﻿H. 
  A. 
  Bumstead 
  — 
  Velocities 
  of 
  Delta 
  Bays. 
  101 
  

  

  hydrogen 
  ion 
  whose 
  velocity 
  was 
  due 
  to 
  a 
  fall 
  of 
  potential 
  of 
  

   only 
  9 
  volts 
  would 
  move 
  in 
  a 
  path 
  whose 
  radius 
  of 
  curvature 
  is 
  

   l'7 
  cm 
  , 
  and 
  might 
  escape 
  from 
  the 
  electrode, 
  while 
  an 
  oxygen 
  

   atom 
  with 
  a 
  single 
  charge 
  certainly 
  would, 
  as 
  its 
  radius 
  of 
  

   curvature 
  would 
  be 
  6'7 
  cra 
  . 
  

  

  Assuming, 
  then, 
  that 
  the 
  negative 
  current 
  is 
  carried 
  by 
  such 
  

   positive 
  ions 
  from 
  the 
  gas 
  film 
  upon 
  the 
  source, 
  it 
  seems 
  

   unnecessary 
  to 
  suppose 
  that 
  they 
  are 
  emitted 
  with 
  an 
  appreci- 
  

   able 
  velocity, 
  as 
  any 
  of 
  the 
  electric 
  fields 
  used 
  in 
  the 
  preceding 
  

   experiments 
  would 
  be 
  sufficient 
  to 
  take 
  them 
  through 
  the 
  mag- 
  

   netic 
  field. 
  It 
  seems 
  more 
  probable 
  that 
  it 
  is 
  simply 
  an 
  ioniza- 
  

   tion 
  of 
  the 
  gas 
  film 
  by 
  the 
  a-rays. 
  When 
  the 
  current 
  in 
  

   question 
  is 
  reduced 
  to 
  its 
  minimum 
  value 
  by 
  three 
  or 
  four 
  

   days 
  duration 
  of 
  the 
  vacuum, 
  the 
  charge 
  carried 
  by 
  it 
  is 
  from 
  

   5 
  to 
  10 
  per 
  cent 
  of 
  that 
  carried 
  by 
  all 
  the 
  a-rays 
  from 
  the 
  

   polonium. 
  (See 
  § 
  6.) 
  If 
  the 
  ions 
  have 
  lost 
  a 
  single 
  electronic 
  

   charge, 
  this 
  means 
  that 
  only 
  one 
  out 
  of 
  ten 
  (or 
  one 
  out 
  of 
  five) 
  

   of 
  the 
  a-particles, 
  in 
  its 
  passage 
  through 
  the 
  surface 
  film, 
  pro- 
  

   duces 
  a 
  positive 
  ion 
  which 
  can 
  get 
  away. 
  When 
  the 
  surface 
  

   film 
  is 
  not 
  so 
  much 
  reduced 
  by 
  long 
  exposure 
  to 
  a 
  high 
  

   vacuum, 
  this 
  number 
  may 
  be 
  considerably 
  increased. 
  

  

  It 
  is 
  possible 
  that 
  negative 
  ions 
  of 
  atomic 
  size 
  may 
  also 
  be 
  

   produced, 
  but 
  the 
  present 
  apparatus 
  is 
  not 
  adapted 
  to 
  decide 
  

   this 
  question 
  for 
  the 
  following 
  reasons. 
  The 
  magnetic 
  field 
  is 
  

   by 
  no 
  means 
  parallel 
  to 
  the 
  electrode 
  and 
  some 
  of 
  the 
  lines 
  of 
  

   force 
  meet 
  the 
  surface 
  of 
  the 
  electrode, 
  though 
  not 
  at 
  very 
  large 
  

   angles. 
  A 
  small 
  proportion 
  of 
  the 
  S-electrons 
  from 
  any 
  point 
  

   of 
  the 
  electrode 
  will 
  leave 
  in 
  paths 
  making 
  only 
  a 
  small 
  angle 
  

   with 
  the 
  magnetic 
  field 
  and 
  will 
  hence 
  escape. 
  Now 
  when 
  a 
  

   positive 
  potential 
  is 
  applied 
  to 
  the 
  gauze, 
  the 
  current 
  of 
  elec- 
  

   trons 
  leaving 
  the 
  source 
  without 
  a 
  magnetic 
  field 
  is 
  more 
  than 
  

   500 
  times 
  the 
  ionic 
  current 
  under 
  consideration. 
  If 
  a 
  fraction 
  

   of 
  one 
  per 
  cent 
  of 
  these 
  escape 
  alone: 
  the 
  lines 
  of 
  force, 
  it 
  will 
  

   be 
  sufficient 
  to 
  cover 
  up 
  the 
  possible 
  small 
  current 
  due 
  to 
  neg- 
  

   ative 
  ions. 
  That 
  this 
  is 
  the 
  case 
  will 
  be 
  seen 
  in 
  the 
  following 
  

   section. 
  

  

  Effects 
  have 
  been 
  observed 
  by 
  other 
  investigators 
  which, 
  I 
  

   believe, 
  indicate 
  the 
  presence 
  of 
  ions 
  from 
  gaseous 
  surface 
  

   films. 
  Thus 
  in 
  the 
  recent, 
  very 
  careful 
  determination 
  by 
  

   Danysz 
  and 
  Duane* 
  of 
  the 
  charge 
  carried 
  by 
  a-rays, 
  the 
  screen 
  

   which 
  limits 
  the 
  beam 
  of 
  a-rays 
  and 
  the 
  opening 
  of 
  the 
  Fara- 
  

   day 
  cylinder 
  which 
  receives 
  them 
  are 
  both 
  covered 
  with 
  thin 
  

   aluminium 
  foil, 
  the 
  two 
  foils 
  being 
  parallel 
  and 
  0'8 
  cm 
  apart. 
  

   A 
  magnetic 
  field 
  of 
  8000 
  units 
  parallel 
  to 
  these 
  foils 
  is 
  used 
  to 
  

   curl 
  up 
  the 
  j3- 
  and 
  S-rays. 
  Even 
  with 
  this 
  field, 
  the 
  authors 
  

   foundf 
  that 
  a 
  difference 
  of 
  potential 
  of 
  only 
  2 
  volts 
  between 
  

  

  * 
  This 
  Journal, 
  xxxv, 
  295, 
  1913. 
  + 
  L. 
  c, 
  p. 
  302. 
  

  

  