102 On obtaining a Unidirectional Current to Earth. [May 31 r 



On reverting to the connexions of fig. 1, a deflection of 130, 

 gradually falling to 98 in 10 minutes, was obtained without any 

 battery; and five Leclanche cells, connected + ve to mains, exactly re- 

 duced the deflection to zero. 



The deflections obtainable with the connexions of fig. 1 without 

 battery for varying lengths of street mains in connexion with the 

 machine were then found to be as follows. 



With the trunk main to Manchester Square Station alone, discon- 

 nected at the far end, no deflection was obtained : 



Adding No. 10 circuit, deflection of 15 

 No. 11 25 



(with a sudden rise to 70 and then a fall to 20). 



Adding No. 12, no increase of deflection 

 (this is a small circuit for station lighting only). 



Adding No. 7 circuit, deflection of 35 



No. 6 40 



No. 5 48 



No. 4 63 



No. 3 70 



No. 2 90 



No. 1 115 



In all cases the first deflection was a few scale divisions greater 

 than that after a few minutes. 



The effect of an artificial leak of about 103,360 ohms resistance, 

 consisting of a pencil of graphite mixed with clay or cement and 

 connected to the water-pipes and to the main MI, was then tried. 



This produced no effect on the deflections without a battery, but 

 slightly increased the deflection with a battery and with all mains 

 connected. 



When tried on the trunk main alone with the lamps removed, 

 galvanometer unshunted and six Leclanche cells, the deflection was 

 increased from about 23 to 360. 



With seven Leclanche cells (say 10 volts) and the impedance coils 

 and shunts as shown in fig. 1, a deflection of four scale divisions was 

 produced when the circuit was completed through the resistance of 

 103,360 ohms in place of the mains and earth ; this gives an indica- 

 tion of the sensibility of the arrangement. 



The explanation of the results obtained appears to be that when 

 the cables are charged with positive electricity the polarisation 

 produced is sufficient during the time of one alternation to con- 

 siderably increase the resistance of the slight leakage to earth by 

 the formation, probably, of a film of oxides ; this obstruction is cleared 



