﻿in 
  the 
  Magnetic 
  Field. 
  333 
  

  

  without 
  a 
  middle 
  line, 
  in 
  which 
  case 
  it 
  shows 
  as 
  a 
  doublet. 
  

   For 
  example, 
  if 
  the 
  vibration 
  is 
  restricted 
  to 
  one 
  plane, 
  and 
  

   if 
  this 
  plane 
  sets 
  itself 
  at 
  right 
  angles 
  to 
  the 
  lines 
  of 
  magnetic 
  

   force 
  under 
  the 
  influence 
  of 
  the 
  magnetic 
  field, 
  then 
  the 
  

   component 
  of 
  the 
  vibration 
  in 
  the 
  direction 
  of 
  the 
  lines 
  of 
  

   force 
  will 
  be 
  zero, 
  and 
  the 
  middle 
  line 
  will 
  vanish 
  from 
  the 
  

   triplet. 
  If, 
  on 
  the 
  other 
  hand, 
  the 
  complete 
  vibration 
  should 
  

   set 
  itself 
  parallel 
  to 
  the 
  lines 
  of 
  force, 
  then 
  the 
  side 
  lines 
  of 
  

   the 
  triplet 
  would 
  vanish, 
  or, 
  in 
  other 
  words, 
  the 
  spectral 
  line 
  

   would 
  be 
  unaffected 
  by 
  the 
  magnetic 
  field. 
  It 
  is 
  clear, 
  there- 
  

   fore, 
  that 
  the 
  study 
  of 
  the 
  way 
  in 
  which 
  the 
  spectral 
  lines 
  are 
  

   affected 
  by 
  the 
  magnetic 
  field 
  is 
  likely 
  to 
  throw 
  light 
  on 
  the 
  

   character 
  of 
  the 
  molecular 
  vibrations, 
  

  

  The 
  Magnetic 
  Substances. 
  

  

  The 
  substances 
  which 
  one 
  would 
  expect 
  to 
  present 
  peculiari- 
  

   ties 
  in 
  this 
  way 
  are 
  iron 
  and 
  nickel, 
  which, 
  if 
  they 
  retain 
  any 
  of 
  

   their 
  magnetic 
  properties 
  at 
  the 
  high 
  temperature 
  of 
  the 
  spark 
  

   produced 
  between 
  the 
  terminals 
  of 
  an 
  induction-coil, 
  should 
  

   exhibit 
  some 
  characteristic 
  behaviour 
  in 
  the 
  magnetic 
  field. 
  

   I 
  was 
  led 
  to 
  expect, 
  indeed, 
  that 
  many, 
  if 
  not 
  all, 
  of 
  the 
  iron 
  

   lines 
  would 
  be 
  resolved 
  into 
  doublets 
  rather 
  than 
  triplets 
  when 
  

   the 
  spark 
  is 
  viewed 
  across 
  the 
  field. 
  I 
  found 
  it 
  no 
  easy 
  matter, 
  

   however, 
  with 
  the 
  magnetic 
  field 
  at 
  my 
  disposal 
  to 
  resolve 
  the 
  

   iron 
  lines 
  into 
  anything 
  : 
  in 
  the 
  first 
  place 
  because 
  the 
  effect 
  

   is 
  much 
  smaller 
  (about 
  one-half) 
  for 
  iron 
  than 
  for 
  the 
  

   4678 
  line 
  of 
  cadmium 
  or 
  zinc 
  ; 
  and 
  in 
  the 
  second 
  place, 
  

   because 
  it 
  is 
  not 
  possible 
  to 
  work 
  with 
  the 
  pole-pieces 
  of 
  the 
  

   magnet 
  so 
  close 
  together 
  when 
  the 
  spark 
  is 
  passed 
  from 
  a 
  

   solution 
  of 
  a 
  salt 
  as 
  when 
  it 
  is 
  passed 
  between 
  small 
  metal 
  

   electrodes. 
  But 
  in 
  the 
  case 
  of 
  a 
  highly-magnetic 
  substance 
  

   like 
  iron, 
  the 
  metal 
  becomes 
  almost 
  unmanageable 
  in 
  a 
  power- 
  

   ful 
  magnetic 
  field, 
  and 
  so 
  it 
  happened 
  that 
  in 
  my 
  first 
  attempts 
  

   I 
  was 
  not 
  successful 
  in 
  resolving 
  the 
  iron 
  lines 
  into 
  either 
  

   doublets 
  or 
  triplets 
  ; 
  yet, 
  even 
  at 
  this 
  stage, 
  I 
  observed 
  two 
  or 
  

   three 
  lines 
  converted 
  into 
  what 
  I 
  considered 
  doublets. 
  Finally, 
  

   I 
  succeeded 
  in 
  resolving 
  the 
  vast 
  majority 
  of 
  the 
  lines 
  of 
  iron 
  

   by 
  enclosing 
  pieces 
  of 
  iron 
  wire 
  in 
  small 
  glass 
  tubes, 
  so 
  that 
  

   the 
  ends 
  of 
  the 
  wire 
  protruded 
  slightly 
  from 
  the 
  glass 
  where 
  

   the 
  spark 
  occurred. 
  The 
  pole-pieces 
  were 
  then 
  pushed 
  up 
  to 
  

   touch 
  the 
  glass 
  jackets, 
  and 
  the 
  spark 
  was 
  thus 
  obtained 
  in 
  a 
  

   very 
  strong 
  field, 
  in 
  fact 
  in 
  a 
  field 
  strong 
  enough 
  to 
  resolve 
  

   the 
  majority 
  of 
  the 
  iron 
  lines 
  into 
  distinct 
  triplets, 
  showino- 
  

   that 
  these 
  vibrations 
  possess 
  freedom 
  in 
  the 
  magnetic 
  field 
  

   (at 
  the 
  temperature 
  of 
  the 
  spark) 
  ; 
  but, 
  in 
  addition 
  to 
  this, 
  

   Phil. 
  Mag. 
  S. 
  5. 
  Vol. 
  45. 
  No. 
  275. 
  April 
  1898. 
  2 
  A 
  

  

  