DILATATION

, a motion of the parts of a body by which it expands, or opens itself, so as to occupy a greater space.

Many authors confound dilatation with rarefaction; but the more accurate writers distinguish between them; defining dilatation as the expansion of a body into a greater bulk, by its own elastic power; and rarefaction, the like expansion produced by means of heat.

The moderns have observed, that bodies which, after being compressed, and again left at liberty, restore themselves perfectly, do endeavour to dilate themselves with the same force by which they are compressed; and accordingly they sustain a force, and raise a weight equal to that with which they are compressed.

Again, bodies, in dilating by their elastic power, exert a greater force at the beginning of their dilatation, than towards the end; as being at first more compressed; and the greater the compression, the greater the elastic power and endeavour to dilate. So that these three, the compressing power, the compression, and the elastic power, are always equal.

Finally, the motion by which compressed bodies restore themselves, is usually accelerated: thus, when compressed air begins to restore itself, and dilate into a greater space, it is still compressed; and consequently a new impetus is still impressed upon it, from the dilatative cause; and the former remaining, with the increase of the cause, the effect, that is the motion and velocity, must be increased likewise. Indeed it may happen, that where the compression is only partial, the motion of dilatation shall not be accelerated, but retarded <*>s is evident in the compression of a spunge, soft bread, gauze, &c.

DILUTE. To dilute a body, is to render it liquid; or, if it were liquid before, to render it more so, by the addition of a thinner to it.