Notices respecting New Books. — 71 
as to. cause it to descend. If the hot body be withdrawn, or 
a skreen be interposed between the mirrors, the temperature 
falls, aud the liquid im the thermometer rises to its former 
height. In this experiment, there has been projected a 
calorific matter from the heated body, on the surface of the 
nurror in the focus of which it is placed; this has been re- 
flected in right lines from the surtace of this mirror to the 
one opposed to it, it is again reflected from the surface of 
that mirror, and is collected in its focus, where it produces 
a heating effect. 
“* The effect is similar with a single mirror. Ifa hot body 
be placed before its concave surface, at the distance of a 
few feet, and a thermometer he placed in its focus, rays of 
caloric are projected from the hot body, and are reflected 
from the surface of the mirror on the thermometer, pro- 
ducing elevation of temperature. 
«¢ That it is not the contiguity of the hot body to the ther- 
mometer that produces the effect in these experiments, is 
well shown, not only by the distance at which it happens, 
but also by moving the thermometer a little out of the focus, 
even nigher to the heated surface, when its temperature, if 
it had been previously raised, immediately falls. 
‘©The rise of temperature produced by this radiation is 
greater, the hotter the body is from which it takes place. 
In using the apparatus of the double mirrors, and placing 
in the focus of one of them a ball of iron, two inches in 
diameter, at an obscure red heat, the elevation produced in 
a thermometer, in the focus of the other mirror, at the di- 
stance of 12 feet, is equal to about 20 degrees of Fahren- 
heit’s scale. From a glass matrass, contaming about two 
ounces of water boiling, it does not exceed three degrees. 
From burning charcoal, the heat is such, that it can set 
fire to a burning body at the distance of several feet. 
<The velocity with which radiant caloric moves, is not 
eapable of being measured at any distance at which we can 
make the experiment. In an experiment by Pictet, the ef- 
fect appeared instantaneous at the distance of 69 feet. It 
appears to pass through the atmosphere without interrup- 
tion; nor, according to Scheele’s experiments, is its di- 
rection changed by a current of air. It is stopped, however, 
by liquids, even the most transparent. tae 
‘« Glass also intercepts a large portion of it. If a plate of 
clear glass be interposed half way between the two mirrors, 
a hot body heing in the focus of the one, and the ball of a 
thermometer in the focus of the other, the effect on the 
thermometer is nearly entirely intercepted. The rays of 
E4 caloric 
