312 Prof. L. T. More and Mr. E. G. Eieman on 



magnet and the cathode just in front of the pole ; the mag- 

 netic rays then proceeded from the back of the cathode. 

 The current was obtained from an induction-coil. The 

 magnet-coil was a large one, and the space in the core left by 

 the tube was filled with soft-iron wires to increase the field- 

 strength. The magnet was capable of developing a field 

 much in excess of the requirements, since with a maximum 

 current it became so intense as to destroy the rays ; an 

 effect noted by Professor Righi. 



The tube was filled with air which had been thoroughly 

 dried by passing it through sulphuric acid and phosphorus 

 pentoxide. The first observations were made when the rays 

 were not subjected to a magnetic field. As the pressure 

 was reduced, the appearance of the current passed through 

 the usual stages of the Geissler tube discharge. When a 

 pressure of 0*2 mm. was reached, the two layers of negative 

 glow and the cathode dark spaces were well defined in the 

 little glass tube surrounding the cathode. Under such con- 

 ditions Professor Righi observed that the large part of the 

 tube remained dark, but our experience was that almost the 

 whole tube was filled with pale bluish light. This discharge 

 was evidently a mixture of cathode rays and an induced 

 electrostatic discharge from the walls of the tube. The tube 

 was not covered with a conducting earthed screen, and a 

 finger touched to the glass produced a characteristic brush 

 discharge. The electrostatic effect could be entirely 

 eliminated by slipping over the tube an earthed screen of 

 copper gauze, but even under those conditions some glow per- 

 sisted in the tube. The trial was then made with the field 

 magnet excited. As soon as the discharge was influenced 

 by the magnetic field, the diffuse light in the large tube 

 began to condense and contract into a column of light along 

 the axis of the tube. Suddenly, when a critical pressure 

 and magnetic field were reached, the appearance completely 

 changed ; the induced electrostatic discharge at the far end 

 of the tube disappeared, and in the centre of a faint and 

 diffuse cathode discharge the true magnetic rays appeared 

 as a sharply defined cone of blue light stretching along the 

 axis of the tube and extending into the large part of the tube 

 about one-fourth its length. These magnetic rays bent 

 toward an auxiliary magnet if the poles of it and the field 

 magnet nearest each other were opposite in sign, and were 

 repelled if the poles were alike. At the end of the mag- 

 netic rays appeared the induced column EF (fig. 1). This 

 light was rather reddish in colour, and showed the 

 characteristic opposite curvature when the auxiliary magnet 



