Notices respecting New Books. 73 
the same temperature, and their comparative pawers, jn ra- 
diating caloric at a given temperature, can be ascertained, 
In this respect they differ widely: as an average it may be 
stated, that the calorific effect from the blackened surface 
being 100, that from the paper is 98, from the glass 90, 
and from the clean metal not more than twelve. | 
_ £8It thus appears, that those surfaces most disposed tb ab- 
sorb radiant caloric, when it is thrown upon them, are 
those likewise most disposed to radiate it when they are at 
a high temperature, and the absorbing and radiating pro- 
perty are opposed to the reflecting power. 
‘‘ Itis an interesting question on this subject, Does radiant 
caloric suffer refraction? ‘This was attempted to be deter- 
mined by Pictet, but the experiment was so impertectly 
performed, that no conclusion could be drawn from it. 
Herschel found reason to conclude, that rays of caloric 
exist in the solar beam, apart from the rays of light, and 
that these are separated when the beam is decomposed, bv 
being passed through the prism, the calorific rays being 
thrown beyond the red ray; this, if the experiment were 
accurate, proved, that these calorific solar rays atJeast are 
subject to refraction. He further submitted to experiment, 
the radiant caloric projected from heated bodies; andhe found 
them to be refracted by alens, and in the spot where they 
were collected by the refraction, to produce a heating effect. 
«* Mr. Leshie observed, that a considerable aberration hap- 
pens in the reflection of heat ; hence, when reflected from 
a mirror, the maximum of heat i is not in the true focus, but 
is found to be considerably nearer to the surface of the 
mirror. 
«If the experiments of Herschel be admitted as accurate, ~ 
they establish the important discovery, that radiant caloric 
exists in the rays from the sun, and that on this depends 
their heating power. In decomposing the solar beam by 
transmission through a triangular glass prism, it is resolved 
into different coloured rays, and these Herschel found were 
possessed of different degrees of heating power, the violet 
ray, which is the most refrangible, and which bounds the 
coloured spectrum on one side, being least powerful in ex- 
citing heat ; and the calorific power, increasing towards the 
other side, bounded by the red ray, which far exceeds the 
others in heating power. 
“6 All this, however, might be considered as arising from 
diversity of heating power in the visible rays of light 5 ; but 
Herschel further found, that calorific rays which produce 
no lumination exist in the solar beam, ‘which being less 
: refrangible 
