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so a sound is produced between a solid body and air condensed, and again between two opposite bodies of condensed air. For, with respect to the chords in musical instruments, it is plain that the sound is not emitted by touch, or by the percussion between the finger or the bow, but between the chord and the air.

For a chord when it rebounds, and that with celerity from its being stretched, first condenses the air, and then strikes it. Instruments also put into sound by the breath, on account of the very weak motion of the breath compared with that of a stringed instrument, are of necessity made hollow to assist the compression of the air, which is also considered an assistance in stringed in

struments.

Water pent up makes a way for itself with a powerful impetus, and diffuses itself on all sides, in order to obtain its natural latitude, as under the arches of bridges. In the same manner also wind narrowed and condensed bursts forth with violence. Whirlpools produce whirlpools, for, since the natural relaxation is impeded, each part sustains an equal pressure.

Water emitted on a sudden with force from a confined space, reflects the resemblance of a continuous body, as of a thread or rod, or branch of a tree, and becomes straight, afterward bends, then divides itself, and disperses itself into a circle into drops, as in little pipes, or syringes, and gutters.

There is a kind of pool not uncommon in ponds, especially after hay has been mown, or rather seen from that circumstance. The hurricane sometimes raises a quantity of hay in the air, and carries it along for a time together and not scattered, until, after it has been borne to a considerable height, the hay disperses itself and forms, as it were, a canopy.

A wooden platter, empty and turned downwards, and placed evenly on the surface of the water, and afterward put under the water, bears with it down to the bottom of the vessel the air before contained in the platter; but if, with the like equilibrium, it be again taken out of the water, you will find the air to have conveyed itself into not much less space than it before filled. This will appear from the colouring of the lip of the platter at the place whither the water had ascended, and from which the air received itself within.

In a bed-room, if a window be left open when the wind blows, if there be no other vent, it is not very much felt, (unless it be violent,) since it is not received by the body of wind which had filled the room, and was somewhat condensed by the first gentle wind, and afterwards does not admit of condensation; but as soon as a vent is given, it is then manifestly perceived.

For the more comfortable continuance of workmen under water, it has been thought that a large

hollow vessel might be constructed of metal, or of some other kind of material, to be let down to the bottom of the water; that it might be sustained by a tripod, with the feet affixed to the brim of the vessel, and the feet to be a little less than the human stature. The vessel was let down into a great depth, with all the air it contained, in the same manner as was described in the case of the platter, and was set upon its feet, and stood just by the spot where the work was to be carried on. But the divers, who were the workmen, when they wanted respiration put their heads into the hollow of the vessel, and having taken a supply of air, returned to their work. And I myself in a bath made my servant put his head into a basin under the water depressed with air, and he so remained for half the quarter of an hour, until he felt that the air, warmed by his breath, brought on a feeling of suffocation.

To try by the bladder whether air readily admits of some small contraction, would be a fallacious experiment. For when the bladder is filled with wind, the air is condensed by the wind itself, so that the air within the bladder is more dense than common air, and therefore may be expected to be less adapted to a new condensation. But in the usual experiment of the wooden plate forced down beneath the water, you may see that the water, entering from the extreme part of the vessel, has occupied some space, and that the air has occasioned a defalcation of the same space.

But in order more clearly to illustrate the proportion, I placed a small globular, or other solid body, and that would sink, at the bottom of the vessel, above which the plate was to be placed; then I placed above that another plate, metallic and not wooden, that could stand of itself at the bottom of the vessel. But if that body be small in size, when it is received into the hollow of the plate, it forces the air together, and does not expel it; but if of greater magnitude than to admit of the easy yielding of the air, the air, impatient of this greater pressure, somewhat lifts up the plate, and ascends in bubbles.

And I had a hollow leaden globe made, the sides of it sufficiently firm to bear the force of a mallet or of a press: and this globe, being struck at either pole with mallets, approached nearer and nearer to a planisphere. And it yielded more readily under the first contusions, afterward less so, according to the measure of the condensation; so that at the last the mallets were of but little service, and there was need of pressing, and that with some violence. But I enjoined, that, after the pressing, a few days should be suffered to elapse, but this has no relation to our present design, but looks another way.

Air, by a powerful exsuction into closed vessels, is extended or dilated, so that part of the air being removed, the remainder, nevertheless, fills the same measure as the whole had filled; and yet

so as to endeavour, as much as possible, to restore itself and to get rid of that extension. You may perceive this in eggs, which contain scented water, and are broken in play, so that they imbue the air with their scent. The way to try it is to let all the food that is in the egg be drained, then let a person confine, by a powerful exsuction, the air itself which has found its way in, and immediately on exsuction bore a hole with the finger, place the egg thus closed under the water, and then take away your finger. But the air, turned aside by this tension, and endeavouring to recover its place, draws the water, and enters till that portion of air regains its former consistency.

I have tried the same experiment with a glass (or philosopher's) egg, and find that the water received is about an eighth part of the capacity; so much was the air extended by exsuction. But this depends upon the greater or less violence of the exsuction. But toward the end of the exsuction, it drew with it the brim of the vessel itself. I moreover made use of a new experiment, namely, after exsuction to stop up the hole with wax, and let the egg remain so sealed up for a whole day. I did this to try whether that day would lessen the inclination of the air, as is the case in consistent bodies, in twigs, bars of iron, and the like, the motions of which, to recover themselves from tension, become feebler through delay; but I find that the effect remains in this instance the same; the egg continues to draw, and with the same force, the same quantity of water as if it had been forthwith put in after exsuction: so that when the hole was opened out of the water, it drew in new air with an audible sound, but the effect of further delay I did not try.

If bellows are suddenly raised and opened, and no breathing place is given, they break; for since so great a quantity of air, as can fill the inside, rising suddenly from a level to a height, cannot be drawn through the narrow strait of the beak of the bellows, and the air which is already within it cannot be extended over such a space, the bellows must break.

cording as the sand does at the bottom. I think also that many infusions load the water, and that it cannot extend according to the bulk of the body received; but I pass by the experiment on this subject.

Caution.

I do not confound the motion of succession, which is called motion, to avoid the supposition of a vacuum, with the motion of reception from extension. For these two motions are in time and effect conjoined, but differ in their proportion to each other, as will appear in the proper history of the motion of succession.

Air received through breathing becomes in a little while vapour, so as to cover a lookingglass with a kind of steam, or in winter time so as to be congealed about the beard. But that dew, as it were, upon the bright blade of a sword, or upon a diamond, vanishes like a little cloud, so that the polished body seems to purify itself.

The mode of the process of water in the expansion and contraction which take place in the body of it through the medium of fire, is thus. Water acted upon by moderate heat emits a little and clear vapour, before any other change is seen within the body of it; the heat then continuing and increasing, the body yet remaining whole, it does not rise nor foam, as it were, in small bubbles, but, ascending through greater ones, dissolves itself into copious vapour, but the water soon flies off, and is consumed. And that vapour, if it is not impeded, mingles with the air, being at first visible, and even after it has vanished from sight, perceptible, either by sending forth a scent, or by moistening and softening the air at the touch or at breathing. And at length it hides itself, and is lost in that sea of air. But if first a solid body meet it, (and so much the more if it be equal to it and polished,) the vapour gently enters into itself, and is returned into the water either by the exclusion or ejection of the air, which was before mixed with the vapour. And that whole process is manifest, as well in the decoction of water as in distillation. But we moreover see vapours which are emitted from the earth, if they If water be in a just quantity put into a glass, have not been thoroughly subdued and scattered and the water's ascent be marked, and a common by the heat of the sun, nor from the coldness of cinder cleaned through a sieve be put into the the air equally commingled with that body of air, water and settle in it, you will see the space although they do not meet a solid body, yet occupied by the cinder at the bottom ascend higher returned into water from the very cold and destiby one-fourth than the body of water had ascended tution of heat, so that in evening dew it takes on the surface from the place before marked; and place earlier, in showers later. I have, therefore, hence it is plain, that the water mixed with the upon patient and diligent inquiry set down that cinder either changes its orbit and contracts itself, the expansion of air, if it be compared with or that it receives the cinder within the hollow water, amounts to a ratio of one hundred and part of the water, since it by no means expands twentyfold or thereabout. itself in proportion to the cinder received. But if you try this in the very lightest and thinnest sand, (but not calcined or reduced by fire,) you will find that the water rises at the surface ac

History.

History of the Extension of Matter in Pneumatics. I have taken a glass phial which could perhaps hold one ounce; I made choice of so small a

vessel as for two reasons particularly suited to the experiment, first, that it might sooner bring on the boiling with less heat, lest the bladder, which was to be put above the phial, should be burned and dried up by an intenser heat: secondly, that it might receive a less portion of air in that part which was not to be filled with water: since I was aware that the air itself received extension through fire. I determined, therefore, of making use of but a little air, that that extension might not disturb the ratios of the water. The phial was not straight-necked, without any lip, (for, then, the vapour of the water would distil more rapidly, and the dew would glide down that part of the bladder, which was joined to the neck of the phial,) but with the neck at first straightened a little, and then returned as it were with the lip. This vessel I half filled with water, (supposing that this would hasten the boiling,) and took the weight of the water with the phial itself by sand put in the scale of a balance. Then I took the bladder, which might contain about half a pint, taking care that it should be neither old nor dry, and given to resist more from dryness, but new and rather soft. I, then, tried the soundness of the bladder by blowing, to be certain that there were no holes in it, and then emptied all the air out of it as much as possible. I also first of all applied oil to the outside of the bladder, and made it take the oil by rubbing it in. This I did to make the bladder closer, and to stop up the pores (if there might chance to be any) with the oil. I fastened the bladder securely about the mouth of the phial, the mouth of the phial being received into the mouth of the bladder; this was done with a string waxed a little, that might adhere better and tie more closely. But this is made better by clay made out of meal and the white of an egg, and bound with black paper and well dried, as I myself have found. At last I placed the phial over burning coals on a little hearth. The water soon after began to boil, and by degrees to inflate every part of the bladder, till it seemed as though it would break. I immediately removed the glass from the fire and placed it upon the carpet, lest the glass should be broken by the cold, and instantly I made a little hole at the top of the bladder with a needle, lest, on the vapour being restored to water at the ceasing of the heat, should fall back and confound the ratios. But afterward I took away the bladder itself with the string, and cleared it from the clay, if any had been used, and then weighed the remaining water with the phials again. And I found that about the weight of two pennyweights had been consumed. And I saw that whatever of the body had filled the bladder when it was full of wind, was made and produced from that which had been lost from the water. The matter, therefore, when it was contracted in the body of the water, filled as much space as two pennyweights of the body of water filled:

but the same matter expanded in a body of vapour filled half a pint. I, therefore, set down the ratios according to the dimension expressed in the table: a vapour of water can bear a ratio of eightyfold to a body of water. The bladder filled with wind in the manner I have mentioned, if no breathing-place be given, but it be removed whole from the fire, immediately decreases from the inflation, and subsides and is contracted. The vapour whilst the bladder swells, being emitted from the hole, had another kind of vapour distinct from the common one of water, more thin, clear, and upright, and not so soon mingling itself with the air.

Cautions.

We must not suppose that if there were a greater consumption of water, a greater bladder could be filled in proportion. I tried this and found that it would not answer, but the inflation that follows upon it does not take place gradually, but altogether. This I attribute partly to the inflaming of the bladder, which was made harder and would not yield so easily, and was perhaps more porous; (but this might be corrected by a moist heat as by the balneum Mariæ;) but still more to this, that the vapour being increased through the constant succession, inclines to recover itself and condenses itself. The vapour, therefore, which is received into the bladder is not to be compared to those which are received into stoves, because these latter mutually following and urging each other, thicken, but those expand themselves at will from the soft and yielding nature of the bladder, especially at the beginning, (as I said,) before the copiousness of the vapour brings on its recovery.

The expansion of the vapour of water is not to be judged entirely from the appearance of the vapour which flies off into the air; for that vapour being immediately mixed with the air, borrows by far the greatest dimensions of its mixed body from the air, and does not remain in its own size. And so it is amplified to the bulk of the air into which it is received, as a little red wine or any other coloured fluid which imparts a colour to a great quantity of water. The exact ratios in so minute a case cannot be obtained without laborious and unprofitable research, and are very slightly connected with our present design. It is enough that from this experiment it is plain that the ratio of vapour to water is not twofold, nor tenfold, nor fortyfold, nor again a thousandfold, two hundredfold, &c. For the limits, not degrees of natures, are the subjects of our investigation. If, therefore, any one, by any accident or slight variation in the mode of his experiment, whether from the shape of the glass he makes use of, or the hardness or softness of the bladder, or the degree of heat, does not fall upon the ratio of eightyfold, the

consequence is immaterial. For I suppose that there are none so ignorant as to imagine that pneumatic and volatile vapours, which fly off from heavy bodies, lie hid in the pores of the same bodies, and are not of the same matter with the ponderous body, but are separated from the ponderous part, when the water is, as it were, entirely consumed, and evaporates into nothing. A live coal, if placed in the scale of a balance and left till it becomes a cinder, will be found to be much lighter. Metals themselves are changed in a wonderful degree in weight by the evolutions of their smoke. The same matter, therefore, is tangible and has weight, and is yet pneumatic, and can be divested of weight.

History.

The mode of the process of oil is this. If oil be poured into a common glass phial and placed upon the fire, it will boil much more slowly, and will require a greater heat than water. And at first some drops and small grains appear scattered through the body of the oil, ascending with a creaking sound: the bubbles in the mean time do not play on the surface, as is the case with water, nor does the body rise whole, and in general no steam flies off, but a little afterward the whole body is inflated and dilated in a remarkable proportion, as if rising in a twofold degree. Then, indeed, a very copious and dense steam arises: if a fire be applied to the steam, even a good way above the mouth of the phial, the steam forth with produces a flame, and descends immediately to the mouth of the phial, and there fixes itself and continues burning. But if the oil is heated to a greater degree, the steam burning to the last, out of the phial, without any flame or ignited body being applied, completely inflames itself, and takes the expansion of the flame.

Caution.

See that the mouth of the phial is rather narTow, that the phial may confine the fumes, lest by their largely and immediately mixing with the air, they lose their inflammable nature.

History.

The method of process of spirit of wine is this: it is excited by much less heat, and brings itself to expand sooner and more than water. It boils up with great bubbles without froth, and even with the raising of its whole body, but the vapour, whilst it is collected, will on the application of fire produce fire, at a good distance from the mouth of the glass, not so bright (but at least as compact) as oil, but thin and scant of a blue colour, and almost transparent. But being inflamed, it is borne to the mouth of the glass, where is a supply of more copious fuel, as it is also with oil. VOL. II.-72

But if the vapour is inflamed in the part verging a little obliquely from the mouth of the phial, the inflammation becomes pensile in the air, undulating or winding after the appearance of vapour, and would doubtless attend it longer if the vapour remained together and did not confound itself with the air. And the body itself of spirit of wine, if no remarkable vapour goes before, the fire being applied to it and kept to it a little while is changed into the flame, and it expands with so much the greater ease and swiftness, as the spirit is more widely diffused and occupies a less altitude. But if the spirit of wine is put in the hollow of the palm of the hand, and a lighted candle between the fingers is placed near the palm of the hand, (as boys are wont to play with powder of resin,) and the spirit is gently moved forward, and straight forward, not upward; the body itself burns in the air, and when burning sometimes descends in a right direction, sometimes unfolds a little cloud flying in the air, which nevertheless verges itself to descent; sometimes when set on fire it cleaves burning, to the roof or sides, or floor of the room, and gradually becomes extinct.

Vinegar, verjuice, wine, milk, and other simple liquors (I speak of vegetable and animal substances, for of minerals I will treat by themselves) have their modes of expansion, and some remarkable differences attending them, which it would be out of place here to enumerate: but they are in those natures which we have remarked in the processes of water, oil, and spirit of wine; namely, in the degree of heat; and mode of expansion which is threefold, either in the whole body or in froth, or in rather large bubbles; for fat bodies, of unripe juice, as generally ascend in greater bubbles, of dried sap, as vinegar, in less. A collection of spirit moreover differs in its site. For in the boiling of wine, the bubbles begin to collect themselves about the middle, in vinegar about the sides and it is the same in ripe and strong wine, and again in vapid or stale, when they are infused. But all liquors, even oil itself, before they begin to boil, cast up a few and thin half bubbles about the sides of the vessel. And all liquors boil and are consumed quicker in a small than in a great quantity.

Caution.

I consider that compounded liquors are not proper to the history of the expansion and union of matter through the medium of fire, because they disturb and confuse the ratios of simple expansion and coition by their separations and mixtures. I leave them, therefore, for the proper history of the separation and mixture of matter.

History

Spirit of wine, put in an experiment with that elastic cap, (which I described when speaking of water,) obtains this sort of expansion. I find

3 B 2

that a weight of six pennyweights, consumed and dissolved into vapour, filled and fully inflated a great bladder which could contain eight pints; which bladder was greater by sixteen times than that which I used in the case of water, which received only half a pint. But, in the experiment of the water, there was a consumption of the weight of only two pennyweights, which is only the third part of six pennyweights. The ratios being thus calculated, the expansion of the vapour of spirit of wine bears a fivefold ratio and more, to the expansion of the vapour of water. And that very great expansion did not keep the body, on the removal of the vessel from the fire, from hastening to recover itself, the bladder forthwith becoming red and remarkably contracted. And, from this experiment, I began to estimate the expansion of the body of flame on probable, though not indisputable conjecture. For, since the vapour of spirit of wine is so inflammable, and approaches so near the nature of fire, I considered that the ratios of spirit of wine, compared with fire, agreed with the ratios of the vapour of water compared with air. For, we may suppose that the ratios of perfect and fixed bodies (as of air and fire) are in harmony with those of the elements, or imperfect and moving bodies, (as of vapours.) And it will follow from this, that fire exceeds air by five degrees, in the rarity or expansion of matter. For such is the excess of their respective vapours, as was before said. For, the fire itself may bear the ratio of one and a half to the proper vapour, not the impure, but the highly prepared vapour; as I have laid it down, also that air can have the same ratio to the vapour of water highly prepared. And these experiments do not disagree materially with what we may frequently observe. For, if you blow out a lighted wax candle, and mark the dimension of the smoky thread which ascends, (in the lowest part before it is dispersed,) and place the candle near the fire, and again look at that portion of the fire which first reaches it, you will not imagine that it exceeds more than double the magnitude of the smoke. If you mark with accuracy the dimension of gunpowder, or, for greater certainty, measure it in a little box, and again take the dimension of its flame, after it has been lit, you will readily grant that the flame exceeds the body, as far as it can be told at first sight, a thousand degrees. And, from what has been before laid down, there should be a considerable proportion of fire according to the nitre. But this I will explain more perfectly in my observations upon this history. We very

clearly see that air itself is expanded and contracted from heat and cold in those bodies of wind which physicians use for attraction. For, these warmed over the fire, and then applied immediately to the body, draw the skin, the air contracting itself and gradually recovering itself. And this it does of itself, although the hemp may not have been put on and heated, which is used to produce a more powerful attraction. Moreover, if a cold sponge be applied outside over the blister, the air contracts itself so much the more by virtue of the cold, and the attraction becomes more determined.

I have put a silver saltcellar of the usual belltower form, in a bath or goblet filled with water, bearing the air depressed with itself to the bottom of the vessel. I then put two or three live coals in the little hollow space in which the salt is placed when applied to its ordinary use, and raised a flame by blowing. Very soon after, the air, rarefied by the heat, and impatient of its former orbit, lifted up the bottom of the saltcellar on one side, and ascended in bubbles. Hero describes an altar so constructed as that, if you laid a holocaust upon it and set it on fire, suddenly water would fall to extinguish the fire. This might be accomplished by air being received under the altar in a hollow space closed up, and with no other way of exit, (when the air was extended by the fire,) but where it might force out the water prepared for this purpose in the channel. There were lately in this country some Hollanders who had invented a musical instrument, which, on being struck by the rays of the sun, gave out a certain harmony. This was very probably owing to the extension of the heated air, which could produce the motion of the instrument, since it is certain that air acted upon by the contact of the very slightest heat, immediately begets expansion.

But, in order to come at a more accurate knowledge of the expansion of the air let into that elastic bladder, I took an empty glass, (I mean, filled only with air,) and placed upon the bladder, the cap of which I before treated. But when the phial was placed over the fire, the air extended itself more quickly and with less heat than water or spirit of wine, but with not a very ample expansion. For it bore this proportion. If the bladder held less by six ounces than the phial itself, the air completely filled and inflated it; it did not ascend easily on greater expansion; and no visible body proceeded out of it, after making a little hole in the top of the bladder, until it was inflated. A. T. R.

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