﻿Velocity 
  of 
  8 
  Rays. 
  775 
  

  

  p. 
  233), 
  which 
  proves 
  conclusively 
  that 
  most 
  o£ 
  these 
  slow 
  

   8 
  rays 
  are 
  liberated, 
  not 
  by 
  the 
  primary 
  ionizing" 
  rays, 
  but 
  by 
  

   the 
  fast 
  8 
  rays 
  excited 
  by 
  those 
  rays. 
  The 
  velocity 
  of 
  the 
  

   8 
  rays 
  should 
  be 
  independent 
  of 
  that 
  of 
  the 
  exciting 
  rays 
  

   only 
  so 
  long 
  as 
  the 
  latter 
  is 
  large 
  compared 
  with 
  the 
  energy 
  

   required 
  for 
  ionization 
  ; 
  this 
  condition 
  is 
  not 
  fulfilled 
  when 
  

   the 
  8 
  rays 
  are 
  liberated 
  by 
  other 
  8 
  rays 
  ; 
  the 
  proportion 
  of 
  

   8 
  rays 
  with 
  very 
  small 
  velocities 
  should 
  be 
  greater 
  than 
  it 
  

   would 
  be 
  if 
  they 
  were 
  all 
  produced 
  by 
  very 
  fast 
  ionizing 
  

   rays. 
  

  

  Further, 
  Bumstead 
  shows 
  that 
  the 
  number 
  of 
  fast 
  8 
  rays 
  

   (velocity 
  greater 
  than 
  40 
  volts) 
  liberated 
  with 
  a 
  velocity 
  of 
  

   TV 
  volts 
  is 
  approximately 
  proportional 
  to 
  1/W 
  ' 
  75 
  . 
  According 
  

  

  W 
  

  

  to 
  the 
  theory 
  given 
  it 
  should 
  be 
  proportional 
  to 
  ^ 
  w 
  , 
  

  

  where 
  W 
  is 
  the 
  energy 
  required 
  for 
  ionization. 
  But 
  it 
  

   must 
  be 
  remembered 
  that 
  the 
  number 
  of 
  such 
  8 
  rays 
  observed 
  

   is 
  less 
  than 
  that 
  liberated, 
  because 
  some 
  of 
  the 
  rays 
  spend 
  

   their 
  energy 
  in 
  producing 
  other 
  slower 
  8 
  rays 
  ; 
  and 
  disappear 
  

   from 
  the 
  beam. 
  So 
  long 
  as 
  W 
  is 
  greater 
  than 
  200 
  volts, 
  the 
  

   ionizing 
  power 
  of 
  an 
  electron 
  of 
  speed 
  W 
  is 
  nearly 
  pro- 
  

   portional 
  to 
  1/W 
  ; 
  hence 
  we 
  should 
  expect 
  the 
  number 
  of 
  

   fast 
  rays 
  in 
  the 
  emergent 
  beam 
  to 
  be 
  approximately 
  pro- 
  

   portional 
  to 
  ^ 
  — 
  W"(^~ 
  w)' 
  wnere 
  a 
  i 
  g 
  a 
  constant. 
  If 
  

  

  this 
  expression 
  is 
  to 
  be 
  represented 
  by 
  a 
  formula 
  &/W 
  n 
  , 
  

   n 
  must 
  be 
  somewhat 
  less 
  than 
  1 
  in 
  accordance 
  with 
  

   Bum 
  stead's 
  measurements. 
  

  

  An 
  accurate 
  deduction 
  of 
  the 
  distribution 
  of 
  the 
  emergent 
  

   velocities 
  of 
  the 
  emergent 
  8 
  rays, 
  taking 
  into 
  account 
  the 
  

   emission 
  of 
  secondary 
  /3 
  rays 
  and 
  the 
  effect 
  of 
  that 
  emission 
  

   on 
  the 
  primary 
  yS 
  rays, 
  involves 
  so 
  many 
  assumptions 
  con- 
  

   cerning 
  which 
  there 
  is 
  no 
  experimental 
  knowledge, 
  that 
  it 
  

   does 
  not 
  appear 
  to 
  be 
  worth 
  while 
  to 
  enter 
  on 
  the 
  necessary 
  

   complexities. 
  There 
  appears 
  to 
  be 
  nothing 
  in 
  our 
  present 
  

   knowledge 
  of 
  the 
  8 
  rays 
  which 
  is 
  inconsistent 
  with 
  the 
  view 
  

   that 
  they 
  represent 
  the 
  electrons 
  ejected 
  from 
  atoms 
  by 
  the 
  

   passage 
  through 
  them 
  of 
  charged 
  particles 
  in 
  accordance 
  

   with 
  the 
  simple 
  theory 
  of 
  that 
  action 
  given 
  by 
  Thomson. 
  

  

  Leeds 
  University, 
  

   August 
  1913. 
  

  

  3 
  F 
  2 
  

  

  