Rays of Positive Electricity. 



56a 



are as close together as the glass tube will permit, and 

 are arranged so that the lines of magnetic force are hori- 

 zontal and at right angles to the path of the rays. The 

 magnetic force produces a vertical deflexion of the patch of 

 phosphorescence on the screen. To bend the positive rays it 

 is necessary to use strong magnetic fields, and if any of the 

 lines of force were to stray into the discharge-tube in front 



of the cathode, they would distort the discharge in that part 

 of the tube. This distortion might affect the position of the 

 phosphorescent patch on the screen, so that unless we shield 

 the discharge-tube we cannot be sure that the displacement 

 of the phosphorescence is entirely due to the electric and 

 magnetic fields acting on the positive rays after they have 

 emerged from behind the cathode. 



To screen off the magnetic field, the tube was placed in a 

 soft iron vessel W with a hole knocked in the bottom, through 

 which the part of the tube behind the cathode was pushed. 

 Behind the vessel a thick plate of soft iron with a hole bored 

 through it was placed, and behind this again as many thin 

 plates of soft iron, such as are used for transformers, as there 

 was room for were packed. When this was done it was 

 found that the magnet produced no perceptible effect on the 

 discharge in front of the cathode. 



The object of the experiments was to determine the value 

 of e/m by observing the deflexion produced by magnetic and 

 electric fields. AY hen the rays were undeflected they pro- 

 duced a bright spot on the screen ; when the rays passed 



2Q2 



