﻿392 
  

  

  Dr. 
  H. 
  Stansfield 
  on 
  

  

  comparison 
  in 
  their 
  original 
  form, 
  because 
  Gehrcke 
  and 
  

   Baeyer*, 
  Janickif, 
  and 
  Galitzin 
  and 
  WilipJ, 
  give 
  the 
  dis- 
  

   tances 
  from 
  the 
  centre 
  of 
  the 
  principal 
  line, 
  while 
  Fabry 
  and 
  

   Perot 
  §, 
  Baeyer 
  II 
  (in 
  a 
  later 
  paper), 
  and 
  Nagaoka^, 
  divide 
  

   the 
  principal 
  line 
  into 
  two 
  components 
  and 
  measure 
  the 
  

   distances 
  from 
  the 
  brighter 
  one. 
  

  

  Another 
  difficulty 
  in 
  the 
  comparison 
  is 
  that 
  the 
  values 
  

   obtained 
  by 
  Gehrcke 
  and 
  Baeyer, 
  and 
  later 
  by 
  Baeyer, 
  by 
  the 
  

   use 
  of 
  crossed 
  plane-parallel 
  plates, 
  are 
  systematically 
  higher 
  

   than 
  the 
  values 
  obtained 
  with 
  echelon 
  spectroscopes, 
  which 
  

   agree 
  fairly 
  well 
  amongst 
  themselves. 
  I 
  have 
  reduced 
  all 
  

   Baeyer's 
  intervals 
  5 
  per 
  cent., 
  and 
  the 
  earlier 
  values 
  of 
  

   Gehrcke 
  and 
  Baeyer 
  (the 
  means 
  of 
  three 
  sets 
  of 
  measurements 
  

   given 
  in 
  their 
  paper) 
  by 
  3 
  per 
  cent. 
  ; 
  and 
  it 
  will 
  be 
  seen 
  that, 
  

   apart 
  from 
  these 
  differences 
  in 
  the 
  constants, 
  the 
  two 
  inde- 
  

   pendent 
  methods 
  are 
  in 
  close 
  agreement. 
  

  

  Table 
  II. 
  — 
  Measurements 
  of 
  the 
  Green 
  Mercury-line 
  

  

  Spectrum. 
  

  

  The 
  distances 
  of 
  the 
  component 
  lines 
  from 
  the 
  component 
  of 
  

  

  shortest 
  wave-length 
  are 
  given 
  in 
  milli- 
  Angstrom 
  units. 
  

  

  Fabry 
  & 
  

   Perot. 
  

  

  Crossed 
  Plates. 
  

  

  Echelon 
  Spectroscopes. 
  

  

  Eeference 
  

   Numbers. 
  

  

  Gehrcke 
  

   & 
  Baeyer. 
  

  

  Baeyer. 
  

  

  Janicki. 
  

  

  Galitzin 
  

   &Wilip. 
  

  

  •01 
  A. 
  units 
  

  

  

  

  15 
  

  

  17 
  

  

  reduced 
  3 
  p.c. 
  

   

   126 
  

   169 
  

  

  reduced 
  5 
  p.c. 
  

  

  

  

  136 
  

  

  169 
  

  

  189 
  

  

  

  

  133 
  

   166 
  

  

  

   137 
  

   168 
  

   189 
  

  

  1 
  

   2 
  

   3 
  

  

  22 
  

  

  23 
  

  

  234 
  

  

  214 
  

  

  238 
  

  

  I 
  232 
  

  

  236 
  ■ 
  

  

  * 
  1 
  Central 
  

   5 
  jBand. 
  

  

  31 
  

   36 
  

  

  318 
  

   364 
  

  

  320 
  

   363 
  

   449 
  

  

  320 
  

   365 
  

  

  321 
  

   365 
  

  

  6 
  

  

  7 
  

   8 
  

  

  The 
  brightest 
  component 
  in 
  each 
  case 
  is 
  underlined. 
  

  

  * 
  F. 
  Gehrcke 
  and 
  O. 
  Von 
  Baeyer, 
  Annalen 
  der 
  Physik, 
  vol. 
  xx. 
  p. 
  269 
  

   (1906). 
  t 
  L. 
  Janicki, 
  Annalen 
  der 
  PMjsik, 
  vol. 
  xix. 
  p. 
  36 
  (1906). 
  

  

  ;|: 
  Fiirst 
  B. 
  Galitzin 
  und 
  J. 
  Wilip, 
  Memoires 
  de 
  VAcademie 
  Impei-iale 
  

   des 
  Sciences 
  de 
  St. 
  Petersbourff, 
  s6y. 
  8, 
  vol. 
  xxii. 
  no. 
  1 
  (1906). 
  

  

  § 
  Astrophysical 
  Journal, 
  xv. 
  p. 
  218 
  (1902). 
  

  

  II 
  0. 
  V. 
  Baeyer, 
  Verhandlungen 
  der 
  Deutschen 
  Physikalischen 
  Geselhchaft, 
  

   ix. 
  no. 
  4, 
  p. 
  84 
  (1907). 
  ^!" 
  Nagaoka, 
  ' 
  Nature,' 
  vol. 
  Ixxvii. 
  p. 
  582 
  (1908). 
  

  

  