﻿726 Mr. E. W. Varder on the 



was obtained for which the average value of Hp, where H is 

 the magnetic field and p the radios o£ curvature, could be 

 accurately determined. The value o£ p was fixed at 3*19 cm. 

 in all the experiments, and readings could be obtained up 

 to about Hp = 12,000 gauss cm. From the dimensions of the 

 source, slit, and opening, it was calculated that the variation 

 of Up for the issuing rays was less than o per cent. 



The lead blocks L helped to screen the ionization apparatus 

 from the effects of the 7 rays. E is a hemispherical chamber 

 of 2 cm. radius made of coarse copper gauze covered with 

 copper leaf and thin tissue-paper. This vessel was charged 

 to + 200 volt. F is a brass cylindrical vessel charged to 

 — 200 volt. A copper electrode G- passed through two 

 ebonite plugs at the ends of F and terminated at one end 

 in E. The other end of G was connected to a YTilson-Kaye 

 electroscope, which was screened by the lead block T. K is 

 a kev for earthing G-. and R a o-uard-rino-. A wooden frame 

 "W, coated on the inside with celluloid, minimised the effect 

 of reflected j3 radiation. The vessel F was put in to balance 

 partly the 7 ray ionization in E. By altering the position of 

 the lead block O relative to the vessel F. the 7 ray ionization 

 in F could be varied so as to neutralize nearly the 7 ray 

 ionization in E. Pieces of celluloid U were placed in front, 

 below, and at the back of E as shown. This was done to 

 minimise the reflexion effects of the /3 rays. 



The magnetic fields were measured by comparing the 

 throws of a ballistic galvanometer when an exploring coil 

 was removed from the field, with the throw produced when a 

 known current was broken in the primary of a standard 

 mutual induction. The current in the primary of the 

 mutual induction was measured on a standardized ammeter, 

 and the coils used had also been standardized in some 

 previous work. In this way the fields were measured to 

 about one part in 400. By means of a fiuxmeter it was 

 found that the fields were practically uniform over the 

 region traversed by the rays in the box. A oiyen field could 

 always be reproduced by setting the current in the magnet- 

 coils to a certain value and reversing it a number of 

 times. 



In takino- a reading, the current throuo-h the mao-net-coils 

 was set at a particular value and reversed a number of times 

 to reach a cyclic stale. The vessel B was exhausted by 

 means of a Fleuss pump. The block O was adjusted so that 

 the motion of the electroscope-leaf was slow when a thick 

 aluminium plate was placed over the flat face of E. Readings 

 were taken of the rate of motion of the electroscope-leaf 



