﻿252 
  Pierce 
  — 
  Application 
  of 
  the 
  Radio-Micrometer 
  

  

  Art. 
  XXI 
  Y. 
  — 
  Application 
  of 
  the 
  Radio- 
  Micrometer 
  to 
  the 
  

   Measurement 
  of 
  Short 
  Electric 
  Waves 
  ; 
  by 
  Gr. 
  W. 
  Pierce. 
  

  

  Klemencic* 
  first 
  made 
  use 
  of 
  the 
  thermal-junction 
  as 
  a 
  

   means 
  of 
  measuring 
  electric 
  waves. 
  His 
  device 
  consisted 
  of 
  

   two 
  thin 
  sheets 
  of 
  brass, 
  M, 
  10 
  cm 
  broad 
  and 
  30 
  cm 
  long, 
  placed 
  

   3 
  cm 
  apart 
  and 
  having 
  soldered 
  to 
  them 
  respectively 
  a 
  very 
  tine 
  

   platinum 
  and 
  a 
  very 
  fine 
  platinum-nickel 
  wire, 
  which 
  were 
  

   crossed 
  at 
  k 
  and 
  were 
  thence 
  conveyed 
  off 
  at 
  right 
  angles 
  and 
  

   soldered 
  at 
  their 
  other 
  ends 
  to 
  the 
  leads, 
  I, 
  of 
  a 
  sensitive 
  gal- 
  

   vanometer. 
  This. 
  resonating 
  system 
  was 
  fixed 
  at 
  the 
  focal 
  line 
  

   of 
  a 
  suitable 
  cylindric 
  l 
  

  

  metal 
  reflector. 
  Elec- 
  

   tric 
  oscillations 
  be- 
  

   tween 
  M 
  and 
  M 
  pro- 
  

   duce 
  heating 
  at 
  the 
  

   knot, 
  Jc, 
  which 
  gives 
  

   rise 
  to 
  a 
  thermo-elec- 
  

   tromotive 
  force 
  at 
  the 
  

   knot 
  and 
  consequently 
  

   to 
  a 
  current 
  through 
  

   the 
  galvanometer. 
  By 
  

   the 
  use 
  of 
  this 
  instru- 
  

   ment, 
  Klemencic 
  has 
  

   studied 
  the 
  reflection 
  

   of 
  electric 
  waves 
  from 
  metals 
  and 
  sulphur, 
  but 
  on 
  account 
  of 
  

   the 
  length 
  of 
  his 
  waves, 
  he 
  has 
  not 
  been 
  able 
  to 
  obtain 
  results 
  

   possessed 
  of 
  quantitative 
  accuracy. 
  

  

  Employing 
  a 
  similar 
  device 
  of 
  smaller 
  dimensions, 
  Colef 
  has 
  

   measured 
  the 
  coefficients 
  of 
  reflection 
  from 
  the 
  surfaces 
  of 
  

   water 
  and 
  alcohol 
  in 
  the 
  two 
  principal 
  azimuths, 
  and 
  from 
  these 
  

   coefficients 
  has 
  calculated, 
  by 
  the 
  use 
  of 
  Fresnel's 
  formulas, 
  

   the 
  index 
  of 
  refraction 
  and' 
  the 
  specific 
  inductive 
  capacity 
  

   of 
  these 
  substances. 
  Also, 
  later,;); 
  Cole 
  has 
  measured 
  by 
  the 
  

   us^ 
  of 
  a 
  thermal 
  junction 
  the 
  absorption 
  of 
  electric 
  waves 
  by 
  

   w.. 
  er 
  . 
  nd 
  alcohol. 
  ' 
  P. 
  Lebedew,§ 
  employing 
  a 
  slightly 
  different 
  

   form 
  of 
  thermal-junction, 
  has 
  worked 
  with 
  waves 
  of 
  still 
  smaller 
  

   dimensions, 
  and 
  has 
  obtained 
  important 
  results. 
  

  

  In 
  the 
  present 
  paper, 
  a 
  description 
  is 
  given 
  of 
  an 
  apparatus 
  

  

  * 
  Ignaz 
  Klemencic: 
  Ueber 
  die 
  Reflexion 
  von 
  Sfcrahlen 
  electrischer 
  Kraft. 
  Wied. 
  

   Ann., 
  xlv, 
  p. 
  62, 
  1892. 
  

  

  f 
  A. 
  C. 
  Cole: 
  Wied. 
  Ann., 
  lvii, 
  p. 
  290, 
  1896. 
  

  

  jCole: 
  Phys. 
  Review, 
  vol. 
  vii, 
  Nov., 
  1898. 
  

  

  § 
  Peter 
  Lebedew: 
  Doppelbrechung 
  der 
  Strahlen 
  electrischer 
  Kraft. 
  Wied. 
  

   Ann., 
  lvi, 
  p. 
  1, 
  1895. 
  

  

  