506 Mr. A. W. Ashtoii on the 



readings for 5, 10, 20, 40, and 120 minutes' charge, at 200 volts 

 and a practically constant temperature. In these experiments 

 readings were generally taken of the current during electri- 

 fication; but separate experiments in which electrification was 

 continued for longer periods were also made to ascertain the 

 equations representing the charging current. Readings o£ 

 the current both when charging and discharging the mica 

 and the paraffined-paper condensers were also taken in a 

 manner similar to that described above. 



8. The curves in fig. 1 show the readings obtained by the 

 method described in section 6 from a condenser made from 

 the rubber called No. 1. Before this experiment was made, 

 the condenser had been dried for some weeks in order to get 

 rid of the benzene used in the solution by means of which 

 the tinfoil was fixed to the rubber. From the curve of re- 

 sistance with pressure given, it will be seen that this dielectric 

 shows a considerable decrease in resistance as the pressure is 

 increased. A large number of similar experiments, which 

 have been made on this condenser and on three other con- 

 densers made from the same rubber, all give curves very 

 similar to that shown in fig. 1. An endeavour was then 

 made to obtain similar curves of resistance from the okonite 

 cable. This cable was first put into the tank on June 1st, 

 1899, and was kept continuously in the water until the end 

 of July. The results of the experiments made during this 

 immersion are given in the Tables I. & II., and in fig. 2. 

 In the first experiment on July 4th (see Table I.) readings 

 of current were taken at five different voltages, increasing 

 in steps from 52 to 249 volts. After 75 minutes' electrifica- 

 tion at 52 volts, the resistance was increasing ^ per cent, 

 per minute. The pressure was then raised to 100 volts, and 

 after 70 minutes' electrification this rate of increase amounted 

 to ^ per cent, per minute. As the experiment proceeds 

 the final reading at each pressure becomes more constant, 

 until at the highest pressure the variation is only 24 P er 

 cent, per minute. It will be seen that the steady resistances 

 at the first four pressures do not differ very much, but at the 

 highest pressure, viz. 249 volts, the resistance shows a 

 decrease of 1-J per cent. On July 5th an endeavour was 

 made to compare the curves of resistance with time at 51*1 

 volts and 197*4 volts. The results are given in fig. 2. Two 

 sets of readings at 51 volts were taken, one before and one 

 after the experiment at 197 volts, the cable being short- 

 circuited for If hours between experiments. The mean of 

 the two sets of readings at the lower voltage is shown for com- 

 parison as the broken line above the curve at 197 volts. It 



