140 REPORT—-1850. 
also noticed that the red rays produced no change on a solution of corrosive 
sublimate (bichloride of mercury) in ether, but that the blue rays rapidly de- 
composed it*, Dr. Davy much more recently repeated a similar set of expe- 
riments to those of Vogel. He found that corrosive sublimate was not 
changed by exposure ; but that the Liquor Hydrarg. Oxymur. of the London 
Pharmacopeia quickly underwent decomposition in the sunshine, depositing 
calomel. 
Seebeck in, and subsequently to 1810, made some important additions to 
our knowledge of the influences of the solar radiations, the most striking of 
his statements being the production of colour on chloride of silver ; the violet 
rays rendering it brown, the blue producing a shade of blue, the yellow pre- 
serving it white, and the red constantly giving a red colour to that salt. Sir 
Henry Englefield about the same time was enabled to show that the phos- 
phorescence of Canton’s phosphorus was greatly exalted by the blue rays. 
Dr. Wollaston’s experiments on the tincture of gum guaiacum also tended 
to prove the peculiar differences in the most and the least refrangible rays. 
Cards moistened with this tincture acquired a green colour in the violet and 
blue rays, and the original yellow colour was rapidly restored in the red rays. 
Gay Lussac and Thenard, being engaged in some investigations on chlorine, 
on which elementary body Davy was at the same time experimenting, ob- 
served that hydrogen and chlorine did not combine in the dark, but that they 
combined with great rapidity, and often with explosion, in the sunshine, and 
slowly in diffused light. Seebeck collected chlorine over hot water, and com- 
bining it with hydrogen, placed different portions of it in a yellowish red 
bell glass and in a blue one. In the blue glass combination took place im- 
mediately the mixture was exposed to daylight, but without explosion. The 
mixture in the red glass was exposed for twenty minutes without any change ; 
but it was found that the chlorine had undergone some alteration, probably a 
similar one to that noticed by Dr. Draper, which I shall have shortly to 
describe. If the gases were placed in a white glass and exposed to sunshine, 
they exploded ; but if the gas had been previously exposed to the action of 
the solar radiations in the yellow red glass, it combined with hydrogen in 
the white glass in the brightest sunshine without any explosion. 
Berzelius noticed some peculiar conditions in the action of the solar rays 
upon the salts of gold; and Fischer pursued some researches on the influence 
of the prismatic rays on horn silver+. 
The most important series of researches however were those of Berard in 
1812, which were examined and reported on by Berthollet, Chaptal and Biot. 
These philosophers write, ‘‘ He (M. Berard) found that the chemical intensity 
was greatest at the violet end of the spectrum, and that it extended, as Ritter 
and Wollaston had observed, a little beyond that extremity. When he left 
substances exposed for a certain time to the action of each ray, he observed 
sensible effects, though with an intensity continually decreasing in the indigo 
and blue rays. Hence we must consider it as extremely probable, that if he 
had been able to employ reactions still more sensible he would have observed 
analogous effects, but still more feeble, even in the other rays. ‘To show 
clearly the great disproportion which exists in this respect between the ener- 
gies of different rays, M. Berard concentrated, by means of a lens, all that 
part of the spectrum which extends from the green to the extreme violet ; 
and he concentrated, by means of another lens, all that portion which extends 
from the green to the extremity of the red. This last pencil formed a white 
* Ann. de Chimie, vol. Ixxv. p. 225. 
+ Philosophical Magazine, vol. vii. Second Series, p. 462. 
* 
"ὧδ 
+, >>. 
