through Heterogeneous Telegraph Circuits. 213 



look outside the line and fix our attention on the sending- and 

 receiving-apparatus. The actual cause or causes must, how- 

 ever, be of such a nature that they only come into operation 

 when the capacity, or the leakage, is unsyinmetrically situated 

 in the circuit. ISTo perceptible difference in working-speed 

 was observed on the Anglo-Danish circuit when the corre- 

 spondence was maintained between the two ends of the cable 

 itself. Now, since in all the cases described Wheatstone's 

 transmitter was employed, it is natural to inquire whether the 

 difference is due to any peculiarity in the method of making 

 the signals with that instrument. If so, then we need not 

 expect any difference to exist when simple reversals are made. 

 But, in fact, it exists even then. An instance bearing this out 

 was described by Mr, Varley before the Submarine-Cable 

 Committee (Sub. Report, p. 156). Experimenting with his 

 " wave-bisector " on the underground lines between London 

 and Liverpool, Mr. Varley found that the introduction of re- 

 sistance at the battery-end of the line lowered the speed to a 

 greater extent than its introduction at the receiving-end, where 

 indeed it made little difference. Here the speed was inversely 

 as the retardation, since the wave-bisector made simple rever- 

 sals. Mr. Varley attributed the difference to the leakage ; 

 but this is in direct contradiction to the theoretical result, that 

 neither leakage nor irregularity in distribution of capacity 

 can, acting alone, cause any difference. Also the difference 

 existed on the Anglo-Danish circuit when simple reversals 

 were made with the transmitter, but apparently to a smaller 

 extent. It was quite perceptible (10 or 20 per cent.) with 

 key-sending, using a common reversing key — though the 

 exact amount of the difference could then not be exactly esti- 

 mated, since operators differ nearly as much in their hand- 

 signalling as in their hand-writing. Although, therefore, in 

 the case of Wheatstone's transmitter the difference in working- 

 speed may be, and I believe is, mainly due to a peculiarity of 

 that instrument, yet when plain reversals are sent, there must 

 actually be a difference in the retardation in opposite direc- 

 tions ; and this I believe is due to the fact, which comes out' 

 on closer inspection, that it is not the same circuit which is 

 being worked when the direction of working is reversed. 



Let the line consist of a cable of resistance c, having land- 

 lines of resistances a and b attached to its ends, and let the 

 battery and receiver resistances be / and g respectively. Then, 

 fig. 1 shows the arrangement when A sends to B. ; - Further,^ 

 suppose for simplicity, and to avoid analytical calcinations," 

 that the cable's resistance is small compared with the total; 

 resistance of the circuit. Then we may obtain tolerably accu-" 



