﻿250 
  Prof. 
  H. 
  A. 
  Bumstead 
  on 
  the 
  

  

  projected 
  with 
  such 
  speeds 
  is 
  undoubtedly 
  a 
  fact 
  of 
  con- 
  

   siderable 
  importance, 
  whether 
  these 
  electrons 
  be 
  few 
  or 
  

   many 
  ; 
  it 
  must 
  have 
  some 
  bearing 
  upon 
  the 
  theory 
  of 
  ioniza- 
  

   tion 
  by 
  a-particles 
  and 
  of 
  their 
  passage 
  through 
  matter. 
  It 
  

   is 
  not 
  altogether 
  surprising 
  that 
  a-particles 
  should 
  cause 
  

   electrons 
  to 
  be 
  projected 
  with 
  velocities 
  corresponding 
  to 
  

   some 
  hundreds 
  of 
  volts. 
  According 
  to 
  the 
  theory 
  of 
  Einstein, 
  

   the 
  energy 
  of 
  electrons 
  projected 
  under 
  the 
  influence 
  of 
  

   ultra-violet 
  light 
  is 
  a 
  linear 
  function 
  of 
  the 
  frequency 
  of 
  the 
  

   light. 
  This 
  theory 
  has 
  been 
  extended 
  with 
  some 
  degree 
  of 
  

   success 
  to 
  the 
  electronic 
  emission 
  caused 
  by 
  Rontgen 
  rays, 
  

   taking, 
  instead 
  of 
  the 
  frequency, 
  the 
  time 
  occupied 
  by 
  the 
  

   pulse 
  in 
  passing 
  over 
  an 
  electron, 
  and 
  estimating 
  this 
  as 
  well 
  

   as 
  can 
  be 
  done 
  in 
  the 
  present 
  state 
  of 
  knowledge. 
  If 
  we 
  

   assume 
  that 
  the 
  effective 
  field 
  about 
  an 
  a-particle 
  has 
  the 
  

   diameter 
  of 
  an 
  atom, 
  10 
  ~ 
  8 
  cm., 
  then, 
  since 
  its 
  velocity 
  is 
  

  

  cm 
  

   about 
  2 
  X 
  10 
  9 
  — 
  '-, 
  its 
  time 
  of 
  passage 
  over 
  an 
  electron 
  will 
  

   sec. 
  

  

  be 
  ^xl0~ 
  17 
  second. 
  The 
  frequency 
  of 
  ultra-violet 
  light 
  is 
  

  

  about 
  | 
  x 
  10~ 
  15 
  second, 
  so 
  that 
  we 
  might 
  expect 
  the 
  maximum 
  

  

  energy 
  of 
  the 
  S-rays 
  to 
  be 
  of 
  the 
  order 
  of 
  100 
  times 
  that 
  of 
  

  

  photoelectric 
  electrons. 
  

  

  It 
  has 
  been 
  shown 
  that 
  the 
  number 
  of 
  slow 
  S-electrons 
  

  

  varies 
  with 
  the 
  speed 
  of 
  the 
  a-rays 
  in 
  much 
  the 
  same 
  manner 
  

  

  as 
  the 
  number 
  of 
  ions 
  produced 
  in 
  a 
  gas. 
  I 
  have 
  not 
  yet 
  

  

  been 
  able 
  to 
  determine 
  whether 
  this 
  is 
  so 
  with 
  the 
  swifter 
  

  

  S-rays, 
  nor 
  how 
  their 
  distribution 
  in 
  velocity 
  varies 
  (if 
  at 
  all) 
  

  

  with 
  the 
  speed 
  of 
  the 
  a-rays. 
  Knowledge 
  of 
  this 
  sort 
  might 
  

  

  throw 
  considerable 
  light 
  upon 
  the 
  relations 
  between 
  the 
  

  

  electrons 
  of 
  various 
  speeds, 
  and 
  upon 
  the 
  mechanism 
  of 
  

  

  ionization 
  by 
  a-rays, 
  about 
  which 
  very 
  little 
  is 
  known 
  at 
  

  

  present. 
  

  

  Summary. 
  

  

  1. 
  When 
  a-rays 
  fall 
  upon 
  a 
  metal, 
  electrons 
  are 
  emitted 
  

   with 
  velocities 
  varying 
  continuously 
  from 
  a 
  very 
  small 
  value 
  

  

  to 
  more 
  than 
  2*7 
  x 
  10 
  9 
  — 
  ', 
  which 
  corresponds 
  to 
  a 
  potential 
  

  

  sec 
  

  

  difference 
  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 
  

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

  

  