1901-2. 



Photography in Natural Colours. 



377 



images should give us a correct representation of the colours of the 

 object. The red, green, and blue-violet images of some fruit against a 

 red background can be shown side by side upon the screen by means of 

 three lanterns. On bringing these images to one position or super- 

 posing them on the screen [s/zozun], their mixture produces, as is seen, a 

 very good reproduction of the original colours. 



The method of obtaining these coloured images, as will be at once 

 observed, is to back with coloured glass photographs on glass or 

 transparencies in black and white, exactly similar to ordinary lantern 

 slides. Consider the red image only for simplicity. A transparency of 

 the object must be obtained in which the relative transparency of the 

 various parts corresponds exactly to the amount of the primary red 

 required (in union of course with the green and blue-violet), to match 

 the colours of the object. Working backwards from the transparencies, 

 the negatives from which they are made must have the relative opacities 

 of their parts corresponding exactly with the amounts or intensities of 

 the reproduction colours required to match the colours of the object. 

 Negatives fulfilling these conditions will be correct, not only for the 

 method of positive superposition already referred to and shown, but for 

 every method of synthesis. 



The colour-mixture curves of Maxwell (Fig. i), indicate graphically 

 the amounts of red, green, and blue-violet light required to match the 



Fig. 3. — Colour-Record Negatives of the Spectrum. 



