1875.] Theory of Duplex Telegraphy. G3 



By February next, duplex working will therefore have been submitted 

 to a most severe test, applied as it will have been for a whole year to a long 

 line the electrical condition of which is highly variable with respect to 

 season and locality, and its practicability will doubtless again be clearly 

 proved, as has already been the case on the Calcutta-Bombay line, 1600 miles, 

 where under no more favourable climatic conditions, duplex has, for the past 

 twelve months not only fulfilled but surpassed the expectations formed of it. 

 No difficulties have been experienced, and it is believed never will be. 



Strange as it may appear from a theoretical point of view, it will 

 nevertheless be found in practice, that a line worked duplies' carries more 

 than double the traffie of the same line worked singly ; for it represents two 

 lines carried on different posts far distant from one another, instead of 2 

 parallel lines on the same posts, and consequently the highly injurious effects 

 of voltaic induction are eliminated. 



Further the receiving signallers, not being provided with keys, are 

 unable to interfere with messages during their transmission. 



Corrections and repetitions do not necessitate a stoppage of work, for 

 they are obtained in the following manner : the receiving signaller marks 

 with a cross, or underlines the words to be repeated, and places the message 

 by the side of the sending signaller, who calls for the repetitions directly he 

 has finished the message he is transmitting, and during this call the distant 

 station may either send fresh messages or may also call for repetitions ; 

 consequently single working need never be resorted to, and the simultaneous 

 exchange of messages and corrections becomes continuous. 



The Indian system of receiving (the sounder system which has now 

 been universally recognised as the only right one hand for signalling) thus 

 necessitates constant attention on the part of the receiving signallers, for any 

 inattention on their part at once becomes known to the controlling officer. 



