﻿Specific 
  Charge 
  of 
  the 
  Ions 
  emitted 
  by. 
  Hot 
  Bodies. 
  741 
  

  

  paper 
  * 
  the 
  author 
  has 
  considered 
  in 
  detail 
  the 
  evidence 
  

   bearing 
  on 
  the 
  origin 
  of 
  the 
  ionization 
  caused 
  by 
  different 
  

   gases, 
  and 
  has 
  arrived 
  at 
  the 
  conclusion 
  that 
  the 
  ions 
  arise 
  

   from 
  the 
  gas 
  absorbed 
  by 
  the 
  metal 
  and 
  are 
  not 
  positive 
  

   electrons. 
  The 
  argument 
  is 
  discussed 
  particularly 
  on 
  p. 
  61 
  

   of 
  the 
  paper 
  referred 
  to. 
  According 
  to 
  this 
  view 
  we 
  should 
  

   expect 
  the 
  mass 
  of 
  the 
  positive 
  ions 
  to 
  be 
  comparable 
  with 
  

   that 
  of 
  the 
  atoms 
  or 
  molecules 
  of 
  the 
  gas 
  surrounding 
  the 
  

   hot 
  substance. 
  It 
  was 
  felt 
  at 
  the 
  time 
  that 
  most 
  of 
  the 
  

   evidence 
  adduced 
  was 
  rather 
  indirect 
  and 
  that 
  the 
  case 
  

   might 
  be 
  greatly 
  strengthened 
  by 
  a 
  direct 
  investigation 
  of 
  

   the 
  specific 
  charge 
  of 
  the 
  ions. 
  The 
  present 
  investigation 
  

   was 
  commenced 
  with 
  that 
  object 
  in 
  view, 
  but 
  the 
  interest 
  of 
  

   the 
  subject 
  has 
  been 
  increased 
  by 
  the 
  announcement 
  by 
  

   J. 
  J. 
  Thomson 
  f 
  of 
  experiments 
  in 
  which 
  he 
  believes 
  to 
  have 
  

   isolated 
  positive 
  corpuscles 
  in 
  the 
  canal 
  rays. 
  Incidentally 
  

   the 
  specific 
  charge 
  of 
  the 
  negative 
  ions 
  for 
  the 
  substances 
  

   experimented 
  upon 
  has 
  also 
  been 
  measured. 
  

  

  § 
  2. 
  The 
  Method 
  Employed. 
  

  

  The 
  method 
  used 
  by 
  Thomson 
  in 
  measuring 
  e/m 
  for 
  the 
  

   positive 
  ions 
  emitted 
  by 
  an 
  incandescent 
  iron 
  wire 
  was 
  to 
  

   place 
  the 
  wire 
  parallel 
  to 
  and 
  4 
  mms. 
  distant 
  from 
  an 
  

   insulated 
  metal 
  plate. 
  The 
  wire 
  was 
  positively 
  charged 
  and 
  

   a 
  magnetic 
  field 
  applied 
  so 
  that 
  the 
  lines 
  of 
  magnetic 
  force 
  

   were 
  parallel 
  to 
  the 
  plate. 
  Under 
  these 
  circumstances 
  the 
  

   paths 
  of 
  the 
  moving 
  ions 
  tend 
  to 
  curve 
  round 
  the 
  lines 
  of 
  

   magnetic 
  force, 
  and 
  if 
  the 
  magnetic 
  field 
  is 
  strong 
  enough 
  

   the 
  curvature 
  will 
  be 
  such 
  that 
  none 
  of 
  them 
  will 
  ever 
  reach 
  

   the 
  plate. 
  If 
  the 
  plate 
  were 
  infinite 
  in 
  extent, 
  if 
  the 
  electric 
  

   and 
  magnetic 
  fields 
  were 
  uniform, 
  and 
  if 
  all 
  the 
  ions 
  were 
  shot 
  

   off 
  from 
  the 
  hot 
  body 
  with 
  zero 
  velocity, 
  tnis 
  limiting 
  value 
  

   of! 
  the 
  magnetic 
  force 
  would 
  be 
  the 
  same 
  for 
  all 
  of 
  them. 
  

   Under 
  these 
  conditions 
  the 
  current 
  to 
  the 
  plate 
  would 
  be 
  

   independent 
  of 
  the 
  magnetic 
  field 
  until 
  a 
  certain 
  value 
  of 
  

   this 
  was 
  reached, 
  at 
  which 
  it 
  would 
  fall 
  to 
  zero 
  and 
  remain 
  

   zero 
  for 
  all 
  higher 
  values 
  of 
  the 
  field. 
  From 
  this 
  limiting- 
  

   value 
  of 
  the 
  magnetic 
  field 
  the 
  value 
  of 
  e/m 
  can 
  be 
  calculated. 
  

  

  The 
  chief 
  objections 
  to 
  this 
  method, 
  which 
  has 
  the 
  merit 
  

   of 
  simplicity 
  and 
  quickness 
  in 
  practice, 
  arise 
  from 
  the 
  

   difficulty 
  of 
  satisfying 
  the 
  theoretical 
  conditions 
  with 
  the 
  

   large 
  magnetic 
  fields 
  which 
  it 
  is 
  necessary 
  to 
  employ. 
  It 
  is 
  

   found 
  that 
  the 
  current 
  to 
  the 
  plate 
  does 
  not 
  suddenly 
  

  

  * 
  Phil. 
  Trans. 
  A. 
  vol. 
  ccvii, 
  p. 
  1. 
  

   | 
  Phil. 
  Mag. 
  May 
  & 
  Sept. 
  1907. 
  

  

  