Magnetic Rays. 311 



resulting electromagnetic force is not in the plane of rota- 

 tion but has a small translational component along the axis 

 of rotation. The direction of this component is such that a 

 doublet whose stability is increased by the magnetic field 

 moves toward regions of lower magnetic intensity. 



This hypothesis, if accepted, would account for the exten- 

 sion of the luminous column from the region near the 

 cathode out into the large tube, since the stability of the 

 doublets is increased and a translational motion given to 

 them by the non-uniform field created by the magnet R. 

 It also explains why this column bends towards the magnet 

 S or away from it according as the unlike or like poles of 

 the two magnets are nearest each other. As these doublets 

 move out into the tube, collisions with the gas in the tube, 

 together with the diminishing electromagnetic force, cause 

 their destruction, which is marked by the position E. The 

 freed electrons cause dissociation in the gas, and the limit 

 of range of the positive ions is marked by the region p 

 which, on account of the accumulation of positive electricity 

 there, acts like a virtual anode. The free electrons tend to 

 go past the point p and, in fact, usually travel to the far 

 end of the tube for two reasons : the range of electrons is 

 in general greater than that of positive ions, and the cathode 

 exercises a repulsive force on the electron and an attractive 

 force on the positive ion. The effect of this action is a 

 Geissler tube discharge in the ionized gas toward both ends 

 of the tube from this virtual anode. The oppositely directed 

 currents in the induced column are indicated by the reversed 

 curvature of the rays around the pole of S on the two sides 

 of p. 



Such, in brief, is Professor Righi's hypothesis to account 

 for the action of a magnetic field on the current in a vacuum 

 tube. It is simple, plausible, and accounts for most of the 

 observed phenomena. Still there are some facts brought out 

 in our experiments which indicate that the actions occurring 

 are rather more complex and obscure. Apparently, Professor 

 llighi limited his work to experiments with air ; we find that 

 other gases give rise to quite distinctive effects. 



Our apparatus was, for the most part, similar to that of 

 Professor llighi. Some of the tubes were obtained from 

 Herrn Richard Mtiller-Uri and were made according to 

 Professor Righi's specifications ; others were made in our 

 laboratory. They were of various sizes; in some the anode 

 was placed in a side tube, and in others the narrow portion 

 of the tube was made long and pushed into the core of the 

 iield magnet. The anode was, in the latter tubes, inside the 



