RESIDUAL CHARGE OF THE LEYDEN JAR. 
611 
was as high as 72° F. The flask was again put away till Aug. 9th, when the charge 
was found to be 178. On September 14th it was 163. Lastly on October 14th it had 
fallen to 140. 
As might be expected from the last experiment, the residual charge in this glass is 
small. The flask was charged for nine hours with 48 elements ; it was discharged, and 
after 4 minutes insulated; in 2 minutes the residual charge had only attained 11^ divisions, 
giving \|/(5)=0'0017. It was again insulated after 44 minutes; in 12 minutes the 
charge was 104, giving \J/(50)=0'00026. 
Since the loss by conduction is so small, the flask may be strongly charged by an 
electrophorus instead of with the battery. If it is left insulated for a considerable 
time, and then discharged, and the return charge observed, it may be assumed that the 
exciting charge has been sensibly constant during the latter portion of the period of 
insulation. 
The flask was strongly charged and remained insulated for 3 hours 40 minutes ; it 
was then discharged, and from time to time was temporarily insulated to ascertain the 
rate of return of charge. 
At •§ minute 250 divisions in 
-4 minute 
=1500 per minute. 
5 minutes 247 
1 „ 
= 247 „ „ 
10 „ 285 
>1 
2 minutes 
= 142i „ „ 
15 „ 304 
11 
3 „ 
= ioi „ „ 
30 „ 326 
» 
6 „ 
= 54 „ „ 
It was immediately charged again, insulated for 70 minutes, and then the observa- 
tions repeated. 
At minute 120 divisions in 
minute 
= 720 per minute. 
1 „ 135 
11 
i ” 
=405 „ „ 
2 minutes 125 
11 
1 
2 ii 
=250 „ „ 
5 „ 121 
11 
1 „ 
=121 „ „ 
10 „ 142 
11 
2 minutes 
= 71 „ „ 
15 „ 106 
„ 
2' „ 
= 53 „ ,, 
The ratios of the numbers in the two experiments agree fairly. 
Glass No. 8. — “Dense flint.” Density 3 - 66. Composed of silica, lead, and potash, 
the proportion of lead being greater than in No. 7. 
Experiment a. — The flask was charged for three hours to 500 divisions, and then 
insulated 
After 1 minute from insulation 499f 
„ 5 minutes „ „ 499 
>5 °0 >5 5 , 495 
hence 4/(180) = 0-0004. 
