﻿Velocities 
  of 
  Delta 
  Rays. 
  

  

  235 
  

  

  previous 
  experiments 
  upon 
  8-rays, 
  and 
  helps 
  to 
  explain 
  the 
  

   discrepancies 
  which 
  have 
  appeared 
  in 
  the 
  work 
  of 
  different 
  

   investigators. 
  

  

  Unfortunately 
  this 
  effect, 
  which 
  is 
  easy 
  to 
  observe 
  and 
  

   measure, 
  does 
  not 
  lend 
  itself 
  readily 
  to 
  a 
  quantitative 
  study 
  

   of 
  the 
  swifter 
  3-rays. 
  The 
  number 
  of 
  secondary 
  electrons, 
  

   due 
  to 
  a 
  single 
  incident 
  electron, 
  varies 
  markedly, 
  and 
  not 
  in 
  

   a 
  very 
  simple 
  way. 
  with 
  the 
  speed 
  of 
  the 
  latter*. 
  In 
  a 
  beam 
  

   of 
  S-rays 
  one 
  has 
  a 
  complex 
  of 
  electrons 
  of 
  many 
  different 
  

   speeds, 
  and 
  when 
  the 
  opposing 
  electric 
  field 
  is, 
  for 
  example, 
  

   increased, 
  the 
  slower 
  of 
  these 
  are 
  eliminated 
  and 
  all 
  the 
  

   remaining 
  ones 
  have 
  their 
  velocities 
  reduced 
  ; 
  under 
  these 
  

   circumstances 
  it 
  appears 
  quite 
  impossible 
  to 
  draw 
  any 
  con- 
  

   clusions 
  as 
  to 
  the 
  variation 
  in 
  the 
  number 
  of 
  incident 
  &-rays 
  

   from 
  observations 
  upon 
  the 
  tertiary 
  electrons. 
  

  

  In 
  attempting 
  to 
  determine 
  the 
  distribution 
  in 
  velocity 
  of 
  

   the 
  swifter 
  S-rays, 
  the 
  essential 
  thing, 
  therefore, 
  is 
  to 
  eliminate 
  

   the 
  effects 
  due 
  to 
  the 
  tertiary 
  electrons. 
  The 
  first 
  method 
  by 
  

   which 
  I 
  attempted 
  to 
  do 
  this 
  was 
  to 
  receive 
  a 
  beam 
  of 
  8-rays 
  

   in 
  a 
  Faraday 
  cylinder, 
  the 
  whole 
  arrangement 
  being 
  in 
  a 
  very 
  

   high 
  vacuum. 
  Two 
  different 
  forms 
  were 
  tried 
  for 
  the 
  source 
  

   of 
  the 
  £-rays 
  (A 
  and 
  B, 
  fig. 
  1). 
  In 
  both 
  of 
  these 
  the 
  a-rays 
  

  

  Fie. 
  1. 
  

  

  CEKTIMCTXRS 
  

  

  from 
  the 
  polonium, 
  P. 
  struck 
  the 
  inner 
  walls 
  of 
  a 
  small 
  brass 
  

   chamber; 
  a 
  hole 
  in 
  this 
  chamber 
  was 
  placed 
  so 
  as 
  to 
  allow 
  

   some 
  <>t' 
  the 
  8-rays 
  to 
  escape 
  but 
  none 
  of 
  the 
  a-rays. 
  The 
  

   beam 
  of 
  S-ravs 
  issuing 
  from 
  this 
  hole 
  was 
  caught 
  in 
  a 
  Faraday 
  

   cylinder 
  after 
  passing 
  through 
  an 
  opposing 
  electric 
  field 
  ; 
  

   there 
  were 
  suitable 
  diaphragms 
  and 
  earthed 
  screens 
  about 
  

   the 
  Faraday 
  cylinder. 
  But 
  although 
  I 
  had 
  approximately 
  

   a 
  millicurie 
  of 
  polonium, 
  the 
  arrangement 
  was 
  not 
  sensitive 
  

  

  * 
  Gelirts. 
  Ann. 
  d. 
  Phys. 
  xxxvi. 
  p. 
  1000 
  etteq. 
  (1911). 
  

  

  