392 M. MELLONI ON LIGHT AND RADIANT HEAT. 
of the successive zones constantly decrease on each side with the great- 
est regularity. Thus, notwithstanding the interposition of the coloured 
glasses, the intensity of the heat uniformly increases from the violet to 
the red, while the intensity of the light undergoes very irregular va- 
riations, which render a given zone sometimes stronger and sometimes 
more feeble than the succeeding zone. 
Let us disregard that which takes place in the obscure part, and fix 
our attention on the alterations produced in the visible part of the 
normal spectrum, in which each luminous band is accompanied by a 
calorific band possessing the same refrangibility. On the one hand we 
see uncoloured media which have no influence on the luminous rays 
and totally alter the ratios of intensity in the accompanying calorific 
rays; on the other, coloured media which totally change the relative 
energies of the luminous, without affecting the regularity of the propor- 
tions existing between the corresponding calorific rays. 
But if heat and light were both produced by the same movement of 
the ethereal molecules, it is evident that each reduction of foree in a 
given ray of pure light should be accompanied by an exactly propor- 
tionate reduction in the ray of heat possessing the same refrangibility. 
Now the variations of intensity produced in each of the two agents by 
the interposition of uncoloured or coloured media, so far from corre- 
sponding through the whole of the luminous part of the spectrum, ex- 
hibit the most striking diversity. Light and radiant heat, therefore; 
proceed from two distinct causes*. 
This being admitted, the complete separation of light from heat be- 
comes intelligible; and such is the conclusion at which I have arrived, 
with respect both to terrestrial fire and the solar rays. The process of 
separation is exceedingly simple: it consists in causing the radiation 
from the luminous sources to pass through a system of diaphanous bo- 
dies which absorb the whole of the calorific, while they extinguish but 
a part of the luminous rays. The only substances hitherto employed 
by me are water, and a peculiar species of green glass coloured by 
means of the oxide of copper. The pure light emerging from this 
system contains much yellow, and possesses at the same time a tinge of 
bluish green: 2 exhibits no calorific action capable of being rendered 
perceptible by the most delicate thermoscopes, even when it is so concen- 
trated by lenses as to rival the direct rays of the sun in brilliancy. 
* These two causes themselves are, perhaps, but different effects of a single - 
cause. The conclusion which appears to me to follow so clearly from my ex- 
periments is therefore by no means opposed to the general theory of undula- 
tions, according to which light and radiant heat arise from the motions commu- 
nicated to the zether by the molecular vibrations of luminous bodies and bodies 
possessing heat. It will only be necessary to admit that the luminous and the 
calorific rays are two essentially distinct modifications which the zthereal fluid 
suffers in its mode of existence. ‘ 
