A24 On the Chemical Phenomena of Heat, (JUNE, 
each other penetrating in right lines through space: this is so evi- 
dent from numerous phenomena of the radiation of terrestrial and 
solar heat ; from the motions of light, as deduced from observations 
upon the aberration of the fixed stars, &c., that there is no occa- 
sion to attempt to give further proof. There appears no necessity 
for the motion of these particles round an axis ; which motion does 
not explain one fact which may not be established without it. ‘These 
ideas have gained considerable strength from an experiment made 
by Count Rumford, in which a piece of metal was kept hot for a 
great length of time by friction without any apparent diminution ; 
from this it was concluded that the heat could be kept up for an un- 
limited time, and therefore cannot depend upon the presence of any 
thing material; it was in consequence supposed that the heat was 
the effect of a vibratory motion communicated to the particles of the 
metal by the friction. This inference is not just: the experiment 
was continued for a Jong time, during which time the metal was 
suffering diminution in consequence of the friction, and the parts 
immediately below the surface becoming more and more com- 
pressed. Now if we suppose every solid to contain, in the inter- 
stices between its particles, a large quantity of caloric, and that 
when these particles are brought into closer contact, part of this is 
separated, there must be a constant evolution of heat, so long as 
any part of the metal remains. Were there no other objections to 
this mode of accounting for the effects of heat, the phenomena of 
its radiation would be sufficient to overturn the hypothesis, Radia- 
tion takes place in vacuo ; how can the vibratory motion be, in this 
case, produced in. a body at a distance? Some argue that the best 
vacuum is imperfect. Certainly it is: but air at all times conducts 
heat very slowly from one body to another, and cannot easily con- 
duct it downwards, yet radiation takes place in every direction ; if 
the radiation depended upon the conducting power of the air, this 
effect must almost cease when the rarity of the air is indefinitely 
great, which is not the case. As, however, in consequence of the 
imperfection of the best vacuum, the motion of the particles of one 
body may be supposed to communicate motion to those of another 
ata distance, it will be proper to bring forward another example of 
radiation, to which this objection cannot be made, viz. that of solar 
heat. Heat is communicated from the sun to the earth; and we 
are certain that there is no conducting medium between them by 
which it cati be transferred to so great a distance. 
‘The hypothesis advanced by Dr. Black is totally different to that 
which has thus been briefly examined ; is more simple and rational, 
but in many respects very defective. I shall now proceed to inves- 
tigate it, and show how the principal facts of chemical philosophy 
may by it be explained. . 
This supposes, that there is a peculiar matter of heat, consisting 
of particles mutually repellent, but attracted by every species of 
ponderable matter, capable of insinuating itself into the interstices 
