488 Professor W. Stirling [May 10, 



to the pictures, and many processes have been tried and found wanting. 

 The work of W. F. Greene and Frederick E. Ives on still life are 

 well known. Again, to refer once more to the Royal Institution, 

 another novelty was shown by W. F. Greene in January 26, 1906. 

 The trichromic theory of colour vision, so ably supported and eluci- 

 dated by Professor J. Clerk Maxwell in the Royal Institution and else- 

 where, is the basis of all attempts to reproduce colour in the films 

 thrown on the screen. Clerk Maxwell, when demonstrating Young's 

 Theory of Colour Vision, on May 17, 18G1, at the Royal Institution, 

 assuming red, green, and blue as primary colours, used troughs con- 

 taining respectively sulphocyanide of iron, chloride of copper, and 

 ammoniated copper. Clerk Maxwell was fully aware of the necessity 

 for " finding photographic materials more sensitive to the less 

 refrangible rays, whereby the representation of the colour of objects 

 might be greatly improved." The technical difficulties, not to speak 

 of the expense — triple as least that of a monochrome film — of three- 

 colour Cinematography are well known. 



Bicolor and Kinemacolor . 



W. F. Greene used two screens — red and green. Albert Smith 

 also attacked the problem and he also used only two screens. For a 

 perfect white, however — red, green and blue are required. The 

 patent now known as " Kinemacolor " was introduced to the public 

 in 1908. The effects though beautiful are far from perfect. The 

 pure yellows are wanting, while the true blues and purples cannot be 

 effectively reproduced. The blue, which is lacking, is partly intro- 

 duced in the green screen, and if the electric arc is used an additional 

 blue tone is introduced. But even this compensates only in a small 

 degree for lack of the blue, while the red and green stand out almost 

 all too vividly. 



Mons. Gaumonfs Tricolour Method. 



For these and other reasons M. Gaumont has reverted to the three- 

 colour theory. The method consists in projecting at the same time 

 on the screen, by means of a cinematograph provided with three objec- 

 tives, three views of the same subject, each taken through a differently 

 coloured filter-screen. These views are arranged in sequence on an 

 ordinary Cinematograph film. Many attempts have been made in 

 many countries, but so far no single solution is perfect and complete. 

 We have referred to Smith's bicolor method and the kinemacolor and 

 their imperfections. 



Difficulties of the Colour Problem. 



The following are some of the difficulties of the problem — 

 1. To obtain a negative film of a sensibility approximately the 

 same for all rays of the spectrum. 



