Discharge in a Magnetic Field. 251 



having fallen still further. Fig. 8 the next stage. Fig. 9 



Fig. 8. 



!Z> 



Fig. 



the appearance of the tube when the magnetism ceases to 

 have influence. 



Before proceeding to describe other experiments it is well 

 to analyse what takes place. My own view is that we have 

 here shown in a very pretty way Ampere's well-known 

 experiment of the influence of a current flowing in one con- 

 ductor upon a current flowing in an adjacent conductor. 

 This experiment is usually shown by wires, one arranged as a 

 moving conductor. In the instance of the vacuum-tube the 

 current is passing through a conductor perfectly free to move, 

 or, perhaps, it would be better to say that the current is i'vee 

 to place itself, without any appreciable opposing resistance, 

 in the position it tends to take up under the influence of the 

 magnetic field, which latter may be regarded as a current 

 travelling in a circular conductor, which may be resolved into 

 straight line currents parallel to the tube currents. 



The experiment described, therefore, shows that the two 

 currents try, not to move out of the field, as it might be ex- 

 pressed, but tend to take up definite positions, which naturally 

 mu'st be in opposite directions, when influenced by certain 

 powerful currents in their proximity, i.e., the magnetic field, 

 it might appear that the resistance of the gas in the centre 

 of the field, where no bands appear, has been increased, 

 and therefore the current chooses a path of least resistance, 

 viz., at the sides of the tube, farthest from the strongest 

 portion of the field. This may, or may not 7 be an accessory 

 in the case. I venture to believe, for the reason that the 

 alternate current has been separated into its two constituents 

 on opposite sides, that the true explanation is that of Am- 

 pere's theory. When the resistance of the tube is actually 

 measured it is found to be higher when the magnet is excited, 

 and this, of course, would be expected, since the current is 

 then travelling through a much smaller sectional area. 

 Consequently the test of resistance has no value to prove that 

 the gas contained within the tube has a higher resistance, 

 because under no circumstances can the resistance of the gas 

 in the strongest part of the field be measured, as the current 



