doctor's Objections, you will easily judge, how deservedly he shuts up the Arguments, we have been examining, with this Conclusion. 
* p. 143.  Adeo ut extra omnem controversiam positum videatur, quòd nulla est ejusmodi vis elastica in aere, qualem è doctis nonnulli supponunt, multoque minus tam fortis ut centum librarum pondus superet. Quod erat Demonstrandum.   

CHAP. V.  
BUt this is not all the Doctor urges against me in this Chapter; for in the 14th Paragraph he seconds his former argument by another, drawn from this Experiment of mine, That having taken two round Marbles, whose surfaces, that were to be contiguous, were as well ground very flat as carefully polished; and having placed them one directly upon the other, they did in a horizontal posture so firmly cohere, without the help of any Glue, 
See the Hist. of Fluidity and Firmness, p. 222. of the second E●ition.  or viscous Body, that the upper Marble being pulled up, would take up the lower, though clogged with a weight of fourscore and odd pounds.  
This Experiment, when I many years ago first published it, I referred to the action of the Atmosphere, which pressing equally and strongly against the surfaces of both the Marbles, except where they were contiguous, the higher could not be drawn directly upwards from the lower (and consequently must be followed by it) by a less force than that which was equivalent to the weight of as great a Cylinder of the Atmosphere as leaned upon the upper Marble.  
This Experiment thus explained, though it hath been judged a very favourable one to the Hypothesis on whose behalf I alleged it, does yet to the justly famous Doctor seem a very considerable Argument against it, though for this judgement of his he urges only this reason, That if the force, with which the Air presses the lower Marble against the upper, be able to sustain that Marble, though clogged with the great weight above mentioned, the same pressure of Air would much more easily support a Plate of wood brought to a true plain, and not loaded with any weight, if the wooden Plate were substituted to the lower Marble, and instead of it applied to the upper.  
But since the Experiment, as I proposed it, did upon trial succeed very well, it had not been amiss if the Learned Examiner had considered it as it was really and successfully made, and shown why the pressure of the ambient Air was not able to hinder the separation of the Marbles: And his needless substitution of a Wooden plate instead of the lower Marble easily suggests a suspicion, that there may lie some fallacy, though not intended by him, in the variation he proposes of the Experiment. And he seems to have himself had thoughts of this kind, by taking notice, that it may be answered on our behalf, that a Wooden Plate cannot be so exactly applied to the upper Marble, but that there will be a little Air intercepted between it and the bottom of that stone. And though having granted that it may be so, he employs two pages to show, that this intermediate Air could not keep the pressure of the Atmosphere from supporting the unclogged plate of wood, if it had been That pressure, which, when there was no such intermediate Air, had sustained the lower Marble with all the appendent weight; yet I confess his Proofs seem not to me to be answerable to the Assurance he uses in speaking of them. His Examples taken from Gunpowder and Wind, you will easily judge not to be very proper, where we are not considering a force that acts by a sudden and vanishing Impetus, but a constant and equal pressure. And as to his other Instance, which is taken from five men that thrust against the sixth (standing with his back to a Wall) who is but as strong as any one of them: I answer, that neither is this example near enough of kin to our case. For each of these five men is supposed to have an equal power of thrusting, proper to himself, and independent from all or any of the other four. And the sixth man is likewise supposed to resist but by his own single force, without having his power of reacting increased by the force wherewith the others thrust against him. But in our case the thing is quite otherwise; for supposing that some aerial particles be so placed that a solid Body hinders them to recoil or expand themselves, we are to consider, that, as the contiguous corpuscles of air press against them not by their own single weight or pressure, but as they transmit the action of all the other particles of the air which by their weight or pressure thrust them on; so the aerial particles, contiguous to the solid Body, resist not barely by that force which they would have if they were not compressed, but by virtue of the Springiness they acquire upon the score of the forcible inflection they sustain from the action of the corpuscles, that either mediately or immediately thrust against them; and consequently, in proportion to that external force, the Elasticity of these compressed Particles will be increased, as we see that a Bow or other Springy body, the more it is bend by an external force, the greater power it has to resist further compression. Upon which grounds it need to be no wonder, that a small portion of Air, being almost included in a solid Body, and having for some (though but very little) time been exposed to the outward air, should be capable of resisting the pressure of as much of the whole Atmosphere, as can come to press against it. For, this pressure of the Atmosphere being continual, if the Springiness of the aerial particles were not now great enough to resist that pressure, they must necessarily have been beforehand inflected or compressed by it, till the endeavours of the one and the other were reduced to an Aequipollency. Of which I shall give you an instance in so obvious a body as a Bubble at the top of water: For though there be but a little Air included in a very thin and transparent film of water; yet this little air is so well able to resist the weight of all the Atmosphere that can come to bear against it, that all the pressure of it is not able to make the film shrink, or become wrinkled; which it would do, if the corpuscles of the Internal air were not reduced to a Springiness, which makes its power of resisting equal to the endeavour of the External Atmosphere to compress it. And to let you see, that we may well conceive such a Springiness of the air included in the Bubbles, I have elsewhere related, how by barely withdrawing the pressure of the ambient air from Glass-Bubbles hermetically sealed with air in them not compressed beyond its usual state, the Spring of the Internal air would make the Bubbles fly in pieces: And this will happen to stronger Glasses than Bubbles, as you will find in one of the former Experiments 
* See the Tract about the Pressure of the Airs Spring on bodies under water. . And if we would illustrate what we are debating of by an Example; it should not be by considering, as the Doctor does, the endeavour of five men against the sixth that hath his back to the Wall; but that of five Bladders full of air, piled up, and resting upon a sixth. For in this case, whatever force or power of pressing we suppose in the incumbent Bladders, they all bear jointly upon the lower, which continuing at a stand, must thereby be so compressed as to be able to resist their joint endeavours, as 'tis manifest; because otherwise it would not continue in that state, but be farther compressed; which is against the supposition.  
This Notion about Pressure and Resistance I have the more particularly deduced, because I found many modern Naturalists, and even Hydrostaticians themselves to be great strangers to it. For which reason I shall add, that I have evinced it by purposely devised Experiments in the Continuation of the Physicomechanical Experiments 
* Exper. 25. and elsewhere.  about the Air. Were it not for this, I should perhaps have spared myself the labour of setting down these thoughts as not necessary to the solution of the Doctor's Objections. For he admits a Layer, or (as he aptly speaks) an Area of Aerial Particles to be interposed between the upper Marble and the Wooden Plate; and therefore the flatness and stiffness of those two Bodies must keep them from an immediate contact as well at the edges as by the help of the same Area they do elsewhere; and consequently that interposed Air may communicate with the ambient Air. From whence the Laws of the hydrostatics (which I have elsewhere shown) will allow me to conclude, that the weight of the Atmosphere endeavours to depress the upper surface of the wooden Plate; and so what the Examiner urges of the inconsiderable resistance, that the few Aerial Particles interposed between the flat Bodies can make to the great pressure of the Column of Air that thrusts the Wooden against the Marble Plate, would not conclude, though our former answer could not have been made; since the resistance, made by the interposed Aerial Particles to the pressure upwards of the Atmosphere, is not in our present supposition made by those Particles alone, but by the weight of the lateral and superior part of the Atmosphere exercised by the intervention of these Particles. Which being so, what the Learned Doctor adds, that the weight of the wooden Plate itself is here of no consideration, must needs be a mistake. For the two equal Atmospherical Pressures, the one against the upper surface of the wooden Plate, and the other against the lower, countervailing and consequently frustrating the endeavour of each other, the gravity of the wood itself will suffice to make it fall, as well as if it were pressed against by neither of them. And from this Discourse you will easily judge, whether the Doctor had reason to say as he does, 
* p. 146.  Quam ab omni ratione (igitur) absonum est, ut superficies illa sive area aerearum particularum, quae insinuant se laminam ligneam inter & marmor, solidam columnam hujusmodi particularum, vi elastica sursum enitentium, contra laminam ligneam obnitendo vincat, ipsamque laminam in terram deturbet.   

CHAP. VI  
WHat he adds in the sixteenth number against those that fancy the Aerial Particles to be endowed with Perception, and to act with Design pro re nata, does not at all concern me; and what he adds in the next Paragraph, wherewith he concludes his twelfth Chapter, I shall altogether pass by, as far as it concerns the extravagant conceit he opposes. But because at the close of the Paragraph, he makes an Inference, which comprises our Opinion also; since he concludes, that the Experiment by him alleged, 
* p. 150.  Certissimum est indicium, particulas Aerias nec cum consilio nec sine consilio inferius marmor sustinere nec suffulcire: It will not be amiss to show, that our Opinion is undeservedly included in the Inference; which I shall do by briefly solving the Phaenomenon the Doctor lays so much weight on. For if we conceive with him, that the two flat Marbles formerly mentioned be suspended, and that to the lower of them a flat wooden plate of the same shape and extent be applied; I see no cause to wonder, why the two Marbles should stick together, and not the lower of them to the wooden plate. For, as I lately noted, there being an Area or Bed of Aerial Particles interposed betwixt the Marble and the Wood, the weight of the Atmosphere, exercised by the intervention of those Aerial Corpuscles, aught to be aequipollent to the pressure of the Atmospherical Cylinder, that bears against the lower surface of the Plate; which consequently by its own weight must drop down: whereas there being no such Layer of Aerial Particles interposed betwixt the two Marbles, the pressure of the ambient Atmosphere, which touches them every where, save where their polished surfaces are contiguous, must keep them strongly coherent.  
I presume I need not mind you, that hitherto I have discoursed upon supposition, that the Doctor experimentally knows, what he delivers concerning the Non-adhesion of an exactly smooth wooden Plate to a Marble one: And upon his concession, that, because of the want of sufficient congruity between the surfaces of two Bodies, there is a bed of Aerial Corpuscles interposed between them. But now I think, it will not be unfit to take notice to you, that though, to illustrate on this occasion a subject that is generally so little understood, as the exercise of Pression among fluid Bodies, I have answered my Learned Adversaries Objections, as if I had nothing more to say for my Explication of the Suspension of coherent Marbles, than what I many years since delivered in the little Tract by him cited; yet I have since abundantly confirmed that Explication by the 50th of the Experiments published in my Continuation; which if the Doctor had been pleased to read, perhaps he would have received the same satisfaction that other Learned men have done: since there I experimentally show, that the undermost Marble without the accustomed Clog, would, upon the bare withdrawing of the sustaining air, drop off from the upper. And whereas the two Marbles in our Vacuum would not cohere; as soon as the formerly excluded Air was let in upon them, it did by its supervening pressure make them stick together very strongly.    

THE SECOND SECTION.  

CHAP. I.  
I Proceed now to the second of those two Chapters, that I am interested to consider, in which the Learned Examiner is pleased to attaque three or four of my Hydrostatical Opinions and Explications; in the defence whereof, I hope, I shall be the less put to exercise your Patience, because the Learned Doctor himself is pleased to grant me almost as much as I need desire concerning the Truth of the Hypothesis, whereon my Paradoxes and Explications are founded. For whereas the main thing I supposed in my Hydrostatical Papers, is, that in water, though stagnant, the superior parts do actually, though not always prevalently, gravitate upon the inferior, or (if you will) press upon them even when they do not sensibly depress them; the Doctor in divers places allows this Hypothesis to be consonant to the Principles of the Mechanical Philosophy; and accordingly having showed, that in a suspended tub of water the whole liquor gravitates upon the bottom of the tub; He subjoins, 
* P. 161.  Jam verò cum tota haec aqua constet ex particulis aqueis non compactis vel concretis, sed solutis à se invicem, impossibile est ut omnes fundum situlae premant, nisi infima quaeque ab omnibus superioribus prematur, quemadmodum clarè demonstravimus in secunda sectione hujus capitis; nempe, si nullae causae nisi purè Mechanicae (quales sunt Motus localis, Magnitudo, Figura, etc.) in edendo hoc Phaenomeno se intermiscent.  
And elsewhere in the same Chapter he speaks thus of the gravitation of liquors (towards the close of the second Paragraph.) 
* p. 152.  Necesse utique est, ut partes singulae gravitent, cum totius sit gravitatio, si non sit aliquid immateriale Principium in rerum natura, etc. And adds, at the beginning of the next Number; Atque sanè huic externi motûs Hypothesi, & gravitationis Elementorum in propriis locis inde necessariò emergentis, apprimè consonum est primum illud Experimentum, quod Scriptor profert in Paradoxis suis Hydrostaticis.  
And now, Sir, I presume you do not much wonder, if I think these concessions reach the main thing I pretend to. For though I do as freely and hearty, as the Doctor himself, (who, I dare say, does it very sincerely,) admit or rather assert an Incorporeal Being that made and governs the world; yet all that I have endeavoured to do in the Explication of what happens among Inanimate Bodies, is to show, that, supposing the World to have been at first made and to be continually preserved by God's divine Power and Wisdom; and supposing his General concourse to the maintenance of the Laws he has established in it, the Phaenomena, I strive to explicate, may be solved Mechanically, that is, by the Mechanical affections of Matter, without recourse to Nature's abhorrence of a Vacuum, to Substantial Forms, or to other Incorporeal Creatures. And therefore, if I have shown, that the Phaenomena, I have endeavoured to account for, are explicable by the motion, bigness, gravity, shape, and other Mechanical affections of the small parts of liquors, I have done what I pretended; which was not to prove, that no Angel, or other immaterial Creature could interpose in these cases; For concerning such Agents, all that I need say, is, that in the cases proposed we have no need to recur to them. And this, being agreeable to the generally owned rule about Hypotheses, that Entia non sunt multiplicanda absque Necessitate, has been by almost all the modern Philosophers of different Sects thought a sufficient reason to reject the agency of Intelligences, after Aristotle and so many Learned men, both Mathematicians and others, had for many ages believed them the Movers of the Celestial Orbs.   

CHAP. II.  
But you will tell me, that the Doctor's Concessions will not avail me, since he urges against the Gravitation of the Elements in their proper places, which (gravitation) he would have to be suspended by his Incorporeal Principle, an Experiment, which he says is most manifestly repugnant to our Hypothesis. He conceives then, that in a tub or pail full of water with a perfectly Cylindrical cavity, whose Diameter is of sixty two parts, there is violently kept at the bottom, by the help of a stick, a round Plate of wood, whose Diameter amounts but to sixty one of those parts; and that, as soon as ever the stick is removed, the wooden plate will emerge to the top and float. Quod (says he) prorsus impossibile esset, si omnes partes aquae ab (FG) ad (HJ) non solùm junctim fundum vasis, sed singulae singulas in eadem serie subjectas actu premetent. To which assertion he immediately subjoins this Argument to prove it by; 
* p. 155.  Cum Diameter laminae ligneae (H M) parts 61. habeat aequales, Diameter vasis (HI) habeat 62, manifestum est, quod superficies fundi vasis ad superficiem laminae se habet ut 3844. ad 3721; quorum differentia est 123. Itaque rotundum intervallum inter latera vasis & marginem laminae ligneae habet se ad aream laminae ut 123. ad 3721, hoc est, area laminae ligneae excedit aream dicti intervalli plusquam triginta vicibus. Ac proinde aqua incumbens ligneae laminae excedit magnitudine aquam incumbentem dicto intervallo inter marginem laminae & later a vasis plus quàm triginta vicibus, pondúsque sive pressio hujus, alterius pondus pressionémque vincit plusquam triginta vicibus. Adeò ut impossibile sit, ut aqua incumbens praedicto intervallo ita premat aquam ipsi subjectam, ut hujus vi sublevetur lamina, quam vis tricies major deprimit. Quod (says he, by way of inference) aeque absonum atque absurdum Phaenomenon esset, etc.  
How little this Ratiocination agrees with the Experiments I have formerly told you of, about the cases wherein Light bodies will be detained under water, or emerge to the top of it, you will easily perceive, if you compare the one with the other, which you may quickly do, if you please to compare the Doctor's discourse with the following Narratives of those Trials 
* See the Tract of the Positive or Relative Levity of Bodies under water. Exp. 1. etc. , to which alone I might therefore refer you. But yet in the mean time, you may, if you think fit, consider a little, whether the Argument, whereon the Doctor lays so much stress, be any more than a Paralogism.  
First then, since according to his computation the Area of the interval between the sides of the Vessel and the edges of the round boards, is 123 of such parts, whereof the Area of the board amounts to 3721; 'tis evident, that there must be room enough for the water to pass between the sides of the vessel and the edges of the board, which is supposed on all hands to be of some wood lighter in specie than water, since else it would not emerge upon the withdrawing of the stick.  
Next, this Board or wooden Plate is not here intimated or supposed to be (and indeed in practice can scarce be) made exactly congruous to the bottom of the Vessel; and consequently the water may get in between them; for which cause 'tis necessary to keep the wooden Plate forcibly down with a stick, which else were needless. And consequently this interposed water will communicate with the laterally superior water in the Vessel, which superior water may, according to the Laws Hydrostatical, by the intervention of the interposed, exercise its pressure upwards against the lower surface of the wooden Plate.  
Thirdly, the Doctor's Scheme allows and assists us to conceive, (which we may do however,) an imaginary Plane of water to be parallel to the bottom of the Vessel, and to pass along the bottom of the Board; so that, of the water that lies between this Plane and the bottom of the Vessel, one part is covered by the wooden Plate; and the other, between the edges of that and the sides of the tub, is covered with the incumbent water only.   

CHAP. III.  
THese things being premised, I thus argue: 'Tis manifested by Hydrostaticians after Archimedes, that in water, those parts that are most pressed, will thrust out of place those that are less pressed: which both agrees with the common apprehensions of men, and might, if it were needful, be confirmed by Experiments. 'Tis also evident, that that part of the abovementioned imaginary Plane, that is covered by the wooden Plate, must be pressed by a less weight than the other part of the same Plane; because the wood being bulk for bulk lighter than water, the aggregate of the wood and water incumbent on the covered part of the same Plane must be lighter in specie, than the water alone that is incumbent on the uncovered part of the same Plane; and consequently this uncovered part being more pressed than the other part of the Plane, the heavier must displace the lighter, which it cannot do but by thrusting up the board, as it does, when the external force that kept it down is removed. And, to add this upon the by, this greater pressure against the bottom than against the top of bodies immersed in water specifically heavier than they, is a true reason of their emersion, as I have elsewhere shown. So that there happens no more in this case than what usually happens in the ascension of bodies in liquors specifically heavier than themselves, on the account of the newly mentioned difference of Pressure. And 'tis with an (express or supposed) exception of such a difference, which in many other cases may be safely neglected, that (which I desire you to take notice of,) in most places of this discourse I speak of the Pressure of ambient Fluids on immersed Solids as uniform or every way equal.  
'Tis true, that according to the Doctor's supputation, if the solid Cylinder, consisting of the wooden Plate, and all the water directly incumbent on it, were put into an ordinary balance, it would there many times outweigh the hollow Cylinder of water alone that leans upon the uncovered part of the imaginary Plane. And that is it that seems to have deceived the Learned Doctor. But there are divers Hydrostatical Cases, wherein the Phaenomenon depends not so much upon the absolute weight of the compared Bodies, as upon their respective and their specific Gravity; on whose account it is, that a small Bible, for instance, that weighs not a quarter of an Ounce, will readily sink to the bottom of the river, on whose surface a log of wood of a hundred pound in weight will float. 'Tis a Rule in hydrostatics, that when two portions of water or any other Homogeneous liquor press against each other, the prevalency will go, not according to the absolute weight, but the perpendicular height of those Portions. And accordingly we find, that if a slender pipe of glass, being filled with water, have its lower orifice unstopped at the bottom of a vessel of water, which contains much more of that liquor than the pipe; yet if this last named water were, for instance, two foot high, and that in the Vessel but one, the water in the pipe will readily subside, till it come almost to a level with the external water, though it cannot do so without raising the whole mass of water that stagnated in the vessel.  
And now I shall subjoin an Experiment, which, though at first it may seem slight, and was made in lesser glasses & quantities than I would have employed if I could have procured better Accommodations, has the advantage of requiring no curious instruments, and yet I hope will serve for an ocular proof of the fallaciousness of that reasoning the Doctor is so strangely confident of.  
We took an open mouthed glass, such as some call Jars, and Ladies often use to keep sweet meats in, which was three inches and a half or better in Diameter, and somewhat less in depth; and had the figure of its cavity Cylindrical enough. Into this having put some water to cover the protuberance, wont to be at the bottom of such glasses, we took a convenient quantity of Bees-wax, and having just melted it, we poured it cautiously into the glass, warmed beforehand to prevent its cracking, till it reached to a convenient height. This vessel and the contained liquors we set aside to cool, in expectation, that when the heat, that had dilated the wax, was gone, it would shrink from the glass, and consequently leave a little interval every where between the concave superficies of the vessel, and convex of the hardened wax; which accordingly came to pass, and saved me the labour of getting the wax shaped for my purpose with tools; which might have been done but not without trouble and less exactness. And now 'twas easy for me to try the experiment I designed; for, pouring in warily some water between the glass and the wax, so that it filled all the interval, left between those two bodies both at the bottom and the sides, the wax was made presently to float, being visibly lifted up from the bottom, and its upper part appearing a little above the level of the water, which was no more than I did, and had reason to expect, according to the true Principles of hydrostatics. For water being somewhat, though but little, heavier, in specie, than wax, and that which was poured into the bottom and stagnated there, being pressed by the collateral water, every way interposed between the concave part of the Glass and the convex of the Wax (so that this collateral liquor answered what I lately called a hollow Cylinder of water in the Doctor's Experiment) that part of the stagnant water, that was leaned upon by the wax, being less pressed than the other part of the same stagnant water was by the water incumbent on it; this latter must displace the former, which it could not do but by raising up the wax that leaned upon it. And yet this collateral water was so far from being heavier than the wax its pressure impelled up, that both the collateral, and the stagnant water all together, being weighed in good scales, amounted to little above a quarter of the weight of the wax, which happened by reason of the narrowness of the Vessel, which, if it had been wide enough, I doubt not but the experiment would have succeeded, though the wax had outweighed the collateral water ten times more than in our experiment it did. But that the solid body exceeded almost four times the weight, not only of the collateral but the stagnant liquor too, does sufficiently overthrow the Doctor's ratiocination. Whose fallaciousness will yet further appear by two other improvements, among others, which I made of one Experiment.  
For I. though we poured in more and more water, as long as the Vessel would contain any, the Cylinder of wax was but lifted higher and higher from the bottom of the glass, but did not appear raised more than at the first, above the upper surface of the water; which argues, that 'twas not at all the Quantity of the inferior water, which was continually increased, but the pressure of the collateral water, which continued still at the same height in reference to that wax, that caused the elevation of the body.  
And II. to manifest yet more clearly the Doctor's mistake, I devised the following trial. We took a round plate of Lead about the thickness of a shilling, and having made it stick fast to the bottom of the Cylinder of wax, to make this body sink the more directly, we placed one after another upon the upper part of the wax divers grain weights (first wetted to keep them from floating) till we had put on enough to make the wax subside to the bottom: For the facilitating whereof we had pared off its edges; by this means, the glass having been at first almost filled with water, there swum about an inch or better of that liquor above the upper surface of the wax. And lastly, we took off by degrees the grain weights that we had put on, till we saw the wax, notwithstanding the adhering Lead, rise, by degrees, to the top of the water, above which some part of it was visibly extant.  
From this experiment I thus argue: 'Tis manifest, that, according to the Doctor's supposition, here was incumbent upon the wax a Cylinder of an inch in height and of the same Diameter or breadth with the round surface of the wax, whereas upon the removing part of the water, that lay at the bottom when the wax began to rise, there was incumbent no greater weight than that of the collateral water, and as much of the superior and stagnant, as was directly imcumbent upon that collateral water (and would have deserved the same name, if we had supposed the convex surface of the wax to have been continued upwards as high as the glass reached.) But now, whereas, according to the Doctor's ratiocination, this Cylinder of water incumbent on the wax, being an inch deep, and a good deal above three inches broad, must press the wax with a greater weight by several times, than that which the lateral and hollow Cylinder of this stagnant water could have upon the rest of the collateral water; yet the height of this aggregate of collateral waters being the same with that of the wax and the water swimming upon it, the difference of the pressure was so small, that barely taking off a weight of four or five grains, the wax would, notwithstanding the pressure of the water incumbent on it, be impelled up and made to float: And by the like weight, put again upon it, it would be made to sink, and by another removal of such a weight, (for I purposely reiterated the trial more than once,) it would, though slowly, reascend. And these Phaenomena do so much depend upon a Mechanical aequipollence of pressure, that even four grains would not have been necessary to make the wax rise or sink, if it had not been for some little accidental impediments, that are easily met with in such narrow glasses; for otherwise in a larger Vessel we have made the same Lump of Wax readily enough sink or float, by the putting in or taking off a single grain or perhaps less.  
By this you may see, that for the Regulation of Hydrostatical things, Nature has her balance too as well as Art, and that in the balance of Nature the Statical Laws are nicely enough observed.  
You may also take notice, upon the by, how little the weight of the Cylinder of water upon a body immersed in stagnant water is considerable, whilst there is a pressure of collateral water to counterbalance it; since in this last trial, though the Cylinder of incumbent water did continually increase or decrease in length, whilst the lump of Wax was sinking or emerging; yet the same despicable weight of a grain or less, that was just able to depress it beneath the upper surface of the water, did by its pressure or removal procure its sinking to the very bottom, or rising again to the top, and on both occasions with an equal slowness, bating that little acceleration of motion, that aught to happen upon another account, and which therefore is to be observed in the wax, during its rising as well as during its sinking.   

CHAP. IU.  
SOme other Phaenomena I produced, by varying the hitherto mentioned experiment, which are very  to our Notions about hydrostatics. But, since they do not directly concern the present Controversy, I shall in this place only annex a couple, the former whereof affords an easy confirmation of that Paradox, which we lay as the ground of divers others, and the contrary whereof is maintained not only by Doctor More, but by many other famous and Learned men, namely, that in stagnant water the upper parts do actually press the lower.  
We took then a very slender pipe of glass, whose Cavity was narrower than that of an ordinary Goos-quill, that heterogeneous Liquors may not be able to get by one another in it. This Pipe near one end was bend upwards like a Syphon, that it might have a short leg as Parallel as the Artificer could make it to the longer. Into this crooked Pipe we put a little oil, and then held it perpendicularly in a somewhat deep and wide-mouthed Glass filled partly with Water and partly with a Lump of Wax, of the bigness and shape of that already mentioned; that so the pressure of the incumbent Water upon the open orifice of the shorter Leg, might impel the oil into the longer Leg, somewhat above the surface of the water in the Vessel; which 'twas convenient should be done, that we might the better see the motions of the Oil, and which we knew must be done by the course we took; both because Oil is lighter in specie than Water, and consequently required not an equal height of Water to counterbalance it; and because in very slender Pipes, Water is wont to ascend a little above the Level of the External Water, whereinto they are immersed. The Pipe being, as was said, held upright, 'twas easy to take notice by a mark, fixed on the outside, to what height the Oil reached in it.  
Now if we conceive a Horizontal Plane, Parallel to the bottom of the Vessel, to pass by the Basis of the floating Wax, 'tis evident by what has been formerly shown, that, of this Imaginary Plane, that part on which the Wax is incumbent is as strongly pressed by the weight of the Wax, as the Lateral part of the same Plane is by the weight of the Water incumbent on it; (otherwise these Pressures would not be aequipollent, but the Wax would be raised:) And consequently that part of this Plane, that is placed directly over the Orince of the shorter Leg of the Pipe, is no more pressed, than any equal portion of that part of the same Plane that is covered by the Wax. This Body being taken out of the Water, the Liquor subsided a great way in the Vessel, and so did proportionably the Oil in the longer Leg of the Pipe. And lastly, having weighed out in a good pair of Scales as much Water, as we found the Wax to amount to, this Liquor was, instead of the Wax, poured into that which remained in the Glass; whereupon the Oil, in the longer leg of the Pipe, was again impelled up (very near) to the former Mark to which it had been raised by the Wax. Whence we may gather, that the Water newly put in, though in the Air it weighed no more than the Wax; yet it did as much press the Water, that lay beneath the forementioned Imaginary Plane, and consequently that, which was directly over the shorter Leg of the Pipe, as the Wax, that had been taken out, had done. And since we have already proved, that the Wax did confiderably press that Plane, it ought not to be denied, that the Water also (which instead of it was able to impel up the Oil in the Pipe) did in like manner press that Plane; and consequently that Water may gravitate in Water, as well as a solid Body, such as Wax is, can. And this is the first additional use I told you I would make of our Experiment.  
But, (to come now to the second) there is another Phaenomenon of it, viz. the abovementioned tenderness of Nature's Balance, whose use seems to be of no less general concernment to the true Doctrine of the hydrostatics. For, by duly considering that Phaenomenon, and reasoning a while upon it, we may be helped to rectify that plausible Mistake, which has long deluded both Philosophers and Mathematicians, and does yet impose on most of them; namely, that a Body does not actually gravitate when it does not descend. For we have seen already, and shall further show by and by, that the sunken Wax and the Brass grains that lie on it, do actually press or gravitate upon the subjacent Water and Bottom of the Vessel on which 'tis incumbent; and consequently its pressure being not surmounted by that of the Collateral Water, which is unable to raise it, must be as great, as that of this collateral Water. Therefore, when upon the removal of a single Grain, the Wax with its incumbent weight is made to ascend, and that but very slowly, 'tis evident, that 'twas so far from not gravitating before, because it did not actually descend, that it retained its Gravity even whilst it ascends: As may appear not only by the slowness of its motion upwards, proceeding from its being in Nature's Balance very little less heavy than it need be to countervail the pressure of the Collateral Water; but by this also, that if but a single grain be laid on it when it gins to rise, its ascension will be checked and hindered, which could not be done by the addition of so inconsiderable a weight, if the Wax and the adhering Metal did not, even during their ascent, retain their former gravity, though that were frustrated as to the act of descending, or so much as keeping their station by the prevailing pressure of the collateral Water: So that, since, (as we found) the Wax and adhering Metal amounted to a good deal above 4000 Grains, it did in the Balance of Nature weigh, whilst it was ascending, not so much as a 4000th part less than it did, whilst it was actually descending.   

CHAP. V.  
I Should beg your pardon, Sir, for having detained you so long with my Reply to a single Objection of the Doctors, how pompously soever proposed; but that I thought it not amiss to do some service to the true Theory of hydrostatics, by taking this occasion to present you some things that I thought not unlikely to illustrate some parts of that Theory; though above what was necessary to answer the Doctor's Argument; to which I confess I was troubled to see so Learned a man subjoin the following conclusion: Haec tam luculenta Demonstratio contra Gravitationem particularum aquae inter se quamvis junctae situlae fundum urgeant, si non sit vera atque solida, equidem nec mei ipsius nec ullius unquam mortalis in posterum ratiociniis credam. But I hope he will not be as bad as his word, but will be pleased to consider as well as I do for him, that a man may be very happy in other parts of Learning and of greater moment, that has had the misfortune to mistake in hydrostatics, a discipline which very few Scholars have been at all versed in, and about which divers of those few have had the misfortune to err, not only in the conclusions they have drawn, but in the very Principles they have embraced.  
To the foregoing Argument the Doctor, though he declares he thinks it needless, adds in the 5th Paragraph another, taken from the Last experiment of my Hydrostatical Paradoxes, by which he ingenuously acknowledges, that I seem at first sight to have demonstrated what I pretend to, about the gravitation of the upper parts of stagnant water upon the lower. And I am sorry that I cannot in return acknowledge, that his objection at first sight seemed to me a cogent one: For, neither at the second nor third perusal can I clearly discern where his Ratiocination lies, supposing it to be meant for an answer to my experiment. And though I consulted with some Learned Members of the Royal Society, whereof two are Mathematicians, and one his particular friend; yet they all confessed he had not sufficiently explained himself on this occasion, nor could they show me to what argumentation I might properly direct my reply. Only one of the Doctor's Correspondents, having seriously perused his discourse and the annexed scheme, told me that what seemed the most probable to him, was, that though the Doctor was too Civil to give me, in ter ninis, the Lie; yet he did indeed deny the matter of fact to be true. Which I cannot easily think, the Experiment having been tried both before our whole Society, and very Critically, by its Royal Founder his Majesty himself. But, since you have yourself seen and made it more than once, I need not spend words to convince you that the matter of fact is true.  
But after I had in vain sought the Doctor's meaning where I expected it, chancing lately to cast my Eyes on another place, where I saw my Scheme repeated, I find this passage in the Explication he endeavours to give of the Phaenomenon by his Hylarchical Principle; Cùm verò tam profundè immergitur tubus, ut obturaculum tangat Superficiem V W, vis retractionis Aeris ita augetur ut etiam ponderis appensi superadditam depressione● superet. Videtur igitur quasi quaed●m sursum-suctio Aeris in tubo contenti, & conformis ac contemporanea aquae compulsio in obturaculum, quo tam firmiter in os valvulae comprimitur, ibique cum appenso pondere sustentatur. What considerable interest the supposed, but unproved, Retraction of the Valve or the Air itself can have in this Phaenomenon, I confess I do not discern, not being able to see, but that the experiment would succeed when tried in vacuo, although all the Atmosphetical Air were annihilated. But if I mistake the Doctor's meaning I am to be excused, since I do it not willingly, and his own obscurity has been accessary to it. Nor am I very apprehensive of being unable to defend my account of an experiment, which (as you know) has had the good fortune to recommend the Doctrine, for the Proof whereof I devised it, to many Learned and curious Persons, several of which were sufficiently indisposed to admit it.  
And to avoid all mistakes and disputes that may arise (which I think they must do needlessly) upon the score of the Valve employed in our Experiment, I shall remind you of another, that I remember I have some times shown you and divers other Virtuosos, though I remember not whether I have mentioned it in any of my published writings. The Sum of this trial is, that an arbitrary Quantity of Quicksilver, being by Suction raised into a very slender glass-pipe, whose upper Orifice is stopped with the Experimenters' finger, to keep the Mercury from falling before its time, the open end of the pipe with the Mercury in it is thrust into a competently deep glass of water till the little Cylinder of Mercury have, beneath the surface of the water, attained to a depth, that is at least 14 times as great as the Mercurial Cylinder has of height. For then, the finger being removed from the upper orifice, the glass-pipe will be open at both ends, and there will be nothing to hinder the Quicksilver falling down to the bottom, but the resistance of the Cylinder of water, that is under it, which Cylinder can resist but by virtue of the weight or pressure of the stagnant water that is superior to it, though but collaterally placed above it: And yet this water being by the pipe, whose upper part is higher than its surface, and accessible only to the air, kept from pressing against the Mercury any where but at the bottom of the Pipe, and being about a 14th part of the weight of an equal bulk of Mercury, it is able at that depth to make the subjacent water press upward against the Mercury, which is but a 14th part as high as the water is deep, with a force equivalent to that of the gravity wherewith the Mercury tends downwards. And to manifest, that this Phaenomenon depends merely upon the Aequilibrium of the two liquors; if you gently raise the lower end of the pipe towards the surface of the water, this liquor, being not then able to exercise such a pressure as it could at a further and greater depth, the Mercury preponderating will, in part, (more or less, as the pipe is more or less raised) fall out to the bottom of the glass. But if, when the Quicksilver is at the first depth, instead of raising the pipe you thrust it down farther under the water, the pressure of that liquor against the Mercury increasing with its depth, will not only sustain the Mercury, but impel it up in the pipe to a considerable distance from the lower orifice of it, and keep it near about the same distance from the surface of the laterally superior water. And this experiment may not only serve for the purpose, for which I here allege it; but also, if duly considered and applied, may very much both illustrate & confirm the Explication formerly given of the seemingly spontaneous ascent of the clogged sucker in our exhausted Air-pump.  
The last Argument, the Doctor urges against the Gravitation of water in what they call its proper place, is deduced from what happens to the Divers, who in the midst of the Sea, though the salt water of that be much heavier than that of freshwater Rivers, do not find themselves oppressed, or so much as feel themselves harmed or compressed by the vast load of the incumbent water.  
But that the Equality of the pressures of an ambient fluid will go a great way towards the solving of this Difficulty, you will find, by the Experiments and considerations you will meet with in the following 
* The Author means the New experiments of the differing pressure of heavy solids, & fluids,  Papers, to which, for that reason, I refer you. And though the Doctor in this same Paragraph objects, Tametsi haec pressio aequalis sit, nihil tamen impedit quò minùs subtiliores partes corporis magisque fluidas exprimat & elidat. I remember I answered that exception before, by saying, that those liquors that he supposes should be squeezed out, cannot be so, because there is as great a pressure against those parts at which they should issue, as against any of the rest, if the parts that should be squeezed out be not too spirituous and subtle, which if they be, I should gladly learn how the Doctor knows that no such minute and spirituous particles are really expelled: especially if that be observed, which we shall soon have occasion to relate, that a small animal, being vehemently compressed in water, seemed a little, though but a little, to shrink.  
But that we may the more distinctly consider this grand argument, taken from the experience of the Divers, that is wont to be employed by the Schools and others for the vulgar Opinion, and is now urged by the Learned Doctor to prove His; 'twill be convenient to observe, that it does, at once, both propose a Question, and contain an Objection, grounded upon the surmised insolubleness of that Question.  
And to begin with the Problem, Whence it is, that Divers are so far from being killed or oppressed by the weight of the incumbent water, that they are not so much as hurt by it, nay, that they scarce feel it at all? We may take notice, that there is in it somewhat supposed, as well as somewhat demanded. For, in the Question 'tis taken for granted, that Divers, though at never so great a depth, feel no pressure exercised against them by the water; which is an affirmation in point of fact, of whose truth I make some question, for the reasons I shall ere long have occasion to mention.  
But it will clear the way for what is to follow, if I here divide the noble and difficult Problem, we are to consider, into two Questions; the first, why a Diver should not be oppressed and crushed to death by the pressure of the Incumbent and Ambient water. And the second, why at least he should not be made sensibly to feel it by suffering some considerable inconvenience from it.  
In answer to the first of these Questions, you will easily perceive, that divers things may be pertinently applied, that you will meet with in the following Paper, to show the difference betwixt the pressure of Fluid and that of Solid bodies. And that de facto the pressure of water may be exceeding great without destroying an Animal quite surrounded with that liquor; I have long since shown in another 
* The Author points at the Appendix to the Hydrostatical Paradoxes.  Treatise, by the experiment of a little Tadpole, which being, together with the water it swum in, included in a bend Glass sealed at one end, the animal was not killed or sensibly hurt, but only (according to what was lately noted by anticipation) seemed to shrink into somewhat (and but little) dat dimensions.  
If it be here alleged, that this Experiment makes rather against me than for me, the Learned Doctor having made use of it with a Scheme to explain it in his 16th. Paragraph; it will be fit for me to consider his Objection. Having then recited the matter of fact newly delivered, he adds, Quod certè fieri non posset nisi juxte legem quartam contrusio particularum aquae contra se invicem Principio Hylarchico inhiberetur & eluderetur. Atque hinc fit, ut quamvis Aqua is tubo (A B C) vi trudis (G F) aliquantò facta sit condensatior, parts tamen sic compressae ut propiùs ad se invicem accedant, nihilo inde inter se fiunt comprimentiores. And then subjoining the following passage; Neque emim sequitur ex earum contactu quod premant se invicem, quandoquidem particulae, uti fit in duris Corporibus, in unum coalescere possunt & tamen non mutuò se premere; (Wherein are some things that might be questioned if it were necessary;) He thus pursues his Discourse: Cùm verò hîc particulae aquae si omninò premerent se invicem, pressura in Gyrinum, columnae aqueae, ducentos vel trecentos pedes, aeneae verò, plus viginti vel triginta pedes altae, pressionem adaequaret, luculentum est indicium quod revera particulae se invicem non premant. Nam planè est incredibile, columnum aeneam pro corpore quidem gyrini latam, sed altam viginti vel triginta pedes & amplius, Gyrinóque ad perpendiculum incumbente●n omnia viscera tam tenellae Gelatinae no● esse elisuram. Notwithstanding which allegation I am apt to think, you will judge the Argument from this experiment to be more probable on my side than on the Doctors. For there being in our case an animal, exceedingly much more tender than a man, exposed to a pressure which he affirms is so great, that if it were exercised on the Tadpole, it ought to squeeze out all his guts, I think I may pretend to have given a pertinent instance, that a Diver may be at a considerable depth under water preserved from being crushed to death by the weight of it. And whereas the Doctor tells us, that the cause of the Incolumity of the Tadpole is, that the pressure or contrusion of the particles of the water against one another is hindered or frustrated by the Principium Hylarchicum, I reply; That what I affirm is matter of Fact, and evident, (namely, that there was a great external force duly and yet ineffectually applied to press to Death by means of the water the animal swimming in it;) but that this Mechanical force was suspended or made ineffectual by some invisible and immaterial Agent, is but the Doctor's Hypothesis, and a thing, which, whether it be true or no, is at least not manifest.  
Having said thus much about the first Question; I now proceed to the second, Why Divers though at never so great a depth complain not of the pressure of the water, nor suffer any harm nor inconvenience by it?  
And here, Sir, the Question highly meriting a particular Curiosity, I shall not scruple in the more full enquiry, I am now entering upon, as well sometimes to employ and enlarge particulars already mentioned in the last of the following Papers, as oftentimes to strengthen them with new ones. And I shall also for a while suspend my difference with the Doctor, and addressing myself to you, who, I am sure, will allow me that water weighs in water, propose, according to my custom, not as a Dogmatist, but as an Inquirer, some particulars, that may tend to the Solution of a Problem, which I take to be as difficult as noble. Not that I doubt but it must and will be explicated upon the Mechanical Principles; but partly, because the application of them to the Solution will not offer itself to every seeker; and partly, because we are not yet well furnished, either with experiments made on bodies under water, or so much as with so competent an account of the matter of fact, as I think may keep wary men from hesitations about it. For, what is commonly reported concerning the Divers, is (as has above been intimated) grounded but upon their own Relations and answers, perhaps amplified or procured by leading Questions from persons, who are generally either slaves or ignorant men, taken from the less sober part of the illiterate vulgar, and prepossessed with the common opinion of the non-gravitation of water in its own place; and consequently are not like to make over-accurate observations, but prone to refer the inconvenient alterations, they feel, to any other cause than the pressure of the water, which they are taught to be none at all. If observations about Diving were made by Philosophers and Mathematicians, or, at least, intelligent men, who would mind more the bringing up out of the Sea instructive observations than shipwrecked goods, we should perhaps have an account of what happens to men under water differing enough from the common reports.  
You will in one of the following Papers find mention of a Learned Physician of my acquaintance, that, upon his diving leisurely, perceived a constriction to be made of his Thorax by the action of the surrounding Sea-water.  
A Spanish Prelate, that lived long in America, speaking of the deplorable condition of those wretched Indians that were employed by their inhuman Masters about the fishing for Pearls, gives us this account of them: 
* See Purch. Tom. IU. Lib. 8. p. 1587.  It is impossible that men should be able to live any long season under the water without taking breath, the continual cold piercing them; and so they die commonly parbreaking of blood at the mouth, and of the bloody flux caused by the stomach. Their hair, which are by nature coal-black, altar and become afterwards a branded russet, like to the hairs of Sea-wolves, etc.  
And a General of the English in the East-Indies, being by them employed on an Embassy to the Emperor of Japan, has this passage concerning some female Divers that he met with in his voyage: 
* Purch. Tom. I. Lib. 4. C. 1.  All along this coast & so up to Ozaca, we found women Divers, that lived with their household and family in boats upon the water, as in Holland they do the like. These women would catch fish by Diving, which by net & line they missed, and that in eight fathom depth. Their eyes by continually diving grew as red as blood, whereby you may know a diving Woman from all other Women. I know, it may be said, that these diseases may proceed from the coldness and moisture or other qualities of the Sea; nor would I confidently reject such a surmise: But it may also be possible, that the compression, they suffered under water, might have at least a share in the production of these ill effects. For how are we yet certain, that the pressure of the water against their bodies, though it does not manifestly dislocate any solid or firm part, but only somewhat press inwards, as in the above mentioned Tadpole the outward skin and the fibres, (both which will easily yield a little way without being painfully stretched,) may not, by straightening the Vessels, and otherwise inconveniently, altar the circulation of the blood and the motion of the humours, spirits, and other fluid parts of the body? And I am not sure, that much of the cold, that Divers are wont to complain of, when under water, may not be a disaffection produced in the nervous and membranous parts, occasioned by the compression of the ambient water, there being divers things, and pressure among others, besides actual cold, that will make men complain of being cold; and in our case this sensation may be excited or assisted by the hindering of the usual perspiration at the constipated pores of the skin. And it seems not impossible, that one, not so ignorant and heedless as Divers are wont to be, may refer a new sensation, that really proceeds from pressure, to other Causes; since Learned and Intelligent men, when prepossessed (as these Common Divers usually are) with the vulgar opinion about the Non-gravitation of Water and Air in their natural places, do almost always refer 
* The reason of which experiment may be gathered from the 4th. Chapter of the Author's long since published Defence against Linus.  an experiment of my Engine to Suction, which is indeed the effect of the pressure of the Ambient, (as I have 
† In a Paradox about Suction.  elsewhere clearly shown,) and affirm, that the pulp of the finger or hand is drawn up into a hollow Pipe, into which it is indeed thrust by the weight of the Ambient air. But all these things I have mentioned, not as if I laid any great weight upon each of them, but to let you see, that 'twas not altogether without cause, that I complained of the incompetency of the History of what Divers feel under water; especially at great depths, where this want of information may be more considerable: For, as far as I have yet learned by perusing Voyages and enquiring of Travellers of my acquaintance, the places, where they are wont to dive for Pearl, are but moderately deep, and indeed shallow in comparison of the great depths of the Sea; so that if we were furnished with as many Relations of these profound places, as we have of the others, possibly the accounts would be different enough to render doubtful or to correct the received opinions about the conditions of Divers at the bottom of the Sea. For, I remember that a credible eye-witness, who, (if I mistake not) was the Intelligent Oviedo, speaking of the Pearl-fishing on the American Island of Cubagna, has among many other notable observations such a passage as this; But whereas the place is very deep, a man cannot naturally rest at the bottom by reason of the abundance of airy substance, which is in him, as I have oftentimes proved. For although he may by violence and force descend to the bottom, yet are his feet lifted up again, so that he can continue no time there. And therefore where the Sea is very deep, these Indian Fishers use to tie two great stones about them with a cord, on each side one, by the weight whereof they descend to the bottom, and remain there until them listeth to rise again, at which time they unloose the stones and rise up at their pleasure.  
And now to come closer to the explication of our difficult Problem; there yet occurrs to me nothing more likely in order to it, than what I have already mentioned in the Paper you will meet with about the Differing pressures, etc. And therefore it shall here suffice me to enlarge, and by further Considerations and Experiments confirm, what is there more summarily discoursed; namely, That the Phaenomenon may depend (chief) upon these two things, the uniform pressure of the fluid Ambient, and the robust texture of a humane body exposed to this Pressure.  
In one of the following. 
* New Experiments about the differing Pressure of heavy Solids and Fluids.  Papers, you will find examples of the great pressure that may be sustained unharmed by such frail bodies as Eggs and thin Glasses, that one would expect should be broken in pieces thereby, provided the pressure be exercised by the intervention of an Ambient liquor; as water. And by the account elsewhere referred to, of the Tadpole, it seems highly probable, that even that tender animal, when it seemed by some small diminution of the bulk to be every way a little compressed inwards, was put to no considerable (or perhaps to any sensible) pain or inconvenience, since it seemed to swim without any irregular motions, which would in likelihood have ensued, if it had been much harmed or incommodated. Which example, with those formerly pointed at, may teach us, that there may be a vast difference betwixt the resistance that a body can make when compressed immediately by Solid bodies, & when in the compression every way ambient Fluids intervene. Which you will the less admire, if you consider, that by reason of the grossness, hardness, or rigidness of visible Solid bodies the pressure can never be made every where so equally as by the parts of Liquors, whose smallness, which renders them singly invisible, fits them to accommodate themselves far more closely and conveniently to all the superficial parts of the body immersed in them, and to have the force of the compressing body more uniformly distributed to them. But because the Instances referred to, are taken from bodies surrounded with water, I will take two or three about the resistance of bodies to violently compressed Air; partly, because those made in our Engine are wont to be performed with Air (not condensed, but) rarified or expanded beyond its usual consistence; and partly, because it will not be denied, that the corpuscles of Air may be really compressed or thrust against one another, since 'tis clear, that they may be crowded into far less room, than they possessed before, and bear so strongly against the Glasses that imprison them, as not seldom, if too much compressed, to burst them in pieces.  
Consider then, that among bodies not fluid the Swims of smaller fishes are likely to be judged none of the most able to resist compression, since they consist of bladders so thin and delicate, that a piece of fine Venice-Paper is very thick in comparison, and that they contain nothing in them but soft Air not-compressed by any outward force. I caused one of these bladders of above an inch in length and proportionably great, to be taken out of a Roach, and anointed it with Oil to keep it supple, and preserve it from being pierced or softened by the water; and having by a weight of Lead, fastened to the neck of it, let it down to the bottom of a hollow Cylindrical tube, sealed at one end, and made purposely large, and about 56 inches long, for some Hydrostatical Experiments; we could not perceive, that by the weight of all the incumbent water it was manifestly compressed, or that it did discover the least wrinkle or other depression of the very thin membrane, though stuffed but with Air. And this trial was made more than once with the same success; and yet, that this proceeded rather from the robustness of the bladder, that was able to resist the weight of a taller pillar of water, than from the Non-gravitation of water in the upper part of the tube on that in the lower, we showed, by presently letting down such a Mercurial-Gage as is described, & often mentioned in the Continuation of our New Experiments. For letting down this by a string to the bottom of a tube, the weight of the incumbent water forced up some of the Mercury out of the open leg of the Syphon into the sealed one, and consequently compressed the air included there, which though it were not very much, yet it was very manifest. For the uncompressed Air being 3 inches and ⅝ in length, we judged it at the bottom of the tube about ⅝ by the intrusion of the Mercury that was impelled up; and to satisfy myself and others, that, if the incumbent water had been heavy enough, it would have visibly depressed the bladder in spite of any Principium Hylarchicum, since I could not have a tube long enough, the bladder was sunk into a Chrystal-Glass that had a long and Cylindrical neck, and was so well stuffed with a stopple that was Cylindrical too, that 'twas very difficult for any thing to get out betwixt it and the orifice of the Glass; then, a competent Quantity of air being left above the water, the stopple was warily and by degrees thrust down, and so, lessening the capacity of the Glass, compressed the air that was next it, and, by the intervention of that, the water that was under it. And though there did not upon a slight compression of the outward air appear any sensible operation upon the bladder, that was at the bottom of the water; yet, upon a farther intrusion of the stopple the pressure being increased, the immersed bladder discovered not only one but two considerably deep wrinkles, which presently disappeared upon the drawing up of the stopple. Upon whose being thrust in again, depressions were again to be seen on the Swim. And we having been careful to convey into the same Glass such a Mercurial Gage as has been lately spoken of, we estimated by the condensation of the air in the sealed leg of that Gage, that the bladder had been exposed to a pressure, that might be equivalent to that of a pillar of about 40 foot of water.  
This I hope will lessen the wonder, that Bodies of so firm a texture as those of lusty men, should support the pressure of the water at such depths, as Divers are wont to stay at; since we see, what resistance can be made by so exceeding thin and delicate a membrane stuffed only with air, in comparison of the strong membrans and fibres of a man, stuffed besides Air with more firm parts. I will not here urge, that great weights may be sustained in the Air by such tendons (or cords of fibres,) and by other fibres, as it were, interwoven into membrans, in comparison of what an ordinary man would expect: But I shall invite you to consider with me, that not only upon the account of the stable parts of the humane Body, but of the Spirits too, it may resist very violent pressures (and such as perhaps have not yet been considered) of a fluid Body, not only without any manifest conrusion or dislocation of parts, but without any sense of pain; which I suppose you will grant me, if, considering what great effects Gusts of Wind have upon Doors, Trees, nay Masts of Ships, blowing them down, nay breaking them; and that yet a man without being extraordinary strong will stand against the impetuosity of such a strong Wind, and walk directly against it by virtue of the vigour of his muscles and spirits, without being thrown down or bruised by so violent a Current of Air as beats upon him, but without so much as complaining that he feels any pain; and this, though the Wind that beats against him, however it be a fluid Body, yet because it acts as a stream, does not uniformly compress him, but invade only the forepart of his Body. Likewise, in the lifting up heavy weights by Porters, Carriers and other lusty men, we may see the slender tendons of the hands loaded with 100 or 150, or perhaps a far greater number of pounds, without having their fibres so far compressed or stretched as to make the lifters complain of pain, though sometimes they may of difficulty. So that, (as I could, if it were needful, confirm by other Instances) a humane Body is an Engine of a much firmer structure than Scholars are wont to take notice of. And here let me add, that I doubt, whether, if the structure of a man were not considerably (though not perhaps equally) firm, he would, especially in a deep Sea, be able to bear the pressure of the water, though not immediately applied, without pain. For (to give you one Reason more of my not acquiescing in vulgar reports about Diving,) having several times conversed with a man, apt enough both to inquire and observe, who got his living by taking up Shipwrecked goods, he answered me, when I asked him whether he felt any peculine pressure against the Drums of his Ears, which are membranes ●●t so well backed as those of other parts; that when he stayed at a considerable depth, as 10 or 12 fathoms, under the surface of the Sea, he felt a great pain in both his ears, which often put him to shifts to lessen it; which by his manner of describing it I concluded was from the incompetent resistance of the Air, which he acknowledged to me he found by manifest tokens to be notably compressed by the Superior water. Which Relation from such a person does not only confirm our explication, but likewise warrant us to doubt, whether the Common Reports that are made concerning Divers be fit to be relied on, without farther Examen and observation.  
In the mean time I shall add two or three Experiments more to confirm the resistance, that Animals may make to a great pressure, when exercised by the mediation of a fluid Body And I the rather gave you an account of this way of making trials, because it may be also helpful to discover the resistances of inanimate Bodies, whose Shape and Consistence we may choose and vary (almost at pleasure) to the pressure of (totally or in great part) ambient fluids. And if I had been furnished with a tube wide enough, and a quantity of Mercury great enough, I might by the way have shown you, that, whatever the Learned Doctor More is pleased to suppose, that to Butter itself even as considerable a pressure may be so applied as not to be able to make it yield thereunto. For on this occasion I shall add, that I well remember, that, among other trials to the same purpose, I caused a piece of fresh Butter, about the bigness of a small Hen-Egg, to be brought to an irregular shape, that, if the compression were such as many would expect, the long corners or solid angles being at least flatted, the Butter might be reduced into a more capacious figure and less remote from roundness. But though having put this lump of Butter into a Bladder, almost full of fair water, we proceeded, both in the same brass Cylinder, and much after the same manner that I employed about the Egg mentioned in the Fourth Experiment of the Tract of the Differing pressure of heavy Solids and Fluids; yet I found, that after the plugg had been loaded with a weight of Lead of above 50 pound, neither I, nor the Operator, perceived, the irregular figure of the Butter to be altered. Nor was this the only trial of this kind I made with the like success upon Butter, though I dare not charge my memory with the Circumstances; and therefore I shall without delay proceed to what I was about to recite concerning the Resistance of Animals.  
We took then a common Fleshslie, neither of the biggest sort of all, nor of the least, but of a middle size, and having put it into the shorter leg of a bend Glass, which we caused to be Hermetically sealed at the end, there was put in as much Mercury as filled that leg and a part of the other, leaving little more than an inch of Air between the Quicksilver and the sealed end, that there might be room both for the Fly and the Condensation of the Air, and then with a little Rammer, fitted for the purpose, we caused the Mercury in the open leg to be thrust against that in the sealed leg, which thereupon did necessarily crowd the Air near the Fly into less room; so that, by our guess, it was condensed into about a third part of the space, which it possessed before, and which it regained, when the Rammer was withdrawn: And though this were done more than once, yet not only the Fly was thereby not killed, but not so much, that appeared, as sensibly hurt, and I perceived her, whilst she was penned up, to move her legs and to rub them one against the other, as 'tis usual with that sort of Infects to do of their own accord in the free Air. Nor did I question but that, if the Glass had not been inconveniently shaped to admit the Rammer farther into it, the Fly would have supported a far greater Pressure.  
Another Experiment to the same purpose we tried with Water instead of Mercury; but, whereas this last named liquor could neither wet nor drown our Fly, (for which reason I chief made choice of it,) the other did first wet its wings, and soon after by a mischance drown it. But first we had an opportunity to compress the Air into a third, if not into a fourth part of its former dimensions, and yet the Fly continued to move divers of her parts and especially her legs very vigorously, as if nothing troubled her but her being, as it were, glued to the inside of the Glass by part of her wetted wings. And this I hope will keep the Resistance of Divers to the Ambient water from seeming incredible; since such Flies were able to resist, and (for aught appeared) without harm or pain, the pressure of the crowded particles of the Air; though we guessed this to have been as much compressed by the force of the Rammer, as it would have been by a Gylinder of water of 50 or between 50 and 60 foot high. By which also we may be helped to conceive, how great a difference there is, whether the same pressure be exercised by a solid or by a fluid Body. For, according to our estimate, the pressure against the Body of the Fly was as great as if a slender pillar of Marble, having the Fly for its Base, and 18 or 20 foot in height, had leaned upon the little Animal; which I presume you will easily think was more than enough to crush her to Death.  
But because, though the foregoing trials are not like to be rejected by the skilful, yet they require a somewhat dextrous and nimble Experimenter, and leave something to his estimate, I will subjoin an Experiment more easy to be made, and wherein the weight may be determined by Measure rather than Conjecture, being made to be perpendicularly incumbent on the Fly or other Animal. For the Experiment may be as well made on other Infects, as Worms, though some that I had provided chanced to miscarry before they came to be used.  
We took then some ordinary black Flies (such as use to haunt Butchers stalls in warm seasons,) of a middle size, (the length of the Body and Head of one Animal, which for trials sake we measured, being about three eights of an inch,) and having placed one of them with the head upwards, that there was some distance left betwixt her and the sealed end of the Glass-tube 9 or 10 inches long; we poured in Quicksilver very slowly and cautiously, lest the force of so heavy a body, acquired by the acceleration of its descent, should more than the mere weight itself of the liquor oppress the Fly. To this effect stooping the Glass very much towards the Horizon and letting the Mercury puss into the tube through a Funnel, whose lower part was very slender, that it might come down but by little and little, we at length got in as much Mercury as the tube would receive, and then holding it upright, we watched, whether the Fly would make any motions; and finding, that she did manifestly stir notwithstanding the incumbent Mercury, we measured the height of the Mercurial pillar, reaching from the middle of her body to the top of the liquor, and found it to be about eight inches, and the Quicksilver being poured out, the Fly appeared to be so lively and vigorous, that I doubted not, but if we had had a longer Glass, the Experiment had been much more considerable. But when afterwards I was able to procure a better tube, the season of Flies being almost quite past, I could scarce get any, and those not brisk, as they are wont to be in Summer. But however we repeated the Experiment with one of the best we could take of the  size, and ordering the matter so, that the Mercury incumbent on her, (for there was some beneath her,) appeared to be of a greater height than the formerly employed tube was of, we saw her move one or other of her little legs divers times, though the tube were held upright; and therefore measuring the height of the Mercury above her, we found it to amount to 16 inches and better, and then freeing her from this pressure, we observed, that she immediately found her legs again, and moved up and down briskly enough; but when she was loaden with 23 or 24 inches of the same Quicksilver (though the liquor were soon after poured out) she gave no signs of life, which I suspected might happen, not so much from her having been oppressed by the greatness of her weight, as from the great care of the Operator to let down the Mercury very obliquely and warily upon her. And this I was the rather confirmed in, because having got an other Fly of about the same bigness, though when she was at the bottom of the Quicksilver, she seemed so compressed as not to have any motion we could take notice of, yet, upon her being taken out of the Glass, she presently appeared to be alive by walking about and beginning to display her wings, though the pillar of Mercury, that had leaned upon her, amounted to above 27 inches. And I presume, the success would have been much more considerable, if the Experiment had been tried in the Summer, when these Creatures are brisk and lively, and not as it was in the Winter; besides that probably these little Animals were hurt or weakened by the violence that would scarce fail to be used in catching them, and putting them into such a place and posture in the Glass as was required; the actual coldness of the Quicksilver perhaps also making them somewhat torpid, whilst it touched them so many ways. And it must not be here omitted, that a Fly, that seemed but about half so big as one of those hitherto mentioned, being well placed, with some Mercury under it, in a Glass-pipe held upright, sustained a Mercurial pillar of somewhat above 25 inches; and though she was not observed to move under so great a weight, yet when once it was taken off, she did not appear hurt, much less crushed to Death by it, and probably would have escaped under a much greater weight, if the tube, which was too large, had not already employed all the stock of Mercury we then had at hand. But I do presume, that what we did try will be available to our purpose, since we see clearly, that so small an Animal as a Fly may survive so great a pressure, and that she could not only live, but was able to move such long and slender Bodies as her legs, when she was pressed against by above 16 inches of Mercury, and (consequently) by a weight equivalent to a pillar of water of above 18 foot and a half, which being above 590 times her own length, and (according to the estimate our measure suggested) many times more her own height; so that a Diver, 6 foot tall, (which is somewhat more than an ordinary man's stature,) to have as many times his height of water above him, as our Fly might have had and yet have moved under it, must dive (at least in fresh water,) to near a hundred fathom, which is a far greater depth (perhaps by 5 or 6 times) than, for aught I could learn by inquiry, the Divers either for Coral or Pearl are wont to descend.  
And now, Sir, having tendered you the likeliest conjectures that occurred to me about the solution of this difficult Problem; I shall return to Doctor More, and consider the objection, he frames from the supposed insolubleness of it. And on this occasion I shall have two or three things to represent to you.  
The first is, that there would be much more weight in what he objects, if our Assertion of the gravitation of water in water were, like the Principium Hylarchicum, a mere Hypothesis advanced, without any clear positive proof, whereas our Doctrine is not only elsewhere directly proved, by particular Experiments, but by the very controverted one of the Tadpole; to elude whose force so Ingenious a person is fain to fly to a Principle, that, (to say here no more,) is not Physical. And from this first of the things I lately mentioned I shall hasten to the second, because it will require to be longer insisted on.  
I shall then further represent that whatever power he is pleased to suppose at the bottom of the Sea to suspend the impression of the incumbent Water, I think, that supposition ought to give place, if not to our former Ratiocinations, yet to experience itself, which shows there really is a great pressure exercised by the Water at the bottom of the Sea. I remember, that a friend of the Learned 
* Sir R. M.  Doctors and mine, who is so eminent a Virtuoso as to have been often Precedent of the Royal Society, related a while since to me, that a Mathematical friend of his, whom he named, having had an opportunity to try an Experiment, I have in vain endeavoured to get tried for me, had the Curiosity to let down in a deep Sea a Pewter-bottle with weight enough to sink it, that he might try, whether any sweet Water would strain in at the orifice or any other part; but when he had pulled it up again, he was much surprised to find the sides of his Pewter-bottle very much compressed, and, as 'twere, squeezed inward by the Water. I also not long since enquired of an observing Acquaintance of mine, that has a considerable estate in America, whether he had not tried to cool his drink, when he sailed through the Torrid Zone, by letting down the bottles to a great depth into the Sea, and, if he did, in what Condition he found them when they were drawn up again. To which he answered, that he had several times employed that Expedient for the Refrigeration of his Drinks, but was at first amazed to find the Corks, with which the strong stone-bottles had been well stopped before, so forcibly and so far thrust in, that they could scarce have been so violently beaten in with a Hammer, and 'twas scarce possible to get them out. And an other Ingenious Person, that practices Physic in the Indies, having the like Question put to him, answered me, that he had some while since had the Curiosity to try in a very deep part of the Sea, whether any fresh Water would strain into Stone-bottles through a thick Cork strongly stopped in, and having let it down with a convenient weight to 100 fathom, was much disappointed, when he drew it up, by finding that the pressure of the Water at so vast a depth had quite thrust down the Cork into the Cavity of the bottle (which else perhaps would have been crushed to pieces;) an effect which he would scarce have expected from the strokes of a Mallet. And if to all this it be objected, that 'twas not the pressure, but the coldness of the Water that did the recited feats by condensing the included Air, and obliging Nature to do the rest for fear of a Vacuum; I will not launch into the Controversy, whether Nature do any thing ob fugam Vacui, but only answer, that I cannot find by the Relations of the Divers or otherwise, that 'tis ever so cold at the bottom of the Sea, as 'tis frequently above ground in Winter, when great Fishes are commonly said to return to the deep parts of the Sea for warmth, and yet in the sharpest Winters I never observed Corks to be driven in by the cold of the Ambient; nay, I purposely tried with a Frigorifick mixture, that very intense degrees of cold, such as would quickly freeze many Liquors, would not occasion the breaking of thin bubbles of Glass purposely blown at the flame of a Lamp and hermetically sealed.  
And to show ad oculum (as they speak) that Water may press more and more, as it grows deeper, against the stopple of a Bottle, though the Vessel be inverted, I will subjoin this Experiment. Because we have no Water hereabouts that is near deep enough to force in a Cork, as the Sea-water did in the above recited trials, I thought of a way of so closing the Glass-vessel, as that the stopple should keep asunder the Air in the Vessel and the outward Water, and hinder all immediate intercourse between them, and also make some resistance against the pressure of the external Water, and yet be capable of freely moving up and down, and so be a good Succedaneum to a solid stopple. Taking then a Glass-Vial, furnished with a (somewhat long) Cylindrical neck, whose Cavity was large in proportion to the rest of the Vessel, we put into it as much Quicksilver as would in the neck make a short Mercurial Pillar of between half an inch and an inch; then, a piece of very fine Bladder, dipped in Oil, was so tied over the orifice of the Glass, that no Mercury could fall down or get out, nor Water get in at the orifice, and yet the Bladder, by reason of its great limberness, might be easily thrust up towards the Cavity of the Vial, or depressed by the weight of the Mercury. This little instrument, first furnished with a weight of Lead to sink it, being inverted, the Mercury descended into the neck, and closed the orifice as exactly as a stopple, and yet with its lower part depressed the Bladder beneath the Horizontal Plane, that might be conceived to pass by the orifice; then the Glass, being a while kept in the Water, (that the included Air might be brought to the Temperature of the surrounding Liquor,) and by a string let further down into the same Glass-vessel filled to about two foot in height, the pressure of the Liquor against the orifice of the Vial did by degrees drive up the Bladder and the Mercurial stopple into the cavity of the Neck, as was manifest by the ascension of the Quicksilver; and when the instrument was leisurely drawn up again, the weight of this Mercury made it subside and plump up the Bladder again as before. An Experiment akin to this, and therefore fit to confirm it, I have delivered in another 
* See the Paradox about Suction.  Discourse.  
And here I shall subjoin what very opportunely occurred to me since the writing of the last page. Meeting casually with an Ingenious Mechanician, (whom you will find I have 
* In the Tract of the Differing Pressure of heavy Solids and Fluids.  elsewhere mentioned) that devised a suit of  and other accommodations, (wherein I once saw him let down into the Water,) by whose help and that of a boat he could (and did) continue there a great while at a considerable depth under water, and there work; I asked him afresh (to obtain fuller informations than formerly) whether he felt not the pressure of the water against his breast and belly, to which he answered me (more circumstantially than he had before) that when he was about 4 or 5 yards under water, though but in the River Thames, his breast and abdomen was so compressed, that there being hardly room enough left for the free motion of his Lungs he could scarce fetch his breath, and was necessitated to make them draw him quickly up, and that (among his later trials to improve his Engine) having for remedy hereof, caused a kind of Armour for the Chest and back to be made of Copper, though the stiffness of the Metal defended him from receiving any mischief in those parts, yet in the others, where only the Leather, though strong, was interposed, when he came to the depth of about six fathom, though in fresh water, he found a great pressure against his legs and arms and all the other parts against which the water was able to thrust the Leathern suit inwards. And this pressure being found by him, as he told me, pretty equal (against all the exposed parts, for from the other, which were more yielding and obnoxious, the Armour kept it off,) he received no Mischief from it, not yet much Incommodity (and some he might expect from the stiffness and unequal yielding of the Leather;) so that he could stay under water, though not still at so great a depth, about 2 hours or longer. And upon the whole matter he answered me, that he was well satisfied by his trials, that the ambient water endeavoured to press him & his Diving suit every way inwards. Whether the coldness of the water had any interest in this Phaenomenon, I particularly enquired of the Engineer; but he replied, that by reasion of the tightness of his Diving suit or instrument, the warm steams of his body that were penned in, and other concurring circumstances kept him from feeling any cold, and made him sometimes feel a greater Heat than he wished. He has promised me before it be very long to make for me a trial or two that I propounded to him, from whose success, if he can but reduce them to Experiment, I hope to be able to present you a farther Confirmation of our Hypothesis. In the mean time, the things already recited, together with the preceding Experiments, may well suffice for our present purpose. For, by what hath been said it appears, that Water does actually press against bodies, whether specifically lighter or heavier than itself, placed under water, and that this pressure increases with the height of the water above the immersed Bodies. And this being so, it is not more necessary for me than for men of other Opinions to give a clear reason why Divers can resist so great a pressure of the incumbent water. And the pressure of the water in our recited Experiment having manifest effects upon Inanimate bodies, which are not capable of prepossessions or giving us partial informations, will have much more weight with unprojudiced persons, than the suspicious and sometimes disagreeing accounts of ignorant Divers, whom prejudicated opinions may much sway, and whose very sensations, as those of other vulgar men, may be influenced by Predispositions and so many other Circumstances, that they may easily give occasion to mistakes. I know, that Learned men, that never were conversant in hydrostatics, are wont to think it very difficult, if not impossible, to conceive, how so weak a thing, as they fancy an Animal to be, should avoid the being oppressed or so much as harmed by so great a weight of Water. But they that shall attentively consider what has been offered towards the removal of this difficulty, and remember, how little they would have believed, that there is so great a difference, as we have by the Tadpole, the Fly and other instances, shown there really is between the pressure of Solid and of Fluid bodies, will, I presume, be apt to think it fit, that, if for want of a sufficient History of matters of fact any scruple remain about the Solution we have offered from the nature of the Uniform pressure of Fluids', and the Firm structure of the Humane body; we should, to remove those remaining scruples also, rather range about for other Physical helps to solve more completely the Problem, about such a thing as Compression, which is an action purely Corporeal and Mechanical, than for want of a ready and complete Solution to fly to the immediate interposition of an immaterial and intelligent yet Created Agent, to explain clearly whose manner of working would be a much more difficult Task, than the solution of the Phaenomenon without it.  
And now, Sir, having presented to you the Reflections I thought requisite to write upon the Learned Doctor's discourses against my Hypothesis and Explications, relating to the gravitation and pressure of Fluids', I have little more to trouble you with in this Paper. For, though in the latter part of the 13th. Chapter the Doctor is pleased to spend divers pages in the Explication of divers of my Hydrostatical Phaenomena by the Agency of that incorporeal Director, that he calls Principium Hylarchicum; yet since these Explications of his are rather attempts to accommodate the Phaenomena to the Hypothesis, than objections directly levelled against my Solutions, I shall altogether forbear to examine them; the main thing that I intended in this Paper, according to what I told you at the beginning, being to show, that the Arguments urged against the Mechanical solutions of the Experiments by me recited, do not evince any of them to be erroneous. And I have neither the design nor the leisure solicitously to examine the Doctor's Hylarchical Principle. Of which I shall only say, that though he tells us, it is 
* Page 175.  paratum ad movendum quoquoversum materiam pro data occasione; yet since he also tells us, 
* Page 167.  Quod particulae molis corporeae sive stabilis sive fluidae à Principio Hylarchico in unam aliquam partem omnes junctim urgeri possunt & premi, quamvis singulae singulas in nullam partem premant, quodque pro magnitudine molis major minorve totius fit pressio; and that the force by which it endeavours to keep the Elements in their true and natural Consistence, though it be very great, is not invincible 
* Pag. 167. : I see no need we have to fly to it, since such Mechanical Affections of matter, as the Spring and Weight of the Air, the Gravity and Fluidity of the water and other Liquors, may suffice to produce and account for the Phaenomena without recourse to an Incorporeal Creature, which 'tis like the Peripatetics and divers other Philosophers may think less qualified for the Province assigned it, than their fuga Vacui, whereto they ascribe an Unlimited power to execute its Functions. I leave it therefore to you, Sir, to judge which of the two ways, of explicating an Hydrostatical Phaenomenon, the Learned Doctors, or that which I have made use of, relishes most of the Naturalist. And I shall only tell you, that if I had been with those Jesuits, that are said to have presented the first watch to the King of China, who took it to be a living Creature, I should have thought I had fairly accounted for it, if, by the shape, size, motion, etc. of the Spring-wheels, balance and other parts of the watch I had shown, that an Engine of such a structure would necessarily mark the hours, though I could not have brought an argument to convince the Chinese-Monarch, that it was not endowed with Life. From which comparison you will easily gather, that what I have thought myself concerned to do in this place, was not to demonstrate in general, that there can be no such thing as the Learned Doctors Principium Hylarchicum, but only to intimate, that, whether there be or not, our hydrostatics do not need it. Nor do I think it necessary to the Doctor's grand and laudable design, (wherein I hearty wish him much success) of proving the existence of an Incorporeal substance. For as I think, Truth ought to be pleaded for only by Truth; so I take that, which the Doctor contends for, to be evincible in the rightest way of proceeding by a person of far less learning than He, without introducing any precarious Principle; especially experience having shown, that the generality of Heathen Philosophers were convinced of the being of a divine Architect of the World, by the contemplation of so vast and admirably contrived a Fabric, wherein yet taking no notice of an immaterial Principium Hylarchicum, they believed things to be managed in a mere Physical way according to the General Laws settled among things Corporeal, acting upon one another. And after this I have nothing more to say, but that I would not have any thing that I have said misconstrued to the Learned Doctor's prejudice. For 'tis nor necessary, that a great Scholar should be a good Hydrostatician. And a few hallucinations about a subject, to which the greatest Clerks have been generally such strangers, may warrant us to descent from his opinion, without obliging us to be enemies to his Reputation. And therefore if you have found any thing in this Paper inconsistent with a just tenderness of that, you have not only my consent, but my desire to alter it, as an Expression, that doth not well comply with my Intentions of not appearing any farther his Adversary in our Debate, than the desire of showing myself a Friend to the Truth I was to defend, should exact of,  
SIR, Your, etc.     

An Hydrostatical LETTER, Written Feb. 13. 167 2/ ³;.  
Containing a Dilucidation of an Experiment of the Honourable Author of these Tracts about a Way of Weighing Water in Water, upon the occasion of some Exceptions made to it by Mr. George Sinclaer. 
* In his hydrostatics, printed at Edenburg 1672. p. 146. ss.    

TO THE READER.  
WHen this Discourse was just finishing in the Press, there came to the Publisher's hands a dilucidation of an Experiment of the Honourable Author of these Tracts, about a Contrivance of his for Estimating the Weight of Water in Water, formerly published in Numb. 50. of the Philosoph. Transactions, and by the following Discourse cleared from the exceptions to be met with in Mr. George Sinclair's Book, entitled The hydrostatics, etc. printed at Edenburg, 1672. Which Dilucidation, because of the Affinity of the subject, was thought fit to be here annexed.   

An Hydrostatical LETTER, Written Feb. 13. 1672/ 3.  
Containing a Dilucidation of an Experiment of the Honourable Author of these Tracts about a Way of Weighing Water in Water, upon the occasion of some Exceptions made to it by Mr. George Sinclair. 
* In his hydrostatics, printed at Edenburg 1672. p. 146. ss.   
SIR,  
CAlling this night in Paul's Churchyard for the Ingenious Mr. Rays Travels, that you yesterday commended to me, I was also shown a New Treatise, that I never saw before, of a Learned Gentleman, and hastily running over the Index, found an Experiment of mine declared Insufficient; and though, being hindered to make haste home, it be so late, that far from having time to peruse the book itself, (which I tell you, that you may not now expect any Character of it from me,) I have been scarce able to read over, more than once, what directly concerns me in it; yet I shall adventure to say something about it this night, for fear I should not, in so busy a time as this, be allowed to do it to morrow.  
Whereas then the Learned Objector having recited my experiment about weighing Water in Water, as you were pleased to publish it in a book enriched with so many better things, the 
* Numb. 50.  Philosophical Transactions, gins his animadversion with saying that herein is a great mistake. I shall not in that much oppose him: For possibly the Dispute between us is not much more than verbal. And because my Experiment coming abroad by itself, and supposing things that I had formerly proved, and published, but which were not expressly referred to in it, I wonder not that my meaning should not by all Readers be fully understood. And therefore, to explain myself on this occasion, give me leave both to repeat my Opinion, and to show you, on what occasion and how far I designed to confirm it by this Experiment. My opinion then was, and still is, that as water is a heavy fluid, so it does retain its Gravitation and power of pressing; by which I mean a tendency downwards (whatever the cause of that gravity be,) whether it have under it a body either specifically heavier or lighter than itself or equiponderant to it. For I see not what should destroy or abolish this Gravity, though many things may hinder some effects of it. And therefore I suppose, that Water retains its Gravity not only in Air but in Water too, and in heavier liquors, and consequently, by virtue of this, the liquor presses upon them; but if a surrounding fluid have, upon the score of its specific Gravity, an equal or a stronger tendency downwards than water, it will, by virtue of that, be able to impel up this liquor or to keep it from actually descending: so that a portion of water, supposed to be included in a Vessel of the same specific weight with water, this portion, I say, placed in a greater Quantity of the same water will neither rise nor fall, as I have elsewhere shown; but yet it retains its Gravity there, only this Gravity is kept from making it actually descend by the contrary action of the other water, whose specific Gravity is supposed equal; as when a just balance is loaded with a pound weight in each of its scales, though neither of the weights actually descend, being hindered by its counterpoise, yet each retains its whole weight, and with it presses the scale it leans upon; so that our lately mentioned included portion of water does really press the subjacent water, though it does not actually depress it, or, (as perhaps a School-man would phrase it) does gravitate on it but not pregravitate. Nor do I think, that the only way of judging, whether a body gravitates, is to observe, whether it actually descends, since in many cases its Gravity may be proved by the Resistance it makes to heavy bodies, which, if it were not one, would raise it: As may be declared by what I just now noted about equal weights in a balance: And for want of this distinction I have known even learned men, treating of Hydrostatical things, mistake both me and the Question.  
The next thing I had to tell you, is, that the Adversaries, I had to deal with both in Print and in Discourse, denied, that in (standing) Water, the upper parts did press or gravitate upon the lower; and though they could not but grant, that the whole weight of the Water did gravitate upon the bottom of the Vessel; yet they would have the parts of it to do so actione communi (as they speak) and fancied I know not what power of Nature to keep the homogeneous portions of Water, as well as other Elements, from pressing one another, when it is in its proper place. Against this Opinion, (which I presume my Learned Adversary and I agree in opposing,) it was alleged, besides other things, which I found many, otherwise good, Scholars were not fitted to understand, That if a Glass-vial or bottle, well stopped, were deeply immersed under water, it would strongly tend upwards; but if it were dextrously unstopped, when 'twas thus immersed, so as the water could get in, abstracting from or allowing for the weight of the Glass itself, 'twould by the water, that crowds in and thrusts out the Air, be made strongly to tend downwards and continue sunk. But this not satisfying, because 'twas pretended, that the reason of the empty bottles emerging when stopped was the positive Levity of the Air it was filled with, and the sinking of it, when unstopped, was from the recess of the same Air, that by the intruding Water was driven with large bubbles out of the bottle; I thought this evasion might be obviated by contriving an Experiment, wherein the Water should be plentifully and suddenly admitted into the Glass, and yet no Air expelled out of it, (which Circumstance I therefore took notice of, where I say, no bubble of Air appeared to emerge or escape through the water,) so that, if then the Glass that was kept up before should fall to the bottom with a gravitation amounting to a considerable weight in respect of its capacity, the sinking of it could not by them be ascribed, as before, to the recess of the Air, endowed, as they suppose, with positive Levity, but to the weight of the admitted Water, which, when thus weighed, would be environed with Water of the same kind: And to show, that this admitted Water might have a considerable weight notwithstanding the place it was in, I employed a pair of scales after the manner that is recited in the Experiment.  
By what I have been discoursing, you may conceive, that, however my expressions disagree with those of my Adversary, the distance of our opinions is not so wide as at first sight it seems. For he allows as well as I, that the superior parts of Water do by their Gravity, (for I know not on what other score they can do it,) press the inferior. But this he would not have amount to this expression, that water weighs or gravitates in water; whereas I scruple not to  my sense in that expression, because I think, water does always exercise its gravity, though it does not always pregravitate or actually descend, being often (as I noted above) either impelled up by an opposite and prepollent weight, or hindered from descending by the Resistance of other water that counterpoises it: so that, if he thinks, that in my Experiment I meant to propose a method of making Water descend in Water, and weigh it in that Liquor with a pair of scales, just as if I would weigh in the same Water a piece of Lead or a portion of Mercury, which are bodies much heavier in specie than Water, either he mistakes my intention, or I did not sufficiently declare it. But that which I designed to show, and, for aught I can yet see, have shown, was, that by the help of an ordinary balance, it may be made appear, that Water admitted into the Glass-bubble, I employed, did make the Glass-bubble weigh so much heavier than it did before that Liquor entered into it; and that this new weight, that was manifested by the balance, was not due, as my Adversary supposed, to such a recess of the Air as I mentioned a while ago.  
And now, Sir, It will be proper to take notice of some passages in the Objectors Discourse, in order to dilucidate the subject of it. Whereas he says (page the 149. & 150.) Take a piece of wood, that is lighter in specie than Water, and add weight to it by degrees, till it become of the same weight with Water; knit it with a string to a balance, and weigh it in Water, and you will find the whole weight supported by the water. I answer, that this does not at all overthrow my opinion, but agrees very well with it. For, suppose, the weight you add to the light would be Lead, it cannot be said, that the Metal loses its native ponderosity whilst it rests in the Water; and the reason, why it descends not, is, that it and the wood, it is joined to, are hindered by the counterpoise of the Collateral Water, which by its pressure would raise the surface of the Water, whereon the floating or swimming body leans, if it were not hindered by the weight of these incumbent Solids: And this Resistance of theirs to the endeavour upwards of the Water, being exercised only upon the account of their Gravity, shows that they do in my sense gravitate (though not pregravitate.)  
Again, if you please to consider the case, put by the Objector (page the 151.) and cast your eyes upon his Scheme, which, (supposing you to have his book) I shall for brevity's sake make use of at present; you will find him thus argue. 
* Vid. page 151.  Now, I say, 'tis six ounces of the weight (B) that makes this alteration, and turns the scales: For, if 12 ounces sink the Glass below the Water, when it is full of Air and no Water in it, then surely six are sufficient to sink it when it is half full. And the reason is, because there is a less potentia or force in 6 inches of Air by the one half to counterpoise a weight of 12 ounces, than in 12 inches of Air. Therefore this Air being reduced from 12 inches to six, it must take only 6 ounces to sink it.  
To which I answer, that I know not yet, what, on this occasion, he means by a potentia or force in 6 inches of Air to counterpoise a weight of 12 ounces. For by the term counterpoise, where the Question is about Weighing, one would think he speaks of Weight; and yet Air, according to the vulgar Opinion, is positively light; according to us; though it have a gravity, yet in our case that must amount to so little, that what Air the bubble needed to fill it, could not weigh at most above 4 or 5 grains, which therefore might safely be neglected. But, according to my opinion, the reason of the Phaenomenon is clear enough without meddling with the Potentia of the Air. For, if we conceive a horizontal Plane to divide the Water mentally, and pass by the bottom of the suspended bubble; before the little stem be taken off, there is a far greater pressure upon the other parts of that Plane than upon that which lies under the bubble, in regard they are pressed by the weight of the Collateral Water (A, L, G, D, M, C,) whereas the other is pressed only by the weight of a body very much lighter than its equal bulk of water: so that, to keep the bubble from being forcibly buoyed up, there was requisite 18 ounces of Lead that make up the Plummet (B) to detain it under Water, and keep the beam of the balance Horizontal; that when access is given (at C) to the neighbouring Water, it is by the weight of the collaterally superior Water impelled into the cavity of the bubble, where the Air, being much rarified before, could not resist its ingress, and thereupon 6 ounces of Water getting in, that part of the imaginary Plane, on which the bubble was incumbent, is pressed by a greater weight than formerly by 6 ounces, and consequently there needs the like weight in the opposite scale of the balance, to reduce the scale to an Aequilibrium. And if we suppose, with our Author, the Glass to be completely full of Water, and the counterpoise in the scale (O) to need 6 ounces more to make a new Aequipondium, the account of the Phaenomenon will be the same, as, if you attentively consider it, you will clearly perceive. And the reason, why the additional weight of 6 ounces is required, will be, that the upper half of the bubble, that before contained less than three or four grains weight of the Air, being now filled with Water, amounted to six ounces more of Water than formerly, and so the counterpoise in the opposite scale (O) will need the weight of six ounces to make a new Aequipondium.  
Congruously to this explication when the Examiner says, 
* page 132.  Now I inquire whether these 18 ounces are the Aequipondium of the Water within the Glass or of the weight of the Lead (B)? 'Tis impossible they can counterpoise both, seeing the Water is now 12, and B 18. It must then either be the counterbalance of the Water or the counterbalance of the Lead. It cannot be the first, because 12 cannot be in Aequipondio with 18; it must then be in the second: Or if these 18 ounces in the scale (O) be the counterpoise of the Water within the Glass, I inquire what sustains the weight of the Lead (B)? The weight of it cannot be sustained by the Water, because 'tis a body naturally heavier than Water; it must therefore be sustained by the balance. I answer, that this specious objection seems (for it is somewhat obscurely worded) to be founded upon a mistake of my meaning in the Question. However, as to the Phaenomenon itself; according to my sense the 18 ounces in the scale (O) are the counterpoise of the 18 ounces that hang from the opposite and aequidistant Scale and make up the Leaden Plummet (B,) (which answer I see not how our Author prevents.) But than you will ask, what counterpoises the Water in the bubble, which alone weighs 12 ounces? I answer, that 'tis the gravitation of the collateral Water, which presses the other parts of the lately mentioned imaginary Plane, as much as the Water in the bubble, the weight of the Glass being here not reckoned by either of us; and the Water incumbent on the bubble does press that part of the Plane on which they lean; so that there being in all 30 ounces to be sustained, the 18 of the Plummet and the 12 contained in the Glass, the Lead that hangs in the Water is counterpoised by 18 ounces in the scale, and the Water in the bubble by the pressure of the Collateral Water.  
But you will say, that it appears not, that the included Water presses at all, since it does not at all descend. To which I answer, that as long as the Water was getting into the Cavity of the bubble, so long it did manifestly gravitate upon the subjacent Plane, and actually descend, raising the counterpoise in the scale: But when, by adding more weight to that counterpoise, things are brought to a new Aequilibrium, there is no reason why the gravitation of the Water should again change the now regained Aequipondium. Suppose in the two scales of a balance there were placed two equally capacious and equiponderant Vials, whereof one is quite full and the other almost full; 'tis evident, that the full Vessel will keep the scale it leaned upon depressed, and, if you gently pour in as much Water into the unfilled as the filled has more than it, the scale, that was formerly kept raised, will be now depressed, till the beam be brought to be horizontal; to which posture when it is once brought, the Aequilibrium will continue: And yet it will not be said, that though the added Water, whilst it was filling the Glass, depressed the scale it belonged to, yet it lost its weight, or, which in my sense is all one, did not gravitate upon the Scale, when the balance was come to an Aequilibrium, because then this Water did no longer depress it. And how much the Water in our bubble does, notwithstanding its immersion, gravitate, would be visible, if by supposition it were all annihilated, and no other suffered to supply its room. For, then the subjacent part of the imaginary Plane being much less pressed than immediately before, the weight of the collaterally superior Water would strongly impel up the bubble, if it were not kept in its place by a proportionable addition of weight to the Plummet. Nor should it seem a strange thing that I should say, that the 30 ounces, lately mentioned, should be counterballanced partly by the weight in the opposite Scale, and partly by the Water that fills the immersed bubble, since this notion may be warranted even by the common practice of weighing heavy Solids Hydrostatically. For if you would, for instance, weigh a lump of Copper of 9 pound in common Water, the Metal, hanging by a Horsehair under Water, will need, according to my elsewhere mentioned Experiments, either just or near about 8 pound in the opposite Scale to keep the balance horizontal, so that the whole 9 pound, that the lump weighed in the Air, is counterpoised partly by the 8 pound newly mentioned in the opposite Scale, and partly by the weight, or resistance following from weight, of as much of the Water as the Copper fills the room of; which, as experience shows, is one pound: And if we should conceive Water in a Vessel adiaphorous as to Gravity and Levity to be substituted in the place of the Metalline lump, it would weigh as much as the ninth part of the Copper-lump weighed in the Air, and the same counterpoise of eight pound would maintain the Aequilibrium.  
What the Learned Objector has at the close of his Discourse about the natural and artificial balance, could not without prolixity, and is not here necessary to be dwelled upon; especially since you will see, in what I suppose you have now received from the Press, in answer to the Ingenious Doctor More, what is to be said on that Subject according to my Hypothesis. Wherhfore though my Learned Adversary does in the 152. page conclude, That Water cannot weigh in Water, and asserts, that the Pressure of Water is one thing, and Water to Weigh in Water is another; yet, as I said at first, I conceive much of our Difference may be verbal; and in my sense, when Water presses subjacent Water, because it does so upon the score of its gravity, it gravitates in Water, though it does not pregravitate, that is, actually descend. And since 'tis in the sense of this last expression, that our Author, if I mistake him not, speaks of weighing in Water, his conclusion, that Water cannot weigh in Water, does not contradict me, who affirm not that Water does so weigh in Water. Whether we shall agree in all other points of hydrostatics, you will easily believe that I cannot yet tell, though by the expression he is pleased to use (in the 146. page) to usher in his Objection with, 'tis probable we may. And as to the now dispatched debate, if I have employed some words in another sense than he, I presume he is so equitable as to consider, that I did not write of these things after having seen this book of his, but some years before, and have since found those expressions justified by the use, that eminent Writers have thought fit to make of them. And however I am glad, that he has given me this opportunity of clearing my Experiment, and declaring by examples as well as words the opinion it relates to; especially, if it seems to others that I omitted to express myself so fully; my design being, as I formerly told you, to convince such Adversaries, as I then had met with, by showing, that the above-recited Phaenomena of the Emersion and Sinking of a Glass-Vial, depended upon the Gravity of the Water, and not upon the positive Levity of the Air.  
FINIS.   

NEW EXPERIMENTS Of the Positive or Relative LEVITY of BODIES Under Water.   

NEW EXPERIMENTS Of the Positive or Relative Levity of Bodies under Water.  
'TIs obvious, even to the Vulgar as well as to Philosophers, that if Wood, Wax, or another body that is lighter in specie than water, and naturally floats upon it, be detained under water, it will upon removal of that force emerge to the top. And this it does so readily, and, as it seems spontaneously, that not only the Peripatetic Schools, but the generality of Philosophers both ancient and modern, do as well as the Vulgar ascribe this ascension of lighter bodies in water to an internal principle, which they therefore call Positive Levity.  
But this Principle was not always so universally received among Philosophers, as in later ages it proved to be, Democritus and several of the Ancients both Atomists and others, admitting no absolute but only a relative or respective Levity, which opinion some of the Moderns have ingeniously attempted to revive.  
But because whatever wit they may have employed in arguing; yet the Schools seem to have the advantage in point of Experience, the obvious instances, given by the Peripatetics, having neither been solved by real and practical variations of the same instances, nor counterballanced by new Experiments of a contrary tendency; the importance and difficulty of the subject invited me to attempt, when I was upon Hydrostatical trials, whether I could experimentally show, that whatever becomes of the general Question about Positive Levity, we need not admit it for the true and adequate cause of the emersion of Wood and such lighter bodies, let go under water.  

EXPER. I.  
THe instance that is wont to be urged to prove the Positive Levity of Wood in Water, seems to me to have been too perfunctorily made to be safely acquiesced in. For even as it is proposed with advantage by a learned foreign Mathematician, I cannot think it accurate enough to determine the present Controversy: for I will readily allow him to suppose, that in case a flat board, as for instance a Trencher, have its broad surface kept by a man's hand or other competent force upon the Horizontal bottom of a Tub full of water, if the hand or other body that detained it be removed, it will ordinarily happen that the Trencher will hastily ascend to the surface of the water. But I do not perceive, that a decisive Experiment of this kind is easy (not to say, possible) to be made with such materials. For the wood, whereof both the Trencher and the bottom of the Barrel consist, are supposed to be lighter in specie than Water; and to be so, they must be of a porous and not very close texture. To which agrees very well, that the solider woods, as Lignum Vitae, Brasil, etc. whose texture is more close and compact, will not float on water but sink in it: And therefore, if there be not much more care used, than I have yet heard that any Experimenter has employed, to bring the surfaces of the Trencher and the bottom of the Barrel to a true flatness and as much smoothness as they can be brought to, I shall not think the trial so accurately made as it might be; not to say, which I suspect, that though it be mentally, yet it is scarce practically possible to bring such porous bodies as those of the lighter woods to be fit for such a contact as might be necessary to make the trial accurately. And in case that were actually done, I should be kept from expecting with my adversaries the emersion of the Trencher, by the Experiment by and by to be recited, and by the true reason of it.  
I think then that the cause, why in ordinary instances, Wood, Wax, and other bodies specifically lighter than water, being let go at the bottom of a vessel full of that liquor, emerge to the top, is chief, that there is no such exquisite congruity and contact between the lowermost superficies of the Wood, and the upper surface of the bottom of the Vessel, but that the lateral parts of the Water, being impelled by the weight of the parts of the same liquor incumbent on them, are made to insinuate and get between the lower parts of the Wood and the bottom of the Vessel, and so lift or thrust upwards the Wood, which bulk for bulk is less heavy than the Water that extrudes it.  
That this is the reason of the Emersion or ascension of bodies, lighter in specie than the fluids they swim in, is most consonant to the Laws of 
* See the Hydrostatical Paradoxes.  hydrostatics, as I have elsewhere shown. But whereas the whole force of the argument of those I dispute with, consists in a supposition, that, because the Trencher (formerly spoken of) is placed upon the bottom of the Barrel, no water can come between to buoy it up, whence they conclude it must ascend by an internal and positive principle of Levity, I thought fit to make the Experiment after another, and, if I mistake not, a better manner.  
We took then two round plates of Black Marble shaped like Cheeses, which had those superficies, that were to be clapped together, ground very flat and polished very carefully, that the stones being laid one upon the other might touch in as many of the superficial parts, as the workman could bring them to do; that, whilst they were in that position, the uppermost being taken up, the other would stick to it, and ascend with it. And to keep out the water the better, the internal surfaces were, before they were put together, lightly, and but very lightly, oiled, which did not hinder them from most easily sliding along one another, either forward or backwards, or to the right, or to the left, as long as the contiguous surfaces were kept Horizontal.  
These things being done, a blown Bladder of a moderate size was fastened to the upper marble, and both of them were let down to the bottom of a tub of water, where, by the help of an easy contrivance, the lower marble was kept level to the Horizon. And now the Patrons of Positive Levity would have concluded, that the bladder, being a body, granted to be by vast odds lighter than wood, and being in an unnatural place beneath the surface of the water, should of its own accord and with impetuosity emerge; but I expected a contrary event, because the bladder being tied to the upper marble, so that both of them might in our case be considered as one body, the water could not impel them up, in regard that the close contact of the surfaces of the two marbles kept the water from being able to insinuate itself between them, and consequently from getting underneath the upper marble, and pressing against the lower superficies of it. And to show that this was the reason of the bladders not emerging, I caused one of the bystanders to thrust his arm down to the bottom of the tub, and with his hand to make part of the oiled surface of the upper marble slide off, on any side, from that of the lower, which, by reason of the smoothness and slipperiness of the surfaces, he found most easy to do. But the contact still continuing according to a greater part of the surfaces than was requisite, I bid him yet slide, but by slow degrees, more and more of the upper marbles from the lower, till at length, when, according to his guess, the marbles touched but in one half of their surfaces, the endeavour of the water to extrude the bladder full of Air being stronger than the resistance, which the contact but of part of the surfaces of the stones was able to make, they were suddenly disjoined, and the bladder was by the extruding water impetuously, as it were, shot up, not only to the top of the water, but a good way beyond it.  
With these Marbles we made several other Experiments of this kind, most commonly letting down the Marbles both together; but once or twice at least placing the upper Marble under water upon the lowermost already fixed to the bottom of the barrel.  
That 'twas not the weight of the upper Marble, nor want of Lightness, whether positive or relative, of the Air included in the bladder, that kept it from ascending, was plain, not only by the newly mentioned impetuous emersion of it, upon the disjoining of the Marbles, but by this, that the Bladder would lift up from the lower parts of the water, not only the upper stone when it touched not the other, but a weight of seven or eight pound hanging at it.  
And that a Fuga Vacui was not an adequate cause of the cohesion of the Marbles in our Experiment, may be argued from this, that whether or no nature do any thing at any time out of abhorrence of a Vacuum (which may be much disputed;) yet in our case this abhorrency could not be well pleaded by its Assertors, since many of them hold it to be unlimited, and the more modest, to be at least capable of lifting up prodigious weights; whereas in our Experiment the Levity of a Bladder, that could not raise ten pound weight, was sufficient to disjoin the marbles when they yet touched one another according to half their surfaces.   

EXPER. II.  
TO show now whether it is not rather the Gravity and Pressure of the Water, or other ambient fluid, than the Positive Levity of a body lighter in specie than it, that makes the immersed body ascend to the surface of the liquor, I devised this Experiment:  
We took a bladder out of which a great part of the included Air had been expressed, and tying the neck of it very close, that none of the remaining Air might get out, we fastened to it a considerable weight of some very ponderous body, as Led or Iron. By the help of this we sunk the bladder to the bottom of a wide mouthed glass, full of water, that the surface of the liquor might be a good deal higher than the upper part of the bladder: This wide mouthed glass we included in a great Receiver (whose orifice must be very large to be able to admit such a vessel;) which I caused to be carefully cemented on to the Engine. The main scope of this Experiment was to show, that though the Air, included in the bladder, was very far from being able by its absolute levity to lift up so great a weight as the bladder was clogged with, yet the same Air, continually included in the bladder, would, by its mere expansion, without any new external heat, acquire a power of ascending in spite of that weight; which ascension therefore must be attributed to the water, which according to the Laws Hydrostatical ought (caeterisparibus) to resist or buoy up more potently those immersed bodies, that being lighter in specie, than it, possess the greatest place in it, and hinder the more water from acquiring its due situation: as we see, that among hollow spheres of glass and metal, equally thick and well stopped, there is a much heavier weight requisite to sink a large one than a small one. For the prosecution of this trial we began to pump the Air out of the great Receiver; and its pressure upon the surface of the water being thereby more and more lessened, (according to what we elsewhere more fully declare,) the spring of the included Air began by degrees to distend the sides of the bladder, till at length that vessel of Air swelling every way took up so much more room in the water than it did before, that the water was able to lift the bladder and the annexed weight to the top, and detain it there, till we thought fit to let in again some of the excluded Air, which forcing that in the bladder to shrink in its dimensions, the weight was presently able to sink it to the bottom.  
And here it may be noted, that if, instead of hanging so great a weight at the neck of the bladder, we fastened but a moderately heavy piece of Lead, such as would only serve to sink the bladder, and keep it at the bottom of the water, so that the aggregate of the Bladder, Air, and Metal, was but a little heavier than a bulk of water equal to them: Then upon the first suck or operation of the Pump, which could withdraw but a small part of the Air in the Receiver, the Air in the bladder suddenly expanding itself, would forthwith be impetuously extruded by the water, though after some reciprocations it would float in its due position, till upon the return of a little outward air (sometimes as little as we could conveniently let in) it would immediately subside.  
But this is not so necessary to be insisted on, as 'tis to take notice, that I foresaw it may be objected, that the ascension of the weight was not effected by the pressure of the water, but by this, that Rarity and Levity being Qualities exceedingly of kin, the great Rarefaction of the Air might proportionably increase the Levity of it, and consequently enable it to perform much greater things than it could do before.  
I will not here dispute, whether, generally speaking, a body rarified without heat, would, in Vacuo, or in a fluid not heavier in specie than the body when rarified, merely by such a greater distance of its parts as may suffice to entitle it to rarefaction, become really heavier or lighter than before. I will not (I say) discuss this question here, where it may serve my turn to satisfy the recited objection by the following Experiment.   

EXPER. III.  
ABout the neck of a conveniently shaped Viol capable to hold some few ounces of water, I caused to be carefully tied the neck of a small Bladder, whence the Air had been diligently expressed, so that the Bladder, being very limber of itself, and probably made more so, as well as more impervious to Air and Water, by the fine Oil we had caused it to be rubbed with, lay upon the orifice of the Viol like a skin clapped together with many folds and wrinkles.  
This done, we let down the Viol into a conveniently shaped Vessel full of water, and the Viol, being poised beforehand for that purpose, sunk perpendicularly in the liquor, till the neck of the Glass was partly above and partly beneath the surface of the water: Then covering the external Glass with a large Receiver, we caused the Air to be pumped out, and as the pressure of that was gradually withdrawn, the Air in the floating Viol did little by little expand itself into the Bladder, and unfolded the winkles of it, till at length it became full blown without altering the erected posture of the Glass it leaned upon. But this great expansion, being made above the Water, and consequently in a medium not heavier than the included Air, gave that highly rarified Air no such increase of Levity, as enabled us to perceive, that it made so much as the neck of the Glass arise higher in the Water than it did before. Nor did we take notice, that the return of the Air into the Receiver, by reducing the Air in the Bladder to its former unrarifyed estate, made the Glass sink deeper than before. But when the Experiment was tried with the same Glass and Bladder at the bottom of the Water, then, upon the pumping out the Air, the Bladder being dilated under water was after a while carried up to the top, and took up with it about eight or ten ounces, that had been, to clog it, fastened to the bottom of the Viol.    

NEW EXPERIMENTS About the PRESSURE of the AIR'S SPRING On Bodies under Water.   

NEW EXPERIMENTS About the Pressure of the Air's Spring on Bodies under Water.  
I Do not think it were difficult for an intelligent peruser of our Physicomechanical Experiments, to find there divers Phaenomena, whence it may be deduced, that Bodies under water, though kept by that liquor from the immediate contact of the Air, may yet be exposed to its pressure (whether the Air act as having a Weight or as a Spring.) But because not only the Vulgar, but Philosophers have been so long and generally possessed with an opinion, that a fluid so little heavy as the Air, cannot by its weight act upon a liquor, that is, like water, bulk for bulk a thousand times heavier than it: And because also it seems yet more strange, that a little Air, perhaps not amounting to a scruple or drachm in weight, should in its ordinary state of Laxity act considerably upon Bodies, which, being covered with water, seem by the interposition of that liquor to be fenced from the incumbent Air; it may be worth while to add three or four Hydrostatical Experiments, to confirm a Truth that very few are yet acquainted with; and add to the proofs, already given of the power of the Spring of the Air, some of the operations we have discovered it to have upon Bodies placed under water.  
There are two sorts of Trials, that I shall employ to show, that a small quantity of enclosed Air may by its pressure (which in our cases must depend upon its Spring) have a considerable operation upon bodies under water, notwithstanding the interposition of that liquor.  
For, this pressure we speak of, may be manifested, in the first place by what it directly and positively operates upon bodies covered with water: And in the next place, by the things that regularly ensue upon the removal of the enclosed Air, or the weakening of its Spring.  

EXPER. I.  
TO begin with the former way of showing the pressure of the Air, I thought it sufficient, in regard of the Trials to be referred to the second way, to make the following Experiment.  
We took a square Glass-Viol, guessed to be capable of holding between half a pint and a pint of water; the neck of this we luted on carefully and strongly (for else it would have been buoyed up) over the orifice of the small pipe, at which the Air passes in our Engine out of the Receiver into the Pump: Then whelming over this glass a great Receiver, we luted it strongly to the Engine (that it might as well keep in the Water as keep out the Air) and at the top poured in as much water as sufficed to environ the internal Receiver (if I may so call it) and cover it to a pretty height. This done, we exactly closed with a turning key the hol● in the great Receiver, at which the water had been poured in, that no air might get in or out that way. And lastly we began to pump out the Air contained in the internal Receiver; to the end that that Air, which by the abovementioned pipe had Communication with the External Air, might no longer by its pressure assist the glass to resist the pressure, which the incumbent and enclosed Air; by virtue of its Spring, constantly exercises upon the subjacent water, and by its intervention upon the sides and bottom of the internal Receiver.  
And as we expected not, that this glass by its own single force should resist the pressure of the Air enclosed in the upper part of the great Receiver notwithstanding the interposition of the water; so the event fully justified our conjecture: For at the first exuction, which could not be supposed to have well emptied the internal glass, this vessel was, by the pressure of the superior Air upon the circumstant water, broken into I know not how many pieces. And the same Experiment, though with a little slower success, was repeated with a stronger internal glass.   

EXPER. II.  
I Proceed now to the second way of manifesting the pressure of enclosed Air upon Bodies under water, which is by showing the Phaenomena, exhibited by those Bodies upon the removal or lessening of that pressure.  
Having squeezed out of a moderately sized Bladder the greatest part of its Air, we tied the neck of it very close, and then fastening to it a competent weight, we placed it at the bottom of the tallest and largest glass we could cover with our great Receiver, that so, though the incumbent Air were pumped out, none of the Water might be pumped out with it, but still retain the same height above the Bladder. Having then poured upon the Bladder as much Water as would swim a great way above the upper part of it, we covered this glass of Water with a great Receiver, which being carefully cemented on to the Engine, the Pump was set awork, and as the Air, which by its Spring pressed upon the surface of the included Water, was by degrees pumped out, so the Air that was imprisoned in the Bladder, did gradually expand itself at the bottom of the Water, as if no such liquor had interposed between them otherwise than by its weight, upon whose account it must be allowed to give some little impediment to the expansion of the Bladder in proportion to the height it had above it.  
The Event of our Experiment was such as was expected, namely that the immersed Bladder was at length full blown, by the dilatation of the Air, enclosed in it; and by its intumescence made a considerable part of the Water run over by the sides of the glass, that before contained it all. And when access was given again to the external Air, the internal being compressed, the Bladder was presently reduced to its wrinkled state.   

EXPER. III.  
WE took a small but fine Bladder, whose neck was strongly tied up, when it was, by guess, about half full of Air: This we put into a short brass Cylinder, the lower of whose bases was closed with a Brass-plate, and the other left open; this open orifice we afterwards stopped, but not exactly, with a Cylindrical plugg, that was somewhat less wide than it, and was by a rim at the top hindered from reaching too deep into the cavity of the Cylinder, that it might not do mischief to the Bladder that lay there beneath it; upon this plugg we placed an almost Conically shaped weight of Lead, and this pile of several things being so placed upon our Engine, that we could cover it with a great Receiver, we carefully cemented on this vessel, and at the top of it poured in so much water as would serve to fill the vacant part of the brass Cylinder, and the cavity of the Engine to such a height, that it covered all the leaden weight, which was several inches high, except a rim which was fastened to the top of it for the convenienter removing of it.  
All this being done the Pump was set awork, and long before we had exhausted the Air of the Receiver, that which was enclosed in the lank bladder had by degrees displayed so vigorous a spring, that it had heaved up the weight that lay upon it to a notable height, and kept it there till the Air was let in from without to assist its being depressed by the leaden weight, which amounted to no less than about 28. pound.   

EXPER. IU.  
THere remained yet one trial to be made, which in case it should succeed, seemed likely to appear as great an evidence of the force of the Air's Spring upon bodies under water, as could be reasonably desired of us; it having been looked upon by many Virtuosos as the considerablest instance of the force of the Air's Spring even when no water intervened in the trial.  
To satisfy therefore our curiosity, we took a copper Vessel of a Cylindrical shape, and a considerable height; into this, being first almost filled with water, we put a square Glass-Vial capable by guess to hold nine or ten ounces of water, and exactly stopped with a cork and a close Cement; this Vial by a competent weight was detained at the bottom of the water, from whose upper surface it was considerably distant: then the Copper Vessel being placed upon the Engine, and included in a great Receiver well cemented on, the Air was by degrees pumped out, but before it was quite exhausted, the Glass at the bottom of the water was, by the spring of the Air included in it, burst into many pieces, not without great noise, and a kind of smoke or mist that appeared above the surface of the water.  
Another Glass of the same sort had been broken after the same manner in another Vessel; but having afforded us no particular Phaenomenon, I barely mention it, to show that we made more than one trial of this kind.  
The consequence that will naturally result from the three last Experiments, is this, that since barely upon the withdrawing of the pressure of the included Air (which was perhaps but very little in quantity,) the Air residing in the immersed bodies, did, by virtue of its Spring, expand itself so forcibly as we have recited, and perform notable things, the Air above the Water must have exercised a very powerful pressure upon the surface of it, since, (setting aside the weight of the water, of small moment in our trials,) it must have been at least equivalent to (and probably much exceeded) that force of the immersed Air, whose exercise it was able totally to hinder.  
And from hence it may be easily deduced, that the weight of the Atmosphere acts upon bodies under water, notwithstanding that the interposed liquor is by vast odds heavier in specie than Air; for, we have just now proved the pressure of enclosed Air, (which consists in its Spring,) upon bodies under water; and 'tis manifest, that the strength of the Spring of this inferior Air, we make our trials with, is caused by the weight of the superior Air, which bends and compresses those little Aereal springy particles, whereof our Air consists; so that the weight of the Atmosphere being equivalent to the Spring of the inferior Air, (for else it could not compress it as much as it does,) must lean upon the surface of the subjacent water, with a force equivalent to the spring of that part of it that is contiguous to the water.  
This Experiment brings into my mind another that I once made, which though not properly Hydrostatical, yet relating to positive Levity, may perhaps be not uselessly added on this occasion; wherefore I shall here subjoin a transcript of the Phaenomenon, that belongs to our present purpose, as 'tis registered soon after the Experiment was made.  
[To examine by a visible Experiment the common doctrine, that a portion of Air, by being much dilated, rarified or expanded, does acquire a new and proportionable degree of Positive Levity, I devised to put in practice the following way:  
We took a Bladder of a moderate size, that was very fine and limber, that it might be the lighter and more easily distended. The most part of the Air being squeezed out of the Bladder, the neck of it was tied up very close, that no air might get out of it, nor any (external) get into it. This limber Bladder was hung at one of the Scales of a Balance, whose Beam had been purposely made more than ordinarily short, that the instrument, (which yet was ticklish enough) might be suspended, and capable of playing in the cavity of a great Receiver, into which we conveyed it, having first carefully counterpoised the Bladder with a metalline weight put into the opposite scale.  
This done, the Air was pumped out, and as that was withdrawn, the Bladder was more and more expanded by the Spring of the internal Air, till at length, when the Receiver was well exhausted, it appeared to be quite full. Notwithstanding which great dilatation of the included Air, it did not appear by the depression of the opposite scale, to be grown manifestly lighter than it was at first. And the Bladder seemed also to retain the same weight, after it had, by the Air that was let into the Receiver, been compressed into its former wrinkled state.]    

NEW EXPERIMENTS About the Differing PRESSURE Of Heavy SOLIDS and FLUIDS.   

NEW EXPERIMENTS About the differing Pressure of Heavy Solids and Fluids.  
SInce not only in vulgar Spectators of Physicomechanical Experiments, but even among some Learned men it has proved a great impediment to men's freely acquiescing in the doctrine founded on those Phaenomena, that if the Atmosphere could really exercise so great a pressure as we ascribe to it, it would unavoidably oppress and crush all the bodies exposed to it, and consequently neither other Animals, nor Men would be able to move under so great a load, or subsist in spite of so forcible a compression.  
This I readily grant to be a plausible Objection, but I suppose the force of it will be taken away by the following considerations put together.  
And first, the power of pressing, that we ascribe to the Air, is not a thing deduced, as too many other consequences in Physic are, from doubtful suppositions or bare Hypotheses, but from real and sensible Experiments. And therefore since we have clear and positive proofs of the Pressure of the Air, though we could not explain how Men and other Animals are not destroyed by it; yet we ought rather to acknowledge our ignorance in a doubtful problem, than deny what experience manifests to be a Truth: As is generally practised in treating of the Attractive and other powers of the Loadstone, which are freely acknowledged even by those that confess themselves unable to explicate them; though, if experience did not satisfy us of them, they were liable to divers more considerable objections, than any that is urged against the Pressure of the Air.  
Secondly, but though it be not absolutely necessary that we should answer the above-recited Objection otherwise, than by thus declaring that the Spring of the Air is not to be rejected for it; yet we will endeavour very much to lessen it, if not quite remove the difficulty, before we put an end to the discourse.  
I consider then thirdly, that they that urge the lately mentioned Objection against the great Pressure of the Air, seem not to be ware, that we were conceived and born in places exposed to the pressure of the Atmosphere, and therefore how great soever that pressure appear to be, it ought not to crush us now, since when we were but embryos or newborn Babes, and consequently very much more weak and tender than we now are, we were able to resist it, and not only live, but grow in all dimensions in spite of it.  
If there were any place about the Moon, or some other of the Celestial Globes, that some Learned men fancy to be inhabited, that has no Atmosphere, or equivalent Fluid about it, and where yet men could be generated anew, if one of those men should be supposed to be transported thence, and set down upon our Earth, there might be made an Experiment fitted for our controversy. In the mean time I doubt, that since Nature is not observed to make things superfluously strong, such a humane body being not made to resist any weight or pressure of Air, would be of so tender and compressible a make, that it would easily be crushed inwards by our Atmospherical pressure. And though we cannot give an instance of this kind, yet we make trials somewhat Analogous to it in our Pneumatical Engine. For when we place water in our Receiver, and pump out the Air that was above it, there will be generated a multitude of bubbles, some of which, when the Air is carefully withdrawn, will be of a strange and scarce credible bigness; these bubbles being generated where the Air cannot press upon them, these dimensions are so natural to them, that if the Receiver be supposed not to leak, nor other unfriendly accidents to intervene, they would (for aught we know) last a good while; since I have elsewhere shown, that the Spring of highly dilated Air did continue for many months, and a bladder would for no less time continue blown and filled in our Vacuum by a little Air that was left in it, when the ambient air began to be withdrawn from it. And yet the large bubbles above mentioned, when once the outward air is suffered to come in upon them, are thereby so violently compressed, that in a trice they shrink into dimensions, too small to keep them so much as visible; and if I could have succeeded in my Attempt of producing such living Bodies as I endeavoured (but did not expect) in our Vacuum, I suppose the success would have confirmed what I have been saying.  
Fourthly; but you will tell me, that so great a weight and pressure, as I assign the Atmosphere, must needs make a man feel pain, and, if not otherwise dislocate some of the parts, must at least press the whole body inward.  
But first, being accustomed to the pressure from our very birth, and even before it, so early and long an accustomance hinders us from taking notice of it; those pressures only being sensible to us, that are made so by some additional cause, which by making a new impression excites us to take notice of it. So we are not sensible of the weight of the  we are accustomed to wear; and so a healthy man is not sensible of the heat in his heart because 'tis constant there, and the sentient parts of the heart have been still used to it, whereas that heat oftentimes has been very considerable; and when in living dissections a man puts his finger into the heart of an Animal, which probably has a fainter, or at least not stronger degree of heat than a humane heart, he will feel in his fingers, accustomed to the Air, a manifest degree of heat, if they be but in their usual temper. 2. I have elsewhere proved by Experiments, that a cubick inch of Air, for instance, has as strong a spring as suffices to enable it to resist the weight of the whole Atmosphere, as far as it is exposed thereunto; for else it would be more compressed than de facto it is. And 3. I have also shown, that a very little portion of Air, though it will much sooner lose its spring by expansion than a greater, yet 'twill resist further compression as much as a greater. And 4. I have also shown, that in the pores of the parts of Animals, whether fluid or consistent, as in their Blood, Galls, Urines, Hearts, Livers, etc. there are included a multitude of Aereal corpuscles, as may appear by the numerous bubbles afforded by such Liquors, and the swelling or expansion of the consistent parts in our exhausted Receiver. 5. To this we may add, that, besides the Bones, whose solidity is not questioned, a much greater part of the humane body than is wont to be imagined, does really consist of Membranes and Fibers, and the coalitions and contextures of these; and that these substances are by the Providence of the most wise Author of Things made of a much closer and stronger Texture, than those, that have not tried, will be apt to think; as I could make probable by the great force that Bladders will endure, and the very great weight that Tendons of no great thickness will lift up or sustain, and by other things that I shall not now insist on. Lastly, There is a far greater difference, than men are wont to suspect, between the effects of the Pressures made upon Bodies by incumbent or otherwise applied solid weights, and those that they suffer from heavy but every way ambient fluids; as will appear by the Experiments to be mentioned by and by.  
From the particulars contained in these considerations, we may be assisted to show, why 'tis not necessary, that the pressure of the Atmosphere, though as great as we suppose it, should oppress and crush the bodies of men that live under it: for, the solidity of the bones and the strong Texture of the membranes and fibres, and the spring of the Aereal particles, that abound in the softer as well as in the fluid parts of bodies, is equivalent to the pressure of as much of the Atmosphere, as can exercise its pressure against them, and makes the frame of a humane body so firm, that it may well resist the pressure of the outward Air, without having any part violently dislocated, whilst the external pressure is exercised but by the Air, which being but an environing fluid, presses it equally (as to sense) on every side. And because our bodies have been produced in the Atmosphere, and from our very birth exposed, without intermission, to the pressure of it; our continual accustomance to this pressure, and the firmness of their structure, keep us from being sensible of the weight or pressure. And that it was not impertinent for me to mention the firmness of the frame of our bodies on this occasion, I shall manifest by an instance, that will upon another account also be proper for this place.  
We know, that multitudes of men have had occasion to pass over high mountains; and, besides that I have been myself upon the Alps and Apennineses, I have enquired of Travellers, that have visited the Asian and American Mountains, and some that have been upon the top of the Pick of Tenerif itself: But though divers of them took notice of a great difference in the Air at the top and bottom as to some other Quality, as coldness and thinness; yet I never met with; nor heard of any, that took notice of a difference as to the Weight of Air he sustained, or that complained, that when he was come down to the foot of the Mountain, he felt any greater compression from the Air than at the top. And yet the Experiments made as well by others as by ourselves, sufficiently witness, than on more elevated parts of the Earth, which have a less height of the Atmosphere incumbent on them, the weight and pressure of the Air is not so great as below. And on very high Mountains, 'tis not unlikely that this difference may be very considerable, since, when the Torricellian Experiment was made near Clermont in France, upon the Puy de Domme, (which is none of the highest mountains in the world, being found by the ingenious makers of that observation to be but about 500 Fathoms,) they found the difference of the Mercury at the top and bottom to amount to about three inches: And consequently, if the trial had been made with Water instead of Quicksilver, the difference would have been about three foot and a half in the perpendicular height of the Water. And 'tis very probable, that in much higher Mountains, the difference of the Mercurial Cylinders height at the top and bottom may be much greater; and at the bottom of some very deep Well or Mineral groove, which may without improbability be supposed to be placed at or near the foot of one of these Mountains, if we conceive the Baroscope to be let down, the variation of the height of the Mercurial Cylinder may be yet much more considerable; and yet we find not that the diggers in the deepest Mines, in mountainous Countries, are sensible of being leaned on or compressed by any unusual weight. But not here to build on any thing but matter of fact, it appears by the newly named observation, that, when a man was at the bottom of the hill, he had as much greater weight of Air leaning upon his head than he had at the top, as was equal to the height of an imaginary vessel full of water, which having his head for basis, were three foot and a half high: which is so considerable a weight, as could not but have been, not only sensible, but very troublesome and uneasy to support. And what has been said of the gravity of a pail of water, that leaned on his head, may be proportionably applied to his Shoulders, Arms, etc.  
Whence I think I may infer, that the reason, why such a weight was not felt by the man it compressed, was not, that the Air, that pressed him, was not considerable, but that the pressure was exercised after the uniform manner of fluid Bodies.  
And this may suffice to show that there is no necessity that the compression of the Atmosphere should make it impossible to live in it. But because 'tis observed, that those that dive to great depths under water, are not oppressed by the great weight of the incumbent water, and the cause of this strange Phaenomenon is not so easy to be assigned, and therefore has been made one of the two grand arguments, whereon the non-gravitation of water in water, and air in air has been, and still remains, founded: I shall here offer something ex abundanti towards the solution of that noble and difficult Problem.  
And first, that what is observed by the Divers, does not evince that water does not weigh in water, I have elsewhere 
* See the Hydrostatical Paradoxes.  proved by such reasons and Experiments as had the good fortune to convince eminently learned men, that were sufficiently prepossessed with the vulgar opinion: And in the same Treatise I have given a clear account, why a Bucket full of water is not felt considerably heavy, whilst 'tis under water, in comparison of what 'tis whilst 'tis drawn up into the Air; which is the other Phaenomenon that I freshly intimated the common Opinion to be founded on.  
Next, I do not think it strange, that that follows not which 'tis objected should follow from our Hypothesis; namely, that a Diver should be violently depressed to the bottom of the water, by the weight of so great a Pillar of the Sea as is placed perpendicularly over his body. For if we imagine a plane so to cut the Sea-water, as to pass by the Divers body; then as that part of the plane, on which his body leans, will be pressed by It, together with the water that is perpendicularly incumbent on it; so all the other parts of the same plane will be pressed by equally tall Pillars of water perpendicularly incumbent on them; and consequently, if the man's body were just equiponderant to an equal bulk of water, it and the water that leans on it would be sustained by the pressure of the collateral water incumbent on the other parts of the same plane (as may be easily understood by what I have elsewhere said. 
* See Appendices to the Hydrost. Paradox. ) And therefore there is no reason, why the Divers bodies should be more forcibly depressed than its depression is resisted. 'Tis true, that this body will sink, but that is because 'tis not only, as we lately supposed it, aequiponderant to an equal bulk of water, but heavier than that. But then, since the Water by its gravity and resistance takes off as much of the weight of the Divers body, whilst that is immersed, as a quantity of water equal to it would weigh in the Air, the subsiding of the humane body by its own weight ought to be but slow, because that being not in specie much heavier than water, it can sink but by virtue of the surplusage of weight that it has above water. And in effect, I have been informed by Swimmers, that in the Sea, whose water by reason of the Saltness is specifically heavier than the common water, they could hardly dive when they had a mind; the salt-water did so much support them. And having, because I had no conveniencies to make trials upon the parts of humane bodies, examined the weight of parts of other Animals in Air and Water, I found the overplus of the weight of the animal substances above an equal bulk of water to be but very small. And this may suffice to take off the wonder, why, though water be admitted to gravitate in water, yet Divers are not depressed by that which leans upon them; the endeavour, they use to keep themselves from sinking by striking the resisting water with their arms and legs, easily compensating their weak tendency downwards, which the small surplusage of gravity  gives them.  
But it seems to me far more difficult to render a reason, why those that are a hundred foot beneath the surface of the Sea, are not crushed inwards, especially in their chests and abdomens', or at least so compressed as to endure a very great pain.  
To clear up or lessen this difficulty, I have two things to offer.  
1. I confess, that I am not entirely satisfied about the matter of fact; for I do not yet know, whether it fares alike with the Divers at all depths under water: for, according to the answers I obtained from persons that had been one of them at the Coral-fishing in the straits, and the other at the Pearl-fishing near Manar, I do not find that the Divers are wont to descend to the greatest depths of the Sea, which if they did perhaps they would find a notable difference.  
And in small, or but moderate depths, those that dive without Engines usually make such haste, or are so confounded, or have their minds so intent upon their work, that they take not notice of such lesser alterations, as else they might observe, especially they being persons void of curiosity and skill to make such observations. Which I the rather mention, because having met with a Learned Physician, that living by the Seaside in a hot climate, delighted himself much in diving; and enquiring of him whether he felt no compression, when he passed out of the Air into the Water, he answered me, that when he dived nimbly as others use to do, he took not notice of it, but when he let himself sink leisurely into the water, he was sensible of an unusual pressure against his thorax, which he several times observed.  
A man that gets his living by fetching up goods out of wracked Ships, complained to me, that if with his diving Bell he went very deep into the Sea, and made some stay there, he found himself much incommodated; which though he imputed to the coldness of the water, yet by the symptoms he related I was inclined to suspect, that the pressure of it upon the Genus Nervosum might have an interest in the troublesome effect. And I have been assured by an eminent Virtuoso of my acquaintance, that he was lately informed by a person, whose profession it is to fetch up things from the bottom of the Sea by the help of a diving Bell, that several times when he descended to a great depth under the surface of the water, he was so compressed by it, that the blood was squeezed out at his Nose and Eyes; which Relation seems to favour our conjecture, and would much more confirm it, if I were sure, that the effect was no way caused by some fermentation or other commotion in the blood itself, occasioned by the great density or other alterations of the Air he breathed in and out, or by some other operation of the ambient Medium distinguishable from the compression of the water, though perhaps conjoined with it.  
And on this occasion I remember, that questioning an Engineer, who had made use of an Engine to go under water, quite differing from the Diving-bell; he answered me, that when he came to a considerable depth, he found the pressure so great against the Leathern case, wherein he descended, and by that means against his belly and thorax, that he feared it would have spoiled him, which forced him to make haste up again. But this observation, to have much built upon it, should be further inquired into.  
These things, and not these only, make me wish, that what is felt by those that dive to great depths, and stay at them, might be more heedfully observed by intelligent men, that being fully informed what is true in point of fact, we may the better and more cheerfully indagate the reasons.  
In the mean while, taking things as they are thought to appear, I shall propose two things towards the solution of our difficulty; namely the Firmness of the structure of a humane body, and the Uniformity of the pressure made by fluids.  
Of the first of these I shall add but little to what has been already said, where I spoke of the resistance made by our bodies to the compression of the Atmosphere; only shall here take notice, that whereas the Membranes are very thin parts, and therefore seem unfit to make any great resistance; we have tried, that if a piece of fine Bladder were fastened to the orifice of a Brass-pipe of about an inch in Diameter, we could not by drawing the Air from beneath it, make the weight of the Atmosphere break the bladder, though the weight were perhaps equivalent to an erected Cylinder of water, of the wideness of the orifice and about 30. foot high, and we●e indeed such, that divers men, that laid their hands on the orifice when the Air was pumped out from beneath, complained, that they were not able to lift off their hands again till some of the Air was readmitted.  
But the main thing, I shall propose towards the solving of the difficulty we are considering, is the Uniformity wherewith fluid bodies press upon the solid ones that are placed in them. And because I remember not to have met with Experiments purposely made to show, how this sort of pressure is more easy to be resisted than that of solids against solids, I shall subjoin the following trials.  

EXPER. I.  
IN the short Cylinder of Brass  we put a fine Bladder tied so close at the neck, that none of the Air (whereof it was about half full) could probably get out. Which we did, to the end that the Hen-Egge, we were to bed in it, might lie soft, and have its sides almost covered with the limber and flaccid Bladder and contained Air: This done, we covered the remaining part of the Egg with another Bladder, that nothing that was hard might come to bear immediately upon the shell: then we put the wooden plugg into the Cylinder and a weight upon the plugg, which is to be done very slowly and warily, lest the quick descent of the weight should make the plugg break the Egg it leans on. Lastly, the Cylinder thus fitted, being covered with a large Receiver, and the Air being drawn out, that air, which was tied up in the Bladders, by degrees expanded itself so strongly, as to lift up the plugg and the incumbent weight to a pretty height, and keep it there till the external Air was readmitted.  
Now since 'twill be readily granted, and appears by divers Experiments elsewhere related, that the Air in such cases expands itself vigorously every way, it appears by the recited trial, that it pressed against the Egg with the same force, that it pressed proportionably against the bottom of the Plugg, and that force was more than sufficient to lift up the weight, which (together with the Plugg) amounted to about thirty pound, and yet the Egg being taken out appeared perfectly whole and no way harmed; whereas upon the same Egg (if I mistake not) or at least another of the same kind, laying warily a while after small weights one upon another, the Egg was crushed to pieces by about four pound weight. This Experiment, though it seemed considerable to those that saw it, and may prevent an objection, for which reason I here mention it; yet will appear in no way strange to them that consider, that the weight of the Atmosphere, which the Egg supported, before it was put into the Cylinder, was more than equivalent to such a pressure of the Air, as may suffice to lift up the plugg: Wherefore I thought fit to make further trials of a differing nature.   

EXP. II.  
We took a Glass-buble of about an inch and half in Diameter, which we caused to be blown at the flame of a Lamp, that it might be far more thin and easy to break, than the thinnest Vials that are wont to be blown in the Glasser's Furnaces. This Bubble we included between Bladders, as we did the Egg in the former Experiment; and then having warily put the plugg into the Cylinder, so as it might press upon the Bladder that environed the Glass, we leisurely put the weights upon the Plugg, till they together with the Plugg amounted to 30. pound or more, which being removed, the Plugg was taken out, and the Glass-buble, though it were extraordinarily thin, (perhaps not thinner than fine white Paper) was taken out whole.   

EXP. III.  
But lest the great resistance of so thin a Glass (which yet was not Hermetically sealed) should be ascribed to the Sphaericalness of its figure, we employed, instead of it, the shell of an Egg, whence by a hole, made at one end of it, the Yolk and White had been taken out. This empty and imperfectly closed shell we handled as we did the Glass-buble in the former Experiment; and, notwithstanding the great leaden weight, that leaned by the intervention of the plugg upon the soft body, that environed it, It was taken out, not only uncrushed together, but, for aught we could perceive, without the least crack.   

EXP. IU.  
And to show, that what we observed about the nature of the compression of fluid bodies will hold as well in Water as Air, though it seemed difficult to make the trial with the accommodations we then had, we thought upon the following Expedient.  
Into a limber Bladder, almost full of water, we put a Hen-Egg, and tying the neck very straight, that nothing might get in or out, we so placed the Bladder in the Brass-Cylinder, that the Egg might not be immediately touched by any thing that was hard; then putting the Plugg into the Cylinder, we warily and leisurely heaped upon it flat-bottomed weights of Lead conveniently shaped, till they amounted (if both I and another misremember not) to about 75 pound; notwithstanding all which the Egg was taken out sound and uncracked, and probably might have supported a much greater pressure, if we had been furnished with more weights of a commodious figure to heap upon it.  
If we compare with this what was noted at the close of the first Experiment, about the breaking of an Egg with four pound weight, when no fluid body was interposed, it will be obvious to conclude, how great a difference there is between the resistance that a body may make to the pressure of solid bodies, that bear hard against some parts and not against others; and its resistance to others that compress it uniformly or in all places alike. For though it be denied, and that, I think, upon very insufficient grounds, that bodies under water are pressed by the incumbent water, because, as 'tis pretended, the Elements gravitate not in their proper place; yet this objection cannot be pretended to take place in our last Experiment, where the main thing that leaned upon the water, which surrounded the Egg, being not a Pillar of Homogeneous water, but a great and solid weight of Lead, the included Egg must by the intervention of the water have been compressed. Nor were Eggs the only bodies we endeavoured to crush after this manner, the trial having been also made upon a substance more soft and of a very irregular shape.  
To apply this now to Divers, when they are at a moderate depth under water; it seems not improbable, that the structure of their bodies should be robust enough not to be violated by the pressure of the incumbent and otherwise ambient water. For we have seen by the former Experiments, and especially by the last recited, that a body, easy to be broken inwards by an incumbent solid weight, will remain entire and unaltered in point of figure, under a very much greater weight that compresses it after the manner of an ambient fluid. And though it would seem to many, that even in our supposition the Thorax, being, as they think it, a kind of empty space in the body, the ribs and muscles ought by the weight of the water to be crushed into the great cavity intercepted between them; yet it is to be considered on the other side, that the Air contained in the chest, especially when its Spring is increased by those accidental causes, that may take place when men are deep under water, particularly the preternatural heat, which the want of the usual respiration is apt to produce, will very much help the chest to resist the pressure, as they will easily grant, that have tried the resistance, that Air makes, to be considerably compressed under water, the difficulty of farther compressing it still increasing, as in Springs it ought to do, the more it is compressed. And I further observe, that the structure of the Thorax is much more firm than men are wont to suppose; as appears by the very great solid weights, that some men do, for gain, or to show their strength, suffer to be laid on their breasts, without receiving any mischief thereby. And if I should admit, that at great depths, the water had some little compressive operation upon the chest; yet that can be no other than the pressing the parts a little inwards, and that the structure of the Thorax itself, fitted by nature for constriction and dilatation (as may appear in vehement take in and blowings out of the Air) may admit with small inconvenience. To which purpose I recall to mind, what I lately mentioned concerning the Physician, that found his Thorax somewhat compressed when he leisurely dived; as also what I have 
* In the Append. to Hydrost. Paradox.  elsewhere delivered concerning a Tad-pole, which swimming in water that was strongly compressed, by an external force, seemed through the Glass, that contained the water, to be somewhat lessened in bulk, and yet not killed, nor sensibly crushed notwithstanding its great tenderness. And if there were parts of a human body, that were of a Texture too weak and too disproportionate to the rest, I think it possible, that this compression inwards might be great enough to be very sensible to the Divers. For having purposely inquired of a certain man, whose trade 'twas to fetch up goods out of Ships cast away, by the help of a diving instrument, he told me, that when he was at a considerable depth under water, as about ten or twelve Fathoms, he found, suitably to my conjecture, so great a pressure against the drums or thin membranes of his Ears, which were not sufficiently counterpressed from within, as put him to a great deal of pain, till he had found some contrivances to lessen the inconvenience. Nor was this man the only Diver that has complained of this troublesome pressure, which seems to argue, that, at least at great depths under water, the firmness of the structure of a man's body does concur with the uniformity of the fluids pressure, to keep him from being hurt by the incumbent and otherwise ambient water.  
But I shall now say no more of the Problem obout Divers, since (besides that the matter of fact is not yet in my opinion accurately enough stated and determined,) the true solution of it is not necessary to give a reason, why the weight of the Air, a fluid so much lighter than water, should not oppress nor crush the bodies of Animals; though what has been already said about the resistance of bodies under water, may serve very much to confirm the reasons I proposed, why we that live in the Atmosphere are not (sensibly) compressed, much less oppressed by its weight.   
FINIS.   

ADVERTISEMENT.  
THe Reader is desired to take notice, that of this Tract concerning the Differing Pressure of heavy Solids and Fluids, there have been lost, by the carelessness of the Printer, Eleven written pages, which he under his hand had acknowledged to have received; and with the contents of which (many of them being Quantities, and other circumstances of Experiments, formerly made,) the Author cannot now charge his memory.