Sixth memoir on radiation and absorption

In this paper the author considers the deportment of certain additional elementary bodies towards Radiant Heat. He exposes powders and liquids of the same physical character, but differing from each other chemically, at a focus of dark rays, and describes the different effects produced. He examines and explains the experiments of Franklin on the absorption of solar heat. He then determines the radiative power of a great number of substances in the state of fine powder, and finds, contrary to the current belief, that in this state also chemical constitution exercises a paramount influence. The results obtained by previous experimenters in connexion with this subject are illustrated and explained. The reciprocity of radiation and absorption on the part of fine powders is also illustrated. It is moreover shown that the heat emitted from different sources, at a temperature of 100° C., varies in quality, this being proved by its unequal transmission through plates of rock-salt of perfect purity. The absorption by such plates varies from 4 to 30 per cent, of the incident radiation.