158 PHOTOGRAPHY IN THE COLORS OF NATURE. 



on what parts of the spectrum each negative shoukl fix color, and said : 

 " If successful - - in selecting the color screens in such a man- 



ner that they will let the color pass through which are called for in this 

 table, one will indeed be able to reproduce a pure spectrum in this 

 way." By further calculations he was able to show that this plan, even 

 if successfully carried out, would not insure the correct reproduction 

 of mixed colors. He said: "All pure saturated spectrum colors will 

 also be obtained quite satisfactorily in the reproduction, but the mixed 

 ones only partly." " Oftentimes they have to become more or less 

 impure.'' " But the clearest lights and a number of mixed colors 

 appear very unsatisfactory ." He added : " The intelligent support of 

 the artist can leiul improvement,'' and recommended also the produc- 

 tion of a fourth (ordinary) negative, to be used in combination with 

 the others, to modify the effect, especially in high lights. 



This plan can not be said to definitely represent the application of 

 Young's theory of color, but it may be practically better than any- 

 thing that that theory would indicate if we leave out of account the 

 suggestion of a fourth negative. 



In 1885, Dr.Vogel publisheda plan, which isamoditication of Poiree's.* 

 Like Poiree, ho proposed to nuxke a separate negative for each spectrum 

 region; but, instead of using plates sensitive to all colors and exposing 

 through selective color screens, or illumiiuiting the subject by mono- 

 chromatic lights, Vogel proposed to sensitise plates specially for each 

 spectrum region, which would amount to the same thing, and instead 

 of projecting the pictures with colored lights, he proposed to make as 

 many pigment i)rints as negatives, each in a color complementary to 

 the light which acted to produce the respective negative, and to super- 

 pose them as in the Collen method. 



There are no known dyes witli which this plan could be carried out; 

 and even if there were, it is, I believe, too complicated to be practic- 

 able. 



In February, 1888,t I demonstrated a procedure based upon the 

 assumption that although there are more than three or five or seven 

 primary spectrum colors, all of them — and in fact all the colors of 

 nature — can be counterfeited to the eye by three type colors and mix- 

 tures thereof. This was not a new observation, and my iilan did not 

 differ very materially from that of Dr. Stolze, minus the complication of a 

 fourth negative, except that it was more definite; and instead of merely 

 publishing it as a suggestion, I found means to carry it out, and made a 

 practical demonstration of it. I proved the process by photograijhing 

 the spectrum itself, employing compound color screens carefully 

 adjusted to secure definite intensity curves in the spectrum negatives, 

 so that they would make color prints which counterfeited the color 

 effect of the spectrum when superposed. The adjustment of plates 



* Avnalen dei- Physik (n. s.), vol. xxAai, p. 130; Photographic Netvs, 1887, p. 568. 

 \ Journal of the Franklin Institute, 125, 345. 



