TROWBRIDGE. — POSITIVE RAYS. 



515 



Figure 3. 



mirable wave metre of Professor G. W. Pierce. 1 This instrument ena- 

 bled me to make measurements in a few moments which otherwise would 

 have required days of labor. 



On placing the tube C between 

 the poles of an electromagnet, 

 which produced a field just suf- 

 ficient to divert the cathode rays 

 from the screen, I found that the 

 changes in the phosphorescence 

 represented in Figure 2 were 

 produced by the cathode rays, for 

 the phosphorescence due to the 

 positive rays remained constant 

 through the range measured. The 

 positive rays were deflected in 

 the direction opposite to that in 

 which the cathode rays were thrown, by a field of 530 lines to the 

 centimeter, and produced a narrow band on the willemite screen, 

 which showed a slight discontinuity (Figure 3), although the pressure 

 did not exceed n \ t mm. I was surprised to find that 

 the group of positive rays was so readily deflected by 

 a comparatively weak magnetic field. The length of 

 the band of phosphorescence was 1.5 cm. It is to be 

 noted that the band occurred only on one side of the 

 middle point of the phosphorescent screen. 



On discovering that changes in self-induction had 

 no effect upon the intensity of the phosphorescence 

 produced by this group of positive rays, I resolved 

 to damp out all oscillations by introducing a large 

 water resistance in the oscillating circuit. While the 

 dimensions of the discharge tube between the anode 

 and the cathode remained the same as in the experi- 

 ments described above, the canal region was changed 

 from a circular tube of 3 cm. diameter to the form 

 shown in Figure 4 in plan P and end section E. The 

 width of the cross-section was 3.5 cm. It will be 

 noticed that it had a flattened egg-shaped section, to 

 enable me to place it between the poles of an elec- 

 tromagnet. When all oscillations were damped, and a magnetic field 

 of 500 lines to the centimeter was excited, the positive rays produced 



Figure 4. 



1 Contributions from the Jefferson Physical Laboratory, 4 (1907). 



