422 Action of the AtmospJiere vpon neichj- deepened Soil. 



while they extinguish but a part of the luminous rays. The only 

 substances hitherto employed by me are water and a peculiar 

 species of green glass coloured by means of the oxide of copper. 

 The pure light emerging from this system contains much yellow, 

 and possesses at the same time a tinge of bluish green ; it exhibits 

 no calorific action capable of being rendered perceptible by the 

 most delicate thermoscopes, even when it is so concentrated by 

 lenses as to rival the direct rays of the sun in brilliancy." 

 (^Scientific Memoirs, i. 392.) This result has been lately 

 called in question by Baden Powell, without, however, his 

 adducing any experiments to the contrary. It will be seen, there- 

 fore, how the different actions of the solar radiations can be 

 detached from each other. Thus to a considerable extent the 

 calorific rays can be separated from the luminous, and the lumin- 

 ous from what has been termed the chemical. 



Becquerel, however, seems to view the phenomena in a more 

 philosophical manner. Extending Fresnel's hypothesis, that the 

 chemical effects produced by the influence of light are owing to 

 a mechanical action exerted by the molecules of ether on the 

 atoms of bodies, so as to cause them to assume new states of 

 equilibrium dependent on the nature and on the velocity of the 

 vibrations to which they are subjected, he says it might be 

 simpler to suppose: That a pencil of solar rays is the union of an 

 infinite number of rays of different refrangibility, each ray arising 

 from undulations of ether not having the same velocity. That by 

 refracting a pencil of solar rays through a prism we have the 

 solar spectrum, which possesses different properties on account 

 of its different action on external bodies. That if we consider 

 the retina as an organ which perceives the vibrations of the 

 ether, it is only sensible to rays contained between certain limits 

 of refrangibility, and the active rays form a spectrum, which in 

 this case is found to be the luminous spectrum. And he goes on 

 to say, " according to this hypothesis we shall bring back all the 

 effects produced under the influence of light to the action of one 

 same radiation upon different bodies, and there will be as many 

 spectra as there are sensible substances." {^Scientific MemoirSy 

 iii. 556-7.) 



Professor Moser of Konigsberg has, however, attempted to 

 show that no chemical decomposition is effected by light, and he 

 thinks he can establish the following propositions: — "It is not 

 necessary to suppose — and in those phenomena which have been 

 best observed, it certainly is not the case — that light produces a 

 separation of chemically combined bodies. The action of light 

 is of such a kind that it may be imitated in a perfectly different 

 manner, so that the idea of a chemical decomposition is fully 

 refuted. Even the most continued action of light appears to 



