contrary happens, when we touch a warm body, the caloric then passing
from the body into our hand, produces the sensation of heat. If the hand
and the body touched be of the same temperature, or very nearly so, we
receive no impression, either of heat or cold, because there is no
motion or passage of caloric; and thus no sensation can take place,
without some correspondent motion to occasion it.

When the thermometer rises, it shows, that free caloric is entering into
the surrounding bodies: The thermometer, which is one of these, receives
its share in proportion to its mass, and to the capacity which it
possesses for containing caloric. The change therefore which takes place
upon the thermometer, only announces a change of place of the caloric
in those bodies, of which the thermometer forms one part; it only
indicates the portion of caloric received, without being a measure of
the whole quantity disengaged, displaced, or absorbed.

The most simple and most exact method for determining this latter point,
is that described by Mr de la Place, in the Memoirs of the Academy, No.
1780, p. 364; a summary explanation of which will be found towards the
conclusion of this work. This method consists in placing a body, or a
combination of bodies, from which caloric is disengaging, in the midst
of a hollow sphere of ice; and the quantity of ice melted becomes an
exact measure of the quantity of caloric disengaged. It is possible, by
means of the apparatus which we have caused to be constructed upon this
plan, to determine, not as has been pretended, the capacity of bodies
for containing heat, but the ratio of the increase or diminution of
capacity produced by determinate degrees of temperature. It is easy with
the same apparatus, by means of divers combinations of experiments, to
determine the quantity of caloric requisite for converting solid
substances into liquids, and liquids into elastic aeriform fluids; and,
_vice versa_, what quantity of caloric escapes from elastic vapours in
changing to liquids, and what quantity escapes from liquids during their
conversion into solids. Perhaps, when experiments have been made with
sufficient accuracy, we may one day be able to determine the
proportional quantity of caloric, necessary for producing the several
species of gasses. I shall hereafter, in a separate chapter, give an
account of the principal results of such experiments as have been made
upon this head.

It remains, before fin