No. IV.

A NOTE

CONCERNING

THE ELEMENTARY FLUID OF HEAT;

REFERRING TO

Vol. I. p. 144 in the Octavo Edition,

IT has been briefly intimated in the pages referred to, that the elementary fluid of heat, is that, by means of which fire, and all its effects exist;-and by means of which, even the effects of light, in producing genial warmth, are communicated, from the Sun, to the Earth.

But this matter may be rendered, in other words, perhaps ftill more intelligible; by adding,

E 4

adding, that, Flame,-and the Light of a lamp, or of a candle,-is merely this very fluid of beat, (which is fometimes by chemists called caloric,) let loose, in a more elastic state; and flying off, by its immense elastic force, in bright rays of vapour in a state of ignition. That Burning is merely the process of changing this fluid, in any folid body whatever, from a fixed to an elastic flate; when, by means of its elasticity, it disorganizes every constituent part of the body, and breaks forth.

And that, unless this elementary fluid of heat existed in our atmosphere, the whole would be fo unavoidably denfe, and opake, that the Sun's rays could not penetrate, so as to afford any light or heat at all:-nor indeed, let them shine ever fo long on any substance, would they produce any heat at all, unless this fluid were previously existing in

that fubftance.

Nevertheless it may be true, and most probably is fo, that this elementary fluid of heat has not only a great affinity to fire, into which it is converted; -but even to light itself, and to the rays of the Sun.-Nay that even the Sun's rays, and alfo lightning and the electric fluid, may be ftill this very ele

mentary

mentary fluid of heat, only exifting in a different, and much more perfect, and more elastic state :-differing from its existence in each of its different ftates, as rays of the fame light do differ from one another in different colours.

rays

And as beat is not, according to our gross ideas of it, effentially existing in the Sun's themselves; so it may also be observed, that lightning is fometimes without heat:for that there is what has been fometimes called a cold fufion of metallic fubftances by lightning.

Perhaps we may be allowed to confider the Elementary Fluid of Heat, (or Caloric,) as exifting in Seven diftinct feparate ftates;-in every one of which its whole character is different.

It may be confidered, perhaps,

1. As fixed elementary fire,—or fixed caloric-in a folid ftate, in metals, and plants, and in other fubftances.

2. As nearly quiefcent—and flowly acting caloric;-where it is no longer folid, but begins to expand in metals, or to yield fome degree of warmth ;--but neither flies off, nor burns.