396 



BELL SYSTEM TECHNICAL JOURNAL 



may be desired for comparison. An arrangement is provided for 

 superposing on the records vertical timing lines at intervals of one 

 hundredth of a second. Short pieces of record are shown in Fig. 4. 



*-"^' 



Fig. 3. 



At a prearranged time the oscillographs at both ends are started. 

 A train of reversals is transmitted from one end, a record being taken 

 on the oscillograph at that end, and received at the distant end, where 

 a record is also taken. Both stations quickly change potentiometer 

 connections from send to receive or vice versa, and the distant station 

 transmits a train of reversals, recording it on the same tape as was 

 used for reception. Similarly at the first station the arriving train is 



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Fig. 4. 



