436 OPTICAL PROJECTION 



slides. Professor Joly's process lends itself well to lantern illustra- 

 tion, though the network of lines show rather prominently on the 

 screen. Samples of this method, however, I believe are not now 

 obtainable. 



Messrs. Lumiere's method consists in taking three negatives 

 through carefully selected colour screens. A positive from one of 

 these is obtained on a glass plate and then dyed a corresponding 

 colour. The plate is then varnished and again sensitised, and the 

 print from the second negative imposed ; this again is dyed, 

 varnished, and sensitised, and the print from the third negative 

 superimposed again and treated likewise. 



Mr. Sanger Shepheard's process is somewhat similar, but in his 

 method the variously dyed positives are taken on gelatine films, 

 and the whole then balsamed together. 



In Lippman's process the photograph is taken upon a gelatine 

 plate containing finely divided particles of silver bromide. The 

 plate is ' backed ' by a thin film of mercury in absolute contact 

 with the sensitive surface. When the exposure is made the 

 mercury film reflects the image into the gelatine plate again, so to 

 speak, and the result is to set up a sort of wave formation in the 

 gelatine itself. 



This, when viewed at the right angle by reflected light, gives 

 the image in its natural colours, the wave formation by a diffractive 

 effect reproducing the correct tints. Specimens of the process can, 

 of course, only be projected by reflected light, and then care must 

 be taken to ensure the beam being reflected at the correct angle ; 

 but the result, when enough care and pains are taken, is extremely 

 pleasing, and the colours really very correct. 



The Photochromoscope. This instrument, designed by 

 Mr. Frederick Ives, attracted great attention a few years back. 

 Perhaps the method can hardly be called colour photography, as 

 the image can only be projected or viewed by means of an instru- 

 ment designed for the purpose. 



Three negatives are taken through suitable colour screens, as 

 in the Lumiere and Sanger Shepheard processes. Three separate 

 positives are then printed on glass from these, and the images of 

 these positives are then projected on the screen, each being pro- 

 vided with an optical system and colour screen to itself. By means 

 of an ingenious arrangement of mirrors, one single lime -light 

 jet or arc lamp suffices for the illumination of all three systems, 



