﻿232 
  Discontinuity 
  of 
  Potential 
  at 
  Surface 
  of 
  Glowing 
  Carbon* 
  

  

  surface 
  layer, 
  6 
  being 
  the 
  absolute 
  temperature. 
  The 
  formula, 
  

   considering 
  A 
  and 
  b 
  as 
  constants, 
  very 
  well 
  represents 
  the 
  

   observations 
  of 
  its 
  author 
  and 
  others 
  on 
  the 
  saturation 
  currents 
  

   from 
  hot 
  bodies 
  through 
  the 
  range 
  of 
  temperature 
  for 
  v^hich 
  

   it 
  has 
  been 
  employed 
  ; 
  from 
  such 
  observations 
  the 
  values 
  of 
  

   h 
  for 
  certain 
  substances 
  have 
  been 
  determined. 
  In 
  the 
  theory 
  

   by 
  which 
  the 
  expression 
  is 
  deduced, 
  b 
  is 
  equal 
  to 
  ^/R. 
  where 
  

   <l> 
  is 
  the 
  work 
  done 
  by 
  a 
  corpuscle 
  in 
  passing 
  through 
  the 
  

   surface 
  layer, 
  and 
  R 
  a 
  gas 
  constant, 
  equal 
  to 
  p/1^0, 
  p 
  being 
  

   the 
  pressure 
  and 
  N 
  the 
  number 
  of 
  molecules 
  per 
  cubic 
  centi- 
  

   metre. 
  The 
  discontinuity 
  of 
  potential 
  is 
  thus 
  represented 
  by 
  

   b/B.e, 
  where 
  e 
  is 
  the 
  ionic 
  charge. 
  

  

  The 
  follovving 
  are 
  the 
  values 
  of 
  the 
  discontinuity 
  of 
  potential 
  

   as 
  calculated 
  by 
  Professor 
  Richardson 
  : 
  — 
  

  

  Temperature 
  Discontinuity 
  of 
  

  

  absolute. 
  potential. 
  

  

  Sodium 
  490°-700° 
  2-45 
  volts. 
  

  

  Platinum 
  1378-1571 
  4-1 
  „ 
  

  

  Carbon 
  1520-1770 
  6*1 
  „ 
  

  

  These 
  results, 
  which 
  are 
  not 
  appreciably 
  altered 
  by 
  recal- 
  

   culation 
  with 
  the 
  new 
  value 
  of 
  the 
  ionic 
  charge 
  determined 
  

   by 
  Professor 
  Rutherford 
  and 
  Dr. 
  Geiger 
  *, 
  seem 
  singularly 
  

   high. 
  If 
  bH/e 
  really 
  represents 
  the 
  discontinuity 
  ©f 
  potential, 
  

   the 
  fact 
  that 
  the 
  discontinuity 
  varies 
  somewhat 
  rapidly 
  with 
  

   temperature 
  for 
  higher 
  values 
  shows 
  that 
  b 
  cannot 
  be 
  con- 
  

   sidered 
  altogether 
  constant. 
  

  

  In 
  a 
  recent 
  paper 
  Professor 
  Richardson 
  and 
  Mr. 
  Brown 
  f 
  

   originate 
  the 
  theory 
  of 
  a 
  method 
  for 
  finding 
  the 
  kinetic 
  

   energy 
  of 
  the 
  electrons 
  projected 
  from 
  heated 
  materials, 
  and 
  

   they 
  have 
  experimentally 
  determined 
  the 
  component, 
  per- 
  

   pendicular 
  to 
  the 
  hot 
  surface, 
  of 
  the 
  velocity 
  with 
  which 
  

   electrons 
  are 
  projected 
  from 
  glowing 
  platinum, 
  the 
  result 
  for 
  

   a 
  temperature 
  of 
  1650° 
  absolute 
  being 
  1*5 
  x 
  10^ 
  centimetres 
  

   per 
  second. 
  This 
  velocity 
  of 
  projection, 
  in 
  the 
  case 
  of 
  glowing 
  

   carbon, 
  may, 
  on 
  certain 
  assumptions, 
  be 
  estimated 
  from 
  the 
  

   results 
  already 
  given 
  in 
  the 
  present 
  paper. 
  As 
  suggested 
  by 
  

   one 
  of 
  us 
  t, 
  a 
  point 
  of 
  view 
  is 
  possible 
  from 
  which 
  the 
  work 
  

   done 
  in 
  connexion 
  with 
  the 
  passage 
  of 
  the 
  electrons 
  through 
  

   the 
  surface-layer 
  may 
  be 
  considered 
  as 
  represented 
  by 
  their 
  

   translational 
  energy 
  when 
  they 
  emerge 
  into 
  the 
  gas. 
  In 
  such 
  

   a 
  case 
  the 
  surface 
  discontinuity 
  of 
  potential, 
  Y, 
  may 
  be 
  

  

  * 
  Rutherford 
  & 
  Geiger, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  xxxi. 
  p. 
  162 
  (1908). 
  

   t 
  Richardson 
  & 
  Brown, 
  Phil. 
  Mag. 
  xvi. 
  p. 
  353, 
  Sept. 
  1908. 
  

   i 
  Pollock, 
  Phil. 
  Mag. 
  March 
  1909, 
  p. 
  361. 
  

  

  