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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 sen- 

 sation 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 de- 

 tained by different diaphanous bodies; 6. They are liable to be 

 scattered on rough surfaces; and 7. They have hitherto been sup- 

 posed 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: 1. 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 re- 

 frangible ; 4. of different refrangibility; 5. liable to be detained in 

 their passage through other bodies ; 6. liable also to be scat- 

 tered 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 enume - 

 rated ; 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 

 u former paper concerning the existence of such heat and rays inde- 

 pendent of light. 



It being impracticable to epitomize the ample account of these 

 experiments given in the paper, we must content ourselves with ob- 

 serving 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 propo- 

 sitions. 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. 



