282 
SECOND REPORT -1832. 
Upon combining these results with those of previous experi¬ 
menters, we are led to the following general statement of the 
case:— 
When a body is heated, at lower temperatures, it gives off 
radiant heat stopped entirely by the most transparent glass, 
and affecting bodies in proportion to the absorptive texture of 
their surfaces. 
At all higher temperatures it continues to give off such 
radiant heat distinguished by exactly the same properties. 
At a certain temperature it begins to give out light : precisely 
at this point it begins also to exercise another heating power 
distinct from the former ; this is capable of direct transmission 
through glass, and affects bodies in proportion to their dark¬ 
ness of colour. 
This second species appears to agree with what the French 
philosophers have called “calorique lumineux,” or the “igneous 
fluid ” of Prof. Leslie; but they seem to have considered it as 
constituting the entire effect. 
The distinction thus established easily applies to the explana¬ 
tion of De la Roche’s results before stated. On inspection it 
appears that the numbers in the column belonging to the black¬ 
ened screen are almost exactly in the same ratio to the first or 
direct effect throughout the whole series. 
Upon the principle here laid down, the effects with the 
blackened screen would be those arising from the absorption and 
subsequent radiation of both species of heat; these in each 
instance being absorbed in the proportions in which they ex¬ 
isted in the original radiation, produce a secondary effect pro¬ 
portional to the primary. 
The effect with the transparent screen does not follow' any 
proportion to the primary ; and this is explicable as due to the 
glass intercepting the one kind of heat, which foliow r s no pro¬ 
portion to the other, this last being wholly transmitted. Also 
by comparison of the latter experiments with the two first of 
the series, it is probable that, throughout, a certain degree of 
heat was in this case also absorbed and radiated again by the 
screen. 
The existence of this distinction, and the proportion betw een 
the two species of heat in the radiation from different sources, 
as various kinds of flame, metal at successive stages of incan¬ 
descence, &c., afford many topics of inquiry, on some of 
w r hich I attempted some rough determinations, confessedly 
very imperfect. (. Annals of Phil. N.S. liii. 359; liv. 401.) 
The distinction applies to some results of Mr. Brande on the 
flames of different gases, {Phil. Trans. 1820, Parti, p. 22,) and 
