Page:Popular Science Monthly Volume 5.djvu/738

 718 of light, upon the silver bromide. Both these ends are fulfilled by the coal-tar color known as coralline. A plate dyed with this substance and exposed to the spectrum, exhibited two maxima of photographic action, one the ordinary maximum in the indigo (near G), and the other almost as strong in the yellow, thus affording complete confirmation of Dr. Vogel's views. Aniline green was next tried. This dye is stated to absorb the red rays, and a corresponding increase of sensitiveness for the red rays was observed, the photograph again presenting two maxima of activity, the one in indigo and one in the red, coinciding in position with the absorption band of the dye. Thus, Dr. Vogel's results may be summarized by saying that a dyed film of silver bromide exhibits maxima of sensitiveness in those regions where the coloring-matter exerts its maximum of absorptive power, but the precise conditions under which these results can be obtained must be considered at present as unknown, since many observers, in repeating the experiments, among others Dr. Van Monckhoven, have failed to obtain other than negative results.

In a communication made to the French Academy on the 27th of last month, however, the well-known physicist, M. Edmond Becquerel, stated that some experiments made at his instigation by M. Deshaies at the Conservatoire des Arts et Métiers had been productive of positive effects, and that some of Dr. Vogel's results with coralline and aniline green had been reproduced. M. Becquerel, however, does not confine himself to bromide films; similar results have been obtained by iodized collodion in which coralline was dissolved. A most remarkable action was observed also in the case of chlorophyll when this substance was used as a tinctorial agent. Although the collodion possessed only a faint-green color from the dissolved chlorophyll, the spectral image was of a much greater length than when plain collodion was used. Under these last circumstances the spectrum extended from the ultra-violet to between G and F, with the usual maximum of action near G, while with chlorophyll the region of strongest action extended from the ultra-violet to the line E in the green, and at the same time a weaker but yet distinct impression extended from E to beyond B in the red, with a strong band between C and D. By a close examination of the spectral image a second band of less intensity could be detected on the least refrangible side of the band between C and D, and other still weaker bands appeared in the green. The most striking confirmation of Vogel's results is to be found in the fact, observed by M. Becquerel, that the band between C and D corresponds in position with the characteristic hand of the absorption spectrum of chlorophyll dissolved in collodion. The same results were obtained