PROCEEDINGS 
OF THE 
Cawbritrgt ibilasopjikal jfrrtktg. 
On the Hall Effect in Gases at Low Pressures. By Harold 
A. Wilson, B.A., Clerk Maxwell Student, Fellow of Trinity 
College. 
[Read 28 October 1901.] 
The experiments described in this paper were undertaken 
with the object of detecting and investigating the Hall effect in 
the positive column of the ordinary electric discharge at low 
pressures. 
The existence of a Hall effect in the positive column was to be 
expected because many phenomena connected with the discharge 
indicate that the negative ions have a much greater velocity than 
the positive ions due to the electric field, and it is well known 
that a difference between the velocities of the two kinds of ions 
is the condition theoretically necessary for the existence of a Hall 
effect. 
The present investigation has shown that a very large Hall 
effect can easily be obtained in the positive column which in- 
dicates a very great difference between the velocities of the two 
sorts of ions. After some unsuccessful trials with other forms of 
apparatus the apparatus shown in the figure was constructed and 
found to work satisfactorily. 
It consisted of a glass ‘ vacuum tube ’ AB, having an alumi- 
nium disc electrode at each end. The distance between the 
electrodes was 20 cms. and the diameter of the tube 21 mms. 
Half-wa); between the electrodes a side tube was joined on, into 
the upper end of which a conical tube K was fitted by grinding 
in with emery. This ground joint, which permitted the tube K 
to be rotated, was made air-tight by means of mercury at H. 
19 
VOL. XI. PT. IV. 
