Discharge of long Overland Telegraph Lines. 21 



sending station, are inconvenient for many reasons; the most 

 important of which is, that they are frequently stronger than the 

 singnalling current of a far distant station, and consequently 

 throw the relay out of its adjustment, and so make it unfit to 

 receive a calling signal from such a station. It was therefore 

 necessary to devise some simple means by which these discharge- 

 currents could be safely eliminated from the relay of the sending 

 station* ; and it was found that for terminal stations a peculiarly 

 constructed key answered the purpose best. This key, after 

 each signal sent, by a proper application of well-tempered springs, 

 makes a momentary contact direct with earth, by which the dis- 

 charge of the line is effected before the final contact with earth 

 through the relay is made ; and such keys were supplied to the 

 terminal stations of the Indian main lines, where they have 

 worked well. But to eliminate the discharge-currents from the 

 relays of terminal stations is of far less importance than to do so 

 from the relays at translation stations; for it is clear that the 

 discharges in translation stations may not only be inconvenient, 

 but may momentarily interrupt the line, so that the real signal 

 cannot pass on ; and even if they do not cause interruption 

 during the whole of a signal, they will, at all events, produce 

 points instead of bars at the receiving station, thereby causing 

 considerable delay and confusion. 



It is true that in principle the arrangement in use at terminal 

 stations might also be applied at translation stations, where the 



very decided charges and discharges. Fortunately the charges of the Indian 

 main lines (so long in comparison with the direct-worked lines in Europe) 

 still occupy such a short time as not to influence in the least our maximum 

 working speed attainable with the present signalling system (25 to 30 

 words a minute) ; i. e. a signal sent from Calcutta to Agra arrives there 

 practically at the very moment it is sent. The discharges, however, affect 

 most seriously our instruments ; and it is therefore only this effect that is 

 treated of in the present paper. 



* The method of a station permanently cutting out its own relay while 

 sending has never been adopted in this country, and I believe also never 

 will be ; for however perfect lines and instruments, and accomplished em- 

 ployees may be, or may become, it is always highly desirable that a receiv- 

 ing station should be able to call in the sending station at any moment 

 during the transmission of a message. 



Tn India we invariably use positive currents (or copper to line) for sig- 

 nalling, because^they reduce the leakage. By using positive currents for 

 signalling in one direction and negative currents in the other, and having 

 polarized receiving instruments, the effect of discharges would be, of course, 

 so far eliminated that the receiving instruments would not actually be 

 worked by them, the discharges going in the wrong direction through the 

 polarized relays. But this is a bad plan. The continued passage of strong 

 discharges through a polarized relay make it, on account of remanent mag- 

 netism, unsensitive, and consequently a continual and most tedious adjust- 

 ment of the receiving relay would be necessitated; this, again, would pro- 

 duce great irregularity in the working of the lines. 



