178 COLOR PHOTOGRAPHY. 



The colors of iodide of silver are, however, not those due to thin 

 films, for they change "when one replaces the air in the interlying 

 spaces by water or varnish." It would be consistent with this obser- 

 vation to suppose that they are caused by the interference of light 

 passing through the iodide of silver particles and that passing directly 

 through the intervening spaces. 



I refrain, however, for the sake of brevity, from more thoroughly 

 examining this hypothesis. The question at present considered is this : 

 Are the methods of color reproduction in the older processes of color 

 photography satisfactorily explained, according to Schultz-Sellack, by 

 supposing the colors to be in consequence of mechanical disintegra- 

 tion of the film, so that they may be called disintegration colors? A 

 grave objection occurs to such an explanation, because they are thus 

 classed as transmission colors while in each of the processes the colors 

 are reproduced in reflected light. Since, however, the disintegration 

 colors do not appear in directions at an angle with that of transmis- 

 sion, it follows, if they are caused by interference, that reflected and 

 transmitted light must be complementary to each other, leaving out of 

 consideration the small absorption in the iodide of silver. I actually 

 found that where a metallic yellowish green was seen in normally 

 reflected light that passing through was bluish violet and where blue 

 was reflected yellow was transmitted. Hence, the series of Schultz- 

 Sellack can not hold for the colors of reflected light, for according to 

 it the more refrangible occur by increasing the time of exposure or the 

 intensity of the light. 



The simple appearance of the colors of the older color photography 

 works against the theory of Schultz-Sellack. They appear very well 

 by diffuse illumination, as from a bright window, while disintegration 

 colors are here extinguished. These latter require for viewing a light 

 directly reflected from in front, which would totally destroy colors from 

 bright plates like those of Becquerel, for the light reflected from the 

 front surface would overpower that from behind. 



Disintegration colors, according to his observation, experience also a 

 change in reflected light with increasing angle of incidence. I was 

 able in this way to produce change from metallic yellow to bluish gray 

 and back to metallic yellow. It has not been possible to produce such 

 changes with reproductions of colors by the older processes. 



The Schultz-Sellack explanation may, however, be subjected to a 

 crucial test, for the different colors of illumination would produce 

 no different kinds but only different intensity of action upon the sensi- 

 tive film, and if the nature of the colors resulting is to be determined 

 only by the intensity all colors of illumination would in the beginning- 

 produce the same color, and so far as their action proceeded the same 

 succession of colors. 



Such a behavior is contradicted by the observation of Becquerel, 

 according to which the colors corresponding to those of illumination 



