Magnetic Field on the Discharge through a Gas, 255 



If any other part of the tube but the cathode is placed in 

 the field there is always produced a decrease in current and 

 an increase of potential between the terminals. 



If a point anode is used and the field is produced just in 

 front of it, the effect of the magnet gradually decreases in a 

 linear manner as the pressure is lowered, reaches a minimum 

 and then again increases. The pressure at which there is 

 least effect corresponds to the critical pressure for the cathode 

 with the same current through the tube and the same field 

 strength. It should be noted that this critical pressure is 

 the same for the cathode no matter what its shape. 



Kesults somewhat similar are found with a point anode 

 when the field is produced just at the end of the positive 

 column, which in the tubes I used came somewhere near the 

 middle of the tube. See fig. 4. 



With a disk anode the decrease in current produced by 

 the magnet is nearly constant for all pressures, whether the 

 poles are placed at the centre of the tube (fig. 1 A) or near the 

 anode (fig. 1 (J) . 



Fig. 4 shows the results obtained when the current goes 



Fio». 4. 



from a disk to a point, B when the field is produced at the 

 cathode, C when it is produced at the anode, and A at a point 

 midway between the two. In the last case, owing to the 

 variable length of the positive column, it is sometimes the 

 Faraday space and sometimes the positive column which 

 comes in the field. 



The effect of the magnet is always greater when the poles 

 are at the middle of the tube, than when they are at the 

 anode. 



Experiments were next made to determine how the 



