﻿Positive 
  Rays. 
  679 
  

  

  2 
  amperes, 
  thus 
  the 
  difference 
  which 
  sets 
  in 
  between 
  the 
  

   results 
  when 
  t 
  = 
  l 
  and 
  t 
  = 
  2 
  at 
  160 
  volts 
  indicates 
  the 
  presence 
  

   of 
  a 
  considerable 
  number 
  of 
  ions 
  for 
  which 
  £/>?? 
  = 
  10 
  4 
  . 
  

  

  For 
  voltages 
  between 
  30 
  and 
  160 
  there 
  is 
  no 
  appreciable 
  

   difference 
  with 
  currents 
  ranging 
  from 
  1 
  to 
  4 
  amperes, 
  while 
  

   for 
  voltages 
  less 
  than 
  30 
  there 
  is 
  an 
  appreciable 
  diminution 
  

   in 
  the 
  number 
  which 
  get 
  to 
  the 
  disk 
  when 
  the 
  current 
  through 
  

   the 
  electromagnet 
  is 
  raised 
  from 
  1 
  to 
  4 
  amperes. 
  This 
  in- 
  

   dicates 
  that 
  there 
  are 
  some 
  ions 
  which, 
  under 
  a 
  voltage 
  of 
  

   say 
  25 
  volts, 
  are 
  stopped 
  when 
  the 
  magnetic 
  field 
  is 
  that 
  due 
  

   to 
  4 
  amperes, 
  but 
  can 
  get 
  across 
  when 
  it 
  is 
  due 
  to 
  2 
  amperes. 
  

   Since 
  1100 
  volts 
  would 
  just 
  drive 
  particles 
  for 
  which 
  

   e/m 
  = 
  10 
  A 
  across 
  the 
  field 
  due 
  to 
  4 
  amperes^ 
  25 
  volts 
  will 
  drive 
  

   particles 
  for 
  which 
  £/m 
  = 
  10 
  4 
  /(1100/25) 
  = 
  10 
  4 
  /44 
  across 
  this 
  

   field. 
  For 
  the 
  field 
  due 
  to 
  2 
  amperes 
  620 
  volts 
  are 
  required 
  

   to 
  drive 
  particles 
  for 
  which 
  e/7n 
  = 
  10 
  i 
  , 
  25 
  volts 
  will 
  drive 
  

   particles 
  for 
  which 
  e/m 
  = 
  10y( 
  620/25) 
  = 
  10 
  4 
  /25. 
  From 
  the 
  

   preceding 
  results 
  we 
  infer 
  the 
  presence 
  of 
  ions 
  for 
  which 
  e/m 
  

   is 
  between 
  10 
  4 
  /44 
  and 
  10 
  4 
  /25. 
  Such 
  ions 
  might 
  be 
  molecules 
  

   of 
  nitrogen 
  or 
  oxygen 
  due 
  to 
  traces 
  of 
  air 
  in 
  the 
  discharge- 
  

   tube 
  ; 
  these, 
  however, 
  are 
  only 
  a 
  small 
  fraction 
  of 
  the 
  whole 
  

   number 
  of 
  ions. 
  The 
  pressure 
  of 
  the 
  hydrogen 
  in 
  this 
  case 
  

   was 
  about 
  '003 
  mm. 
  It 
  is 
  necessary 
  to 
  work 
  at 
  pressures 
  

   so 
  low 
  that 
  the 
  mean 
  free 
  path 
  of 
  the 
  ion 
  is 
  large 
  compared 
  

   with 
  the 
  distance 
  d. 
  

  

  Let 
  us 
  now 
  compare 
  the 
  results 
  obtained 
  when 
  the 
  apparatus 
  

   had 
  been 
  repeatedly 
  filled 
  with 
  oxygen 
  obtained 
  by 
  heating 
  

   permanganate 
  of 
  potash 
  in 
  a 
  tube 
  fused 
  on 
  to 
  the 
  discharge- 
  

   tube, 
  running 
  the 
  coil 
  with 
  the 
  gas 
  at 
  the 
  pressure 
  when 
  the 
  

   discharge 
  passes 
  most 
  easily, 
  and 
  then 
  filling 
  and 
  repumping 
  ; 
  

   the 
  oxygen 
  on 
  its 
  way 
  from 
  the 
  permanganate 
  to 
  the 
  dis- 
  

   charge-tube 
  went 
  through 
  a 
  worm 
  immersed 
  in 
  liquid 
  air 
  to 
  

   free 
  it 
  from 
  any 
  traces 
  of 
  water 
  vapour 
  given 
  off 
  from 
  the 
  

   permanganate. 
  No 
  hydrogen 
  lines 
  could 
  be 
  detected 
  in 
  the 
  

   spectrum. 
  The 
  Faraday 
  cylinder 
  had 
  been 
  taken 
  down 
  

   between 
  this 
  experiment 
  and 
  the 
  preceding 
  one, 
  and 
  slightly 
  

   altered 
  so 
  that 
  the 
  radius 
  of 
  the 
  critical 
  circle 
  in 
  this 
  case 
  

   when 
  d=4:, 
  a=2'5, 
  is 
  "47 
  cm,, 
  hence 
  the 
  potentials 
  required 
  

   to 
  force 
  ions 
  for 
  which 
  e/?n=10 
  4 
  across 
  to 
  the 
  disk 
  when 
  

   currents 
  1, 
  2, 
  3, 
  4 
  amperes 
  flow 
  through 
  the 
  coils 
  of 
  the 
  

   electromagnet 
  are 
  respectively 
  72, 
  270, 
  400, 
  and 
  480 
  volts. 
  

   The 
  pressure 
  of 
  the 
  oxygen 
  was 
  "009 
  mm. 
  

  

  The 
  following 
  are 
  the 
  results 
  of 
  the 
  experiments, 
  n 
  as 
  before 
  

   being 
  the 
  percentage 
  of 
  ions 
  which 
  reach 
  the 
  disk 
  : 
  — 
  

  

  