﻿H. 
  S. 
  Uhler 
  — 
  Note 
  vn 
  Paper 
  by 
  Ch. 
  Fabry. 
  143 
  

  

  Art. 
  IX. 
  — 
  Note 
  on 
  the 
  Paper 
  by 
  Ch. 
  Fabry 
  entitled: 
  

   "Methode 
  par 
  Immersion, 
  pour 
  la 
  Mesure 
  des 
  Indices 
  

   de 
  Refraction 
  des 
  Corps 
  Solides" 
  ; 
  by 
  H. 
  S. 
  Uhler. 
  

  

  The 
  article 
  referred 
  to 
  may 
  be 
  found 
  in 
  the 
  Journal 
  de 
  

   Physique, 
  9, 
  11, 
  January 
  1919. 
  A 
  brief 
  outline, 
  by 
  the 
  

   present 
  writer, 
  of 
  Fabry's 
  paper 
  is 
  also 
  given 
  on 
  a 
  later 
  

   page 
  of 
  this 
  number. 
  One 
  of 
  the 
  many 
  advantages, 
  — 
  

   mentioned 
  by 
  the 
  original 
  author,— 
  of 
  the 
  new 
  modifica- 
  

   tion 
  of 
  the 
  general 
  method 
  of 
  immersion 
  is 
  that 
  his 
  inno- 
  

   vation 
  requires 
  only 
  such 
  apparatus 
  as 
  may 
  be 
  found 
  

   in 
  every 
  well-equipped 
  physical 
  laboratory. 
  Since, 
  how- 
  

  

  

  R 
  

  

  N 
  / 
  ' 
  \ 
  N 
  

  

  

  V 
  

  

  / 
  n 
  \ 
  

  

  E 
  

  

  

  , 
  5-AV./ 
  \ 
  v 
  

  

  

  

  

  

  

  / 
  n 
  \ 
  

  

  ever, 
  Fabry's 
  formulae 
  and 
  calculations 
  are 
  restricted 
  to 
  

   standard 
  prisms 
  of 
  90° 
  refracting 
  angles, 
  as 
  accurate 
  60° 
  

   prisms 
  are 
  usually 
  associated 
  with 
  spectrometers, 
  and 
  as 
  

   no 
  proof 
  of 
  the 
  fundamental 
  power 
  series 
  (3) 
  is 
  given 
  in 
  

   the 
  original 
  article, 
  it 
  may 
  not 
  be 
  superfluous 
  to 
  present 
  

   the 
  following 
  proof 
  of 
  the 
  generalized 
  formula. 
  The 
  

   series 
  developed 
  below 
  will 
  be 
  useful 
  to 
  practical 
  opti- 
  

   cians 
  and 
  to 
  other 
  experimenters 
  who 
  desire 
  to 
  apply 
  

   Fabry's 
  method 
  to 
  tests 
  on 
  prisms 
  having 
  refracting 
  

   angles 
  either 
  greater 
  or 
  less 
  than 
  90°, 
  since 
  it 
  is 
  given 
  

   in 
  terms 
  of 
  the 
  more 
  general 
  refracting 
  angle 
  A. 
  

  

  The 
  standard 
  prism 
  is 
  so. 
  placed 
  that 
  its 
  refracting 
  

   edge 
  is 
  parallel 
  to 
  the 
  common 
  direction 
  of 
  the 
  slit 
  and 
  

   of 
  the 
  axis 
  of 
  rotation 
  of 
  the 
  telescope, 
  and 
  its 
  refracting 
  

  

  