in the situations of their maxima. And we also collect that the projecting part of the heating rays, being on the side of the red or least refrangible coloured ray, the aggregate of the former may be said to be less refrangible than that of the latter.
The Doctor now goes on to prove by experiments, that the sines of refraction of the heat-making rays are in a constant ratio to their sines of incidence, and points out the results of a correction of the different refrangibility of heat, by contrary refractions in different media.
Experiments are also described which show that the focus produced by a lens is in fact twofold, that which is produced by the rays of heat being in the same axis, but at some distance further from the lens than the luminous focus,—a property that might have been in ferred, à priori, from the less refrangibility of the heat-making rays.
In the fifth article, which treats of the transmission of heat-making rays through diaphanous bodies, besides the accurate description of the various apparatus which it was necessary to contrive for the purpose, and which can only be clearly understood by inspecting the figures added to the paper, we find the results of 170 experiments distinguished under the six following sections.1. On the transmission of solar heat through colourless substances; through glasses of the different prismatic colours; through liquids, such as well and seawater, and different spirits; and through scattering substances, such as ground glasses, paper, linen, silk, &c.2. On the transmission of the heat of terrestrial flame through various substances.3. On the transmission of the solar rays, which are of an equal refrangibility with the red prismatic rays.4. On the transmission of fire-heat through various substances.5. On the transmission of invisible rays of solar heat. And lastly, (the subject which appears most pregnant with useful inferences for the common purposes of life,) on the transmission of invisible terrestrial heat. Not only the general position, that the rays of heat, both solar and terrestrial, are detained in their passage through various bodies, appears to be here completely evinced, but the great variety in the power of the transmitting bodies seems also to be determined with abundance of accuracy, and affords matter of much consideration and curiosity.
From the sixth article, in which it is intended to prove that the rays of heat, both-solar and terrestrial, are liable to be scattered on rough surfaces, it appears that all bodies, even the most polished, are sufficiently rough to scatter heat in all directions. And the chief object of the twenty-four experiments here described, is to compare the effects of rough surfaces on heat with their simultaneous effects on light. The general and rather unexpected result is here brought for ward, that colours have no concern whatever in the laws that relate to the scattering of heat.
The chief object of the whole of this inquiry follows next in the seventh article, where the question is discussed, “Whether light and heat be occasioned by the same or by different rays?” One of the leading facts deduced from the experiments in the fourth section, is that there are rays of heat, both solar and terrestrial, not endowed
