40 



BELL SYSTEM TECHNICAL JOURNAL 



Starting at the extreme right end of the schematic drawing Fig. \c, 

 we have an arc lamp A, a cyHndrical lens Li, a condensing lens L2, the 

 two lenses together concentrating a line of light on the film F. Be- 

 tween the film and the disc is a lens Ls which images the film on the 

 disc. Directly behind the disc Di, with its circle of prism covered 

 holes, is a second cylindrical lens L^ which concentrates the transmitted 



Fig. 2 — Sending end of three-channel television apparatus, showing film driving 



arrangements. 



light laterally, upon the three photoelectric cells ^i, 52, Sz. By virtue 

 of this lens arrangement, the light falls upon the cells in three small 

 practically stationary spots. Additional apparatus not shown in the 

 diagram but visible in the photographs are gears by means of which the 

 film is driven from the disc axle through a differential, which permits 

 the film to be framed up and down. The light beam is directed through 

 the film at right angles to the axis of the discs by means of two prisms, 

 w^hereby certain conveniences in driving and handling the film are 

 attained. 



The photoelectric cells are similar to ones previously described. 

 The amplifier system was substantially identical with that used in the 

 two-way television system, and need not be described again. Simi- 



