1894.] establishment of Difference of Potential, 



257 



observations could be taken beyond a charging pressure of 440 volts, 

 while between weights C and D the P.D., even with 610 volt charging 

 pressure, was too small for exact measurement. 



By interpolating an approximate value for the fall of potential 

 between A and B from the readings obtained on the Cardew volt- 

 meter, a rough curve of the fall of potential on the surface of the 

 ground for a charging pressure of 610 volts is obtained, as shown in 

 fig. 3, Curve a, the height of the curve above absolute zero being 



FIG. 3. 



C 



D Distance. 



made consistent with the evident approach of the curve to its 

 asymptote at D. In this case, therefore, the effect of the leakage 

 extended to a distance of about 14 ft. from the pipe, and the fall of 

 potential on the surface appears to have been most rapid at a distance 

 from the line immediately above the pipe equal to twice the depth at 

 which it was buried. 



A third experiment was carried out on the 22nd May, 1894, with 

 the same arrangements as in the second experiment. The objects for 

 which this was undertaken were chiefly to obtain a record of the 

 variation of P.D. on the surface with the charging current, which 

 had not been previously recorded, to obtain results from charging 

 with continuous, as well as alternating, current, and to extend the 

 investigation as regards the latter. 



Unfortunately, the continuous current generator could not be used, 

 owing to a mechanical defect, which could not be removed in the 

 limited time available. Still, the results obtained with alternating 

 current are, it is considered, of some value, especially as the condition 

 of the ground was different from that which existed at the time of 



VOL. LTI. S 



