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Transactions of the Canadian Institute. 



[Vol. VII. 



negative colour mixture, the addition of absorptions, or the super- 

 position of coloured dyes or pigments. 



In positive synthesis, a transparency in black and white, an ordinary 

 lantern slide in fact, is made from each of the three negatives ; and each 

 transparency is illximinated by its own reproduction colour. That is to 

 say the transparency from the negative taken through the red filter is 

 illuminated with pure red light, that from the green filter with pure 

 green light, and that from the blue-violet filter with pure blue-violet 

 light ; this is effected, practically, by backing each transparency with its 

 corresponding reproduction glass. Since the relative transparency or 

 redness of the red positive is proportional to the amount of the primary 

 red, of the green positive to the amount of the primary green and of the 

 blue-violet positive to the amount of the primary blue-violet required, 

 when united, to match the colours of the object, evidently any method 



Fig. 5. — Ives' Lantern Kromskop. 



of seeing these three images at one time and in one position on the 

 retina should reproduce the colours of the object. One method of 

 effecting this is by 'triple projection in which the three images are 

 superposed and registered on the screen. The three lantern slides from 

 the three negatives are placed one in each lantern and backed with 

 their suitable reproduction glasses, thus giving the required red, green 

 and blue-violet images on the screen. Each of these images, it may be 

 mentioned in passing, according to the Young- Helmholtz theory, 

 stimulates its respective process to the same degree as the original object. 

 Again, the superposition of the green and blue-violet images, on the 

 same theory, would, to the red colour-blind person appear similar to 

 the original object, the superposition of the red and blue-violet would 



