﻿240 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  the 
  Absorption 
  

  

  limits 
  on 
  the 
  plate. 
  The 
  bowing 
  at 
  ^^ 
  was 
  out 
  ot* 
  the 
  ques« 
  

   tion, 
  and 
  we 
  were 
  driven 
  to 
  adopt 
  the 
  positions 
  J 
  and 
  \ 
  

   from 
  the 
  bridge, 
  which 
  produce' 
  softer 
  passages. 
  

  

  Curves 
  38-40. 
  — 
  It 
  was 
  noticed 
  in 
  connexion 
  with 
  curves 
  

   26-28 
  that, 
  as 
  the 
  sound 
  of 
  the 
  string 
  approached 
  ?>'[?, 
  the 
  

   response 
  of 
  the 
  belly 
  w^as 
  very 
  powerful. 
  This 
  led 
  to 
  the 
  

   idea 
  that 
  5b, 
  or 
  some 
  note 
  near 
  it, 
  was 
  the 
  pitch 
  of 
  best 
  

   resonance 
  of 
  the 
  instrument. 
  A 
  French-horn 
  was 
  accord- 
  

   ingly 
  tried 
  with 
  its 
  bell 
  just 
  over 
  the 
  violin 
  belly 
  and 
  the 
  

   notes 
  aH, 
  hv^ 
  and 
  6t! 
  sounded 
  in 
  succession, 
  a 
  plate 
  being 
  shot 
  

   each 
  time. 
  The 
  string, 
  of 
  course, 
  did 
  not 
  respond, 
  being- 
  

   tuned 
  to 
  g 
  ; 
  it 
  therefore 
  shows 
  as 
  a 
  straight 
  black 
  line 
  on 
  the 
  

   prints. 
  The 
  belly's 
  motions 
  are, 
  however, 
  shown 
  by 
  curves 
  

   of 
  moderate 
  amplitude 
  in 
  prints 
  38 
  and 
  40 
  for 
  the 
  extreme 
  

   pitches 
  and 
  by 
  one 
  of 
  greater 
  amplitude 
  in 
  print 
  39 
  for 
  the 
  

   intermediate 
  pitch 
  of 
  61? 
  (say 
  244 
  per 
  second). 
  This 
  is 
  

   accordingly 
  the 
  pitch 
  of 
  the 
  instrument 
  as 
  a 
  resonator, 
  when 
  

   we 
  judge 
  it 
  by 
  the 
  vibrations 
  of 
  the 
  spot 
  of 
  the 
  belly 
  under 
  

   examination. 
  

  

  University 
  College, 
  Nottingham. 
  

   May 
  nth, 
  1909. 
  

  

  XXIX. 
  The 
  Ahsorption, 
  Fluorescence^ 
  Magnetic 
  Rotation 
  and 
  

   Anomalous 
  Dispersion 
  of 
  Mercury 
  Vapour. 
  By 
  R. 
  W. 
  

   Wood, 
  Professor 
  of 
  Experimental 
  Physics, 
  Johns 
  Hopkins 
  

   University 
  *. 
  

  

  [Plates 
  VII. 
  & 
  VIII.] 
  

  

  SHORTLY 
  after 
  Hartly's 
  observation 
  that 
  the 
  vapour 
  of 
  

   mercury 
  exhibited 
  fluorescence 
  under 
  the 
  stimulus 
  

   of 
  the 
  light 
  from 
  the 
  electric 
  spark, 
  I 
  commenced 
  a 
  careful 
  

   study 
  of 
  the 
  optical 
  properties 
  o£ 
  the 
  vapour, 
  in 
  the 
  hope 
  

   that 
  phenomena 
  analogous 
  to 
  those 
  which 
  have 
  been 
  observed 
  

   in 
  the 
  case 
  of 
  sodium 
  vapour 
  might 
  be 
  found. 
  Though 
  the 
  

   vapour 
  has 
  proved 
  disappointing 
  in 
  some 
  respects, 
  a 
  number 
  

   of 
  very 
  interesting 
  observations 
  have 
  been 
  made, 
  some 
  of 
  

   which 
  appear 
  to 
  be 
  quite 
  new. 
  

  

  I 
  have 
  already 
  described 
  the 
  remarkable 
  absorption-band 
  

   at 
  wave-length 
  2536, 
  which 
  is 
  probably 
  the 
  most 
  unsym- 
  

   raetrical 
  band 
  ever 
  observed, 
  and 
  the 
  modifications 
  produced 
  

   in 
  its 
  appearance 
  caused 
  by 
  the 
  admixture 
  of 
  any 
  chemically 
  

   inert 
  gas 
  (' 
  Astrophysical 
  Journal,'' 
  1907). 
  

  

  In 
  the 
  present 
  paper 
  I 
  shall 
  briefly 
  review 
  the 
  results 
  set 
  

   forth 
  in 
  the 
  above 
  note, 
  as 
  they 
  have 
  some 
  bearing 
  upon 
  the 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  