﻿162 
  C. 
  Bancs 
  — 
  2Iethods 
  in 
  Spectrum 
  Interferometry. 
  

  

  should 
  increase 
  similarly 
  to 
  '12 
  X 
  3*8 
  = 
  4'6 
  cm 
  . 
  The 
  plane 
  

   ruled 
  grating 
  (D 
  = 
  352 
  X 
  10" 
  6 
  cm.) 
  was 
  now 
  again 
  mounted 
  in 
  

   place 
  of 
  P 
  and 
  under 
  good 
  illumination 
  the 
  range 
  *48 
  cm 
  was 
  

   found 
  experimentally. 
  This 
  agrees 
  very 
  well 
  with 
  the 
  esti- 
  

   mated 
  value. 
  Moreover 
  on 
  close 
  inspection 
  it 
  is 
  discernible 
  

   that 
  the 
  linear 
  phenomenon 
  really 
  consists 
  of 
  extremely 
  eccen- 
  

   tric 
  ellipses 
  which 
  in 
  case 
  of 
  the 
  best 
  adjustment 
  manifest 
  the 
  

   very 
  sharp 
  arrowlike 
  forms. 
  It 
  also 
  enters 
  and 
  vanishes 
  in 
  

   multilinear 
  form, 
  though 
  the 
  lines 
  are 
  not 
  hair 
  lines. 
  Thus 
  

   the 
  assertion 
  that 
  increased 
  uniformity 
  of 
  wave 
  train 
  accounts 
  

   for 
  the 
  long 
  range 
  of 
  displacement 
  and 
  visibility 
  in 
  case 
  of 
  the 
  

   grating 
  is 
  not 
  warranted. 
  

  

  [To 
  BE 
  CONTINUED.] 
  

  

  Brown 
  University, 
  

   Providence, 
  E. 
  I. 
  

  

  