192 
and that, in all cases, the same conditions are requi- 
red for their operation, and the same laws of action 
are. respectively observed. We do not deem it ne- 
cessary, for our purpose, to institute a comparison be- 
tween the physical properties of these subtile fluids ; 
for it is only with their chemical agencies that we are 
at present concerned. Neither do we venture, from 
the examples which have now been selected, to decide 
on the question of identity between the two species of 
invisible light, and the two states or kinds of electric 
matter. Our present object will have been gained, 
if we have succeeded in shewing such a similarity of 
chemical action between these subtile agents, as will 
entitle us to infer, that, where similar effects are, in 
other instances, produced by them, we may reason- 
ably impute to them a corresponding similarity of ac- 
tion. 
463. HAVING thus endeavoured to establish the 
similarity of chemical operation between light and 
electricity, let us next proceed to an explanation of 
those decompositions which are effected by solar 
light. We have seen, that, by the direct agency of 
the calorific rays (453.), various bodies are decom- 
posed, and their elements recombine into new forms, 
under which changes the phenomena of light and 
heat are exhibited. But the decomposition of many 
bodies is, likewise, accomplished by the chemical 
rays of light (454.), without the attendant phenome- 
na of heat or luminous appearance ; neither do the 
