men whom nature has endowed with the precious
privilege of arranging a thousand isolated facts, of making seductive
theories spring from them; but let us not forget to state, that the
scythe of the reaper had cut the stalks before one had thought of
uniting them into sheaves!

Heat presents itself in natural phenomena, and in those which are the
products of art under two entirely distinct forms, which Fourier has
separately considered. I shall adopt the same division, commencing
however with radiant heat, the historical analysis which I am about to
submit to you.

Nobody doubts that there is a physical distinction which is eminently
worthy of being studied between the ball of iron at the ordinary
temperature which may be handled at pleasure, and the ball of iron of
the same dimensions which the flame of a furnace has very much heated,
and which we cannot touch without burning ourselves. This distinction,
according to the majority of physical inquirers, arises from a certain
quantity of an elastic imponderable fluid, or at least a fluid which has
not been weighed, with which the second ball has combined during the
process of heating. The fluid which, upon combining with cold bodies
renders them hot, has been designated by the name of _heat_ or
_caloric_.

Bodies unequally heated act upon each other _even at great distances,
even through empty space_, for the colder becomes more hot, and the
hotter becomes more cold; for after a certain time they indicate the
same degree of the thermometer, whatever may have been the difference of
their original temperatures. According to the hypotheses above
explained, there is but one way of conceiving this action at a distance;
this is to suppose that it operates by the aid of certain effluvia which
traverse space by passing from the hot body to the cold body; that is,
to admit that a hot body emits in every direction rays of heat, as
luminous bodies emit rays of light.

The effluvia, the radiating emanations by the aid of which two distant
bodies form a calorific communication with each other, have been very
appropriately designated by the name of _radiating caloric_.

Whatever may be said to the contrary, radiating heat had already been
the object of important experiments before Fourier undertook his
labours. The celebrated academicians of the _Cimento_ found, nearly two
centuries ago, that this heat is reflected like light; that, as in the
case of light, a concave mirror conc