Popular Science Monthly 



227 



reflected by the silver; the other passes 

 through the transparent openings. 



The film which is made by this process 

 when it is projected 

 is not a succession of 

 blue and green pic- 

 tures. The pictures 

 are black and white. 

 They represent, how- 

 ever, the red and blue 

 color qualities of the 

 original object photo- 

 graphed. Why, then, 

 do they appear in 

 colors on the screen? 



Study the accom- 

 panying picture of 

 the projector and the 

 answer is plain. The 

 projector required is 

 fitted with two lenses 

 spaced two pictures 

 apart. The upper 

 lens is provided with 

 a green-blue screen through which the 

 images representing the red shades on the 

 film are projected; the lower lens is pro- 

 \'ided vinth a \dolet-red screen which 

 supplies the blue 

 sensation. These 

 two colors appear at 

 the same time on 

 the screen, one over 

 the other. The two 

 colors are accurate- 

 ly registered on the 

 screen chiefly by ob- 



servation of the general effect produced. 

 However, it is not necessary for the 

 operator to rely entirely on his judgment 



Registering 

 ielescope 



Double lens 

 projecioc 



The operator of the projector is 

 looking through a microscope in order 

 to make the two sets of exposures 

 register accurately on the screen 



Silvered sectiorr 



Light s|iliUin9 

 device 



Course of direct 

 ray \ 



Lighf raY striking 

 clear class passes 

 directly through 



Green-blut 

 colof screen 



Scene with 

 violet- red sKades 



Projection lei 



The double lens systen" co-oper- 

 ates with the doubly exposed 

 film to secure natural effects 



to secure registration. 

 In one corner of each 

 red film is a minute 

 circle, and in the 

 corresponding corner 

 of each blue film is a 

 very small solid circu- 

 lar spot. The opera- 

 tor shifts the pictures 

 so that the solid spot 

 on one film is cen- 

 tered within the cir- 

 cle of the correspond- 

 ing film. These regis- 

 tration marks are so 

 small that they can- 

 not be detected on 

 the screen. They are 

 located by means of a 

 microscope perma- 

 nently attached to 

 the projection machine. The images are 

 shifted by an additional lens to avoid 

 the distortion resulting when the entire 

 main line system is shifted. 



The two pictures which were 

 taken at the same time by the 

 camera are projected simultane- 

 ously, so that colors 

 are actually mixed on 

 the screen, but by a 

 process akin to that 

 which is used in mak- 

 ing the colored covers 

 on the Popular Sci- 

 ence Monthly and 

 other magazines. 



It is true that double 

 the film length used in 

 ordinary motion pic- 

 ture work is required. 

 On the other hand, the 

 rate of speed is that 

 ordinarily adopted. 

 The pictures are ad- 

 vanced, two at each 

 shift, and sixteen two- 

 color pictures are dis- 

 played every second on 

 the screen, which is the 

 average speed of all 

 ordinary motion pic- 

 ture projections. 



Cleai- glass 



section 



The light-splitting device 

 consists of a glass plate 

 part of which is silvered 

 and part of which is 

 transparent, producing a 

 checkerboard effect. Some 

 of the rays are reflected by 

 the silvered portions and 

 others pass through the 

 transparent portions. The 

 reflected rays strike cer- 

 tain parts of the film to 

 produce one set of ex- 

 posures, and also the 

 transmitted rays strike 

 other parts to produce the 

 second set of exposures 



