86 L. Schwendler — Discharge of long 'Telegraph lines. [No. 1, 



and it is only for a long line that such a discharging arrangement 

 is required. 



As regards the absolute value of r, it was found that 200 S. U,. 

 using a Siemens' polarized relay, were quite large enough. Such 

 a relay works safely with 30 Minotti's cells through 10,000 8. U. 



The shunt itself, even without having iron in it, produces an 

 extra current which is in the same direction in the shunt, as the 

 primary current, and consequently opposes the extra current pro- 

 duced by the coil r in the closed circuit (r -j- x). 



In order to have, therefore, the action of the coil r not too much 

 lessened by the extra current, produced by the shunt, it is necessary 

 to make the latter of the thinnest possible German silver wire, and 

 wind it on a large bobbin with the convolutions as far distant from 

 one another as possible. Another method would be to wind the 

 bobbin bifilarly. 



In conclusion I may mention that the longest main line in India 

 is the one between Calcutta and Kurrachee 1,700 miles in length 

 which has been worked direct now for more than two years, — Agra 

 (which is about at the middle) only in translation. During the dry 

 season, when the lines up-country often have an insulation of more 

 than 200 millions S. U. per mile, it is possible to work this enor- 

 mous distance altogether direct without Agra in translation ; but 

 practically nothing would be gained by this, since then on account 

 of the great length the charge becomes so large as to reduce the 

 speed to less than 15 words a minute, while by having Agra in 

 translation the speed, if only the signalling system would allow 

 of it, would reach to upwards of 60 words a minute. 



( Note,) Mr. A Cappel, in his report on the Central London Office of the Electrics 

 and International Telegraph Company, states that a shunt in connection with 

 an electro-magnet for discharging one of the cables was made use of as early 

 as 1867, and was pronounced to him by Mr. Culley as an invention of one of 

 the Telegraph clerks This appears to be the first application of the extra 

 current for this purpose, but I am not aware whether this simple principle 

 has since been used for overland telegraph lines. 



Mr. Cappel says — 



" The duration of the zinc current, (necessary to neutralize, after each 

 signal sent, the positive dischax-ge of the cable), can be regulated by varying 

 the resistance of the shunt, but no definite law or conclusion has yet been 

 arrived at on the subject." 



