through different solid and liquid bodies. 235 



In fact, if rays of heat, issuing from a prism, be made to pass 

 through a plate of water, between two plates of glass, it will be found 

 that in traversing the fluid, the least refrangible rays suffer tlie great- 

 est loss. The rays of heat mixed with the blue or violet light pass 

 through in great abundance, — those which lie in the obscure part 

 just beyond the red are almost totally stopped. The first act like 

 the heat of a lamp, and tlie last like that of mercury or water in 

 ebullition. It was formerly imagined that the temperature of differ- 

 ent parts of the solar spectrum was proportional to the intensity of 

 the light, and hence that the yellow contained the most heat. It 

 was afterwards maintained that the maximum of heat lay in the red 

 or just beyond it. The first opinion, based on the experiments of 

 Berard was much in vogue in France, — the latter, on those of Her- 

 shell was generally adopted in England and in Italy. Seebeck's re- 

 searches in 1828 prove that all this may be true, for the maximum 

 of heat depends on the composition of the prism. It was wrong 

 therefore to draw such general inferences from such particular facts. 

 But the error was in some measure justified by the false idea that 

 had been formed of tlie invariable action of colorless diaphanous 

 substances on all sorts of calorific rays ; so tlie facts announced by 

 Seebeck, remained isolated in science until the researches of Mel- 

 loni. Now they may be explained with the greatest facility. Let 

 us recollect, 1st, that in the common spectrum formed by a glass 

 prism, the maximum of heat lies in the red ; 2d, that the solar rays, 

 in traversing a mass of water sufier loss inversely proportionate to 

 their refrangibility. 



This premised — the author reasons thus : The solar heat which 

 falls upon the anterior face of a prism of water, comprehends rays 

 of all degrees of refrangibilty. Now, the ray which possesses the 

 sanle refractive index as the red light, suffers, in traversing the prism, 

 a loss proportionally greater than the ray endowed with the refran- 

 gibility of orange light, and the latter less in traversing it than the 

 heat of the yellow. These ratios increasing in the loss of the less 

 refrangible rays, evidently tend to cause the maximum to move from 

 the red to the violet ; it may then stop at the yellow. By supposing 

 the action of sulphuric acid to be analogous to, and less active than, 

 that of water, we shall understand why, in the case of a prism of 

 acid, the maximum is stationed at the orange. 



In fact, the glass itself of v.hich common prisms are composed, 

 must operate in the same manner and produce upon each ray a loss 



