Signalling with Condensers, 433 



line is to earth, reaches its maximum in 3a, as against 7a when 

 the end of the line is insulated. Thus it would appear that a 

 considerable increase in the speed of signalling should result 

 from connecting the line to earth through a resistance, as shown 

 in fig. 4, where / is the battery, A the cable, e the receiving in- 



Fig. 4. 



-^uwm-^ 



c* 



strument, C r the condenser, and R the resistance introduced 

 between the end of the line and earth. This resistance is ne- 

 cessary in order to raise the potential of the end of the cable, 

 and give signals of a workable strength. That this plan does 

 increase the speed, *l have verified on the circuit before men- 

 tioned, using a polarized instrument and double current key. 

 The increase in speed was about 20 per cent., compared with 

 the speed obtained by making R infinite. The signals were, of 

 course, weaker in the former than in the latter case; 



The effects of defective insulation may be traced by giving h 

 different small values in equation (7). In the first place the 

 signals are weakened ; and next, the effect of loss is to decrease 

 the time required for the signal to arrive at its maximum 



7T 



strength. Thus whenA= ■=■' the maximum is reached in 4a, as 



against 7a when ^=0. This is an extreme case, and would 

 nearly correspond to the French Atlantic cable if its insulation- 

 resistance were 3 megohms per knot, instead of more probably 

 300. Whether loss does or does not increase the speed of work- 

 ing depends on a great many circumstances. It is an undoubted 

 fact that, under some systems of signalling, a cable with a very 

 bad fault in it has worked quicker than when it was perfect ; 

 and it is also a demonstrable fact that under other systems the 

 effect of loss is greatly to diminish the speed. In a particular 

 case which I have examined theoretically and practically, the fact 

 that each signal should be more quickly made through a faulty 

 than a perfectly insulated cable is quite consistent with the 

 fact that the speed of working is reduced. 

 Phil. Mag. S. 4. Vol. 47. No. 314. June 1874. 2 F 



