CAPACITY AND RESIDUAL CHARGE OF DIELECTRICS. 
125 
The following are the values of t in seconds, so deduced, in terms of revolutions 
of the milled head n from zero :— 
Turns of milled head from zero. 
0 1 1 2 3 4 5 G 
Time of contact in seconds. 
•00002 -00035 -00099 -0028 -006 -009 ’Oil -014 
The experiments have so far dealt with frequencies ranging from 2 X lO*" 
to 8,000, and 100 to 10. The gap between 8,000 and 100, during which the great 
effects of residual charge become apparent, is filled up by experiments with the 
pendulum apparatus just described. An attempt was made to fill up this gap 
by means of the method shown in fig. 6, from which the effect on the capacity 
could be found for various times of contact, but this method was finally abandoned 
and used only for the determination of times of contact. 
lleferring to fig. 5, F is the same window-glass flask mentioned above, and 
mounted as in fig. 1 ; rt is a non-inductive metal resistance, the effect of the capacity 
of which was at the most, when a is large, only capable of disturbing our experi¬ 
ments to the extent of eight per cent., but in most cases the disturbance is a 
small fraction of this ; is a one-third microfarad condenser, and Kg the large 
slide condenser used in the other experiments. The advantage of this method 
of experiment is that the charging potential difference V is great, and the actual 
ohmic resistance of a is small as compared with that of the flask F. In this manner 
the effect of the instantaneous capacity of tlie flask is overcome at once and tlie 
after effects due only to residual charge can be examined directly. The results are 
shown in Table V. 
