PROCEEDINGS 



OF THE 



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On the Hall Effect in Gases at Low Pressures. By Harold 

 A. Wilson, B.A., Clerk Maxwell Student, Fellow of Trinity 

 College. 



[Bead 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-way 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^^hic^ permitted the tube K 

 to be rotated, was made air- tm^^^Sreaiis of mercury at H. 



vol. xi. pt. iv. fr 9 .,.. ^ . „ v)l 19 



8 1902// 



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