REPORT ON RADIANT HEAT. yw 
‘He afterwards describes an experiment with the solar rays 
transmitted by a green glass, and then intercepted by other 
media. They pass copiously through rock salt, but feebly 
through alum. Hence he concludes, that there are among the 
solar rays some which resemble those of terrestrial heat ; and 
in general, that “ the differences observed between solar and 
terrestrial heat, as to their properties of transmission, are 
therefore to be attributed merely to the mixture in different 
proportions of these several species of rays.”’ 
In a note to this memoir, M. Melloni refers to my original 
experiment (Phil. Trans. 1825), in which the action of the rays 
on surfaces is observed in connexion with their transmissi- 
bility. 
He confirms the accuracy of my result, by a careful repe- 
tition of the experiment with the thermo-multiplier, but makes 
no reference to the conclusion I had drawn, viz. the co- 
existence of two distinct sorts of heat in the radiation from 
luminous sources, one of which is the same as that from dark 
sources. He explains the result by supposing the transmitted 
rays to acquire, in and by the act of transmission through the 
glass screen, new properties in their relation to the surfaces on 
which they fall, 7. e. to the degree of absorption they undergo 
respectively on a black and a white surface. 
He extends the investigation by a table of results of the same 
kind with a series of screens, both transparent, and of various 
degrees of opacity. The ratio of the effects on the black and 
white surfaces is nearer to equality as the screen is more 
opake. 
On this subject there appears a short paper by M. Melloni 
in the London and Edinburgh Journal of Science, vol. vii. 
p- 475; to which I replied in the same journal, Jan. 1836. 
While referring to my own experiments, I may be allowed to 
add, that in Dr. Thomson’s Treatise on Heat, &c., first edition, 
the bearing of my investigation was incorrectly represented; and 
accordingly I pointed this out in the London and Edinburgh 
Journal of Science, Nov. 1830. 
In the second edition of Dr. Thomson’s work, which has 
lately appeared, the author omits all mention of the subject 
whatever. 
Transmission and Refraction of Heat: Forbes. 
The subjects of transmission and refraction of heat were taken 
up by Prof. Forbes; and Melloni’s experiments repeated and 
extended by him; the details being given in the first and part 
of the second sections of his first Memoir “on the Refraction 
