528 M. MELLONI ON A NEW NOMENCLATURE 
Very recent experiments indeed showed that there existed, in 
the phenomena of the absorption and diffusion of luminous and 
calorific radiations through opake bodies, a series of facts alto- 
gether analogous to the differences observed in their transmis- 
sion by diaphanous media. In fact we see the whitest sub- 
stances, as paper, snow, carbonate of lead, wholly absorb certain 
rays of heat, and disperse others in the manner of the luminous 
diffusion ; whilst coloured substances, like metals, disperse and 
absorb, in proportions sensibly equal, all kinds of calorific radi- 
ations: the first act just as a red body would do exposed in suc- 
cession to green light and to red ; the second like white bodies 
receiving lights of different colours. Thus the coloured and 
the white calorifics exist ; but they have no connexion with the 
colours properly so called, and must be carefully distinguished 
Srom them. 
The necessity, then, for a new nomenclature to express the 
properties of bodies relatively to radiant heat cannot be doubtful. 
In the last edition of his Hlémens de Physique Expérimentale, 
M. Pouillet proposes to designate by the term ¢hermanism the 
faculty which ponderable substances possess of absorbing and 
retaining such amongst the several elements of which the inci- 
dent calorific stream is composed as best suit them, leaving 
the rest at liberty. Thus the bodies which alter the com- 
position of the stream of heat by a special absorption would 
be thermanizing substances, and the heat which has undergone 
the action of thermanizing substances would be thermanized 
heat. I own that these denominations are at first sight attract- 
ive by their extreme simplicity; but unfortunately they are 
open to several very strong objections: first, because their radi- 
cal contains no expression relative to the fact of elective absorp- 
tion, which however they ought to define or at least indicate; 
in the next place, because they hardly satisfy all the wants of 
science: in order to be convinced of this it is sufficient to ob- 
serve that black bodies relatively to heat, as well as white bodies, 
would be non-thermanizing substances, so that two contrary ac- 
tions would be confounded together under the same name. 
Having formed the project of publishing a work in which I 
shall try to bring together all that we positively know at present 
on the properties of radiant heat, I have found myself stopt, 
at the first setting out, by the imperfection of the language of 
this branch of physics, which has naturally led me to the forma- 
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