﻿506 
  L. 
  Page 
  — 
  The 
  Photoelectric 
  Effect. 
  

  

  accorded 
  to 
  the 
  aluminium 
  disk 
  was 
  slightly 
  different 
  from 
  

   that 
  accorded 
  to 
  the 
  receiving 
  electrode. 
  

  

  For 
  any 
  given 
  wave 
  length 
  the 
  uncorrected 
  maximum 
  

   velocity 
  is 
  seen 
  to 
  be 
  independent 
  of 
  the 
  nature 
  of 
  the 
  metal 
  

   which 
  has 
  been 
  exposed 
  to 
  the 
  light. 
  This 
  is 
  quite 
  closely 
  the 
  

   case 
  for 
  all 
  curves. 
  In 
  the 
  case 
  of 
  the 
  scraped 
  metals 
  this 
  

   point 
  appears 
  to 
  be 
  about 
  0*1 
  volt 
  further 
  to 
  the 
  left 
  than 
  in 
  

   the 
  case 
  of 
  the 
  unscraped 
  metals. 
  

  

  "When 
  the 
  metal 
  has 
  been 
  scraped 
  not 
  only 
  is 
  the 
  maximum 
  

   velocity 
  point 
  shifted 
  about 
  0*1 
  volt 
  to 
  the 
  left, 
  but 
  the 
  satura- 
  

   tion 
  point 
  is 
  shifted 
  about 
  0*5 
  volt 
  to 
  the 
  right. 
  This 
  shift 
  is 
  

   quite 
  clearly 
  shown 
  in 
  all 
  the 
  curves 
  except 
  those 
  in 
  which 
  

   zinc 
  was 
  the 
  metal 
  exposed 
  to 
  the 
  light. 
  In 
  the 
  case 
  of 
  

   scraped 
  zinc 
  the 
  saturation 
  points 
  are 
  much 
  less 
  distinct, 
  due, 
  

   no 
  doubt, 
  to 
  the 
  very 
  rapid 
  fatigue 
  noticed 
  in 
  the 
  case 
  of 
  zinc. 
  

  

  Discussion 
  of 
  Results. 
  

  

  The 
  shift 
  of 
  the 
  curves 
  to 
  the 
  left 
  by 
  0*9 
  volt 
  when 
  the 
  

   aluminium 
  electrode 
  was 
  replaced 
  by 
  the 
  copper 
  one, 
  in 
  the 
  

   case 
  of 
  both 
  scraped 
  and 
  unscraped 
  metals, 
  is 
  a 
  conclusive 
  con- 
  

   firmation 
  of 
  Richardson 
  and 
  Compton's 
  contention 
  that 
  the 
  

   contact 
  difference 
  of 
  potential 
  must 
  be 
  taken 
  into 
  account 
  in 
  

   plotting 
  the 
  curves. 
  The 
  fact 
  that 
  in 
  the 
  unscraped 
  Copper- 
  

   Copper 
  and 
  the 
  unscraped 
  Aluminium-Aluminium 
  curves 
  the 
  

   saturation 
  point 
  comes 
  practically 
  on 
  the 
  current 
  axis 
  shows 
  

   that 
  this 
  point 
  corresponds 
  to 
  no 
  field 
  or 
  true 
  zero 
  potential. 
  

  

  If 
  the 
  contact-difference 
  of 
  potential 
  is 
  allowed 
  for, 
  the 
  

   maximum 
  energies 
  in 
  volts 
  are 
  as 
  follows 
  : 
  

  

  

  

  a 
  = 
  2190 
  

  

  a 
  = 
  2460 
  

  

  Scraped 
  Al 
  ] 
  

   " 
  Zn 
  

  

  Al 
  electrode 
  

  

  2-8 
  

   2-3 
  

  

  2-2 
  

   1-7 
  

  

  " 
  Cu 
  ) 
  

  

  

  1-5 
  

  

  1-0 
  

  

  Scraped 
  Al 
  ) 
  

   " 
  Zn 
  

  

  Cu 
  electrode 
  

  

  2-8 
  

   2-3 
  

  

  2-3 
  

   1-8 
  

  

  " 
  Cu 
  ) 
  

  

  

  1-6 
  

  

  1-1 
  

  

  Unscraped 
  Al 
  

   Zn 
  

  

  > 
  Al 
  electrode 
  

  

  2-1 
  

   1-9 
  

  

  1*6 
  

   1-4 
  

  

  Cu 
  

  

  i 
  

  

  1-1 
  

  

  0-6 
  

  

  Unscraped 
  Al 
  

   Zn 
  

  

  »• 
  Cu 
  electrode 
  

  

  2-2 
  

   1-8 
  

  

  1-7 
  

   1-3 
  

  

  Cu 
  

  

  

  1-0 
  

  

  0'5 
  

  

  Einstein* 
  has 
  shown 
  that 
  the 
  maximum 
  energy 
  L 
  of 
  the 
  

   electrons 
  emitted 
  under 
  the 
  influence 
  of 
  light 
  should 
  satisfy 
  

   the 
  equation 
  

  

  L 
  = 
  hv 
  - 
  P 
  

  

  * 
  A. 
  Einstein, 
  Ann. 
  d. 
  Phys., 
  xvii, 
  p. 
  146, 
  1905. 
  

  

  