﻿328 
  Mr. 
  T. 
  Preston 
  on 
  Radiation 
  Phenomena 
  

  

  purpose 
  it 
  is 
  necessary 
  to 
  obtain 
  high 
  resolving 
  power 
  and 
  a 
  

   magnetic 
  field 
  strong 
  enough 
  to 
  separate 
  completely 
  the 
  

   constituent 
  parts 
  of 
  the 
  modified 
  line, 
  so 
  that 
  each 
  can 
  be 
  

   observed 
  separately, 
  without 
  the 
  complications 
  attending 
  the 
  

   overlapping 
  of 
  the 
  others. 
  

  

  With 
  the 
  ordinary 
  U-shaped 
  electromagnet 
  at 
  my 
  disposal 
  

   I 
  had 
  considerable 
  difficulty 
  at 
  first 
  in 
  obtaining 
  any 
  effect 
  

   whatsoever, 
  even 
  a 
  broadening 
  of 
  the 
  spectral 
  lines. 
  How- 
  

   ever, 
  by 
  pushing 
  the 
  pole-pieces 
  very 
  close 
  together 
  and 
  

   working 
  with 
  a 
  very 
  short 
  spark 
  as 
  the 
  source 
  of 
  light, 
  I 
  

   was 
  able 
  to 
  obtain 
  not 
  only 
  a 
  distinct 
  broadening 
  but 
  ulti- 
  

   mately 
  a 
  complete 
  separation 
  of 
  the 
  constituents 
  of 
  the 
  

   affected 
  line 
  — 
  in 
  the 
  case 
  of 
  certain 
  lines 
  — 
  so 
  that 
  the 
  photo- 
  

   graphic 
  negative 
  showed 
  them 
  as 
  distinct 
  triplets 
  with 
  each 
  

   component 
  sharp 
  and 
  clear 
  when 
  viewed 
  through 
  any 
  ordinary 
  

   hand 
  magnifying-glass. 
  Finally, 
  with 
  a 
  more 
  powerful 
  

   magnet 
  of 
  the 
  same 
  U-shaped 
  type, 
  kindly 
  lent 
  to 
  me 
  by 
  

   the 
  Rt. 
  Rev. 
  Monsignor 
  Molloy, 
  I 
  was 
  able 
  to 
  obtain 
  photo- 
  

   graphs 
  which 
  showed 
  triplets 
  visible 
  to 
  the 
  naked 
  eye 
  without 
  

   any 
  magnification 
  whatever. 
  

  

  With 
  this 
  apparatus 
  I 
  have 
  made 
  a 
  general 
  survey 
  of 
  the 
  

   spectra 
  of 
  various 
  substances, 
  from 
  the 
  lowest 
  visible 
  to 
  the 
  

   highest 
  ultra-violet, 
  and 
  the 
  various 
  effects 
  which 
  I 
  have 
  so 
  

   far 
  observed 
  I 
  shall 
  now 
  briefly 
  describe. 
  

  

  General 
  Types 
  of 
  Effect 
  observed. 
  

  

  If 
  we 
  take 
  the 
  case 
  of 
  a 
  single 
  substance, 
  say 
  cadmium 
  or 
  

   zinc, 
  the 
  most 
  casual 
  observation 
  is 
  sufficient 
  to 
  show 
  that 
  the 
  

   effect 
  produced 
  varies 
  considerably 
  for 
  the 
  different 
  spectral 
  

   lines 
  ; 
  for 
  while 
  some 
  lines 
  are 
  clearly 
  separated 
  into 
  distinct 
  

   triplets, 
  others 
  are 
  not 
  so 
  resolved, 
  but 
  show 
  on 
  the 
  photo- 
  

   graphic 
  plate 
  as 
  " 
  quartets 
  " 
  or 
  u 
  doublets/' 
  the 
  source 
  being 
  

   viewed 
  across 
  the 
  lines 
  of 
  force, 
  i. 
  e. 
  while 
  some 
  lines 
  show 
  as 
  

   sharp 
  triplets, 
  others 
  (if 
  we 
  wish 
  to 
  express 
  it 
  so) 
  show 
  as 
  

   triplets 
  in 
  which 
  the 
  middle 
  line 
  is 
  replaced 
  by 
  two 
  fainter 
  

   lines, 
  while 
  others 
  appear 
  to 
  have 
  lost 
  the 
  middle 
  line 
  

   completely. 
  Further, 
  some 
  lines 
  on 
  the 
  same 
  plate, 
  that 
  is, 
  

   photographed 
  under 
  exactly 
  the 
  same 
  conditions, 
  show 
  only 
  a 
  

   very 
  small 
  broadening 
  ; 
  but 
  in 
  no 
  case 
  have 
  I 
  found 
  a 
  line 
  

   which 
  could 
  with 
  certainty 
  be 
  said 
  to 
  be 
  absolutely 
  unaffected 
  

   by 
  the 
  magnetic 
  field. 
  

  

  Thus, 
  while 
  some 
  lines 
  are 
  largely 
  affected, 
  others 
  (and 
  

   these 
  may 
  be 
  of 
  not 
  very 
  different 
  wave-length) 
  are 
  scarcely 
  

   affected 
  at 
  all. 
  With 
  a 
  stronger 
  magnetic 
  field, 
  however, 
  I 
  

   hope 
  to 
  resolve 
  these 
  latter, 
  and 
  so 
  obtain 
  the 
  data 
  necessary 
  

   to 
  a 
  full 
  comparison 
  of 
  the 
  effects 
  produced 
  on 
  all 
  the 
  spectral 
  

  

  