﻿366 
  Messrs. 
  F. 
  Bryson 
  and 
  J. 
  Logie 
  on 
  the 
  

  

  allowed 
  for. 
  The 
  present 
  theory 
  shows 
  that 
  

  

  Q,n 
  dp 
  

  

  a 
  relation 
  which 
  of 
  course 
  reduces 
  to 
  Becquerel's 
  formula 
  

   if 
  a 
  = 
  0. 
  

  

  It 
  might 
  also 
  be 
  mentioned 
  that 
  Disch 
  * 
  has 
  concluded 
  

   from 
  the 
  results 
  of 
  some 
  experiments 
  conducted 
  with 
  a 
  few 
  

   solutions, 
  that 
  the 
  course 
  of 
  the 
  magnetic 
  rotatory 
  dispersion 
  

   as 
  the 
  frequency 
  of 
  the 
  light 
  varies 
  is 
  similar 
  to 
  that 
  of 
  the 
  

   natural 
  rotatory 
  dispersion. 
  This 
  result 
  is 
  confirmed 
  by 
  the- 
  

   present 
  theory, 
  although 
  Disch's 
  deduction 
  that 
  the 
  two 
  are 
  

   actually 
  proportional 
  does 
  not 
  appear 
  to 
  be 
  exact. 
  

  

  The 
  present 
  simple 
  theory 
  has 
  of 
  course 
  limits 
  to 
  its 
  

   applicability. 
  For 
  example, 
  it 
  only 
  admits 
  of 
  a 
  rotation 
  in 
  

   a 
  definite 
  sense 
  with 
  respect 
  to 
  the 
  lines 
  of 
  force 
  in 
  the- 
  

   magnetic 
  field. 
  But, 
  as 
  in 
  the 
  case 
  with 
  solutions 
  of 
  iron 
  

   salts, 
  it 
  is 
  found 
  that 
  changes 
  in 
  concentration 
  may 
  produce 
  

   reversal 
  in 
  the 
  direction 
  of 
  rotation, 
  and 
  even 
  quite 
  neutral 
  

   solutions 
  of 
  active 
  salts 
  may 
  be 
  obtained. 
  The 
  extension 
  of 
  

   the 
  present 
  theory 
  to 
  include 
  cases 
  of 
  this 
  kind 
  is, 
  however, 
  

   fairly 
  obvious, 
  and 
  will 
  be 
  fully 
  discussed 
  in 
  a 
  future 
  

   communication. 
  

  

  XXVI. 
  On 
  the 
  Constitution 
  of 
  the 
  Mercury 
  Green 
  Line 
  

  

  O 
  = 
  5461 
  A.U.). 
  By 
  Frederick 
  F. 
  S. 
  Bryson, 
  M.A. 
  9 
  

   B.Sc, 
  Carnegie 
  Scholar, 
  and 
  John 
  Logie, 
  M.A., 
  B.Sc, 
  

   Fglinton 
  Fellow, 
  the 
  University 
  of 
  Glasgoio. 
  Communicated 
  

   ivith 
  an 
  Introductory 
  Note 
  by 
  Professor 
  A. 
  Gray, 
  F.R.S. 
  

  

  Note 
  by 
  Professor 
  Gray 
  (March 
  25, 
  1913). 
  — 
  In 
  a 
  paper 
  

   (Proc. 
  R. 
  S. 
  lxxii. 
  May 
  14, 
  1903) 
  by 
  Dr. 
  Walter 
  Stewart 
  

   and 
  myself 
  (with 
  Messrs. 
  E. 
  A. 
  Houstoun 
  and 
  D. 
  B. 
  

   McQuistan) 
  it 
  was 
  pointed 
  out 
  with 
  regard 
  to 
  the 
  green 
  line 
  

   of 
  mercury, 
  of 
  wave-length 
  5461 
  tenth-metres, 
  "that 
  what 
  

   appeared 
  in 
  an 
  ordinary 
  spectroscope 
  as 
  a 
  single 
  bright 
  line 
  

   was 
  in 
  fact 
  a 
  group 
  of 
  six 
  or 
  seven, 
  consisting 
  of 
  one 
  bright 
  

   line 
  with 
  a 
  triplet 
  of 
  faint 
  satellites 
  on 
  the 
  side 
  next 
  the 
  violet 
  

   end 
  of 
  the 
  spectrum, 
  and 
  a 
  triplet 
  or 
  at 
  least 
  a 
  doublet 
  of 
  

   faint 
  lines 
  on 
  the 
  other 
  side. 
  These 
  faint 
  lines 
  were 
  very 
  

   difficult 
  to 
  observe 
  and 
  to 
  determine, 
  and 
  the 
  measurements 
  

   of 
  wave-lengths 
  which 
  we 
  obtained 
  do 
  not 
  agree 
  with 
  those 
  

   supplied 
  to 
  Zeeman 
  by 
  MM. 
  Fabry 
  and 
  Perot. 
  The 
  lines, 
  

   however, 
  we 
  found 
  were 
  only 
  visible 
  in 
  our 
  tubes 
  when 
  the 
  

   discharge 
  had 
  been 
  kept 
  going 
  for 
  a 
  long 
  time, 
  and 
  when, 
  

  

  * 
  Ann. 
  d, 
  Phys. 
  xii. 
  p. 
  1153 
  (1903). 
  

  

  