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BELL SYSTEM TECHNICAL JOURNAL 



Station. To correct for the ninety-degree phase shift, the spiral of 

 apertures on the transmitting disk is continued by additional apertures 

 a quarter of a turn beyond the starting point. The first turn alone 

 of the spiral is used for scanning; and the last turn alone, to form the 

 pilot image; consequently, this image appears exactly in frame. A 

 small mirror on the front of the motor cabinet reflects this image to 

 the operator and enables him to see the character of the picture that 

 he is sending out over the channel of communication. 



Fig. 9 — Large grid, liie large grid is a neon lamp with iSUU electrodes on a 

 tube bent back andj,forth to form a luminous screen that is visible throughout a 

 large auditorium. 



When it is desirable to present television images to a large audience, 

 a special grid type of receiver is used. The grid has the appearance 

 of an illuminated screen and can be seen throughout a large auditorium. 

 The image is not projected on the screen from a lantern like a moving 

 picture; such optical projection would be inefficient and demand 



