﻿Interference 
  Phenomena 
  of 
  Chlorate 
  of 
  Potash 
  Crystals. 
  535 
  

  

  Nicol 
  prisms 
  cannot 
  be 
  used 
  on 
  account 
  o£ 
  the 
  absorption 
  of 
  

   the 
  ultra-violet 
  by 
  the 
  Canada 
  balsam. 
  We 
  may, 
  however, 
  

   substitute 
  glycerine 
  for 
  the 
  balsam, 
  or 
  employ 
  the 
  Foucault 
  

   prism 
  with 
  its 
  air-fihn. 
  Both 
  methods 
  were 
  used. 
  The 
  

   curvature 
  of 
  the 
  fringes 
  at 
  the 
  ultra-violet 
  lines 
  was 
  very 
  

   slight 
  at 
  the 
  3303 
  line, 
  and 
  scarcely 
  discernible 
  at 
  the 
  2852 
  

   line, 
  but 
  it 
  was 
  in 
  the 
  same 
  direction 
  on 
  each 
  side 
  of 
  the 
  

   absorption 
  line, 
  and 
  in 
  the 
  same 
  absolute 
  direction 
  as 
  at 
  the 
  

   D 
  lines. 
  Nothing 
  has 
  as 
  yet 
  been 
  accomplished 
  with 
  the 
  

   lines 
  in 
  the 
  ultra-violet 
  channelled 
  spectrum, 
  and 
  I 
  feel 
  very 
  

   doubtful 
  about 
  getting 
  results 
  in 
  these 
  regions. 
  In 
  the 
  

   visible 
  spectrum, 
  as 
  I 
  have 
  already 
  shown 
  ^, 
  the 
  rotation 
  is 
  

   positive 
  at 
  some 
  of 
  the 
  lines 
  and 
  negative 
  at 
  others. 
  

  

  More 
  complete 
  data 
  regarding 
  this 
  point 
  will 
  appear 
  in 
  a 
  

   paper 
  which 
  will 
  appear 
  shortly 
  in 
  the 
  Astro-physical 
  Journal, 
  

   in 
  which 
  the 
  more 
  recent 
  results 
  obtained 
  by 
  Dr. 
  Hachett 
  

   and 
  myself 
  on 
  the 
  fluorescence 
  and 
  magnetic 
  rotation 
  of 
  the 
  

   vapour 
  will 
  be 
  described. 
  

  

  July 
  1908. 
  

  

  LX. 
  High 
  Purity 
  Interference 
  Phenomena 
  of 
  Chlorate 
  of 
  

   Potash 
  Crystals. 
  By 
  E. 
  "W. 
  WoOD 
  f. 
  

  

  [Plate 
  XV. 
  fig. 
  4.] 
  

  

  SOME 
  years 
  ago 
  I 
  endeavoured 
  to 
  prepare 
  large 
  crystal 
  

   laminse 
  of 
  chlorate 
  of 
  potash 
  for 
  the 
  purpose 
  of 
  isolating 
  

   spectrum 
  lines 
  by 
  reflexion 
  for 
  monochromatic 
  illumination 
  

   of 
  fluorescent 
  vapours. 
  The 
  experiments 
  resulted 
  in 
  only 
  

   moderate 
  success 
  ; 
  but 
  I 
  obtained 
  a 
  few 
  crystals 
  which 
  I 
  

   believe 
  showed 
  narrower 
  reflexion 
  maxima 
  than 
  any 
  that 
  

   have 
  been 
  previously 
  described. 
  

  

  One 
  flake, 
  measnring 
  about 
  6 
  mm. 
  on 
  a 
  side, 
  exhibited 
  

   total 
  reflexion 
  at 
  normal 
  incidence 
  of 
  a 
  region 
  of 
  the 
  spectrum 
  

   only 
  10 
  or 
  12 
  Angstrom 
  units 
  in 
  width, 
  that 
  is, 
  only 
  double 
  

   the 
  distance 
  between 
  the 
  D 
  lines. 
  The 
  spectrum 
  of 
  the 
  

   transmitted 
  light 
  exhibited 
  a 
  very 
  black 
  band 
  at 
  the 
  same 
  

   point, 
  and 
  of 
  the 
  same 
  width. 
  This 
  band 
  was 
  photographed, 
  

   after 
  having 
  been 
  brought 
  into 
  the 
  vicinity 
  of 
  the 
  D 
  lines 
  by 
  

   suitable 
  inclination 
  of 
  the 
  plate, 
  and 
  the 
  D 
  lines 
  themselves 
  

   impressed 
  on 
  the 
  plate 
  by 
  holding 
  a 
  sodium 
  flame 
  in 
  front 
  oi 
  

   the 
  slit 
  for 
  a 
  few 
  seconds. 
  The 
  photograph 
  is 
  reproduced 
  on 
  

   Plate 
  XV. 
  flg. 
  4, 
  spectrum 
  " 
  c." 
  The 
  position 
  of 
  the 
  D 
  lines 
  

  

  * 
  " 
  On 
  the 
  Existence 
  of 
  Positive 
  Electrons 
  in 
  the 
  Sodium 
  Atom," 
  

   Phil. 
  Mag. 
  Feb. 
  1908. 
  

  

  t 
  Communicated 
  by 
  the 
  Author. 
  

  

  