Two-way television part I-image transmission system

A two-way television system, in combination with a telephone circuit, has been developed and demonstrated and is now in use between the Bell Telephone Laboratories, at 463 West Street, and the American Telephone and Telegraph Company, 195 Broadway. With this system two people can both see and talk to each other. It consists in principle of two television systems of the sort described to the Institute in 1927. Scanning is by the beam method, using disks containing 72 holes, in place of 50 as heretofore. Blue light, to which the photoelectric cells are quite sensitive, is used for scanning, with a resultant minimizing of glare to the eyes. Water-cooled neon lamps are employed to give an image bright enough to be seen without interference from the scanning beam. A frequency band of 40,000 cycles width is required for each of the two television circuits. Synchronization is effected by transmission of a 1275-cycle alternating current controlling special synchronous motors rotating 18 times per second. Speech transmission is by microphone and loud speaker concealed in the television booth so that no telephone instrument interferes with the view of the face.