Discharge of long Overland Telegraph Lines. 



23 



signal is completed (i. e. when the key leaves contact 1 and 

 makes contact 2) all the discharge of the long line would pass 

 through the receiving relay R if contact 3 ceased just before con- 

 tact 2 were reestablished. This, however, is not the case, because 

 by the application of the shunt b, in virtue of which an extra 

 current can form itself through the coils of the discharging relay, 

 contact 3 is sufficiently prolonged to exist for a moment simul- 

 taneously with contact 2; consequently the whole discharge, or 

 at least the greatest part of it, has time to pass through contact 

 3 direct to earth, instead of going through the receiving relay It. 

 The same process will, of course, repeat itself at each signal sent, 

 and will also be the case when Agra is sending instead of Calcutta. 



Such an arrangement answers the purpose perfectly at Agra 

 on the great and important main line between Calcutta and Kur- 

 rachee, where it has been in use (in translation) for some time. 



It may be mentioned here that it does not-at all interfere with 

 the maximum working speed attainable with our present system 

 of signalling, namely 25-30 words a minute. 



The very great prolonging-power of such a shunt not having 

 been known at first, it was thought necessary to assist the pro- 

 longing effect by a fine spring of very small play fixed to the 

 tongue of the discharging relay. But such a spring is not wanted ; 

 and it is much better to dispense with it, because, however small 

 the play of this contact spring may be made, it will always in 

 some measure lessen the sensitive adjustment of the discharging 

 relay. 



Fig. 2. 



As it was evident that the prolonging effect of the shunt must 

 greatly depend upon its resistance (supposing the resistance of 

 the discharging relay and also all other circumstances were given), 

 the following investigation was made in order to ascertain its 

 amount. 



Fig. 2 represents the simple circuit as obtained from fig. 1. 



