﻿Energy 
  of 
  the 
  Ions 
  emitted 
  by 
  Hot 
  Bodies. 
  915 
  

  

  of 
  the 
  ions, 
  both 
  positive 
  and 
  negative, 
  emitted 
  by 
  hot 
  metals 
  

   is 
  the 
  same 
  as 
  that 
  of 
  a 
  molecule 
  of 
  a 
  gas 
  at 
  the 
  temperature 
  

   of 
  the 
  metal. 
  

  

  The 
  previous 
  work 
  of 
  Richardson 
  and 
  Brown 
  (loc. 
  cit.) 
  has 
  

   shown 
  that, 
  within 
  the 
  limits 
  of 
  experimental 
  error 
  and 
  

   under 
  normal 
  conditions, 
  the 
  part 
  of 
  the 
  kinetic 
  energy 
  of 
  

   the 
  negative 
  ions 
  emitted 
  by 
  hot 
  platinum 
  which 
  depends 
  

   on 
  the 
  component 
  of 
  velocity 
  normal 
  to 
  the 
  metal 
  surface 
  

   has 
  the 
  same 
  mean 
  value 
  as 
  the 
  corresponding 
  quantity 
  

   for 
  a 
  molecule 
  leaving 
  any 
  surface 
  drawn 
  in 
  a 
  gas 
  at 
  the 
  

   temperature 
  of 
  the 
  metal 
  ; 
  and 
  moreover 
  that 
  the 
  normal 
  

   velocity 
  component 
  is 
  distributed 
  among 
  the 
  different 
  ions 
  

   according 
  to 
  Maxwell's 
  law 
  of 
  distribution 
  of 
  the 
  same 
  

   quantity 
  among 
  the 
  molecules 
  of 
  a 
  gas 
  of 
  equal 
  molecular 
  

   weight 
  under 
  the 
  same 
  conditions. 
  An 
  investigation 
  by 
  

   Dr. 
  Brown, 
  not 
  yet 
  published, 
  shows 
  that 
  the 
  positive 
  ions 
  

   from 
  hot 
  platinum 
  obey 
  the 
  same 
  laws 
  in 
  this 
  respect 
  as 
  the 
  

   negative 
  ions. 
  

  

  The 
  present 
  investigation, 
  taken 
  in 
  conjunction 
  with 
  the 
  

   foregoing 
  results, 
  shows 
  that 
  the 
  ions 
  emitted 
  by 
  hot 
  

   platinum, 
  whether 
  positive 
  or 
  negative, 
  are 
  kinetically 
  

   identical 
  with 
  the 
  molecules 
  of 
  a 
  gas, 
  of 
  equal 
  molecular 
  

   weight, 
  at 
  the 
  temperature 
  of 
  the 
  metal. 
  This 
  identity 
  is 
  

   true 
  not 
  only 
  of 
  the 
  average 
  velocity 
  but 
  of 
  its 
  mode 
  of 
  

   distribution 
  among 
  the 
  different 
  ions 
  or 
  molecules 
  as 
  well. 
  

   The 
  present 
  investigation 
  may 
  be 
  regarded 
  as 
  completing 
  the 
  

   evidence 
  on 
  which 
  the 
  conclusion 
  has 
  been 
  based 
  *, 
  that 
  the 
  

   free 
  electrons 
  inside 
  the 
  metal 
  have 
  the 
  same 
  amount 
  and 
  

   mode 
  of 
  distribution 
  of 
  kinetic 
  energy 
  and 
  velocity 
  as 
  the 
  

   molecules 
  of 
  a 
  gas 
  of 
  equal 
  molecular 
  weight 
  at 
  the 
  tem- 
  

   perature 
  of 
  the 
  metal. 
  The 
  significance 
  of 
  this 
  conclusion 
  

   in 
  other 
  branches 
  of 
  physical 
  theory 
  has 
  already 
  been 
  pointed 
  

   out 
  by 
  Richardson 
  and 
  Brown 
  (loc. 
  cit.). 
  

  

  The 
  argument 
  developed 
  by 
  those 
  authors, 
  from 
  the 
  

   smallness 
  of 
  the 
  currents 
  dealt 
  with, 
  which 
  compels 
  the 
  

   rejection 
  of 
  the 
  continuous 
  medium 
  method 
  of 
  looking 
  at 
  

   the 
  phenomena 
  in 
  favour 
  of 
  the 
  atomic 
  view, 
  applies 
  with 
  

   equal 
  force 
  to 
  the 
  present 
  enquiry. 
  

  

  In 
  the 
  experiments 
  carried 
  out 
  in 
  this 
  investigation, 
  and 
  

   the 
  others 
  to 
  which 
  allusion 
  has 
  been 
  made, 
  the 
  ions 
  are 
  

   prevented 
  from, 
  or 
  helped 
  in, 
  returning 
  to 
  the 
  metal 
  by 
  an 
  

   external 
  electric 
  field. 
  The 
  conditions 
  are 
  therefore 
  not 
  the 
  

   same 
  as 
  would 
  hold 
  in 
  the 
  steady 
  state 
  which 
  must 
  ultimately 
  

   ensue 
  if 
  the 
  metal 
  is 
  surrounded 
  by 
  a 
  vacuous 
  space 
  bounded 
  

   by 
  a 
  closed 
  insulating 
  surface. 
  We 
  are 
  therefore 
  not 
  justified 
  

   * 
  Phil. 
  Mag. 
  [6] 
  vol. 
  xvi. 
  pp. 
  374-6. 
  

   3 
  02 
  

  

  