﻿tJie 
  Echelon 
  Spectroscope* 
  395 
  

  

  broader 
  and 
  brighter, 
  but 
  the 
  dark 
  space 
  between 
  4 
  and 
  5, 
  

   the 
  two 
  components 
  of 
  the 
  principal 
  line, 
  is 
  greatly 
  increased 
  

   (from 
  6 
  to 
  26 
  m.A.) 
  and, 
  being 
  no 
  longer 
  brighter 
  or 
  broader 
  

   than 
  the 
  rest, 
  they 
  look 
  like 
  ordinary 
  companion 
  lines. 
  

  

  The 
  " 
  side-on 
  " 
  spectrum 
  of 
  the 
  Bastian 
  lamp 
  resembles- 
  

   more 
  nearly 
  that 
  given 
  by 
  the 
  Arons 
  lamp. 
  

  

  The 
  separation 
  of 
  the 
  components 
  of 
  the 
  principal 
  line 
  in 
  

   the 
  " 
  end-on 
  " 
  radiation 
  has 
  been 
  investigated 
  by 
  Galitzin 
  

   and 
  Wilip^, 
  who 
  observed 
  the 
  phenomenon 
  first 
  in 
  the 
  case 
  

   of 
  a 
  Geissler 
  tube 
  arranged 
  so 
  that 
  the 
  axis 
  of 
  the 
  discharge 
  

   was 
  normal 
  to 
  the 
  slit 
  plate. 
  

  

  Spectrum 
  of 
  the 
  Green 
  Mercury 
  line 
  given 
  hy 
  a 
  hot 
  

   Mercury 
  lamp. 
  

  

  Janickif 
  describes 
  the 
  broadening 
  of 
  the 
  components 
  of 
  

   the 
  green 
  and 
  yellow 
  mercury 
  lines 
  which 
  takes 
  place 
  when 
  

   a 
  mercury 
  lamp 
  is 
  allowed 
  to 
  become 
  sufficiently 
  hot, 
  and 
  a 
  

   peculiar 
  system 
  of 
  five 
  equidistant 
  bands 
  which 
  he 
  observed 
  

   when 
  the 
  original 
  components 
  of 
  the 
  lines 
  were 
  lost 
  in 
  a 
  

   continuous 
  spectrum. 
  Galitzin 
  and 
  WilipJ, 
  who 
  give 
  

   measurements 
  of 
  the 
  bands, 
  suggest 
  that 
  they 
  may 
  be 
  due 
  to 
  

   a 
  reversal 
  of 
  the 
  lines, 
  or 
  perhaps 
  to 
  some 
  peculiar 
  property 
  

   of 
  the 
  echelon 
  spectroscope. 
  

  

  The 
  theory 
  of 
  the 
  secondary 
  echelon 
  spectra 
  (see 
  page 
  388) 
  

   indicates 
  that 
  the 
  secondary 
  bands 
  would 
  be 
  w^ell 
  defined 
  in 
  

   a 
  short 
  continuous 
  spectrum, 
  and 
  it 
  seemed 
  probable 
  that 
  

   they 
  were 
  the 
  bands 
  which 
  Janicki 
  and 
  Galitzin 
  & 
  Wilip 
  

   observed. 
  

  

  I 
  have 
  tested 
  this 
  point 
  with 
  a 
  quartz-lamp 
  fitted 
  with 
  an 
  

   air-manometer, 
  similar 
  to 
  that 
  described 
  by 
  Galitzin 
  and 
  

   Wilip 
  §. 
  

  

  When 
  an 
  arc 
  is 
  started 
  with 
  the 
  lamp 
  cold, 
  the 
  central 
  

   line 
  (4 
  and 
  5 
  together) 
  and 
  all 
  the 
  companion 
  lines 
  are 
  at 
  

   first 
  plainly 
  visible, 
  but 
  the 
  pressure 
  in 
  the 
  lamp 
  increases 
  

   rapidly 
  and 
  the 
  broadening 
  and 
  coalescing 
  of 
  the 
  lines 
  

   soon 
  takes 
  place. 
  The 
  position 
  occupied 
  by 
  the 
  bright 
  

   central 
  line 
  in 
  the 
  various 
  orders 
  is 
  now 
  marked 
  by 
  a 
  dark 
  

   line, 
  probably 
  due 
  to 
  absorption. 
  As 
  the 
  companion 
  lines 
  

   become 
  merged 
  in 
  the 
  general 
  brightness 
  the 
  fine 
  secondary 
  

   bands 
  become 
  clearly 
  visible 
  in 
  all 
  the 
  bright 
  parts 
  of 
  the 
  

  

  * 
  Fiirst 
  B. 
  Galitzin 
  und 
  J. 
  Wilip, 
  " 
  Ueber 
  die 
  Eigenschaften 
  einiger 
  

   Emissionslinien 
  des 
  Quecksilberdampfes," 
  Memoires 
  de 
  I' 
  Academic 
  

   Imperiale 
  des 
  Sciences 
  de 
  St. 
  Fetersbourff, 
  86r. 
  8, 
  vol. 
  xxii. 
  no. 
  1 
  (1907). 
  

  

  t 
  Loc. 
  cit. 
  pp. 
  49- 
  55. 
  

  

  X 
  Loc. 
  cit. 
  pp. 
  34 
  & 
  76. 
  

  

  § 
  Loc. 
  cit. 
  p. 
  4. 
  

  

  