1907.] 



on Rays of Positive Electricity. 



579 



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

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

 phorescent 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 posi- 

 tive 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 



Fig. 2. 



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 — 

 ' ' ■■ '-" ■ >; ^ m 



by observmg the deflection produced by magnetic and electric fields. 

 When the rays were undeflected they produced a bright spot on the 

 screen ; when the rays passed through electric and magnetic fields, 

 the spot was not simply deflected to another place, but was drawn 

 out into bands or patches, sometimes covering a considerable area. 



To determine the velocity of the rays, and the value of -, it was 



m 

 necessary to have a record of the shape of these patches. This might 



2 p 2 



