CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORATORY, 



HARVARD UNIVERSITY. 



LONGITUDINAL MAGNETIC FIELD AND THE 

 CATHODE RAYS. 



By John Trowbridge. 



Presented December 11, 1907. Received January 6, 1908. 



In a previous article on the Magnetic Field and Electric Discharges ^ 

 I described various phenomena which occur under the effect of a lon- 

 gitudinal field, both at the auode and the cathode. The present 

 article deals with the effects of the field on the cathode rays after they 

 have passed into the region beyond the anode. The form of tube which 

 contained the rarefied gas was similiar to that generally employed to 

 study the canal rays : a cylindrical tube with a concave aluminium cath- 

 ode, an iron anode with an orifice at its centre, and a prolongation of 

 the cylindrical tube behind the anode. Two exactly similiar tubes of 

 this form, equal in size, were connected by the same adjunct to the 

 exhausting pump, and were, therefore, under the same pressure. 



In one of these tubes (Figure 1) the back of the anode, or iron termi- 

 nal, was completely shielded from the prolongation of the tube in which 

 canal rays are usually studied. A glass tube passed through the orifice 

 in the iron terminal and was welded to the walls of the prolonged larger 

 tube. No rays could enter the canal ray region except through the 

 orifice in the iron terminal. In the companion tube the back of the ter- 

 minal was not protected, and rays could pass over the periphery of the 

 iron terminal and also through the orifice at the centre of the terminal. 



It was found that the tube (Figure 1) apparently reached a much 

 higher state of exhaustion than the companion tube, which I shall call 

 B, although they were connected by the same large adjunct to the 

 pump and, therefore, there could be no question of slow transpiration. 

 One tube, A, was close to the X-ray stage, while B was hardly beyond 

 the stratification stage. 



I replaced these tubes by two spherical bulbs (Figure 2) similiar to 

 those commonly employed as X-ray tubes ; these tubes also had pro- 

 longations, or canal regions, similiar to those of the previously mentioned 



, ^ These Proceedings, 28. 



