256 
EIGHT AND RADIANT HEAT 
These are iiGt 
governed 
either by the 
light or the 
heat. 
Approbation 
m the re- 
porters. 
M. Ritter and Dr. Wollaston had announced, a small distance 
beyond that extremity. And farther, by leaving the substances 
exposed for a certain time to the action of each ray, which the 
immobility of his spectrum enabled him to do, he succeeded in 
observing sensible effects, though of an intensity continually 
decreasing, in the indigo and blue rays , whence we may con- 
sider it as extremely probable, that if he could have employed 
re-agents still more sensible, he might have seen effects of the 
same description, though more feeble even in the other rays. To 
shew clearly the extreme disproportion which exists in this 
respect in the energies of the different rays, M. Berard con- 
centrated by a lens, all that part of the spectrum which extends 
from the green to the extreme violet, and he collected in the 
same manner by another lens, all that portion which extends 
from the green to beyond the extremity of the red. This last 
beam was united in a white spot, of which the eye could 
scarcely support the brilliancy 5 but nevertheless the muriate of 
silver remained exposed for more than two hours, to this strong 
light, without any sensible alteration. On the contrary, by 
exposing it to the other beam, of which the light was much less 
vivid, and the heat less strong, it became blackened in less than 
ten minutes. M. Berard concludes from this experiment, that 
the chemical effects produced by light are not owing to the 
heat alone, which it developes in bodies by combining with 
their substance j because on this supposition the faculty of pro- 
ducing chemical combinations ought, it should seem, to be 
stronger in the rays which have the greatest power of producing 
heat. But we may, perhaps, find less difficulty in these two 
manners of contemplating the subject, if we pay attention to 
the diversity of results, which maybe produced by the same 
agent placed in different circumstances, and also that agents of 
a nature totally dissimilar, may nevertheless determine combina- 
tions perfectly identical when they are used. 
Such is the abstract of the principal facts which M. Berard 
has established in his memoir. To great accuracy he has 
joined a most methodical exposition. He has presented the 
physical properties of the different rays, as the results of an 
experimental 
