﻿336 
  Mr. 
  T. 
  Preston 
  on 
  Radiation 
  Phenomena 
  

  

  These 
  numbers, 
  although 
  they 
  possess 
  only 
  a 
  rough 
  accur- 
  

   racy, 
  are 
  yet 
  sufficient 
  to 
  show 
  that 
  for 
  both 
  these 
  metals 
  the 
  

   effect 
  at 
  first 
  increases 
  as 
  the 
  wave-length 
  diminishes, 
  and, 
  in 
  

   a 
  parallel 
  manner, 
  after 
  rising 
  to 
  a 
  maximum, 
  gradually 
  

   diminishes. 
  The 
  measurements 
  were 
  made 
  on 
  a 
  photograph 
  

   taken 
  from 
  a 
  spark 
  passing 
  between 
  a 
  cadmium 
  electrode 
  and 
  

   a 
  zinc 
  electrode, 
  so 
  that 
  the 
  lines 
  of 
  both 
  substances 
  were 
  

   taken 
  under 
  exactly 
  the 
  same 
  circumstances. 
  They 
  there- 
  

   fore 
  represent 
  the 
  effects 
  produced 
  on 
  these 
  two 
  substances 
  

   by 
  the 
  same 
  magnetic 
  field. 
  

  

  Other 
  substances 
  were 
  studied 
  in 
  the 
  same 
  way 
  with 
  one 
  

   electrode 
  of 
  cadmium 
  or 
  zinc, 
  so 
  that 
  the 
  effects 
  produced 
  by 
  

   the 
  same 
  field 
  could 
  be 
  compared. 
  

  

  For 
  example, 
  in 
  the 
  case 
  of 
  tin 
  and 
  zinc 
  (one 
  electrode 
  of 
  

   each) 
  , 
  when 
  the 
  violet 
  line 
  of 
  zinc 
  4680 
  showed 
  a 
  widening 
  

   of 
  42, 
  in 
  the 
  units 
  used 
  above, 
  the 
  tin 
  lines 
  4525 
  and 
  3801 
  

   showed 
  widenings 
  amounting 
  to 
  21 
  and 
  13 
  respectively. 
  

   Thus 
  the 
  resolution 
  for 
  tin 
  is 
  about 
  half 
  as 
  much 
  * 
  as 
  for 
  zinc 
  

   or 
  cadmium. 
  

  

  Similar 
  results 
  apply 
  to 
  other 
  metals. 
  For 
  example, 
  

   measurements 
  made 
  on 
  the 
  spectrum 
  of 
  platinum 
  gave 
  a 
  

   separation 
  ranging 
  from 
  30 
  downwards. 
  The 
  magnetic 
  

   metals 
  iron 
  and 
  nickel 
  gave 
  separations 
  varying 
  from 
  18 
  

   downwards, 
  and 
  rhodium 
  gave 
  similar 
  results. 
  

  

  Many 
  other 
  substances 
  have 
  been 
  examined, 
  but 
  no 
  further 
  

   novelty 
  is 
  exhibited 
  by 
  them. 
  The 
  above 
  are 
  mentioned 
  

   merely 
  as 
  typical 
  elements. 
  For 
  splendour 
  and 
  variety 
  of 
  

   effect 
  throughout 
  the 
  whole 
  range 
  of 
  the 
  spectrum, 
  the 
  sub- 
  

   stances 
  calcium 
  and 
  barium 
  are 
  noteworthy. 
  

  

  These 
  results 
  do 
  not 
  point 
  to 
  any 
  parallel 
  between 
  the 
  

   magnetic 
  effect 
  and 
  the 
  pressure-effect 
  investigated 
  by 
  Messrs. 
  

   Humphreys 
  t 
  and 
  Mohler. 
  

  

  It 
  has 
  not 
  been 
  considered 
  necessary 
  to 
  refer 
  to 
  the 
  theo- 
  

   retical 
  explanation 
  of 
  this 
  magnetic 
  influence 
  on 
  the 
  spectral 
  

   lines, 
  as 
  Dr. 
  J. 
  Larmor 
  J 
  has 
  already 
  furnished 
  a 
  completely 
  

   satisfactory 
  explanation 
  of 
  the 
  typical 
  phenomena 
  on 
  the 
  basis 
  

  

  * 
  [Dr. 
  Zeeman 
  obtains 
  an 
  effect 
  for 
  the 
  tin 
  line 
  4585 
  which 
  is 
  much 
  

   greater 
  than 
  the 
  greatest 
  obtained 
  for 
  either 
  zinc 
  or 
  cadmium, 
  but 
  this 
  

   must 
  be 
  either 
  a 
  misprint 
  or 
  a 
  mistake. 
  The 
  line 
  4525 
  gives 
  a 
  well- 
  

   marked 
  sharp 
  triplet, 
  and 
  lends 
  itself 
  to 
  accurate 
  measurement, 
  but 
  the 
  

   line 
  4585 
  is 
  diffuse 
  on 
  both 
  sides 
  and 
  merely 
  becomes 
  more 
  diffuse 
  when 
  

   subjected 
  to 
  the 
  magnetic 
  field. 
  Hence, 
  although 
  considerably 
  broadened, 
  

   it 
  does 
  not 
  lend 
  itself 
  to 
  measurement, 
  even 
  when 
  a 
  nicol 
  is 
  interposed. 
  

   This 
  diffusive 
  broadening 
  occurs 
  in 
  many 
  other 
  cases 
  where 
  the 
  lines 
  

   have 
  the 
  character 
  of 
  air 
  lines. 
  — 
  Cf. 
  Zeeman, 
  Phil. 
  Mag., 
  Feb. 
  1898.J 
  

  

  t 
  ' 
  A 
  strophysical 
  Journal, 
  1 
  1897. 
  

  

  % 
  Phil. 
  Mag. 
  xliv. 
  p. 
  503 
  (1897). 
  

  

  