178 
bodies j a second species is luminous, and: imparts 
colour to objects j and the third species exerts a 
chemical action on bodies, and causes the separation 
of oxygen from them, It likewise appears, that, 
while the luminous rays differ gradually from each 
other in their degrees of refrangibility, the calorific 
and chemical rays are, in this respect, eiitirely op- 
posed, and are therefore found, in greatest intensity, 
near to and beyond the opposite boundaries of the 
prismatic spectrum. 
444. The different chemical effects, produced in 
bodies by the agency of light, which M. Berthollet 
so strongly remarked (439.), but was unable to ex- 
plain, receive, we think, an easy solution from these 
views of the different nature and operation of its ca- 
lorific and chemical rays 5 for these two portions 
of light seem respectively fitted to produce the 
opposite effects of combination and decomposition, 
which he has noticed. These effects, M. Ritter 
has farther remarked, to resemble those which 
are produced by the opposite electricities of the 
Voltaic pile \ for, while positive electricity, in the 
decomposition of water, occasions* like the calorific 
rays, the combination of oxygen with the metallic 
wire, no such effect takes place at the opposite, or 
negatively electrified wire *. To follow this analo- 
gy with greater precision and effect, let us consider, 
somewhat more particularly, the chemical operation 
of Galvanic electricity, as it has been developed in 
the late important experiments of Mr Davy. 
* Huiiy, vol. ii. 
