rounds
them exactly in the same situation as the particles of bodies are with
respect to the caloric; with this difference only, that the balls are
supposed to touch each other, whereas the particles of bodies are not in
contact, being retained at a small distance from each other, by the
caloric.

If, instead of spherical balls, we substitute solid bodies of a
hexahedral, octohedral, or any other regular figure, the capacity of the
intervals between them will be lessened, and consequently will no longer
contain the same quantity of sand. The same thing takes place, with
respect to natural bodies; the intervals left between their particles
are not of equal capacity, but vary in consequence of the different
figures and magnitude of their particles, and of the distance at which
these particles are maintained, according to the existing proportion
between their inherent attraction, and the repulsive force exerted upon
them by the caloric.

In this manner we must understand the following expression, introduced
by the English philosophers, who have given us the first precise ideas
upon this subject; _the capacity of bodies for containing the matter of
heat_. As comparisons with sensible objects are of great use in
assisting us to form distinct notions of abstract ideas, we shall
endeavour to illustrate this, by instancing the phenomena which take
place between water and bodies which are wetted and penetrated by it,
with a few reflections.

If we immerge equal pieces of different kinds of wood, suppose cubes of
one foot each, into water, the fluid gradually insinuates itself into
their pores, and the pieces of wood are augmented both in weight and
magnitude: But each species of wood will imbibe a different quantity of
water; the lighter and more porous woods will admit a larger, the
compact and closer grained will admit of a lesser quantity; for the
proportional quantities of water imbibed by the pieces will depend upon
the nature of the constituent particles of the wood, and upon the
greater or lesser affinity subsisting between them and water. Very
resinous wood, for instance, though it may be at the same time very
porous, will admit but little water. We may therefore say, that the
different kinds of wood possess different capacities for receiving
water; we may even determine, by means of the augmentation of their
weights, what quantity of water they have actually absorbed; but, as we
are ignorant how much water they cont