PHOTOGRAPHY, SCIENTIFIC ASPECTS 



were merely the result of an intricate incidence and 

 reflection of light, with the consequent interference, 

 and not pigmentary matter at all. 



Without going into the discussion, which was long 

 and very technical, it is only necessary to state that 

 it has been finally shown that "the colors produced 

 by Becquerel's process were found to be chiefly in- 

 terference colors due to the action of the standing 

 waves, but there was pigmentary matter also present," 

 the latter being due to the subchloride of silver, though 

 why "this should be changed by colored light into a 

 substance that has some approach to the color of the 

 light that falls upon it is a problem still unsolved." 



Prof. Gabriel Lippmann of Paris, in 1891, proposed 

 a direct method of color photography, which, like that 

 of Becquerel, is based on the production of interference 

 layers in a photographic plate having a film sensitive 

 to all colors and a good reflectory surface to send back 

 the incident light. This surface was obtained by a 

 slide filled with mercury which backed up the film. 

 The results were never entirely satisfactory although 

 the process was improved upon by later experimenters. 

 It required very delicate adjustments and long ex- 

 posures. This method must not be confused with 

 the newer process of Professor Lippmann, announced 

 in 1906, which will be described later. It is of quite 

 another nature. 



In 1 86 1, Clerk-Maxwell demonstrated the possibility 

 of projecting colored objects by means of three colored 

 plates, red, yellow, and blue, basing his experiments 

 upon the fact that all colors in nature may be simulated 



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