denser than the body of the aliment itself (as the meat and drink of animals are converted into bone, skull, and horn) are manifestly condensed in the assimilation.

Transition.

To the action of dilatation by external violence, either with or against the desire of the body dilated, is opposed the action of contraction by a like external violence, when bodies are placed by those things which act upon them under the necessity of yielding and compressing themselves.

The History.

CONTRACTIONS OF BODIES CAUSED BY EXTERNAL

VIOLENCE.

1. Air easily bears some condensation from violence or external compression; but it does not endure much; as is shown in the violent force of winds and in earthquakes.

2. Take a wooden bowl, invert it, and put it into water, forcing it down perpendicularly with the hand. It will carry air with it down to the very bottom, and will not take in any water except a little about the edges, as will appear from the colour of the wetted wood. Now just so much and no more was the condensation or compression of the air. This was remarkably shown in the invention of the diving-bell, which was this. A large concave vessel filled with air was pressed down into the water. It stood on three feet, made of metal, and thick, that it might be better sunk ; the feet being not so high as a man. When the

divers wanted to take breath they stooped, put their heads into the vessel, and breathed. By a repetition of this process they continued their work for some time; till the air, which escaped in small quantities every time the head was inserted into the vessel, was diminished almost to nothing.

3. You may ascertain and calculate the amount of condensation which the air will willingly admit of, in this way. Take a basin full of water; put into it a globule of metal, or a stone, which will settle at the bottom. Place a bowl over this globule, either made of metal so as to sink of itself, or forced down with the hand. If the globule be so small that the air will willingly admit of condensation enough to take the globule within the bowl, it will condense itself quietly, and there will be no other motion; but if the globule be larger than the air can well bear, the air will resist, raise up one side of the bowl, and escape in bubbles.

4. You will likewise see from the compression of a bladder how far it may be compressed without bursting; or again from a pair of bellows, first opened and then sealed up; the valve having been first shut. With respect to the condensation of water I made the following experiment. I had a leaden globe made, with very thick sides, and a small hole at the top. This globe I filled with water, and then soldered up the hole (as I remember) with metal. I then forcibly compressed the globe at the two opposite sides, first with hammers and afterwards with a powerful pressing-machine. Now when this flattening had diminished the capacity of the globe by about an eighth part, the water, which had borne so much condensation, would bear no more; the water admitted of no

greater condensation; but on being further squeezed and compressed it exuded from many parts of the solid metal, like a small shower.

5. All violent motion, as they call it, such as that of bullets from guns, arrows, spears, machines, and many other things, is produced by the preternatural compression of bodies and their efforts to restore themselves; which, when they cannot do on the instant, they shift their place. For solid things, especially if they are hard, submit very unwillingly to further compression. But the inquiry of this matter I refer to the title of Motion of Liberty. For, as I have often said, the present title of Dense and Rare only gleans the ears, and does not reap the crop.

6. The more rarefied bodies are, the more easily do they contract themselves at first; but if they be compressed beyond their limits, the more powerfully do they restore themselves, as is shown in flame and confined air.

7. Flame simply compressed (though it be without a blast, as in gunpowder) is yet made more furious ; as may be seen in reverberatory furnaces, where the flame is checked, confined, repelled, and curved.

Admonition. To dilatation by diffusion no reciprocal action is opposed; because bodies diffused are not united in mass again, except by being melted together; as in the restoration of metals, of which I have spoken above.

Speculation.

There is likewise, perhaps, another kind of contraction of bodies, not reciprocal, but positive and by itself. For I judge that in the solution of bodies by liquids,

as in the solution of metals, gums, sugar, and the like, the body is to a certain extent received into the liquid; and yet the liquid is not dilated or expanded in proportion to the amount of body received. And if this is the case, there must be some condensation, for there is more body in the same space. Certainly in the solution of metals, if the water has once received as much as it will bear, it dissolves no more, and has no further operation. Now this condensation (if there be any such) I may call contraction of bodies by sat

uration.

Injunction. Compress ashes as close as you can, and pour water upon them; and observe carefully how much less they are in bulk, after they have taken in the water, than they were before when mixed with air.

Observations.

The efficients of the dilatation of bodies, as revealed in the foregoing inquiry, are nine in number. 1. Reception within, or admission of a foreign body. 2. Expansion, natural or preternatural, of the native spirit. 3. Fire or external actual heat; or even remission of cold. 4. External potential heat, or auxiliary spirits. 5. Liberation of the spirits from the bonds of the parts. 6. Assimilation by the predominance of a rarer body. which is more active. 7. Embracing, or going to meet a friendly body. 8. Distraction through external violence. 9. Diffusion or levelling of the parts.

The efficients of the contraction of bodies are eight. 1. Exclusion or deposition of the body received. 2. Shrinking or contraction of the parts after the emission of the spirit. 3. External actual cold, or even

remission of heat. 4. External potential cold. 5. Flight and antiperistasis. 6. Assimilation by the predominance of a denser body which is more active. 7. Compression by external violence. 8. Saturation, provided such a thing be.

The actions of dilatation by the native spirit, by liberation of the spirits, and by diffusion; and again, the actions of contraction by astringency; are actions without reciprocals. The other actions are reciprocal.

Dilatations by reception within, and by diffusion, are pseudo-dilatations; as likewise contractions by exclusion are pseudo-contractions. For they are in place, not in substance.

Expansion by fire or heat without separation is the simplest of all. This takes place in a pure pneumatic body, as air, where nothing exhales and nothing settles, but there is a mere dilatation, and that with a considerable increase of expansion and bulk. Whether there be anything like this in flame; that is, whether flame after the expansion of the first kindling (which is great) being now made flame (where there is great eagerness of circumambient bodies) expand itself still further; is difficult to ascertain, by reason of its quick and momentary extinction; but of this I will inquire in the title respecting Flame. Next to this dilatation (in point of simplicity) is the expansion which takes place in the melting of metals, or in the softening of iron and wax, and the like, for a time, before anything becomes volatile and is emitted. But this dilatation is secret, and takes place within the confines of the integral body, without visibly changing or increasing its bulk. But as soon as anything begins to escape in any body, then the actions become complicated, partly rare