in it.

MRS. B.

The cold you experience consists in the loss of caloric that your hand
sustains in an attempt to bring its temperature to an equilibrium with
the marble. If you lay a piece of ice upon it, you will find that the
contrary effect will take place; the ice will be melted by the heat
which it abstracts from the marble.

CAROLINE.

Is it not in this case the air of the room, which being warmer than the
marble, melts the ice?

MRS. B.

The air certainly acts on the surface which is exposed to it, but the
table melts that part with which it is in contact.

CAROLINE.

But why does caloric tend to an equilibrium? It cannot be on the same
principle as other fluids, since it has no weight?

MRS. B.

Very true, Caroline, that is an excellent objection. You might also,
with some propriety, object to the term _equilibrium_ being applied to a
body that is without weight; but I know of no expression that would
explain my meaning so well. You must consider it, however, in a
figurative rather than a literal sense; its strict meaning is an _equal
diffusion_. We cannot, indeed, well say by what power it diffuses itself
equally, though it is not surprising that it should go from the parts
which have the most to those which have the least. This subject is best
explained by a theory suggested by Professor Prevost of Geneva, which is
now, I believe, generally adopted.

According to this theory, caloric is composed of particles perfectly
separate from each other, every one of which moves with a rapid velocity
in a certain direction. These directions vary as much as imagination can
conceive, the result of which is, that there are rays or lines of these
particles moving with immense velocity in every possible direction.
Caloric is thus universally diffused, so that when any portion of space
happens to be in the neighbourhood of another, which contains more
caloric, the colder portion receives a quantity of calorific rays from
the latter, sufficient to restore an equilibrium of temperature. This
radiation does not only take place in free space, but extends also to
bodies of every kind. Thus you may suppose all bodies whatever
constantly radiating caloric: those that are of the same temperature
give out and absorb equal quantities, so that no variation of
temperature is produced in them; but when one body contains more free
caloric than another, the exchange is always in favour of the colder
body, until an equilibriu