﻿and 
  Anomalous 
  Dispersion 
  of 
  Mercury 
  Vapour. 
  24^ 
  

   Anomalous 
  Dispersion 
  and 
  Magnetic 
  Rotation, 
  

  

  Strong 
  anomalous 
  dispersion 
  has 
  been 
  found 
  at 
  the 
  2536 
  

   line, 
  as 
  shown 
  in 
  fig. 
  8, 
  PI. 
  VII. 
  These 
  photographs 
  were 
  

   made 
  by 
  the 
  method 
  of 
  crossed 
  prisms 
  in 
  the 
  manner 
  which 
  

   I 
  have 
  employed 
  in 
  the 
  study 
  of 
  sodium 
  vapour. 
  The 
  

   mercury 
  was 
  placed 
  in 
  a 
  long 
  steel 
  tube, 
  closed 
  by 
  quartz 
  

   windows 
  and 
  heated 
  along 
  the 
  under 
  side 
  by 
  a 
  row 
  of 
  small 
  

   flames. 
  As 
  will 
  be 
  seen 
  from 
  the 
  photographs, 
  the 
  curvature 
  

   of 
  the 
  spectrum 
  is 
  much 
  more 
  marked 
  on 
  the 
  short-wave- 
  

   length 
  side 
  of 
  the 
  band, 
  which 
  is 
  the 
  steep 
  side. 
  A 
  quanti- 
  

   tative 
  study 
  of 
  the 
  dispersion 
  of 
  the 
  vapour 
  will 
  be 
  made 
  

   next 
  year, 
  by 
  an 
  interferometer 
  method, 
  which 
  will 
  doubtless 
  

   be 
  of 
  considerable 
  value 
  in 
  connexion 
  with 
  the 
  theory 
  of 
  

   dispersion, 
  for 
  it 
  will 
  be 
  possible 
  to 
  determine 
  the 
  exact 
  

   density 
  of 
  the 
  vapour, 
  the 
  length 
  of 
  the 
  column, 
  and 
  its 
  

   temperature, 
  which 
  was 
  never 
  possible 
  in 
  the 
  case 
  of 
  sodium 
  

   vapour. 
  The 
  determination 
  of 
  the 
  dispersion 
  curve 
  will 
  also 
  

   be 
  extremely 
  interesting 
  on 
  account 
  of 
  the 
  asymmetrical 
  

   nature 
  of 
  the 
  absorption-band. 
  

  

  The 
  magnetic 
  rotation 
  of 
  the 
  plane 
  of 
  polarization 
  was 
  

   also 
  investigated 
  in 
  the 
  vicinity 
  of 
  the 
  2536 
  line. 
  The 
  effect 
  

   of 
  the 
  absorption-band 
  upon 
  the 
  rotation 
  was 
  very 
  marked 
  

   on 
  the 
  short 
  wave-length 
  side, 
  but 
  there 
  was 
  little 
  or 
  no 
  

   increase 
  on 
  the 
  other 
  side, 
  doubtless 
  due 
  to 
  the 
  broadening 
  

   of 
  the 
  band 
  in 
  this 
  direction. 
  The 
  light 
  from 
  the 
  cadmium 
  

   spark 
  was 
  passed 
  through 
  a 
  polarizing 
  prism 
  (Foucault), 
  

   then 
  through 
  the 
  quartz 
  bulb 
  between 
  the 
  poles 
  of 
  the 
  electro- 
  

   magnet, 
  a 
  Fresnel 
  biquartz 
  parallelepiped, 
  and 
  a 
  second 
  

   polarizing 
  prism, 
  the 
  image 
  of 
  the 
  fringes 
  formed 
  by 
  the 
  

   Fresnel 
  parallelepiped 
  being 
  focussed 
  on 
  the 
  slit 
  of 
  the 
  quartz 
  

   spectrograph. 
  Xicol 
  prisms 
  cannot 
  be 
  used 
  for 
  the 
  ultra- 
  

   violet 
  on 
  account 
  of 
  the 
  absorption 
  by 
  the 
  film 
  of 
  Canada 
  

   balsam. 
  The 
  direction 
  of 
  the 
  rotation 
  resulting 
  from 
  the 
  

   2536 
  line 
  was 
  the 
  same 
  as 
  for 
  the 
  D 
  lines 
  of 
  sodium^ 
  from 
  

   which 
  we 
  may 
  infer 
  that 
  the 
  line 
  is 
  due 
  to 
  negative 
  

   electrons. 
  

  

  A 
  further 
  study 
  of 
  the 
  dispersion 
  and 
  magneto-optics 
  of 
  

   the 
  vapour 
  will 
  be 
  commenced 
  as 
  soon 
  as 
  the 
  necessary 
  

   apparatus 
  of 
  fused 
  quartz 
  has 
  been 
  constructed. 
  A 
  wide 
  

   tube 
  with 
  plane-parallel 
  end-plates 
  also 
  of 
  fused 
  quartz 
  welded 
  

   directly 
  to 
  the 
  tube 
  is 
  being 
  made 
  by 
  Heraeus. 
  

  

  