﻿Energy 
  of 
  the 
  Ions 
  emitted 
  hy 
  Hot 
  Bodies. 
  687 
  

  

  the 
  melting-point 
  of 
  potassium 
  sulphate 
  being 
  subsequently 
  

   observed 
  and 
  used 
  as 
  a 
  fiducial 
  point. 
  It 
  was 
  not 
  possible 
  

   to 
  vary 
  the 
  range 
  o£ 
  temperature 
  over 
  which 
  observations 
  

   were 
  taken 
  much 
  ; 
  since 
  at 
  lower 
  temperatures 
  complications 
  

   were 
  caused 
  by 
  the 
  presence 
  of 
  positive 
  ionization 
  in 
  amounts 
  

   comparable 
  with 
  that 
  o£ 
  the 
  negative, 
  whilst 
  at 
  temperatures 
  

   slighly 
  higher 
  than 
  those 
  used 
  the 
  negative 
  ionization 
  became 
  

   too 
  big 
  to 
  be 
  measured 
  on 
  the 
  electrometer 
  when 
  all 
  the 
  

   available 
  capacity 
  was 
  inserted. 
  In 
  addition 
  to 
  this 
  the 
  

   theoretical 
  conditions 
  are 
  vitiated 
  in 
  the 
  case 
  of 
  large 
  currents 
  

   as 
  the 
  theory 
  neglects 
  the 
  dynamical 
  action 
  of 
  the 
  electrons 
  

   on 
  each 
  other 
  after 
  they 
  have 
  left 
  the 
  metal. 
  

  

  The 
  writer 
  never 
  succeeded 
  in 
  getting 
  the 
  conditions 
  so 
  

   that 
  the 
  proportion 
  of 
  the 
  thermionic 
  current 
  which 
  passed 
  

   through 
  the 
  slit 
  was 
  independent 
  of 
  the 
  direction 
  of 
  the 
  

   primary 
  heating 
  current. 
  No 
  matter 
  how 
  the 
  earthing-point 
  

   in 
  the 
  shunt 
  was 
  adjusted 
  the 
  ratios 
  were 
  all 
  invariably 
  from 
  

   ten 
  to 
  twenty 
  per 
  cent, 
  greater 
  with 
  the 
  heating 
  current 
  in 
  

   one 
  direction 
  than 
  in 
  the 
  other. 
  There 
  are 
  two 
  effects 
  de- 
  

   pending 
  on 
  the 
  direction 
  of 
  the 
  heating 
  current 
  which 
  are 
  

   not 
  altogether 
  eliminated 
  in 
  the 
  apparatus 
  used. 
  These 
  are 
  

   the 
  effects 
  of 
  the 
  electrostatic 
  force 
  parallel 
  to 
  the 
  length 
  of 
  

   the 
  strip 
  arising 
  from 
  the 
  fall 
  of 
  potential 
  required 
  to 
  drive 
  

   the 
  heating 
  current 
  and 
  the 
  magnetic 
  force 
  in 
  a 
  perpendicular 
  

   direction 
  arising 
  from 
  the 
  same 
  current. 
  Both 
  of 
  these 
  will 
  

   give 
  the 
  ions 
  a 
  drift 
  parallel 
  to 
  the 
  slit 
  which 
  will 
  reverse 
  in 
  

   direction 
  with 
  the 
  current. 
  This 
  ought 
  not 
  to 
  make 
  any 
  

   difference 
  provided 
  the 
  slit, 
  the 
  plates, 
  the 
  box-shaped 
  elec- 
  

   trode, 
  and 
  the 
  strip 
  are 
  perfectly 
  symmetrical 
  about 
  a 
  vertical 
  

   plane 
  down 
  the 
  centre 
  of 
  the 
  apparatus. 
  These 
  conditions 
  

   were 
  satisfied, 
  so 
  far 
  as 
  was 
  possible 
  with 
  an 
  apparatus 
  of 
  

   this 
  kind 
  in 
  a 
  reasonable 
  time, 
  but 
  there 
  was 
  always 
  a 
  small 
  

   amount 
  of 
  asymmetry 
  arising 
  from 
  defective 
  mechanical 
  

   construction. 
  There 
  is 
  no 
  doubt 
  that 
  this 
  explanation 
  is 
  

   correct, 
  as 
  there 
  was 
  no 
  disagreement 
  within 
  the 
  limits 
  set 
  

   by 
  the 
  errors 
  of 
  observation 
  in 
  the 
  relative 
  values 
  of 
  the 
  ratios 
  

   for 
  different 
  positions 
  of 
  the 
  slit 
  in 
  the 
  different 
  experiments. 
  

   This 
  will 
  be 
  brought 
  out 
  quite 
  clearly 
  when 
  the 
  actual 
  ex- 
  

   perimental 
  data 
  are 
  tabulated 
  (see 
  fig. 
  3, 
  p. 
  688). 
  Formula 
  (1) 
  

   in 
  fact 
  only 
  involves 
  the 
  relative 
  values 
  of 
  the 
  ratios, 
  so 
  that 
  

   it 
  will 
  hold 
  whether 
  asymmetry 
  of 
  this 
  kind 
  occurs 
  or 
  not. 
  

   For 
  this 
  reason 
  the 
  further 
  refinement 
  of 
  the 
  mechanical 
  

   structure 
  of 
  the 
  apparatus 
  was 
  not 
  proceeded 
  with, 
  as 
  it 
  was 
  

   felt 
  that 
  it 
  would 
  involve 
  an 
  amount 
  of 
  labour 
  and 
  time 
  which 
  

   would 
  be 
  quite 
  incommensurate 
  with 
  the 
  benefit 
  to 
  be 
  ex- 
  

   pected. 
  The 
  point 
  is 
  that 
  this 
  asymmetry, 
  after 
  all, 
  \% 
  not 
  

  

  