DR. J. HOPKINSON ON THE RESIDUAL CHARGE OF THE LEYDEN JAR. 493 
Time of insulation, 
h m 
Time of traversing 100 divisions. 
Remained discharged till 8 51 
min. secs. 
2 11 
f8 55 
8 58 
*9 2 
9 5 
f9 9 
9 12 
54 
2 17 
2 12 
1 2 
2 14 
57 
The same flask was strongly charged at 9.15 in the evening and discharged at 9 the 
following morning, and remained so till 7.13 in the evening, when the following obser- 
vations of the time of traversing 100 divisions were made: — 
Time occupied in traversing 100 
divisions of the scale. 
Time of insulation, 
h m 
min. secs. 
2 43 
1 35 
2 35 
1 53 
2 27 
1 46 
2 26 
1 49 
2 25 
7 13 
f7 18 
7 21 
*7 25 
7 28 
f7 32 
7 35 
*7 39 
7 43 
The result here was less than the author expected, considering the long period of 
discharge and the considerable effect obtained in the previous experiment ; this may 
perhaps be due to change of temperature, or perhaps to a difference in the vigour with 
which the flask was tapped J. 
5. When a charge is given to an insulated flask, owing to polarization the percentage 
of loss per minute continuously diminishes towards a limiting value. When the flask 
is charged, discharged, and insulated, one would expect that after attaining a maximum 
potential the rate of loss would steadily increase towards the same limiting value as in 
the former case. The following experiment shows that this is not always the case. 
A flask of window-glass, much more conductive than the Florence flask, was mounted 
as in (3) and (4). It was charged, and the charge maintained for three quarters of an 
hour, then discharged for a quarter of an hour, and insulated. In four minutes the 
charge attained a maximum value 740. In fifteen minutes the potential was 425, in 
twenty minutes 316, giving a loss in five minutes of 26 per cent. In thirty minutes it 
was 186, and in thirty-five minutes 146, a loss of 21^ per cent. The intermediate and 
t It is recorded by Dr. Young that an electical jar may be discharged either by heating it or Dy causing it 
to sound by the friction of the finger. 
