﻿Long-wave 
  Limits 
  of 
  Normal 
  Photoelectric 
  Effect. 
  1017 
  

  

  instant 
  it 
  finds 
  itself 
  on 
  a 
  nodal 
  sphere, 
  and 
  if 
  it 
  is 
  con- 
  

   strained 
  to 
  remain 
  on 
  this 
  sphere 
  by 
  a 
  force 
  purely 
  radial, 
  

   then 
  the 
  magnetic 
  force 
  and 
  therefore 
  v 
  remains 
  constant, 
  but 
  

   owing 
  to 
  radiation 
  the 
  circular 
  orbit 
  continually 
  diminishes 
  

   until 
  all 
  the 
  kinetic 
  energy 
  is 
  radiated. 
  During 
  this 
  process 
  

   the 
  radiation 
  given 
  out 
  is 
  always 
  of 
  the 
  same 
  frequency 
  and 
  the 
  

   total 
  amount 
  of 
  it 
  given 
  out 
  is 
  hv. 
  The 
  energy 
  remaining 
  now 
  

   is 
  potential 
  and 
  further 
  radiation, 
  if 
  any, 
  is 
  of 
  a 
  different 
  

   type. 
  

  

  XOII. 
  On 
  the 
  Long-wave 
  Limits 
  of 
  the 
  Normal 
  Photoelectric 
  

   Effect. 
  By 
  Dr. 
  B,. 
  Pohl 
  and'Dr. 
  P. 
  Pringsheim 
  * 
  

  

  IT 
  was 
  with 
  the 
  purpose 
  of 
  discovering 
  the 
  relations 
  existing 
  

   between 
  the 
  photoelectric 
  properties 
  of 
  the 
  illuminated 
  

   molecules 
  and 
  their 
  other 
  characteristic 
  properties, 
  in 
  par- 
  

   ticular 
  their 
  chemical 
  behaviour, 
  that 
  the 
  investigations 
  on 
  

   the 
  photoelectric 
  effect 
  have 
  been 
  extended 
  to 
  a 
  rather 
  large 
  

   number 
  of 
  elements. 
  That 
  the 
  characteristic 
  frequency 
  of 
  

   the 
  selective 
  effect, 
  despite 
  uncertainties 
  in 
  the 
  position 
  of 
  

   the 
  resonance 
  maximum, 
  is 
  a 
  material 
  constant 
  related 
  to 
  

   the 
  atomic 
  radius 
  f 
  has 
  been 
  pretty 
  certainly 
  established. 
  

   But 
  in 
  the 
  normal 
  effect, 
  as 
  well, 
  a 
  constant 
  which 
  is 
  charac- 
  

   teristic 
  of 
  the 
  material 
  seems 
  to 
  enter. 
  In 
  connexion 
  with 
  

   Lenard's 
  { 
  pioneer 
  investigations 
  on 
  the 
  velocity 
  of 
  electronic 
  

   emission, 
  Einstein 
  § 
  in 
  1905 
  developed 
  a 
  theory 
  for 
  the 
  

   normal 
  effect 
  (the 
  selective 
  was 
  then 
  unknown) 
  in 
  which 
  

   such 
  a 
  characteristic 
  constant 
  occurs. 
  According 
  to 
  this 
  

   theory, 
  the 
  initial 
  velocity 
  of 
  the 
  electrons 
  for 
  a 
  given 
  

   frequency, 
  v, 
  is 
  given 
  by 
  an 
  equation 
  of 
  the 
  form 
  

  

  in 
  which 
  v 
  is 
  the 
  velocity 
  of 
  the 
  electrons 
  e 
  and 
  P 
  the 
  

   maximum 
  potential 
  to 
  which 
  the 
  illuminated 
  plate 
  becomes 
  

   charged. 
  Putting 
  p 
  = 
  hv 
  , 
  we 
  see 
  at 
  once 
  that 
  v 
  is 
  the 
  

   smallest 
  frequency 
  which 
  the 
  incident 
  light 
  can 
  have 
  and 
  

   liberate 
  electrons 
  with 
  a 
  velocity 
  v 
  = 
  0. 
  v 
  is 
  a 
  constant 
  

   characteristic 
  of 
  the 
  material 
  in 
  the 
  normal 
  effect. 
  

  

  * 
  Communicated 
  by 
  the 
  Authors. 
  

  

  t 
  v 
  is 
  probably 
  proportional 
  to 
  r 
  -1 
  . 
  

  

  % 
  Ph. 
  Lenard, 
  Ann. 
  d. 
  Phys. 
  viii. 
  p. 
  149 
  (1902). 
  

  

  § 
  A. 
  Einstein, 
  Ann. 
  d. 
  Phys. 
  xx. 
  p. 
  199 
  (1905). 
  

  

  Phil. 
  Mag. 
  S. 
  G. 
  Vol. 
  26. 
  No. 
  15G. 
  Dec. 
  1913. 
  3 
  Z 
  

  

  