166 



Prof. E. Rutherford 



on some 



it. In this way the fine wire was made extremely active, 

 and produced strong luminosity on a screen o£ zinc sulphide 

 or willemite brought near it. 



Magnetic Deflexion of the ol Rays. 



The method o£ determining the amount of deflexion of the 

 a rays in a magnetic field is shown in fig. 1. 



Fio-. 1. 



To PUMP ■<- 



r" 



i 





i 



i 

 l 

 1 



1 



1 

 i 



P 



s 



1 



T 



1 



i 

 L 







1 

 1 



r-^ 



V M 





/Active wire. 



The active wire was placed in a slot V, at a distance of 

 2 cms. below a narrow slit S. The photographic plate P 

 was supported at a definite distance above the slit. The 

 whole was enclosed in a brass tube T, which could be rapidly 

 exhausted to a pressure o£ a fraction of a millimetre by means 

 of a Fleuss pump. The whole apparatus was placed between 

 the rectangular pole-pieces of a large electromagnet, so that 

 the uniform field extended from a distance of 1 cm. below 

 the slit to the top of the tube T. 



In practice, the photographic plate was placed in position, 

 and the active wire then placed in the slot. The outer tube 

 was then rapidly waxed down to a base-plate and exhausted. 

 The whole operation took less than five minutes, and the 

 magnetic field was then applied parallel to the plane of the 

 wire and slit. The field was reversed every ten minutes for 

 a period of about one hour. On developing the plate, two 

 narrow bands were observed, and the distance between the 

 centres of these bands represented twice the distance of 



