IMAGE TRANSMISSION SYSTEM 



451 



From the standpoint of the user, the operation of the combined 

 television and telephone system is reduced to great simplicity. He 

 enters the booth, closes the door, seats himself in a revolving chair, 

 swings around to face a frame through which the scanning beam reaches 

 his face, and upon seeeing the distant person, he talks in a natural 

 tone of voice, and hears the image speak. Conversation is carried on 

 as though across a table. 



Fig. 2 — The three major cabinets of the television-telephone apparatus. 



Optical Problems 



Some of the more special of the problems encountered in two-way 

 television are primarily optical in character. The principal one is 

 that of regulating the intensity of the scanning light and of the image 

 which is viewed so that the eye is not annoyed by the scanning beam 

 or the neon lamp image rendered difficult of observ^ation. It has 

 been necessary for the solution of this problem to reduce the visible in- 

 tensity of the scanning beam considerably below the value formerly 

 used and to considerably increase the brightness of the neon lamp. 



The means adopted consists first, in the use of a scanning light 

 of a color to which the eye is relativ^ely insensitive but to which 

 photoelectric cells can be made highly sensitive. For this purpose 

 blue light has been used, obtained by interposing a blue filter in the 



