M. MELLONI ON THE TRANSMISSION Of RADIANT HEAT. 39 



is therefore a phaenomenon entirely depending on the order which we 

 have found to exist in respect to the calorific transmissions of diaphanous 

 bodies. 



This phaenomenon 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 ap- 

 pear between these two species of rays when we examine the alterations 

 produced in calorific transmissions by changing the temperature of the 

 radiating source. 



Article II. 



Neiu Researches relative to the Immediate Transmission of Ra- 

 diant Heat through different Solid and Liquid Bodies ; pre- 

 sented to the Academy of Sciences on the 2\st of April, 1834, 

 and intended as a Supplement to the Memoir on the same sub- 

 ject presented to the Academy on the 4th of February, 18335 

 bi/ M. Melloni. 



From the Annales de Chimie et de Physique, t. lv. p. 337. 



Of the modifications which Calorific Transmissions undergo in consequence 

 of the Radiating Source being changed. 



X 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 ca- 

 loric ; while, on the other hand, thick pieces of smoky rock crystal inter- 

 cept nearly the whole of the light and allow the radiant heat to pass 

 freely. Do the different properties thus exhibited by each body, rela- 

 tively 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 tliat I have undertaken to solve in this second series of 

 researches. 



That the comparison between the quantities transmitted in each par- 

 ticular case might be fairly made, it was necessary to operate upon rays^ 



