536 NOMENCLATURE OF CALORIFIC RADIATIONS. 
the same intensity ; which maintains the com- 
position of the incident stream diffused in the | 
calorific flow, and has an effect absolutely simi- 
lar to that which white bodies produce on light. 
EXAMPLES. 
Black mica, obsidian, black glass,reduced into very thin amine, 
without however losing their complete opacity in respect to light, 
still allow a certain portion of radiant heat to pass through them ; 
these bodies consequently are opake and diathermic. Certain 
glasses of a green colour, in combination with a layer of water 
or a very clear plate of alum, are on the contrary adiathermic, 
that is to say opake for heat, notwithstanding their transparency 
for light. 
Atmospheric air and rock-salt, which, within the limits of our 
experience, transmit every kind of calorific radiation, evidently 
constitute athermochroic media. Glass, water, alcohol, and other 
colourless liquids, being permeable only to certain species of heat, 
and intercepting the other calorific rays in a lesser or greater 
proportion, form, on the contrary, thermochroic media. 
Paper, snow, whitening, or white lead, which, notwithstanding 
their extreme whiteness, do not send back the rays peculiar to 
the different sources of heat with the same intensity, and even 
totally absorb certain calorific radiations, should, strictly speak- 
ing, be called adiathermic thermochroic substances; but it will 
suffice to designate them by the latter word, as is daily practised 
in ordinary language, in which the adjective colowred, being ap- 
plied singly to a word, quite naturally carries with it the want of 
transparency. 
Very pure metals, in any mechanical state, and more par- 
ticularly dead gold and silver, diffuse every kind of calorific 
radiation vigorously, and in the same proportions: these bodies, 
then, should be classed amongst Jewcothermic substances, al- 
though generally coloured. In short, lampblack, which absorbs 
almost all incident light and heat, will form a substance which 
is at the same time black and melanothermic. 
Naples, October 7, 1841. 
