Page:Proceedings of the Royal Society of London Vol 1.djvu/44

Rh respecting the latter, which not only are well known to be founded, but are also best calculated to elucidate the comparison. These are the seven following :—1. Light, both solar and terrestrial, is a sensation occasioned by rays emanating from luminous bodies; 2. These rays are subject to the laws of reﬂection; 3. They are refrangible; 4. They are of different refrangibility; 5. They are liable to be detained by different diaphanous bodies; 6. They are liable to be Scattered on rough surfaces; and 7. They have hitherto been supposed to have a power of heating bodies, which however remains as yet to be examined.

The similar propositions respecting heat which the Doctor intends to prove, are as follows z—l. Heat, both solar and terrestrial, is a sensation occasioned by rays emanating from candent substances; 2. These rays are subject to the laws of reﬂection; 3. They are refrangible; 4. of different refrangibility; 5. liable to be detained in their passage through other bodies ; 6. liable also to be scattered on rough surfaces; and lastly, They may be supposed, when in a certain state of energy, to have a power of illuminating objects; which last, however, remains as yet to be examined.

The paper before us is limited to the experiments on the three ﬁrst of the above-mentioned comparative propositions. They are twenty in number, of which the ten ﬁrst relate to the reﬂection, and the ten last to the refraction of these rays, under all the variety of circumstances deducible from the different kinds of heat above enumerated; to which are added, some attempts to produce a condensation of heat independent of light, by spherical mirrors and lenses. Such mirrors and lenses, together with accurate thermometers, were the instruments used in these experiments, of which those on invisible solar heat, and invisible culinary rays, are perhaps the most striking, as they serve to corroborate the theory laid down by the Doctor in a former paper concerning the existence of such beat and rays independent of light.

It being impracticable to epitomize the ample account of these experiments given in the paper, we must content ourselves with observing in general, that all their results fully evince the truth of the second and third propositions above laid down, viz. that the rays which occasion heat, both solar and terrestrial, in all their different kinds, and under every variety of circumstances that could be devised, 'are subject to the laws of reﬂection and refraction.

The same results also convey sufficient evidence of the radiant nature of light; and hence equally prove the ﬁrst of those propositions. The three following ones, viz. the fourth, ﬁfth, and sixth, are reserved for a future communication; where the author proposes likewise to enter into a discussion concerning the seventh or last of them. relating to the power of heating and illuminating.