SUBMARINE TELEGRAPH CABLES 441 



them by vacuum tube amplifiers having no moving parts, and thus 

 requiring a minimum of maintenance. The vacuum tube amplifier is 

 capable of reshaping the signal almost as completely as is done by 

 the mechanical repeaters, and, in case of a cable worked simplex, 

 the direction in which the amplifier at the intermediate station repeats 

 the signal may be automatically controlled from either the sending 

 or the receiving station. 



