Page:Scientific Memoirs, Vol. 1 (1837).djvu/51

Rh is therefore a phænomenon entirely depending on the order which we have found to exist in respect to the calorific transmissions of diaphanous bodies.

This phænomenon now constitutes a striking relation between the properties of the caloric rays of the sun and those of the radiant heat of terrestrial bodies; but we shall see relations yet more intimate appear between these two species of rays when we examine the alterations produced in calorific transmissions by changing the temperature of the radiating source.

 

HE experiments described in the former Memoir have shown that diaphanous bodies do not act in the same manner on the rays of heat and the rays of light simultaneously emanating from the most brilliant flame. We have seen, in fact, that thin flakes of alum and of citric acid, because of their transparency, perceptibly transmit all the luminous rays of an Argand lamp, and stop from eight to nine tenths of the caloric; while, on the other hand, thick pieces of smoky rock crystal intercept nearly the whole of the light and allow the radiant heat to pass freely. Do the different properties thus exhibited by each body, relatively to the two agents, and the relations of the calorific transmissions of the one screen to those of the other, remain constant, whatever be the source (luminous or obscure) whence the rays emanate? Such are the first questions that I have undertaken to solve in this second series of researches.

That the comparison between the quantities transmitted in each particular case might be fairly made, it was necessary to operate upon rays