﻿[ 
  DOG 
  ] 
  

  

  LXXVIII. 
  Line 
  Spectrum 
  from 
  Uncharged 
  Molecules. 
  

   By 
  Clement 
  D. 
  Child 
  *. 
  

  

  rf^HERE 
  has 
  been 
  much 
  discussion 
  as 
  to 
  whether 
  line 
  

   _l 
  spectra 
  are 
  produced 
  by 
  positive 
  ions, 
  or 
  by 
  the 
  

   molecules 
  which 
  result 
  from 
  the 
  recombination 
  of 
  positive 
  

   and 
  negative 
  ions. 
  Some 
  experiments 
  recently 
  performed 
  by 
  

   myself 
  appear 
  to 
  prove 
  that 
  the 
  spectrum 
  of 
  the 
  mercury 
  

   arc 
  comes 
  from 
  recombined 
  molecules. 
  These 
  experiments 
  

   are 
  described 
  in 
  the 
  following 
  paragraphs. 
  

  

  Description 
  of 
  Experiments. 
  — 
  When 
  a 
  tube 
  containing 
  

   a 
  mercury 
  arc 
  in 
  a 
  vacuum 
  is 
  connected 
  with 
  a 
  condensing 
  

   chamber 
  as 
  in 
  fig. 
  1, 
  the 
  stream 
  of 
  vapour 
  flowing 
  from 
  the 
  

  

  Fig-. 
  1. 
  

  

  arc 
  is 
  luminous 
  and 
  gives 
  a 
  line 
  spectrum. 
  As 
  far 
  as 
  could 
  

   be 
  determined 
  with 
  the 
  apparatus 
  at 
  my 
  command, 
  the 
  same 
  

   lines 
  are 
  shown 
  in 
  the 
  spectrum 
  of 
  this 
  vapour 
  as 
  in 
  that 
  of 
  

   the 
  arc 
  itself, 
  although 
  the 
  relative 
  intensity 
  of 
  the 
  lines 
  in 
  

   the 
  two 
  spectra 
  is 
  somewhat 
  different. 
  

  

  In 
  the 
  following 
  experiment 
  the 
  arc 
  was 
  placed 
  in 
  series 
  

   with 
  a 
  dynamo 
  D, 
  and 
  a 
  resistance 
  R. 
  There 
  was 
  a 
  tube 
  

   opening 
  into 
  T 
  and 
  connecting 
  at 
  P 
  with 
  a 
  Gaede 
  pump 
  

   and 
  a 
  drying-bath. 
  In 
  this 
  was 
  a 
  piece 
  of 
  wire 
  gauze 
  F, 
  

   rilling 
  the 
  cross-section 
  of 
  the 
  tube 
  and 
  connecting 
  to 
  the 
  

   resistance 
  R 
  at 
  a 
  movable 
  point 
  e, 
  so 
  that 
  it 
  could 
  be 
  

   given 
  any 
  desired 
  potential 
  wiih 
  respect 
  to 
  the 
  arc. 
  The 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  