534 $ M. MELLONI ON A NEW NOMENCLATURE 
species of radiant heat powerfully and equally, as white bodies 
do with respect to light, bear the name of lewcothermic*, that is — 
to say white for heat. 
As to the media which transmit or which intercept the calo- 
rific effluences, I should advise that the first words diatherma- 
nous and athermanous be thrown aside, and that the denomina- 
tions diathermic and adiathermic, which have a more regular 
formation, and are more conformable to the terminations of the 
new nomenclature, should be substituted for them. Then the 
calorific transparence of the bodies, or transcalescence, to use a 
term of Sir J. F. W. Herschel’s, would be called diathermasy t, 
and we should call the contrary property adiathermasy t, that is 
to say, opacity in relation to the radiations of heat §. 
The substances which only transmit: certain kinds of heat, 
constitute, according to this new system of nomenclature, diather- 
mic thermochroic bodies; those which transmit all kinds of radi- 
ations without distinction, are diathermic athermochroic bodies ; 
denominations, however, which may be abridged by simply call- 
ing the first thermochroic media and the second athermochroic 
media. A similar abbreviation may also be used in reference to 
opake substances, which should be called, strictly speaking, 
adiathermic melanothermic, adiathermic leucothermic, adiather- 
mic thermochroic bodies, according to the nature of their tint, 
whether black, white, or coloured a heat, but which will always 
be sufficiently characterized by the latter expressions, if they 
are designated simply as thermochroic, leucothermic, or mela- 
nothermic substances, as the practice is in relation to light, in 
ordinary language, or when, in treating of opake bodies, the 
custom is to suppress all allusion to transparency; which is not 
only expeditious but very philosophical, for transparency is but 
an exception to the general law of opacity, and forms, so to 
speak, a character of transition between ponderable matter and 
zethereal substances. 
I conclude by offering the following synoptical outline, in 
which will be found brought together all that concerns the new 
nomenclature, and some applications. 
* From Aguxos white. 
+ From Degueca to heat, and ie through, across. 
{ From «@ privative, and dscebeouccle calorific transparence. 
§ These changes, as well as some other etymological modifications, are made 
by the advice of °M. Antonio Ranieri, a young Neapolitan, well known in Italy 
by his touching and generous friendship towards that fine genius Jacopo 
Leopardi, snatched by a premature death from the admiration of his countrymen. 
