254 
practically constant. The following table shows the changes which occurred 
as the speed of the machine was increased : 
Potential expressed in volts, current expressed in amperes. Distance 
between points, 18.05 cm. 
TABLE 1. 
Voltage 
: beta Voltage Current Current ifyie Of discharge 
peed) magnet ee oR enh Effect of magnetism on f f disch 
was excited) Magnetism | Magnetism | Magnetism & See ee 
1 23000 24000 .00014 00014 Glow discharge. 
2 24500 24500 .00017 .00017 ~ qf 
3 25300 25300 .00021 .00021 Small brush at anode. 
4 26200 26200 00025 00025 Increased brush at anode. 
5 26500 26500 | .00029 | .00029 | Occasional spark. 
6 27000 28300 =| .00035 00035 Spark changed to brush by magnetism. 
7 25300 28300 | .00037 00037 | “ os ce a) 5 Y 
8 24000 28300 | 00044 00044 be 3 aha, = 7 
9 23000 | 28300 | .00052 .00049 | 2 ti ie be x 
10 22800 28300 | .00059 . 00054 Se a anes z Pe 
11 22300 | 28300 | 00058 00056 < as pie rie NA x 
12 23000 28300 | 00065 00059 ts Uy oP OD tT bet Was 
13 22800 28300 | .00072 00069 | “partially changed té Brush by magnetism. 
14 22300 26500 00078 00076 i pL ss a a 
15 22300 25000 =| 00083 00083 Path curved but spark not stopped. 
16 22300 25000 =| 00086 00084 ue "spark scattered. 
In the above table, the current was measured by means of a Weston 
milli-ammeter, and the potential by means of an electroscope. This elec- 
troscope was made of two brass discs 10 cm. in diameter mounted in ver- 
tical planes on ebonite supports which were fitted to a common base. The 
distance between the plates could be varied by moving the supports. At 
the top of one of the discs was soldered a support holding a small needle 
upon which was suspended a brass yane which carried a pointer at the 
lower end. The pointer moved in front of a scale which was calibrated 
by connecting in multiple with the discs two No. 12 Thomas Harper needles 
(sharps), measuring the critical spark length between them and comparing 
with the table prepared by H. W. Fisher.*. The position of the pointer was 
read through a telescope placed two meters in front of the scale. The 
potential read by this apparatus amounted to only a rough estimate, since 
it could not safely be trusted nearer than 150 volts. This was especially 
true when the sparks did not pass rapidly in succession because the vane 
3H. W. Fisher, Transactions of International Electrical Congress, Vol. 2, pp. 
294-312, St. Louis, 1904. 
