﻿Long-wave 
  Limits 
  of 
  the 
  Normal 
  Photoelectric 
  Effect. 
  1023 
  

  

  not 
  analogous 
  to 
  that 
  recently 
  described 
  by 
  us, 
  which 
  dealt 
  

   with 
  the 
  surface 
  changes 
  produced 
  on 
  K 
  by 
  reaction 
  with 
  

   electronegative 
  gases 
  *. 
  Neither 
  K 
  nor 
  K 
  -amalgams, 
  which 
  

   we 
  had 
  occasion 
  to 
  investigate 
  extensively 
  in 
  another 
  con- 
  

   nexion 
  f, 
  show 
  this 
  time 
  change 
  of 
  surface 
  observed 
  on 
  Ca. 
  

   If 
  the 
  effect 
  is 
  there, 
  it 
  is 
  at 
  any 
  rate 
  of 
  an 
  entirely 
  

   different 
  order 
  of 
  magnitude. 
  On 
  the 
  other 
  hand, 
  obser- 
  

   vations, 
  not 
  yet 
  published, 
  which 
  have 
  been 
  made 
  on 
  Li- 
  

   amalgams 
  indicate 
  a 
  behaviour 
  similar 
  to 
  that 
  observed 
  on 
  

   Ca-amalgams. 
  

  

  S. 
  Werner 
  % 
  has 
  observed 
  a 
  similar, 
  though 
  much 
  smaller, 
  

   displacement 
  of 
  the 
  maximum 
  wave-length 
  capable 
  of 
  

   liberating 
  electrons 
  on 
  Pt 
  and 
  Cu. 
  Under 
  any 
  circum- 
  

   stances 
  it 
  must 
  be 
  concluded 
  from 
  these 
  observations 
  that, 
  

   even 
  on 
  such 
  well-defined 
  surfaces 
  as 
  metals 
  distilled 
  in 
  a 
  

   vacuum 
  would 
  seem 
  to 
  have, 
  the 
  quantity 
  p, 
  the 
  energy 
  of 
  

   separation 
  of 
  the 
  electrons, 
  cannot 
  be 
  satisfactorily 
  measured. 
  

   The 
  expediency 
  of 
  any 
  attempt 
  to 
  bring 
  the 
  results 
  obtained 
  

   for 
  p 
  into 
  relationship 
  with 
  the 
  heat 
  of 
  vaporization 
  of 
  the 
  

   electrons 
  as 
  derived 
  from 
  Richardson's 
  thermionic 
  theory 
  § 
  

   is 
  therefore 
  very 
  questionable. 
  At 
  all 
  events, 
  it 
  would 
  seem 
  

   entirely 
  inadmissible 
  to 
  calculate 
  by 
  this 
  method 
  the 
  energy 
  

   of 
  separation 
  for 
  a 
  metal, 
  and 
  from 
  this 
  by 
  extrapolation 
  to 
  

   conclude 
  as 
  to 
  the 
  correctness 
  or 
  non-correctness 
  of 
  Einstein's 
  

   formula, 
  as 
  Compton 
  has 
  done.. 
  Especially 
  is 
  this 
  the 
  case 
  

   since 
  one 
  would 
  thereby 
  be 
  led 
  to 
  the 
  conclusion 
  that 
  K 
  

   should 
  cease 
  to 
  be 
  photoelectrically 
  sensitive 
  at 
  A 
  = 
  600 
  {ip, 
  ||, 
  

   whereas 
  Elster 
  & 
  Greitel 
  H 
  in 
  an 
  extensive 
  investigation 
  have 
  

   followed 
  the 
  — 
  almost 
  certainly 
  normal 
  — 
  emission 
  of 
  K 
  into 
  

   the 
  infra-red. 
  

  

  Summary. 
  

  

  From 
  the 
  experimental 
  data 
  at 
  present 
  known, 
  it 
  may 
  be 
  

   regarded 
  as 
  pretty 
  firmly 
  established 
  that 
  the 
  long-wave 
  

   limit 
  of 
  the 
  normal 
  photoelectric 
  effect 
  furnishes 
  a 
  measure 
  

   of 
  the 
  binding 
  force 
  between 
  the 
  electrons 
  and 
  the 
  illumi- 
  

   nated 
  molecule. 
  On 
  the 
  other 
  hand, 
  any 
  attempt 
  to 
  formulate 
  

   this 
  relation 
  quantitatively 
  is 
  met 
  with 
  the 
  difficulty 
  that 
  the 
  

   values 
  for 
  the 
  long-wave 
  limits 
  of 
  the 
  normal 
  photoelectric 
  

  

  * 
  R. 
  Pohl 
  & 
  P. 
  Pringsheim, 
  Verh. 
  d. 
  D. 
  Phys. 
  Ges. 
  xv. 
  p. 
  625 
  (1913). 
  

   t 
  R. 
  Pohl 
  & 
  P. 
  Pringsheim, 
  Verh. 
  d. 
  D. 
  Phys. 
  Ges. 
  xv. 
  p. 
  431 
  (1913). 
  

   X 
  S. 
  Werner, 
  Arkiv 
  for 
  Mathematik, 
  Astronomie, 
  och 
  Fysik, 
  viii. 
  

   No. 
  27, 
  Upsala, 
  1912. 
  

  

  § 
  0. 
  Richardson, 
  Phil. 
  Mag. 
  xxlv. 
  p. 
  570 
  (1912). 
  

  

  i! 
  K. 
  T. 
  Compton, 
  Phys. 
  Rev. 
  i. 
  p. 
  382 
  (1913). 
  

  

  % 
  J. 
  Elster 
  & 
  H. 
  Geitel, 
  Phys. 
  Zs. 
  xii. 
  p. 
  758 
  (1911). 
  

  

  