LIGHT AND RADIANT HEAT. 
255 
tbs same time, and the thermometer did not rise. So that in 
this experiment, as well as the preceding, the calorific prin- 
ciple, whatever it may be, accompanies the luminous particles, 
and is never separated from them. 
Instead of the beam of solar light employed in this ex peri- Caloric radia- 
ment, M. Berard substituted a pencil of radiating caioric ^ody not lumi- 
emitted from a very hot body, but either scarcely red, or totally was po- 
larized. 
obscure. The effect was the same as before. The thermome- 
ter rose when the second glass was in a position which would 
have enabled it to reflect light ; but when this reflection was 
not possible, the temperature continued to be the same as 
the surrounding air. Hence it is proved, that the invi-ible 
particles which compose the rays of obscure caloric are modi- 
fied by reflection precisely like the particles which compose 
light. 
After having studied the calorific properties of the different Chemical pro- 
rays of the spectrum, M. Berard has attended to their chemical pertiesof rays 
properties. It is known, that when the muriate of silver, or extremity of 
the other white salts of silver, areexposed to light, they become s P ectmm » 
blackened in a very short time. Gum guaiacum, thus exposed 
to light, passes from yellow to green, as has been observed by 
Dr. Wollaston ; and lastly, Messrs. Gay Lussac and Thenard 
have shewn us a chemical action still more prompt and energetic 3 
for, by exposing to a ray of solar light a mixture of hydrogen 
gas and oxigenated muriatic acid in equal volumes, a detonation 
instantly follows, of which the product is water and muriatic 
acid combined together. These several phenomena have served 
M. Berard as reagents to examine and put in evidence the che- 
mical powers of the different rays of the spectrum ; for, by 
putting into the spaces occupied by the different colours small 
pieces of card impregnated with muriate of silver, or small 
phials filled with a mixture of the two gases, he was enabled to 
judge of the energy of the cause by the intensity and rapidity 
of the chemical changes produced in the substances so exposed 
to the different rays. In this manner he ascertained, that the 
chemical properties are, in fact, the most intense towards the 
violet extremity of the spectrum, and that they extend, as 
M. Bitter 
