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History of Three-Color Photography
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breadth and closeness of these bands are functions of wave-length ; the bands are narrower and nearer together the shorter the wavelength. If the screen is replaced by a photographic plate, there will be on development, bands of deposit whose breadth and closeness depend on the light used, — in other words position of particles in the film takes the place of the original color. Now, if a colored image is formed by a lens on a plate and a grating interposed a short distance in front of the plate, the image will be split up into minute bands corresponding to the wave-lengths at any point. In fact, new gratings whose rulings correspond to the colors at various points of the picture would apparently be formed. In this case the picture, placed in front of a biconvex lens illuminated by a narrow source of light and viewed in the proper position, would appear in natural colors."
In a later paper12 Jourdain said : "If a slit be illuminated and photographed by a model 'prismatic camera/ the image on the sensitive plate would consist of one or more bands according as the slit was illuminated with monochromatic light or not, in fact, the same kind of effect would be obtained as that shown on the corona photographs obtained by Sir Norman Lockyer with his prismatic camera. It is easy to imagine that a positive from this banded negative, when backed with a screen colored or graduated like a spectrum, and viewed through the prism, could be so illuminated that the colors should be recombined and the eye should see the slit in its natural color. Of course, it is extremely doubtful whether such a process could be of any practical use, as obviously the object must be very narrow."
In March, 1906, Cheron13 patented a method and his apparatus consisted of two separate cameras, in front the line screen, with a 1:5 ratio of transparent to opaque lines, the latter being about 0.2 mm. wide, was placed in the focal plane, and almost in contact with it a large field lens to condense the light on to a prism of 2.5 degrees, and the lenses of the second
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