7i8 THE POPULAR SCIENCE MONTHLY, 



of light, upon the silver bromide. Both these ends are fulfilled bythe 

 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 corresi^onding increase of sensi- 

 tiveness for the red rays was observed, the photograph again present- 

 ing two maxima of activity, the one in indigo and one in the red, co- 

 inciding in position with the absorption band of the dye. Thus, Dr. 

 Yogel's results may be summarized by saying that a dyed film of sil- 

 ver 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 2'7th 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 Metiers had been productive of posi- 

 tive effects, and that some of Dr. Yogel'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 re- 

 markable 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 ac- 

 tion 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 Yogel's results is to be found in the fact, ob- 

 served by M. Becquerel, that the band between C and D corresponds 

 in ]josUion with the characteristic hand of the absorption spectrum of 

 chlorophyll dissolved in collodion. The same results were obtained 



1 The green referred to is probably that known as "aldehyde green." The so-called 

 " iodine green," as I have frequently observed, transmits a band in the red. 

 ^ Photographic Journal^ No. 25, June 20, ISH. 



