Bare M. MELLONI ON A NEW NOMENCLATURE 
of this science, will perhaps cause a second objection. “You — 
say that rays of heat are perfectly analogous to coloured rays: 
the science of radiant caloric should then be treated like light. 
Why do you apply to it a denomination which belongs to a 
single branch of optics?” Because radiant heat is manifested 
with data very different in many respects from those which 
preside at the manifestation of light. The sun sends to us, 
mixed up in a single ray, all the elements which constitute 
white light, the general properties of which may, and indeed 
ought to be completely known before we show that this light 
contains an infinity of different rays. But white heat does not 
exist; at least the complete series of the calorific elements is 
never met with in a single pencil; so that all effluxes of heat are 
chromatic, or, to be more exact, chroic. In fact, the radiations 
of bodies feebly heated are destitute of several elements which 
are found in the radiations of heat emitted by flames and in- 
candescent bodies; and, on the contrary, several elements 
contained in the calorific effluxes of sources at a low tempera- 
ture do not exist in the effluxes of sources at a high tempe- 
rature; the light of the sun itself, which contains all the 
colours and different calorific radiations, does not contain any 
of the elements peculiar to the radiations of sources at a low 
temperature. Radiant heat, of whatever origin, is then con- 
stantly coloured, comprehending also solar heat, which, accord- 
ing to what we have just said, possesses here, at the surface of 
the earth, a much more vivid coloration than that of the radia- 
tion of flames and of incandescent bodies. It follows from this 
that the qualities peculiar to each of these radiations constitute 
the first notions which must be acquired for the science of calo- 
rific radiation. Doubtless all the elements of radiant heat pre- 
sent common properties with respect to the mode of free propa- 
gation, and to the laws of refraction, of reflexion and of polariza- 
tion; but these general properties can only be rendered appa- 
rent by a sustained comparison of particular properties, which 
constitute in ultimate analysis what I call the colour of heat. 
Thus coloration forms the true framework (charpente) of radiant 
heat ; the term which represents it is then eminently fit for cha- 
racterizing the science. 
I will add, lastly, that in giving the name of Thermochro- 
ology to the science which relates to the whole of the properties 
which calorific radiations possess, we not only employ a more 
