﻿374 
  

  

  Dr. 
  H. 
  Stansfield 
  on 
  

  

  With 
  the 
  prism 
  on 
  an 
  auxiliarj 
  spectroscope, 
  no 
  evidence 
  of 
  

   this 
  kind 
  is 
  obtained 
  ; 
  and 
  it 
  has 
  simply 
  been 
  assumed 
  in 
  

   some 
  cases 
  that 
  the 
  companion 
  lines 
  belonged 
  to 
  the 
  bright 
  

   central 
  line 
  nearest 
  to 
  them. 
  

  

  Peimaky 
  Action 
  of 
  the 
  Echelon 
  in 
  the 
  Direct 
  and 
  

   Eeversed 
  Positions. 
  

  

  Equations 
  for 
  the 
  Principal 
  Maxima. 
  

  

  The 
  theory 
  o£ 
  the 
  echelon 
  given 
  by 
  Michelson 
  * 
  for 
  the 
  

   case 
  of 
  light 
  falling 
  normally 
  on 
  the 
  larger 
  end, 
  has 
  been 
  

   extended 
  by 
  Galitzin 
  f, 
  who 
  has 
  investigated^ 
  both 
  by 
  calcu- 
  

   lation 
  and 
  experiment, 
  the 
  motion 
  and 
  changes 
  in 
  the 
  dispersion 
  

   of 
  the 
  spectra 
  when 
  the 
  echelon 
  is 
  rotated 
  through 
  small 
  angles 
  

   within 
  the 
  limits 
  of 
  two 
  or 
  three 
  degrees 
  on 
  either 
  side 
  of 
  the 
  

   normal 
  position. 
  As 
  the 
  theory 
  of 
  the 
  echelon 
  in 
  the 
  reversed 
  

   position 
  has 
  not, 
  as 
  far 
  as 
  I 
  know, 
  hitherto 
  been 
  considered, 
  

   a 
  comparison 
  will 
  be 
  made 
  below 
  with 
  the 
  theory 
  of 
  the 
  

   ordinary 
  action. 
  

  

  In 
  fig. 
  2 
  the 
  reversed 
  and 
  direct 
  cases 
  are 
  represented 
  

   diagrammatically. 
  The 
  rays 
  and 
  wave-fronts 
  drawn 
  with 
  full 
  

  

  * 
  A. 
  A. 
  Michelson, 
  Astrophysical 
  Journal, 
  viii. 
  pp. 
  36-47 
  (1898). 
  

   American 
  Journal 
  [4] 
  v. 
  pp. 
  216-217 
  (1898). 
  Journ. 
  de 
  Phys. 
  [31 
  viii. 
  

   pp. 
  305-314 
  (1899). 
  

  

  t 
  Fiirst 
  B. 
  Galitzin, 
  Bulletin 
  de 
  VAcademie 
  Imperiale 
  des 
  Sciences 
  de 
  

   St. 
  Petersbourg, 
  6 
  serie, 
  t. 
  xxiii. 
  pp. 
  67-118 
  (1906). 
  

  

  