Energy of Light and Chemical Energy. 213 



kinetic energy stored in the components of the system under 

 the action of light. The connexion between the terms 

 ( Xfdmf) . . . (\ K f dm n ') and (jiidmj) . . . (fi n 'dm a ') now requires 

 special consideration. 



What is to be understood by " the energy stored in the 

 atoms of the molecules, when the same are exposed to light " ? 

 It is a thermodynamic necessity that the light absorbed by 

 the system (which in this case we assume to represent a thin 

 layer) should transform into some other form of kinetic energy 

 of the atoms, and that at the same time this new energy should 

 be directly proportional to the total mass of each component, 

 i.e., that the new energy created in the system should be of the 

 form (X/dm/) ... (\ndm n '). This, however, does not disclose 

 the nature of this kinetic energy itself. A glance at the 

 above equation (A) shows that more than one interpretation 

 of the terms {X 1 'dm 1 {)...(Xn , dmn) is possible, and these 

 interpretations entirely depend upon how the ultimate nature 

 of the energy stored in the atoms of the molecules under the 

 action of light is conceived. 



One conception is that the light-kinetic potentials (A/), 

 (A 2 '). . . (A,/) are identical in nature with the chemical potentials 

 (//,/), G"-/) ■ • • (Mi/) • I 11 this case it will mean that the kinetic 

 energy stored in the atoms under the influence of light 

 (X'drrii) . . .{Xn'dmn ) is nothing else than chemical energy ; it 

 will mean that under the influence of light the chemical 

 potentials of all and the same substances always increase 

 (simply from one value to another). In the light of this 

 conception, when light-energy is absorbed by any system so 

 far as it does not trans for m into heat it always transforms 

 into chemical energy. 



This. conception would have the advantage of enabling us, 

 in the consideration of the systems in which the variables are 

 dependent one upon another, at once to see that the laws 

 which must govern the two important regions of chemical 

 statics and dynamics under the action of light, must be those 

 found experimentally by the author and communicated in 

 the Philosophical Transactions. It carries, however, little 

 conviction for systems with independent variables where 

 no chemical transformation is to be perceived. There are 

 important regions of phenomena — such as phenomena of 

 absorption, dispersion, refraction, fluorescence, &c., for 

 which the assumption that the energy stored in the mole- 

 cules and atoms under the action of light cannot transform 

 into chemical energy alone, but must also generate an 

 energy sui generis, becomes almost imperative. In the 

 mechanical kinetic explanation of the above phenomena 1 , 

 Stokes, Helmholtz, Lommel, and otl.ers, have to assume that 



