﻿552 
  Mr. 
  K. 
  T. 
  Oompton 
  and 
  Prof. 
  0. 
  W. 
  Richardson 
  on 
  

   and 
  

  

  Ah 
  A 
  etc* 
  \ 
  , 
  TX 
  300 
  

  

  N 
  =^ 
  1 
  -a^)- 
  dV 
  

  

  Aj/ 
  

  

  10, 
  

  

  i. 
  300 
  z 
  n 
  

  

  when 
  zo 
  n 
  < 
  — 
  -- 
  /*v 
  < 
  0. 
  

  

  (4) 
  

  

  In 
  these 
  equations 
  N 
  is 
  the 
  number 
  o£ 
  electrons 
  emitted 
  

   per 
  unit 
  area 
  per 
  unit 
  time 
  by 
  light 
  of 
  unit 
  intensity, 
  A 
  is 
  a 
  

   constant 
  characteristic 
  of 
  the 
  metal, 
  and 
  R, 
  is 
  the 
  absolute 
  gas 
  

   constant 
  reckoned 
  for 
  one 
  molecule. 
  The 
  other 
  symbols 
  have 
  

   the 
  meanings 
  assigned 
  to 
  them 
  previously. 
  

  

  An 
  examination 
  of 
  the 
  expressions 
  for 
  N 
  shows 
  several 
  

   facts 
  in 
  support 
  of 
  the 
  theory. 
  There 
  is 
  apparently 
  a 
  critical 
  

   frequency, 
  given 
  by 
  

  

  300 
  h 
  

  

  — 
  c, 
  . 
  . 
  . 
  (5) 
  

  

  Wq 
  _e_ 
  

   k 
  300' 
  

  

  u\ 
  

  

  below 
  which 
  there 
  is 
  no 
  photoelectric 
  emission. 
  

  

  This 
  we 
  found 
  to 
  be 
  true. 
  The 
  agreement 
  on 
  this 
  point 
  

   between 
  theory 
  and 
  experiment 
  is 
  illustrated 
  by 
  Table 
  I., 
  

  

  Table 
  I. 
  

  

  Metal. 
  

  

  X 
  observed. 
  

  

  \ 
  calculated. 
  

  

  Na 
  

  

  577 
  fifi 
  

  

  360 
  

  

  375 
  

  

  357 
  

  

  337 
  

  

  337 
  

  

  309 
  

  

  280 
  

  

  550 
  uu 
  

  

  360 
  

   390 
  

   340 
  

   305 
  

   290 
  

   275 
  

   270 
  

  

  Al 
  

  

  Me 
  

  

  Zn 
  

  

  Sri 
  

  

  Bi 
  

  

  Cu 
  

  

  Pt 
  

  

  

  which 
  shows 
  the 
  values 
  of 
  the 
  critical 
  wave-lengths 
  for 
  eight 
  

   metals. 
  The 
  calculated 
  values 
  of 
  \ 
  are 
  obtained 
  from 
  

   equations 
  (5) 
  and 
  (2), 
  taking 
  iv 
  for 
  platinum 
  to 
  be 
  4*7 
  volts*, 
  

   and 
  using 
  values 
  of 
  the 
  contact 
  difference 
  of 
  potential 
  of 
  

   each 
  metal 
  with 
  respect 
  to 
  platinum 
  as 
  taken 
  from 
  standard 
  

   tables. 
  The 
  observed 
  values 
  are 
  a 
  little 
  uncertain, 
  since 
  the 
  

   photoelectric 
  currents 
  are 
  small 
  in 
  this 
  region, 
  and 
  since 
  we 
  

   used 
  a 
  quartz-mercury 
  arc, 
  which 
  gives 
  a 
  discontinuous 
  

   spectrum. 
  However, 
  we 
  determined 
  X 
  as 
  best 
  we 
  could 
  

  

  Some 
  of 
  these 
  values 
  were 
  deter- 
  

   The 
  rest 
  are 
  

  

  under 
  the 
  circumstances. 
  

  

  mined 
  during 
  

  

  the 
  course 
  of 
  this 
  investigation. 
  

  

  * 
  H. 
  L. 
  Cooke 
  and 
  O. 
  W. 
  Richardson, 
  Phys. 
  Review 
  [2] 
  vol. 
  i. 
  p. 
  71 
  

   (1913) 
  ; 
  Phil. 
  Mag. 
  vol. 
  xxv. 
  p. 
  624 
  (1913). 
  

  

  