492 DR. J. HOPKINSON ON THE RESIDUAL CHARGE OE THE LEYDEN JAR. 
the neck could be but small, and could scarcely penetrate to the lower part of the flask. 
The experiment was subsequently repeated with the same flask and with a similar result ; 
but it was further found that the effect of tapping was more marked when the periods 
during which the flask was strongly charged and discharged were long than when they 
were short. For example, when the flask was charged half an hour, then discharged 
five minutes, the effect of tapping was very slight although unmistakable. That portion 
of the return charge which comes out slowly is more accelerated by vibration than that 
which comes out fast. A comparison of the rates at 10.18 and 11.16 of the above 
Table also shows that a flask which has been tapped is less susceptible to the effect of 
tapping than it was before it was touched. In some cases also it was noticed that if 
three observations were made, the first quiet, the second tapped, and the third quiet, the 
third charge came out more rapidly than the first. The last experiment on tapping 
below illustrates both of these points. 
A flask was mounted as before, strongly charged at 12 o’clock, discharged at 3, and 
remained discharged till 5.15, when it was insulated, and the time which the image 
took to traverse 200 divisions was noted ; after passing that point the flask was again 
discharged. The first column gives the instant of insulation, the second the time of 
covering 200 divisions. The observations without mark were made with the flask 
untouched, in those marked * it was sharply tapped all over with a glass rod dipping in 
the acid, whilst in those marked f the rod was muffled with a piece of india-rubber tubing. 
Time of insulation, 
h m 
Time occupied in traversing 200 
divisions of the scale, 
min. secs. 
Remained discharged till 
Remained discharged till 
5 
15 
1 
23 
5 
18 
1 
23 
*5 
21 
40 
5 
24 
1 
17 
f5 
27 
48 
5 
30 
1 
27 
5 
46| 
1 
25 
f5 
491 
54 
5 
511 
1 
24 
*5 
54 
1 
O 
5 
56 
1 
24 
6 
39 
2 
*6 
43 
1 
54 
6 
47 
2 
8 
f 6 
51 
2 
2 
6 
55 
2 
13 
