﻿in 
  the 
  Magnetic 
  Field* 
  329 
  

  

  lines, 
  and 
  so 
  be 
  able 
  to 
  attack 
  the 
  problem 
  of 
  throwing 
  the 
  

   lines 
  into 
  groups 
  and 
  series, 
  periodic 
  or 
  otherwise, 
  subject 
  to 
  

   some 
  general 
  law. 
  Although 
  the 
  photographs 
  which 
  I 
  have 
  

   already 
  obtained 
  throw 
  out 
  some 
  hints 
  as 
  to 
  the 
  direction 
  in 
  

   which 
  such 
  a 
  law 
  is 
  to 
  be 
  looked 
  for, 
  yet 
  nothing 
  can 
  be 
  suffi- 
  

   ciently 
  decided 
  till 
  a 
  careful 
  survey 
  has 
  been 
  made 
  and 
  every 
  

   line 
  resolved 
  and 
  measured. 
  

  

  The 
  Plate 
  accompanying 
  this 
  paper 
  (PI. 
  XXIII.) 
  has 
  been 
  

   reproduced 
  from 
  a 
  portion 
  of 
  a 
  negative 
  showing 
  the 
  lines 
  of 
  

   cadmium 
  and 
  zinc 
  taken 
  simultaneously. 
  For 
  this 
  purpose 
  an 
  

   electric 
  spark 
  from 
  an 
  induction-coil 
  was 
  passed 
  between 
  two 
  

   electrodes, 
  one 
  of 
  cadmium 
  and 
  one 
  of 
  zinc, 
  so 
  that 
  the 
  lines 
  of 
  

   the 
  two 
  metals 
  as 
  affected 
  by 
  the 
  magnetic 
  field 
  were 
  photo- 
  

   graphed 
  under 
  precisely 
  the 
  same 
  conditions. 
  The 
  lines 
  shown 
  

   are 
  the 
  blue 
  (4800) 
  and 
  the 
  violet 
  (4678) 
  lines 
  of 
  cadmium 
  

   together 
  with 
  the 
  adjacent 
  lines 
  (4811, 
  4722, 
  and 
  4680) 
  of 
  

   zinc. 
  The 
  Plate 
  shows 
  the 
  various 
  lines 
  unaffected, 
  that 
  is, 
  

   when 
  the 
  magnet 
  is 
  unexcited. 
  as 
  w 
  7 
  ell 
  as 
  the 
  effects 
  produced 
  

   by 
  the 
  magnetic 
  field. 
  The 
  bottom 
  row 
  AA 
  shows 
  all 
  the 
  lines 
  

   converted 
  into 
  doublets 
  when 
  the 
  source 
  of 
  light 
  is 
  viewed 
  

   along 
  the 
  lines 
  of 
  force. 
  The 
  next 
  row 
  BB 
  shoAvs 
  the 
  lines 
  

   unaffected, 
  i. 
  e. 
  with 
  no 
  magnetic 
  field. 
  

  

  The 
  next 
  row 
  CC 
  shows 
  the 
  appearance 
  presented 
  when 
  

   the 
  source 
  is 
  viewed 
  across 
  the 
  lines 
  of 
  force, 
  and 
  it 
  may 
  

   be 
  here 
  observed 
  that 
  while 
  the 
  line 
  4678 
  of 
  cadmium 
  and 
  

   the 
  adjacent 
  line 
  4680 
  of 
  zinc 
  are 
  both 
  converted 
  into 
  

   triplets, 
  the 
  line 
  4722 
  of 
  zinc 
  and 
  the 
  celebrated 
  blue 
  cadmium 
  

   line 
  4800 
  are 
  not 
  so 
  resolved 
  (in 
  appearance), 
  but 
  show 
  as 
  a 
  

   species 
  of 
  quartets 
  in 
  which 
  most 
  of 
  the 
  light 
  is 
  concentrated 
  

   in 
  the 
  side 
  lines. 
  Finally, 
  the 
  line 
  4811 
  of 
  zinc 
  shows 
  as 
  

   nothing 
  very 
  definite, 
  but 
  may 
  in 
  this 
  picture 
  be 
  described 
  as 
  

   a 
  hazy 
  doublet. 
  It 
  is 
  to 
  be 
  remarked, 
  however, 
  that 
  many 
  

   lines 
  show 
  as 
  perfectly 
  distinct 
  doublets 
  when 
  viewed 
  across 
  

   the 
  fines 
  of 
  force, 
  doublets 
  which 
  are 
  scarcely 
  rendered 
  any 
  

   clearer 
  by 
  the 
  interposition 
  of 
  a 
  nicol. 
  

  

  The 
  two 
  rows 
  at 
  the 
  top 
  of 
  the 
  plate 
  show 
  the 
  polarization 
  

   of 
  the 
  affected 
  lines. 
  In 
  these 
  a 
  nicol 
  has 
  been 
  inserted 
  in 
  the 
  

   path 
  of 
  the 
  beam 
  of 
  light. 
  In 
  the 
  top 
  row 
  T 
  EE 
  the 
  nicol 
  is 
  

   placed 
  w 
  r 
  ith 
  its 
  principal 
  plane 
  parallel 
  to 
  the 
  fines 
  of 
  force, 
  

   and 
  in 
  the 
  other 
  row 
  DD 
  with 
  its 
  principal 
  plane 
  at 
  right 
  

   angles 
  to 
  the 
  lines 
  of 
  force. 
  The 
  polarization 
  of 
  the 
  con- 
  

   stituents 
  is 
  thus 
  shown 
  to 
  be 
  complete 
  and 
  in 
  two 
  rectangular 
  

   planes. 
  

  

  The 
  foregoing 
  are 
  the 
  appearances 
  presented 
  on 
  the 
  photo- 
  

   graphic 
  plate. 
  In 
  addition 
  to 
  these 
  there 
  are 
  two 
  other 
  

   modifications 
  depending 
  on 
  a 
  fineness 
  of 
  detail 
  not 
  as 
  yet 
  

  

  