DEVELOPMENT OF THE TELEGRAPH 



messages are being sent by other transmitters, each 

 vibratory receiver selects its own particular message. 



Another "multiplex" arrangement is one in which a 

 circle is divided into as many segments as there are 

 senders and receivers, each segment being connected 

 with a receiver, and a corresponding sender connected 

 with the segment of a similar device at the opposite end 

 of the line. A revolving "contact slider" is so arranged 

 that by revolving rapidly and passing over each of these 

 intervals in succession, each transmitter is allowed to 

 send its message in rotation. This system, first proposed 

 by Lord Kelvin, in 1858, has been developed on practical 

 lines, and wires sending from four to eight separate, 

 simultaneous messages are now in practical operation 

 all over Europe and America. 



It was evident, even in the early days of electric teleg- 

 raphy, that messages could be sent and received by 

 the instruments much more rapidly than the keys could 

 be worked by hand, and automatic transmitters and 

 receivers were soon invented. As early as 1846, Bain 

 invented a method of sending such messages automat- 

 ically, but an apparatus on similar principles was later 

 devised by Professor Wheatstone, which, with various 

 modifications, still remains in use. In this arrange- 

 ment the message to be sent is recorded by means of 

 punched holes on a strip of paper. When this strip is 

 passed through the transmitter, these holes cause the 

 automatic transmission of the message, which is recorded 

 at the other end of the line. In this way five or six 

 hundred letters or more can be sent in a minute. This 

 system, with the various modifications of it, is partial- 



[37] 



