164 PHOTOGRAPHY IN THE COLORS OF NATURE. 



white surface, it will not be difficult to imagine that the effect would 

 be not only the representation of the form of the object, but that of its 

 color also in all its compounds. 



******* 



"Although the idea I have endeavored to express in words maybe 

 utterly worthless, I am unwilling to let it slij) away without notice, as 

 it may on the other hand contain a germ which may grow and bear 

 fruit in due season." 



The language of some parts of this communication is ambiguous, but, 

 taken altogether, with due allowance for the writer's unfamiliarity with 

 photogra|)hic technology, it clearly amounts to a suggestion to make 

 three photographic negatives of an object — one by the action of red 

 light, one by yellow, one by blue; to print from each i)air of these nega- 

 tives (sui)erposed as one) a transparent positive having the color repre- 

 sented by the third negative, and to superpose on a white surface the 

 three prints thus obtained. 



It was not possible to carry out Collen's suggestion at that time, 

 because there was no known process by which plates could be prepared 

 which were sensitive to single colors only, and no photograpliic plates 

 were sensitive enough to red and yellow to admit of the i)ro(l notion of 

 such negatives by exposure through selective color screens. Had it 

 been possible to carry it out, the results must have been very imperfect, 

 not only because the entire procedure is based upon a false and mislead- 

 ing theory of color, but also because superposing two negatives to act 

 as one would double the intensity of such parts as represented Avhite, 

 gray, or pale colored objects, with the result that if the color prints 

 were made to show all the details of the negatives, the finished helio- 

 chromes would show all l)right colors as if mixed with e(iual parts of 

 black pigment. 



On November 23, 18G8, DucosDuhauron,of Paris, applied for apatent* 

 for a process which differed from C-olleu's only in the manner of carry- 

 ing out the same idea. Like Collen, he assumed that the spectrum is 

 made up of three primary color rays and mixtures thereof. He said, 

 "My procedure rests on the principle that the simple colors are limited 

 to three — the red, the yellow, and the blue — the combination of which 

 in divers pToportionsproduces the infinite variety of shades in nature.*' 

 LikeCoUen, he expected to solve the problem by superposing red, yellow, 

 and blue prints taken from negatives made by yellow and blue, red and 

 l)lue, and yellow and red light. But, instead of using plates sensitive to 

 single colors only, he proposed to use plates sensitive to all colors, and to 

 prevent the action of color rays not wanted by filtering them out with 

 color screens i)laced in front of the photographic objective or sensitive 

 plate; and, instead of superposing two negatives to act as one, from 

 Avhich to make the color prints, he i)roposed to make two colors (two- 

 thirds of the spectrum rays) act to produce each negative, which 



* Class XVII, sec. 3, serial No. 83061. 



