76 
MESSES. W. DE LA RUE AND H. W. MULLER ON THE 
Table IX. — Two concentric cylinders. 
Yolts. 
Striking distance. 
Difference. 
Between 
Additional length of 
inch. 
volts. 
for additional 1000 
250 
0-0017 
16 
o -'i 
500 
0-0033 
17 
and 
► 0-0069 
750 
0-0050 
19 
1000 
0-0069 
52 
1000 
i 
1500 
0-0121 
69 
and 
y 0-0121 
2000 
0-0190 
2000 J 
78- 
1 
2500 
0-0268 
92 
and 
L 0-0170 
3000 
0-0360 
90 
3000 J 
1 
I 
3500 
0-0450 
78 
and 
l 0-0168 
4000 
0-0528 
4000 J 
I 
62 
] 
1 
4500 
0-0590 
65 
and 
> 0-0127 
5000 
0-0655 
5000 J 
I 
41 
1 
5500 
0-0696 
46 
and 
V 0-0087 
6000 
0-0742 
6000 < 
1 
50 
6500 
0-0792 
48 
and 
> 0-0098 
7000 
0-0840 
7000 s 
1 
60 
I 
7500 
0-0900 
62 
and 
l 00122 
1 
8000 
0-0962 
8000 
The striking distance for 8000 is 13 ‘94 times that for 1000. 
We now give some numbers to show that the striking distance between a point and 
a disc is remarkably constant for the same number of cells, provided that attention is 
paid to the shape of the point, for we have found by numerous experiments that much 
depends on its actual outline ; for example, a conical point of 20° angle gives a spark 
of considerably less length than one of the same base and altitude, but paraboloidal in 
form; thus, when the point is positive, with 5640 cells, the ratio of the striking 
distance when the conical point is employed to that of a paraboloidal point is as 
07764, and with 8040 cells as 07784 to 1. 
With high tensions, 5000 to 8000 cells, the spark is longest when the point is 
positive, but with low tensions up to 3000 cells it is generally longest when the point 
is negative, as will be seen from the following numbers : — 
