﻿668 
  Dr. 
  F. 
  C. 
  Brown 
  on 
  the 
  Kinetic 
  Energy 
  of 
  the 
  

  

  For 
  different 
  values 
  o£ 
  Y 
  and 
  — 
  curves 
  were 
  plotted 
  

  

  showing 
  the 
  relation 
  between 
  i 
  and 
  x. 
  The 
  area 
  of 
  any 
  

   curve 
  gave 
  the 
  total 
  value 
  o£ 
  the 
  current 
  to 
  the 
  upper 
  disk 
  

   for 
  the 
  given 
  potential 
  on 
  this 
  disk. 
  Such 
  procedure 
  showed 
  

   that 
  between 
  2 
  and 
  3 
  per 
  cent, 
  error 
  should 
  obtain 
  in 
  the 
  

   value 
  o£ 
  the 
  current 
  at 
  V 
  = 
  '01, 
  when 
  the 
  distance 
  was 
  

   ^^0=2 
  mm., 
  and 
  that 
  the 
  error 
  for 
  the 
  same 
  or 
  less 
  distance 
  

   with 
  a 
  potential 
  of 
  0*1 
  volt 
  on 
  the 
  upper 
  disk 
  should 
  be 
  less 
  

   than 
  1 
  per 
  cent. 
  Errors 
  arising 
  from 
  ions 
  striking 
  the 
  

   guard-ring 
  then 
  should 
  give 
  an 
  experimental 
  value 
  of 
  R 
  too 
  

   large, 
  but 
  such 
  errors 
  could 
  not 
  account 
  for 
  values 
  of 
  R 
  as 
  

   large 
  as 
  were 
  obtained 
  with 
  iron. 
  

  

  In 
  addition 
  to 
  the 
  sources 
  of 
  error 
  which 
  we 
  have 
  men- 
  

   tioned 
  there 
  are 
  probably 
  errors 
  of 
  a 
  second 
  order 
  due 
  to 
  the 
  

   photo-electric 
  effect, 
  to 
  the 
  electric 
  and 
  magnetic 
  fields 
  of 
  

   the 
  heating 
  current, 
  and 
  to 
  the 
  high 
  potential 
  effect. 
  In 
  the 
  

   photo-electric 
  effect 
  negative 
  electrons 
  should 
  be 
  given 
  off 
  

   from 
  the 
  upper 
  disk 
  of 
  platinum. 
  Ladenburg 
  and 
  Markau 
  "^, 
  

   in 
  their 
  investigations, 
  obtained 
  currents 
  from 
  a 
  small 
  

   platinum 
  disk 
  of 
  the 
  order 
  of 
  10~^^ 
  ampere, 
  by 
  the 
  use 
  of 
  

   intense 
  ultra-violet 
  light 
  from 
  a 
  mercury-vapour 
  lamp. 
  

   They 
  also 
  showed 
  that 
  the 
  current 
  was 
  larger 
  with 
  the 
  

   shorter 
  wave-lengths 
  of 
  ultra-violet 
  light. 
  As 
  the 
  positive 
  

   thermions 
  were 
  obtained 
  at 
  very 
  low 
  temperatures 
  it 
  is 
  quite 
  

   improbable 
  that 
  the 
  number 
  of 
  photo-electrons 
  emitted 
  could 
  

   have 
  furnished 
  a 
  current 
  as 
  large 
  as 
  10"^^ 
  ampere, 
  which 
  

   should 
  lead 
  us 
  to 
  expect 
  errors 
  of 
  a 
  very 
  small 
  order 
  in 
  our 
  

   results 
  owing 
  to 
  this 
  cause. 
  

  

  High 
  Potential 
  Effect, 
  

  

  In 
  the 
  paper 
  by 
  Richardson 
  and 
  Brown 
  (loc. 
  cit.) 
  mention 
  

   was 
  made 
  of 
  a 
  peculiar 
  effect, 
  for 
  which 
  at 
  that 
  time 
  there 
  

   seemed 
  to 
  be 
  no 
  reasonable 
  explanation. 
  It 
  was 
  named 
  the 
  

   high 
  potential 
  effect, 
  because 
  of 
  the 
  way 
  in 
  which 
  it 
  first 
  

   appeared. 
  When 
  a 
  potential 
  of 
  200 
  volts 
  was 
  applied 
  to 
  the 
  

   upper 
  plate, 
  thereby 
  drawing 
  off 
  thermions, 
  the 
  sign 
  of 
  which 
  

   depended 
  on 
  the 
  sign 
  of 
  the 
  potential, 
  there 
  was, 
  after 
  the 
  

   removal 
  of 
  the 
  high 
  potential, 
  a 
  thermionic 
  current 
  seemingly 
  

   of 
  the 
  opposite 
  sign, 
  and 
  this 
  current 
  would 
  seemingly 
  go 
  

   against 
  a 
  potential 
  as 
  high 
  as 
  75 
  volts. 
  Often 
  the 
  imposed 
  

   effect 
  would 
  remain 
  24 
  hours 
  practically 
  undiminished, 
  pro- 
  

   viding 
  the 
  thermionic 
  radiator 
  were 
  not 
  heated, 
  but 
  when 
  

   ions 
  were 
  being 
  given 
  off 
  from 
  it 
  the 
  effect 
  decayed 
  rapidly, 
  

  

  * 
  Verh. 
  der 
  deutschen 
  Phys. 
  Gesell. 
  x. 
  no. 
  14, 
  p. 
  562 
  (1905). 
  

  

  