74 Notices respecting New Books. 
refrangible than any of the rays of light, occupy a space 
bevond the red ray, when the entire beam is decomposed by 
the prism. In this space, to the extent even of half an 
inch beyond the visible light, the heating power is actually 
greater than in the space occupied by the red ray, which of 
any of the coloured rays produces the greatest heat, and it 
ean be traced even to the extent of an inch and a half. 
This appears to prove the existence of rays of caloric in the 
solarray, which, from being less refrangible, are capable of 
being separated from the visible light; and if the aceuracy 
of the experiments be admitted, scarcely any other conclu- 
sion can be drawn. Herschel further infers, that the heat- 
ing power of the different coloured rays does not belong to 
the light of these rays, but depends on rays of caloric asso- 
ciated with them, there being, according to his hypothesis, 
rays of caloric as well as of light of different degrees of re- 
frangibility, and the former being therefure spread over the 
space occupied by the prismatic spectrum as well as the 
Jatter. This being more intimately connected with the 
chemical history of Light, will be afterwards more fully 
considered. In one respect the calorific rays in the solar 
beam differ from those projected from heated bodies; they 
ass without interruption through transparent media: this 
1s evident indeed from the intense heat produced in the fo- 
cus of alens when the rays of the sun have been trans- 
mitted through it. It was ascertained, too, with more ac- 
euracy by Herschel, the solar calorific rays, whether asso- 
ciated with light or separated from it, passing through 
transparent substances and producing heat; while the ra- 
diant caloric from heated bodies is almost entirely arrested. 
** An important subject of inquiry is still to be considered ; 
What is tlie nature of radiant caloric, or what theory can 
be given of the phenomena it displays ? 
** These pheenomena appeared to prove the existence of a 
subtle caloritic matter, projected from heated bodies, capa- 
ble of moving in right lines with velocity, and obeying laws 
of motion similar to those of light; and this conclusion was 
accordingly generally drawn and received. Mr. Leslie, 
however, advanced a different hypothesis ; the apparent ca- 
Jorific emanation he supposed to be propagated entirely by 
the medium of the air, The heated surface, according to 
his view, communicates increased temperature to the por- 
tion of air in contact with it; this layer of air is expanded, 
and presses on the portion immediately before it. This is 
successively, but rapidly renewed; a chain of undulations 
is propagated from the heated surface to the mirror, reflected 
; and 
ae 
