1871.] L. Schwendler — Discharge of long Telegraph lines. 79 



inconvenient for many reasons, the most important of winch is, 

 that they are frequently stronger than the signalling 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 elimina- 

 ted 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 appli- 

 cation of well tempered springs, makes a momentary contact direct 

 with earth, by which the discharge 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 dis- 

 charge 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 



may be small in comparison with that of any cable, it is evident that a long, 

 •well insulated overland line may shew nevertheless 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 send- 

 ing has never been adopted in this country, and I believe also never will be, 

 for however perfect lines and instruments, and accomplished employes may be, 

 or may become, it is always highly desirable that a receiving station should be 

 able to call in the sending station at any moment during the transmission of a 

 message. 



In India we invariably use positive currents, (or copper to line), for signal- 

 ling, 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 polarised relay make it, on account of remanent magnetism, 

 unsensitive, and consequently a continual and most tedious adjustment of 

 the receiving relay would be necessitated ; this again would produce great 

 irregularity in the working of the lines. 



