TROWBRIDGE. 



MAGNETIC FIELD AND THE CATHODE RAYS. 



403 



article was written I have studied the subject more carefully, and have 

 devised a safe and practical method, which is analogous to that I have 

 used in the study of the phosphorescence of the Canals trahlen. 



The form of tube is shown in Figure 1. A is an iron disc ^node 

 (Figure 3) with a perforation at its middle. S is a solenoid which can 

 be adjusted along an appendix to the X-ray bulb. F is the usual focal 

 plane of polished platinum. Opposite this focal plane the glass is 

 blown thin to permit the egress of the X-rays. The cathode beam is 

 brought to a focus at F by adjustment of 

 the longitudinal field of the solenoid. f^ 



The dimensions of the apparatus are as 

 follows : 



Diameter of the spherical bulb, 10 cm. 

 Distance between the concave aluminium ca- 

 thode and the iron disc anode, 6 cm. Length 

 of the cylindrical appendix containing the 

 focal plane, 10 cm. Internal diameter of the 

 cylindrical appendix, approximately 3 cm. 

 The outer diameter of the solenoid was 10 

 cm., the internal diameter 6 cm. Length, 

 4 cm. There were 10 layers of no. 18 wire, 

 Brown and Sharpe gauge. The solenoid 

 was excited by two or five storage cells. A 

 narrower appendix and a smaller bulb oppo- 

 site the focal plane would give a stronger 

 field with less current. 



When the cathode stream is made to con- 

 verge by the solenoid on the focal plane F, 

 the intensity of the X-rays is increased in 

 a marked manner. Judging the intensity 

 by the distance at which equal intensity is Figure 3. 



obtained with and without the magnetic 



field, I have more than doubled the intensity of the X-rays by the 

 application of the field. The method has the advantage of producing 

 the X-rays from a sharp focus and should, therefore, give better 

 definition. 



It may be urged that the amount of energy employed in exciting the 

 magnetic field could, with equal advantage, be added to that which ex- 

 cites the tube ; but this would result in possible strain or danger to 

 the tube and would not result in bringing the stream to a sharp focus. 

 The large bulb need not be blown thin, and therefore the danger of per- 

 foration can be greatly lessened ; moreover, the application of the mag- 



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