Notices respecting New Books. 139 
tion for them; and if its attraction should be great, it would 
affect that of the first mirror. If, for instance, a piece of ice be’ 
placed in the focus of the second mirror, the ice will rapidly 
absorb the rays of caloric, and attract the caloric from its sur- 
face. This will increase the attraction of that mirror, and con- 
sequently increase the rapidity, and the force of the whole pro- 
cess. The surface of the first mirror will have its attraction 
increased, and the temperature of the heated body will more 
rapidly fall. The effect of a single mirror in reflecting caloric, 
passing from a body placed opposite to it, at a moderate distance, 
may be explained upon the same principles. ‘The calorie in that 
instance would be simply attracted by the mirror, and reflected 
directly to its focus, and would raise a thermometer placed there, 
with a power greater than without the mirror, in proportion to 
the concentration of the rays. The same laws which exist in 
other cases in the attraction of caloric from body to body, re- 
gulate its conveyance in these cases from the heated body to the 
mirror, between the two mirrors, and from the second mirror to 
the colder body ;—the mirror, ouly being required to be com- 
posed of a substance which attracts caloric, without readily per- 
mitting its entrance into it.’ 
The author next examines the supposed epider between the 
particles of caloric, and the elasticity of gaseous bodies. The 
increase of the volume of bodies by the addition of another sub- 
stance—even if that substance be caloric—is what ought to take 
place, and furnishes no proof of the existence of repulsion. Calori¢ 
causes not repulsion in gases, but expansion ; and they obtain 
or retain the substance which causes this expansion by attrae- 
tion. We have no evidence of the existence of a power of re- 
pulsion. 
All solid bodies when raised to a certain temperature become 
luminous. Light is communicated with caloric, and in some 
proportion to it. It must be conveyed either by some affinity 
which it has for caloric, or all bodies must have an attraction for 
light, in some proportion to that which they have for caloric. 
The latter is the more probable hypothesis. Bodies are not 
Juminous by reflected, but by emitted, light ; and they emit it in 
consequence of the attraction of some other body: if emitted 
directly to the eye, “ it must prebably be by the attraction of 
the eye. Nor is it probable that the quantity of light required 
for vision, can bear more than a very minute proportion, to that 
emitted from a heated body. It is probable therefore, that, what- 
ever relation light may have to caloric when bodies are luminous, 
the light which enters the eye must do so in the same manner 
and be governed by the same laws as the caloric. But if light 
be capable. of producing expansion, and be attracted, and i 
taine 
