258 
Mr Wilson, On the Hall Effect in Gases 
angle between the two positions of zero potential difference is 
evidently the rotation of the equipotential surfaces in the dis- 
charge due to the Hall effect. This angle is given by the 
equation 
Substituting for Z and X the values given above, we have 
0 _ 0-0248 H 
tan 2 “ 34 9 p™ 
= 7-1 x lQ- 4 Hp~ 15 . 
Measurements were made by this method, using a magnetic field 
of 23 C.G.S., which was reversed as already described. 
Unfortunately it was found that this method was not capable 
of giving at all accurate results. When p is small 0 varies very 
rapidly with p, and when p is large 0 is very small. Also the 
process of adjusting the electrodes until they are at the same 
potential requires considerable time, so that the discharge is liable 
to change during a measurement of 0. Successive measurements 
of the angle varied sometimes by as much as 1 degree. 
Although this method was not found capable of giving accurate 
results still it afforded a means of confirming the results obtained 
by the first method. 
Table VII. gives the values of 0 observed at a number of 
different pressures and the corresponding angles given by the 
formula 
tan ^ = 7*1 x 10 ~ 4 Hp~ J ’ 5 . 
Table VII. 
Pressure 
Angle 
(Observed) 
Angle 
(Calculated) 
0-30 mm. 
10-1° 
11-2° 
0-36 
7*2 
8-5 
0-55 
5 -5 
4-6 
0-62 
4*8 
3-8 
0-90 
3-2 
2-2 
1-87 
0-3 
0-6 
2-02 
0-9 
0-5 
