Tie it) 
530 M. MELLONI ON A NEW NOMENCLATURE. 
properties drawn from their modes of propagation, ordinary heat 
and radiant heat present a fourth distinctive and well-defined 
character, to which I now call the attention of the reader. 
We know that ordinary heat, that is to say the heat which is 
propagated from layer to layer in the interior of bodies and pro- 
duces their elevation of temperature, possesses a homogeneous 
constitution, and that consequently two calorific streams of this 
kind, endowed with the same intensity, are necessarily identical. 
Two effluxes of radiant heat of the same force but of different 
origin, far from being equal in all points, possess, on the con- 
trary, very distinct properties; for they suffer a more or less 
abundant dispersion at the surface of opake bodies, and pene- 
trate in greater or less proportion into the interior of colourless 
media. Moreover, the different refrangibility of the elements 
which constitute each flow of radiant heat, and their more or less 
perfect absorption under the action of the same substances, esta- 
blish, as we just now said, a complete analogy between the calo- 
rific rays and the luminous rays of different colours. 
Thus the variety of species, the heterogeneity of the elements 
which compose them, and above all their great analogy with the 
coloured rays, form an entire body of properties which belong 
exclusively to radiant heat. These properties are therefore suf- 
ficient to distinguish it from ordinary heat, always homogeneous, 
and not presenting any point of resemblance with light. For 
this reason I propose the name of Thermochroology*, that is to 
say, Doctrine of coloured heat, im order to designate the science 
of radiant heat. 
If it be alleged that you cannot apply to an invisible agent, as 
heat, the name of a quality which in another agent is visible, I 
would say that sound also is in the same case in relation to 
light ; and although Acoustics have by no means the relations 
of analogy with Optics which radiant heat has, yet the intro- 
duction of the term chromatic scale has been allowed, thus 
comparing a series of sounds more or less grave to the princi- 
pal colours of light+. The radical chroma, however, signifies 
and still less to a collection of photometric measures, but to the science which 
treats of the chemical radiations of the sun and of incandescent bodies? 
* From deggeos hot, [heat] xecew colour, by changing @ into o, and Adyos dis- 
course. 
+ Some artists pretend that the term chromatic scale is derived from an an- 
cient custom of marking the notes with red ink; but the origin drawn from 
the comparison of sounds to colours appears much more likely. 
