﻿412 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  18 
  

  

  crystal, 
  remote 
  from 
  the 
  electrodes, 
  produces, 
  in 
  some 
  samples, 
  

   local 
  e.m.fs. 
  which 
  differ 
  in 
  magnitude 
  and 
  in 
  polarity. 
  

  

  Exposing 
  a 
  spot, 
  exhibiting 
  a 
  high 
  local 
  e.m.f., 
  to 
  an 
  equal 
  energy 
  

   spectrum, 
  an 
  electric 
  current 
  is 
  generated 
  which 
  is 
  a 
  function 
  of 
  the 
  

   intensity 
  and 
  the 
  wave-length 
  of 
  the 
  light 
  stimulus, 
  and 
  of 
  the 
  thick- 
  

   ness 
  of 
  the 
  crystal. 
  The 
  maximum 
  effect 
  was 
  produced 
  by 
  wave- 
  

   lengths 
  extending 
  from 
  0.6 
  to 
  0.8 
  micron, 
  and 
  no 
  e.m.f. 
  was 
  found 
  for 
  

   wave-lengths 
  greater 
  than 
  1 
  micron. 
  

  

  The 
  spots 
  exhibiting 
  local 
  e.m.fs., 
  caused 
  by 
  thermal 
  radiation 
  

   do 
  not 
  seem 
  to 
  coincide 
  always 
  with 
  the 
  spots 
  exhibiting 
  the 
  photo- 
  

   electrical 
  reactions 
  (change 
  in 
  resistance) 
  when 
  there 
  is 
  an 
  impressed 
  

   e.m.f. 
  ; 
  though 
  further 
  investigation 
  may 
  show 
  that 
  this 
  is 
  owing 
  to 
  

   the 
  fact 
  that 
  the 
  thermal 
  e.m.f. 
  effect 
  is 
  found 
  to 
  be 
  extremely 
  small 
  

   in 
  comparison 
  with 
  photoelectrical 
  reaction. 
  

  

  The 
  polarity 
  of 
  this 
  newly 
  observed 
  thermal 
  e.m.f. 
  may 
  be 
  photo- 
  

   negative 
  or 
  photopositive, 
  depending 
  upon 
  the 
  wave-length 
  of 
  the 
  

   thermal 
  radiation 
  stimulus 
  just 
  as 
  was 
  previously 
  observed 
  for 
  the 
  

   photoelectrical 
  reaction 
  (resistance 
  change) 
  when 
  there 
  is 
  an 
  external 
  

   e.m.f. 
  It 
  is 
  therefore 
  an 
  interesting 
  question 
  whether 
  the 
  so-called 
  

   photoelectrical 
  reactions 
  in 
  solids, 
  when 
  subjected 
  to 
  an 
  impressed 
  

   e.m.f., 
  are 
  an 
  amplification 
  of 
  the 
  e.m.fs. 
  produced 
  by 
  the 
  thermal 
  radia- 
  

   tion 
  but 
  without 
  an 
  impressed 
  e.m.f. 
  

  

  PHYSICS. 
  — 
  A 
  device 
  for 
  recording 
  electric 
  contact 
  using 
  an 
  electron 
  

   tube 
  generator 
  and 
  a 
  radio-frequency 
  spark. 
  '^ 
  Charles 
  T. 
  Zahn, 
  

   Princeton 
  University, 
  (Communicated 
  by 
  S. 
  W. 
  Stratton.) 
  

  

  It 
  is 
  sometimes 
  desirable 
  to 
  have 
  a 
  convenient 
  means 
  of 
  recording 
  

   an 
  electric 
  contact 
  of 
  relatively 
  short 
  duration, 
  of 
  the 
  order 
  of 
  one 
  

   thousandth 
  of 
  a 
  second. 
  For 
  a 
  particular 
  use 
  it 
  was 
  found 
  that 
  various 
  

   devices 
  which 
  have 
  been 
  used 
  heretofore 
  were 
  either 
  not 
  satisfactory 
  

   or 
  not 
  convenient. 
  It 
  was 
  suggested 
  that 
  the 
  use 
  of 
  the 
  three-electrode 
  

   electron 
  tube 
  generator 
  might 
  be 
  successful. 
  The 
  following 
  is 
  a 
  de- 
  

   scription 
  of 
  some 
  experiments 
  performed 
  at 
  the 
  radio 
  laboratory 
  of 
  

   the 
  Bureau 
  of 
  Standards 
  with 
  this 
  end 
  in 
  view, 
  and 
  is 
  given 
  here 
  simply 
  

   to 
  illustrate 
  a 
  new 
  experimental 
  method. 
  

  

  The 
  three-electrode 
  electron 
  tube 
  generator 
  was 
  used 
  as 
  a 
  source 
  

   of 
  radio-frequency 
  alternating 
  current 
  to 
  produce 
  a 
  radio-frequency 
  

  

  1 
  Published 
  by 
  permission 
  of 
  the 
  Director 
  of 
  the 
  Bureau 
  of 
  Standards 
  of 
  the 
  U. 
  S. 
  De- 
  

   partment 
  of 
  Commerce. 
  Received 
  September 
  19, 
  1922. 
  

  

  