352 Mr. Herapath on the Theory of Evaporation. [May, 



100 and w = 99 will have a ratio equal to that of 1 to *36973, 

 or 100 to 37 nearly. And therefore if the true temperature 

 corresponding to w = 100 be 1172-6 or 212° Fahr. the true 

 temperature corresponding to w = 99 will be only 433*5, or 

 about — 361° Fahr. ; so that here for a loss of weight of only 

 the x^-g-th part, the temperature would be sunk nearly 600° of 

 Fahr. 



We see from the preceding calculation that where the number 

 of particles is much increased by the decomposition, a very 

 trifling or even an utterly inappreciable loss of weight may 

 nevertheless be accompanied by a very considerable diminution 

 of temperature. Hence may easily follow the phenomena of 

 radiation, and even those of the emission of light. Indeed I am 

 fully convinced from many circumstances that evaporation, 

 radiation, and the emission of light, are phenomena similar in 

 kind, and governed by similar, but not precisely, the same laws. 

 Probably the chief difference lies in the inequality of magnitude 

 in the particles when decomposed. Light is most likely the 

 particles decomposed into their smallest parts, which, if they 

 could be inclosed within a vessel whose pores would not allow 

 them a passage, would form a body similar to gas or vapour of 

 extreme levity ; and, on the contrary, if vapour was formed in 

 vacuo, its particles would fly off in direct lines, like light with a 

 great velocity. These views are rendered interesting not merely 

 from their simplicity and their reducing to one simple cause 

 phenomena apparently so very different as vapour and light, but 

 they take from the sun that exorbitant temperature which cer- 

 tain philosophers have hitherto supposed it to have, and thus 

 render it much more fit for a habitable globe. For since the 

 molecules of light are conceived to be many times less than the 

 particles of common matter, they would have with only the 

 same momentum or temperature a velocity many times greater 

 than the latter ; and, therefore, after a particle of common mat- 

 ter had been struck by a molecule of light, and was returning to 

 the other particles of the body of which it formed a part, it may 

 be overtaken and struck again and again before it reached them 

 by other molecules, each impulse of which would add to its 

 motion, and therefore to the temperature of the body ; and if the 

 rays of light be condensed by a mirror or lens on any particular 

 body, the probability of this augmented temperature would be 

 in proportion to the density of the light. Hence, therefore, the 

 sun may in reality have a temperature not higher than that of 

 any other body of the system, and yet produce all the effects 

 attributed to it. This idea comes up nearly to that broached 

 by the late Sir W. Herschel, but without the aid of his luminous 

 atmosphere. I need, I hope, scarcely observe, that these reite- 

 rated impulses by different molecules of light on the same parti- 

 cle of matter, do evidently not at all affect the theory of gases 

 I have heretofore laid down. 



