﻿

  the 
  Photoelectric 
  Effect. 
  551 
  

  

  theory 
  also 
  led 
  to 
  au 
  expression 
  connecting 
  w 
  for 
  two 
  metals 
  

   s 
  and 
  p 
  of 
  the 
  form 
  * 
  

  

  sWo 
  - 
  pWo= 
  Y 
  P 
  -y 
  s 
  -0^(Y 
  s 
  -Y 
  p 
  ), 
  ... 
  (2) 
  

  

  where 
  Yp 
  — 
  Y 
  s 
  is 
  the 
  contact 
  difference 
  of 
  potential 
  between 
  

   the 
  metals, 
  expressed 
  in 
  volts. 
  The 
  term 
  involving 
  the 
  

   absolute 
  temperature 
  6 
  expresses 
  the 
  Peltier 
  effect, 
  and 
  may 
  

   be 
  neglected 
  in 
  comparison 
  with 
  Y 
  p 
  —Y 
  s 
  . 
  The 
  theoretical 
  

   and 
  experimental 
  values 
  of 
  w 
  agree 
  fairly 
  well. 
  The 
  fact 
  

   that 
  k 
  is 
  considerably 
  less 
  than 
  the 
  theoretical 
  value 
  h 
  is 
  

   probably 
  not 
  due 
  to 
  manipulative 
  error, 
  but 
  to 
  experimental 
  

   error 
  of 
  a 
  more 
  insiduous 
  nature. 
  On 
  the 
  whole, 
  however, 
  

   the 
  support 
  of 
  the 
  theory 
  is 
  consistent 
  and 
  satisfactory. 
  

  

  The 
  second 
  line 
  of 
  attack 
  on 
  the 
  photoelectric 
  problem 
  is 
  

   the 
  investigation 
  of 
  the 
  effect 
  of 
  the 
  intensity 
  of 
  the 
  light, 
  

   the 
  frequency 
  of 
  the 
  light, 
  and 
  the 
  nature 
  of 
  the 
  metal 
  on 
  the 
  

   number 
  of 
  electrons 
  emitted 
  in 
  unit 
  time. 
  Lenard 
  | 
  and 
  others 
  

   have 
  shown 
  that 
  the 
  number 
  of 
  emitted 
  electrons 
  is 
  simply 
  

   proportional 
  to 
  the 
  intensity 
  of 
  the 
  incident 
  light. 
  As 
  to 
  the 
  

   influence 
  of 
  the 
  nature 
  of 
  the 
  metal, 
  it 
  is 
  known 
  in 
  a 
  general 
  way 
  

   that 
  the 
  more 
  electropositive 
  metals 
  give 
  larger 
  photoelectric 
  

   currents. 
  It 
  is 
  also 
  known 
  that 
  the 
  slightest 
  oxidation 
  or 
  

   other 
  chemical 
  action 
  on 
  the 
  illuminated 
  surface 
  of 
  the 
  metal 
  

   greatly 
  decreases 
  the 
  size 
  of 
  the 
  photoelectric 
  currents. 
  This 
  

   " 
  fatigue 
  " 
  is 
  prevented 
  in 
  proportion 
  as 
  a 
  perfect 
  vacuum 
  is 
  

   approached. 
  Except 
  for 
  the 
  work 
  of 
  Pohl 
  and 
  Pringsheim, 
  

   which 
  will 
  be 
  discussed 
  later, 
  little 
  is 
  known 
  concerning 
  the 
  

   relation 
  between 
  the 
  frequency 
  and 
  the 
  rate 
  of 
  emission 
  

   of 
  electrons 
  except 
  the 
  fact 
  that 
  photoelectric 
  currents 
  

   apparently 
  increase 
  as 
  shorter 
  wave-lengths 
  of 
  light 
  are 
  

   employed 
  J. 
  

  

  The 
  theory 
  of 
  photoelectric 
  action 
  developed 
  by 
  one 
  of 
  the 
  

   writers 
  § 
  yields 
  an 
  expression 
  connecting 
  the 
  frequency, 
  

   nature 
  of 
  the 
  metal, 
  and 
  number 
  of 
  electrons 
  emitted 
  in 
  unit 
  

   time, 
  as 
  well 
  as 
  the 
  expression 
  for 
  the 
  initial 
  kinetic 
  energy 
  

   already 
  referred 
  to. 
  The 
  complete 
  theory 
  leads 
  to 
  the 
  

   following 
  equations: 
  

  

  N 
  = 
  when 
  < 
  — 
  hv 
  < 
  w 
  , 
  .... 
  (3) 
  

  

  * 
  O. 
  W. 
  Richardson, 
  Phil. 
  Mag. 
  vol. 
  xxiii. 
  p. 
  264 
  (1912) 
  ; 
  vol. 
  xxiii. 
  

   p. 
  615 
  (1912). 
  

  

  f 
  Ann. 
  d. 
  Phys. 
  vol. 
  viii. 
  p. 
  149 
  (1902), 
  

  

  t 
  Hallwachs, 
  Ann. 
  cl. 
  Phys. 
  vol. 
  xxx. 
  p. 
  593 
  (1909). 
  

  

  § 
  Op. 
  cit. 
  

  

  2 
  P 
  2 
  

  

  