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 



z e 



Z =tan 2- 

 Substituting for Z and X the values given above, we have 



00248J7 



, 



tan K 



2 



34-9p 15 

 = 71 x 10-tffp- 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 6 varies very 

 rapidly with p, and when p is large 6 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 6. 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 6 observed at a number of 

 different pressures and the corresponding angles given by the 

 formula 



a 

 tan ^ = 7-1 x lO-'Fjp- 1 *. 



Table VII. 



Pressure 



Angle 

 (Observed) 



Angle 

 (Calculated) 



O30 mm. 



10-1° 



11-2° 



0-36 



7-2 



8-5 



0-55 



5-5 



4-6 



0-62 



4-8 



3-8 



090 



3-2 



2-2 



1-87 



0-3 



0-6 



2-02 



0-9 



0-5 



