﻿Anomalous 
  Dispersion 
  hy 
  Metallic 
  Vapours. 
  407 
  

  

  of 
  the 
  mass 
  of 
  the 
  sub-oceanic 
  sediments, 
  and 
  on 
  the 
  assump- 
  

   tion 
  of 
  a 
  mean 
  radioactivity 
  for 
  these 
  comparable 
  with 
  that 
  

   of 
  globigerina 
  ooze, 
  I 
  recently 
  arrived 
  at 
  a 
  total 
  of 
  about 
  

   10^ 
  tonnes 
  as 
  approximating 
  to 
  the 
  radium 
  rejected 
  by 
  the 
  

   ocean. 
  This 
  calculation 
  may 
  be 
  made 
  in 
  another 
  form 
  in 
  

   which 
  we 
  use 
  as 
  basis 
  the 
  quantity 
  of 
  rock 
  which 
  has 
  probably 
  

   been 
  denuded 
  from 
  the 
  primary 
  to 
  the 
  secondary 
  condition 
  

   and 
  the 
  estimated 
  difference 
  between 
  the 
  radium-content 
  of 
  

   igneous 
  and 
  sedimentary 
  rocks. 
  The 
  result 
  arrived 
  at 
  is 
  very 
  

   similar. 
  Presumably 
  all 
  this 
  radioactive 
  material 
  has 
  been 
  

   at 
  one 
  time 
  in 
  solution 
  or 
  suspension 
  in 
  the 
  ocean, 
  whose 
  

   waters, 
  for 
  all 
  that 
  we 
  could 
  have 
  anticipated, 
  might 
  have 
  

   possessed 
  a 
  content 
  of 
  radium 
  some 
  fifty 
  times 
  greater 
  than 
  

   the 
  figures 
  appear 
  to 
  indicate. 
  

  

  XLVI. 
  Anomalous 
  Dispersion 
  hy 
  Metallic 
  Vapours. 
  

   By 
  P. 
  V. 
  Bevan, 
  M.A., 
  Royal 
  Holloway 
  College 
  *. 
  

  

  [Plate 
  XIII.] 
  

  

  THE 
  experiments 
  of 
  Wood 
  on 
  sodium 
  vapour 
  and 
  the 
  

   anomalous 
  dispersion 
  of 
  a 
  beam 
  of 
  light 
  passing 
  through 
  

   it 
  have 
  provided 
  a 
  beautiful 
  example 
  of 
  this 
  effect 
  and 
  have 
  

   yielded 
  measurements 
  which 
  are 
  of 
  importance 
  for 
  the 
  general 
  

   theory 
  of 
  the 
  transmission 
  of 
  light 
  through 
  absorbing 
  media. 
  

   From 
  Wood's 
  experiments 
  it 
  appears 
  as 
  if 
  sodium 
  behaves 
  

   in 
  some 
  peculiar 
  way_, 
  the 
  metallic 
  vapour 
  retaining 
  its 
  form 
  

   even 
  when 
  it 
  is 
  in 
  a 
  high 
  vacuum. 
  This 
  statement 
  of 
  W^ood^s 
  

   is 
  perhaps 
  the 
  reason 
  why, 
  as 
  far 
  as 
  I 
  am 
  aware, 
  no 
  experi- 
  

   ments 
  of 
  a 
  similar 
  nature 
  have 
  been 
  made 
  with 
  other 
  metals. 
  

   The 
  author 
  of 
  this 
  communication 
  has 
  shown 
  f 
  that, 
  in 
  a 
  

   vacuum, 
  sodium 
  vapour 
  ceases 
  to 
  have 
  the 
  peculiar 
  property 
  

   of 
  not 
  diffusing 
  into 
  the 
  surrounding 
  space 
  and 
  that 
  it 
  behaves 
  

   just 
  as 
  one 
  would 
  expect, 
  diffusing 
  practically 
  instantaneously 
  

   to 
  the 
  colder 
  parts 
  of 
  the 
  tube 
  and 
  condensing 
  just 
  as 
  any 
  

   other 
  volatile 
  substance 
  would 
  do. 
  It 
  seems 
  that 
  the 
  sodium 
  

   cloud 
  of 
  Wood 
  cannot 
  exist 
  in 
  a 
  high 
  vacuum 
  and 
  that 
  it 
  

   probably 
  retains 
  its 
  definite 
  form 
  owing 
  to 
  temperature 
  

   effects, 
  the 
  boundary 
  being 
  a 
  layer 
  at 
  which 
  condensation 
  

   takes 
  place. 
  There 
  seeming 
  to 
  be 
  no 
  special 
  property 
  apper- 
  

   taining 
  to 
  sodium 
  in 
  this 
  way, 
  the 
  author 
  has 
  tried 
  by 
  a 
  

   similar 
  arrangement 
  to 
  detect 
  anomalous 
  dispersion 
  in 
  the 
  

   cases 
  of 
  other 
  metals 
  and 
  this 
  communication 
  is 
  to 
  give 
  the 
  

   results 
  with 
  two 
  other 
  alkali 
  metals, 
  lithium 
  and 
  potassium. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

   t 
  Camb. 
  Phil. 
  Soc. 
  Proc. 
  xiii. 
  p. 
  129. 
  

   2 
  E 
  2 
  

  

  