ained, previous to immersion, we
cannot determine the absolute quantity they contain, after being taken
out of the water.

The same circumstances undoubtedly take place, with bodies that are
immersed in caloric; taking into consideration, however, that water is
an incompressible fluid, whereas caloric is, on the contrary, endowed
with very great elasticity; or, in other words, the particles of caloric
have a great tendency to separate from each other, when forced by any
other power to approach; this difference must of necessity occasion
very considerable diversities in the results of experiments made upon
these two substances.

Having established these clear and simple propositions, it will be very
easy to explain the ideas which ought to be affixed to the following
expressions, which are by no means synonimous, but possess each a strict
and determinate meaning, as in the following definitions:

_Free caloric_, is that which is not combined in any manner with any
other body. But, as we live in a system to which caloric has a very
strong adhesion, it follows that we are never able to obtain it in the
state of absolute freedom.

_Combined caloric_, is that which is fixed in bodies by affinity or
elective attraction, so as to form part of the substance of the body,
even part of its solidity.

By the expression _specific caloric_ of bodies, we understand the
respective quantities of caloric requisite for raising a number of
bodies of the same weight to an equal degree of temperature. This
proportional quantity of caloric depends upon the distance between the
constituent particles of bodies, and their greater or lesser degrees of
cohesion; and this distance, or rather the space or void resulting from
it, is, as I have already observed, called the _capacity of bodies for
containing caloric_.

_Heat_, considered as a sensation, or, in other words, sensible heat, is
only the effect produced upon our sentient organs, by the motion or
passage of caloric, disengaged from the surrounding bodies. In general,
we receive impressions only in consequence of motion, and we might
establish it as an axiom, _That_, WITHOUT MOTION, THERE IS NO SENSATION.
This general principle applies very accurately to the sensations of heat
and cold: When we touch a cold body, the caloric which always tends to
become in equilibrio in all bodies, passes from our hand into the body
we touch, which gives us the feeling or sensation of cold. The direct