160 PHOTOGRAPHY IN THE COLORS OF NATURE. 



yellow and li II methyl violet for the blue sensation. The jDlates aud 

 screens are correct when they will secure negatives of the spectrum 

 showing" intensity curves substantially like the curves in Maxwell's 

 diagram. The negatives can also be made on certain makes of ordinary 

 commercial gelatine bromide plates of the most rapid kind, by the use 

 of quite diflerent color screens for the tirst two, but only with expos- 

 ures of from five to fifteen minutes on well-lighted landscapes, aperture 

 of objective, /-12. 



lu photographing objects in a changing light — laudvscapes, for 

 instance, — it is important that the three sensitive plates be exposed simul- 

 taneously; and in order to accomplish this, I devise a triple camera, hav- 

 ing three lenses so arranged in connection with reflectors as to bring all 

 the i)oiiits of view within a oue-iuch circle. With this camera, the pro- 

 duction of sets of negatives of the required character is a simple and 

 easy matter, it being only necessary to insert the plates, raise the flap 

 until the exposure is made, take the plates out again, and, when con- 

 venient, to develop them together in the ordinary way. 



There are two ways of making the heliochromic pictures from these 

 uegatives. The tirst method does not produce a permanent picture, 

 but a screen i^rojection. 



Lantern slides made from the heliocliromic negatives and exactly 

 reversing their light and shade must also represent the effect of the 

 object ui)oii the respective color sensations. One lantern positive, 

 when seen by transparency in red light, re-produces tlie eflect of the 

 object u]»<)n the primary red sensation. Another, viewed in the same 

 manner by green light, re-produces the effect of the object upon the 

 green sensation. The third, viewed by blue-violet light, re produces 

 the effect upon the blue sensation. Evidently the combination of these 

 three images into one must form a re-i»roduction of the object as seen 

 by the eye, correct in form, color, and light, and shade. Such a com- 

 bination is effected by projecting the three pictures with a triple optical 

 lantern, so that they exactly coincide u|»(m the screen. The result is 

 what we have been je<l to expect. 



We have here a true solution of the jtroblem of re-producing the 

 colors of nature in a screen picture, <lating from November, 1888. Pre- 

 vious to the publication of my new principle it was assumed by Cros, 

 Poiree, and others, that if the projection method were emi)]oyed each 

 picture should be ijvojected by the same kind of rays as those which 

 acted to produce it. In my method, as I have already stated, a i)icture 

 made by the joint action of red, orange, yellow, and yellow-green rays, 

 but chiefly by orange, instead of being projected by a similar mixture 

 of spectrum raj'^s,is projected by red rays only. Similarly, the picture 

 made by orange, yeUow, green, and green-blue rays is projected by 

 green rays only, and that made by blue-green, blue, and violet rays, 

 by blue- violet rays only. 



]Jr. Stolze, who was one of the tirst to recognize the genuineness of 

 this solution of the problem, doubted if, even in theory, color prints 



