A Manual Of Photography

CHEMICAL ACTION OE THE SOLAK RAYS. 11 combined with hydrogen in the white glass in the ngies- sunshine without any explosion. . . . Berzelius noticed some peculiar conditions in the action o the solar rays upon the salts of gold; and Bischer pursue some researches on the influence of the prismatic rays on 10111 silver. , The most important series of researches, however, v. ere its of Berard in 1812, which were examined and reported on by Berthollet, Chaptal, and Biot. These philosophers write: (M. Berard) found that the chemical intensity was greatest at the violet end of the spectrum, and that it extended, as 1 er and Wollaston had observed, a little beyond that extremity. When he left substances exposed lor a certain time 0 e 10 of eacli ray, he observed sensible effects, thong 1 wi 1an inc sity continually decreasing in the indigo and bue ray s. we must consider it as extremely probable, tha 1 it ■ able to employ reactions still more sensible he *oulcl.have observed analogous effects, but still more feeble even m the other rays. To show clearly the great disproportion shichcx1ts in this respect between the energies of different rays ^Berard concentrated, by means of a lens, all that part of the>spectrum which extends from the green to the extreme centrated, by means of another lens, all ma po , tends from the green to the extremity of te re . arcelu pencil formed a white point so brilliant that te eyes able to endure it ; yet the muriate of silver remained than two hours to this brilliant point of light without un ide g J any sensible alteration. On the other hand, sum exp the other pencil, which was much less bright ant tss 1, blackened in less than six minutes." This is the earliest mti mation we have of any hypothesis that the luminous ant , powers may be due to dissimilar agencies. On is," missioners remark :—" If we wish to consider so ar g composed of three distinct substances, one of w111 light, another heat, and the third ehe,meal ™ follow that each of these substances is sparable y, 1 into an infinity of different modifications, like ligl, we find by experiment, that each of the three properties, chemical, colorific, Ind calorific, is spread, though unequally, over a cer- tain extent of the spectrum. Hence we must suppose on that hvnothesis that there exist three spectrums one above another, namely a calorific, a colorific, and a chemical spectrum. We must likewise admit that each of the substances which coinpose the three spectrums, and even each molecule of unequal refran gibility which constitutes these substances, is endowed, like the