~~ 
44 © M. Melloni on the Radiations of Incandescent Bodies, §c. 
which arises visible re These bodies constitute the class of 
phosphorescent substance 
When one body Saati chemically with another, its mole- 
cules acquire in an instant a very violent vibratory motion, and 
then may subsequently assume vibrations that are slower. This 
is what appears to take place in flames, which originate in the 
combustion of bodies ; they commence almost always by a blue 
or violet light, and then become white or yellow 
But to return to the case in which light and heat are developed 
by elevation of temperature only ; we discover that ethereal un- 
dulations incapable of acting on the organ of vision are not alone 
found in radiations coming from hot and dark bodies, but also in 
those that arise from luminous sources. ‘These invisible rays 
cific properties are altogether analogous to those of color. Such. 
is the origin of the curious phenomena of chemical and calorific 
transmission and diffusion mnt I had the honor to ecibeait; 7 
years ‘860: to the Academy.* 
onclusion, L cannot but express my admiration how the 
ascovery of aseries of facts, which seemed contrary to the the- 
f the identity of light and heat, has become now the fun- 
real basis of that theory. Who would not have thought 
at first sight, that’ the radiations of heat were of a nature alto- 
gether different from light, on seemg them transmitted in such 
different proportions through substances endued with the great- 
sary 
for heat combined with different periods of the ethereal undula- 
tions. No one could have ever maintained the identity of light 
and the other of these agents, and the quality that every ray of 
dark heat possesses of propagating itself and being refracted Ina 
solid ies 
* Sitting of Nov. 16th, 1841, and Feb. Ist, 1843. 
