TELEPHONE SYSTEM OF THE UNITED STATES 77 



or other sounds so that they can be heard by an audience of prac- 

 tically unlimited size. Such public address systems as they are called 

 are used very extensively in large auditoriums and at large public 

 gatherings. For example, the ceremonies of inauguration of President 

 Hoover held on the steps of the Capitol in Washington were amplified 

 by the public address system so as to be heard by a gathering esti- 

 mated at a hundred thousand persons, gathered within a radius of 

 about 300 meters. 



Furthermore, by using the public address system with suitable 

 long distance telephone circuits, it is possible to convey the proceed- 

 ings of such occasions simultaneously to audiences in all parts of the 

 country. The local distribution of such proceedings is, however, now 

 done largely by radio broadcast rather than by use of the public 

 address system. 



A use of the public address system which so far has been taken 

 advantage of only on a few special occasions is by providing two-way 

 operation to interconnect two or more meetings held simultaneously 

 in different places. A notable example of this usage is the joint 

 meeting of the American Institute of Electrical Engineers and the 

 Institution of Electrical Engineers in London on February 16, 1928, 

 interconnected by the transatlantic telephone circuit. In this meet- 

 ing, addresses were heard by both audiences and a resolution made 

 in London and seconded in New York was jointly and unanimously 

 carried. It is possible that this may foreshadow a future important 

 use of a public address system. 



Television 



The possibility of transmitting pictures of a scene over electrical 

 circuits at so high a speed that the effect is given of seeing at a dis- 

 tance has naturally interested telephone people for a considerable 

 while. However, the large amount of detail which is taken in by 

 the human eye and the resulting broad band of frequencies required 

 to transmit this detail as well as the necessary complexity of the 

 terminal apparatus has, so far, prevented the development of a prac- 

 tical service of this kind. 



In 1927 the Bell engineers demonstrated to a large number of 

 interested people a television circuit which extended from New York 

 to Washington, a distance of about 440 kilometers. The television 

 pictures so demonstrated had a detail corresponding to 50 lines in 

 each direction, that is 2,500 elementary areas and 18 such pictures 

 were shown each second. Two circuits especially corrected for volume 

 and phase distortion over a band width of about 20,000 cycles were 



