THE PHOTOGRAPHY OF COLOUR 359 



general principles of three-colour photography in its two main 

 sections. 



Three-colour photography is practised commercially on a 

 very large scale, and has been investigated and discoursed upon 

 by a vast number of persons. A great many have dealt with 

 the subject from a purely scientific point of view, while printers, 

 ink-makers, and others look only at practical results. I propose 

 therefore only to indicate the chief facts concerning its develop- 

 ment, and to consider the most important processes that are in 

 use at the present. 



It seems that Clerk Maxwell was the first, in 1855, to suggest 

 the principle of three-colour photography, but he used it as 

 an illustration of the functions of the three systems of nerves 

 according to Young's theory rather than a suggestion for 

 practical photography. He says : " Let a plate of red glass 

 be placed before the camera and an impression taken. The 

 positive of this will be transparent wherever the red light has 

 been abundant in the landscape and opaque where it has been 

 wanting. Let it now be put in a magic lantern along with the 

 red glass, and a red picture will be thrown on the screen. Let 

 this operation be repeated with a green and a violet glass, and 

 by means of three magic lanterns let the three images be super- 

 imposed on the screen ... a complete copy of the landscape, 

 as far as visible colour is concerned, will be thrown on the 

 screen. The only apparent difference will be that the copy will 

 be more subdued or less pure in tint than the original." Then 

 he goes on to consider the eye in connection with colour vision. 

 At the Royal Institution in 1861, Clerk Maxwell showed the 

 experiment, using tanks of coloured liquids instead of coloured 

 glasses, and showed the photograph of a coloured ribbon with 

 three magic lanterns ; but of course the colours were deficient 

 because it was almost impossible at that time to photograph 

 by red or green light. 



Within the next few years others engaged themselves with 

 the subject, but the most notable worker was Louis Ducos du 

 Hauron, who, in 1869, published a small volume, entitled Les 

 Couleurs en Photographic : Solution du Problem. He described 

 the triple lantern " additive " method ; a method of combining the 

 three coloured images by means of mirrors ; the production of 

 prints by superposition of the coloured images — the "subtractive" 

 method and a single-plate method — the three colours being 



