A MULTI-CHANNEL TELEVISION APPARATUS 39 



scanning, in which the object is imaged on the disc, was chosen, since 

 beam scanning would introduce the problem of separating the light 

 reflected from the object from the several spots simultaneously pro- 

 jected from the disc. Since the light going through the disc must be 

 separated into several beams to be directed into separate photoelectric 

 cells, the full aperture of the image forming lens must be di\ided by C, 

 the number of channels, with a consequent proportional loss of light to 

 each cell. (This loss counterbalances the decreased size of disc above 

 noted.) It therefore becomes necessary to insure a very high illumi- 

 nation of the object. In the present case, it was decided to use motion 

 picture him to provide the sending end image, since this can have a 

 large amount of light concentrated through it by an appropriate lens 

 system. 



The use of motion picture him permitted a simplification of the 

 transmitting disc, which is illustrated in Fig. lb. This consists in 

 arranging the scanning holes in a circle instead of a spiral, and pro- 

 ducing the longitudinal scanning of the film by giving it a continuous 

 uniform motion at right angles to the motion of the scanning holes. 

 The continuous motion of the film also avoids the loss of transmission 

 time that an intermittent motion demands for the shutter interval. 



At the receiving end, a spiral of holes is used as shown in Fig. la. 

 There again, because of the division of the light into three beams, the 

 angle which can be subtended by the light source (neon lamp) is much 

 restricted. In consequence, the neon lamp cathodes are of small area, 

 and a lens system has been used to focus their images on the pupil of 

 the observer's eye. Other methods of receiving, which promise to be 

 less restricted as to position of observation, are possible, however, as 

 discussed below. 



With this surve\' of certain of the more important features of the 

 system, we may proceed to a more detailed account of the apparatus as 

 constructed. The general arrangement of parts is shown in Fig. Ic 

 and in the photographs, Figs. 2, 3, 4 and 5 in all of which the symbols 

 are uniform. Both sending and receiving discs were, for simplicity of 

 operation, mounted on the same axis, driven by the motor M. This 

 means that no question of synchronization entered. Synchronization 

 is in fact a separate problem, having nothing to do with multi-channel 

 operation and has been very completely solved in connection with other 

 television projects.^ If it should be decided to transmit the multi- 

 channel image to a distant point, the apparatus could be cut in two 

 and each end, after separation to the desired distance, operated by 

 synchronous motors controlled in approved fashion. Similarh', no 

 long transmission lines were included. 



