308 Prof. L. T. More and Mr. E. G. Rieman on 



The brief abstract of the results and theory of Professor 

 Righi which pertain to the subject of the present article is 

 taken from a German translation of his book, published by 

 Barth under the title Strahlende Materie und Magnetische 

 Strahlen. 



The apparatus best suited to show the magnetic rays con- 

 sists of a Geissler tube about a metre long and five centi- 

 metres in diameter (fig. 1). The anode is either an 



Fig. l. 





aluminium rod or disk placed in a branch tube, A. The 

 cathode is situated at one end, 0, in a somewhat narrower 

 extension of the main tube ; it usually takes the form of a 

 small aluminium disk, enclosed in a little glass tube that 

 extends beyond the disk. The current is supplied by a high 

 tension battery, an electrostatic machine, or an induction- 

 coil. R is a large electromagnet with the iron core 

 removed, placed so that its axis coincides with the axis of 

 the tube. The necessary field-strength varies from 500 to 

 2000 units at a distance of a centimetre and a half from the 

 end of the spool, although most of the results are obtained 

 near the lower limit. 



When the field magnet, R, is not excited, the ordinary 

 discharge takes place between the anode and cathode, and 

 the tube BD remains dark ; but if, while the discharge is 

 passing, the magnet is excited to give a certain critical 

 intensity of field depending on the size of the tube, the 

 pressure of the gas, and the potential of the cathode, the 

 whole tube is suddenly filled with a glow discharge, repre- 

 sented by the column BEF. The nature of this glow dis- 

 charge can best be determined by an auxiliary magnet, S, 

 held near the tube and with its axis horizontal but perpendi- 

 cular to that of the field magnet R. 



While the magnetic field is weak, the two bluish-violet 

 bright bands, separated by the negative dark spaces, are 

 seen in the tube surrounding the cathode, and the pink anode 



