﻿108 
  H. 
  A. 
  Bumstead 
  — 
  Velocities 
  of 
  Delta 
  Rays. 
  

  

  ence 
  of 
  2000 
  volts. 
  It 
  is 
  proposed 
  to 
  include 
  under 
  the 
  name 
  

   " 
  S-rays," 
  all 
  the 
  electrons 
  which 
  owe 
  their 
  origin 
  to 
  the 
  direct 
  

   action 
  of 
  the 
  a-rays, 
  — 
  the 
  swifter 
  ones 
  as 
  well 
  as 
  the 
  slower 
  

   ones 
  previously 
  known. 
  

  

  2. 
  Evidence 
  is 
  given 
  for 
  the 
  view 
  that, 
  in 
  addition 
  to 
  the 
  

   S-rays, 
  positive 
  ions 
  are 
  also 
  produced 
  when 
  a-rays 
  impinge 
  

   upon 
  a 
  metal 
  in 
  a 
  very 
  high 
  vacuum 
  ; 
  these 
  ions 
  appear 
  to 
  

   come 
  from 
  the 
  layer 
  of 
  adsorbed 
  gas 
  upon 
  the 
  metal. 
  By 
  

   maintaining 
  the 
  vacuum 
  for 
  several 
  days, 
  the 
  current 
  carried 
  

   by 
  these 
  ions 
  may 
  be 
  reduced 
  to 
  a 
  small 
  value, 
  — 
  from 
  5 
  to 
  10 
  

   per 
  cent 
  of 
  that 
  carried 
  by 
  the 
  a-rays 
  themselves. 
  The 
  pres- 
  

   ent 
  experiments 
  do 
  not 
  determine 
  whether 
  or 
  not 
  these 
  ions 
  

   leave 
  the 
  plate 
  with 
  an 
  appreciable 
  velocity 
  in 
  the 
  absence 
  of 
  

   an 
  electric 
  field 
  ; 
  but 
  there 
  is 
  some 
  evidence 
  that 
  the 
  velocity 
  

   is, 
  at 
  all 
  events, 
  small. 
  

  

  3. 
  When 
  the 
  swifter 
  S-rays 
  fall 
  upon 
  a 
  solid 
  it 
  emits 
  elec- 
  

   trons 
  of 
  slow 
  speed 
  which, 
  in 
  the 
  present 
  paper, 
  are 
  referred 
  

   to 
  as 
  tertiary 
  electrons. 
  Their 
  number 
  is 
  considerably 
  greater 
  

   than 
  the 
  S-rays 
  which 
  produce 
  them. 
  The 
  existence 
  of 
  the 
  

   tertiary 
  electrons 
  makes 
  it 
  difficult 
  to 
  determine 
  with 
  accuracy 
  

   the 
  distribution 
  in 
  velocity 
  of 
  the 
  S-rays. 
  A 
  large 
  number 
  of 
  

   tertiary 
  electrons 
  come 
  from 
  the 
  source 
  of 
  S-rays 
  itself, 
  and 
  

   their 
  presence 
  in 
  the 
  beam 
  of 
  S-rays 
  makes 
  it 
  impossible 
  to 
  draw 
  

   valid 
  conclusions 
  as 
  to 
  the 
  number 
  of 
  true 
  8-electrons 
  of 
  slow 
  

   speed 
  (less 
  than 
  10 
  or 
  20 
  volts). 
  

  

  4. 
  The 
  distribution 
  in 
  velocity 
  of 
  the 
  8-rays 
  between 
  20 
  and 
  

   1200 
  volts 
  has 
  been 
  determined, 
  and 
  reasons 
  are 
  given 
  for 
  

   believing 
  that 
  the 
  measurements 
  represent 
  a 
  fair 
  approxima- 
  

   tion 
  to 
  the 
  true 
  distribution. 
  The 
  number 
  of 
  electrons 
  having 
  

   a 
  given 
  kinetic 
  energy 
  is 
  not 
  an 
  exponential 
  function 
  of 
  either 
  

   the 
  energy 
  or 
  the 
  velocity. 
  Between 
  30 
  and 
  500 
  volts, 
  the 
  

   results 
  are 
  approximately 
  represented 
  by 
  an 
  equation 
  of 
  the 
  

   form 
  yx 
  n 
  = 
  e 
  where 
  y 
  is 
  the 
  number 
  of 
  electrons 
  whose 
  kinetic 
  

   energy 
  is 
  equal 
  to 
  or 
  greater 
  than 
  a?, 
  and 
  n 
  — 
  0*75. 
  It 
  is 
  

   impossible 
  to 
  say 
  whether 
  or 
  not 
  the 
  departure 
  of 
  the 
  measure- 
  

   ments 
  from 
  this 
  equation 
  at 
  potentials 
  higher 
  than 
  500 
  volts 
  is 
  

   significant 
  ; 
  the 
  quantities 
  measured 
  are 
  small 
  and 
  their 
  values 
  

   are 
  rendered 
  somewhat 
  uncertain 
  by 
  the 
  presence 
  of 
  the 
  posi- 
  

   tive 
  ions 
  and 
  of 
  the 
  tertiary 
  electrons. 
  On 
  the 
  other 
  hand, 
  the 
  

   fact 
  that 
  the 
  slower 
  electrons 
  (under 
  20 
  volts) 
  do 
  not 
  follow 
  

   the 
  same 
  law 
  of 
  distribution 
  in 
  velocity 
  as 
  the 
  swifter 
  ones 
  is 
  

   to 
  be 
  expected 
  ; 
  the 
  presence 
  of 
  tertiary 
  electrons 
  from 
  the 
  

   source, 
  in 
  the 
  beam 
  of 
  S-rays, 
  should 
  greatly 
  increase 
  the 
  

   numbers 
  of 
  the 
  very 
  slow 
  electrons, 
  as 
  is, 
  in 
  fact, 
  found 
  to 
  be 
  

   the 
  case. 
  

  

  Sloane 
  Laboratory, 
  Yale 
  University, 
  

   April 
  15, 
  1913. 
  

  

  