ADVANCES IN SIGNALLING 233 



were made in radio-signalling during the war are attributable 

 in large measure to that success. 



As an example of what was accomplished by means of im- 

 provements in vacuum-tube receivers, it may suffice to describe 

 a single receiving radio station among a number along the Allied 

 lines in Europe. In an ordinary room of a brick building at 

 one of the army headquarters, without any mast or external 

 antenna, was a vertical wooden frame, about 2 meters square, 

 wound with wire and rotatable about a vertical axis. Near the 

 frame sat a soldier operator, with a pair of head telephones ad- 

 justed to his ears. These telephones were connected to the 

 loops of wire on the frame, through a vaccum-tube amplifier of 

 several stages. The room was kept fairly quiet, so that he 

 could listen attentively to the faint intermittent buzzing note in 

 the telephones. He sat writing messages in pencil on a pad 

 before him for an hour or two, when he would be relieved by 

 another soldier. Upon the wall, was a large map of Europe, 

 on which were marked the principal radio stations of the Allied, 

 neutral and enemy countries, with prominent electrical charac- 

 teristics serving for their recognition. By turning the frame 

 in the direction of the particular European radio station sought, 

 its particular ether waves could be tuned to and detected in 

 the telephone, almost to the complete exclusiori of all others. 

 Since these principal radio stations were in action at nearly all 

 hours, each could be located in turn, and made to reveal the 

 burden of its story as launched through the air in every direc- 

 tion over land and sea. In actual service, however, only one 

 station would be followed continuously, and all that it said was 

 written down on sheet after sheet of the message pad. These 

 sheets were then carried, at regular intervals, to the Intelligence 

 Section of the General Staff, for transcription and analysis. 

 This eavesdropping on the ethereal whisperings around the 

 world has become so common now in peace, as well as war, that 

 it ceases to elicit comment ; yet the recent great development is 

 largely due to the Signal Corps of the armies and to the work 

 of men in army uniform. In a certain sense, there has come to 



