﻿94: 
  Ewell 
  — 
  Rotatory 
  Polarization 
  of 
  LigJtt 
  m 
  

  

  been 
  made 
  in 
  only 
  two 
  azimuths. 
  The 
  actual 
  twist 
  of 
  the 
  rod 
  

   was 
  always 
  very 
  small, 
  not 
  exceeding 
  two 
  degrees. 
  The 
  results 
  

   indicate 
  a 
  rotation 
  in 
  the 
  opposite 
  direction 
  to 
  the 
  twist 
  which 
  

   becomes 
  very 
  pronounced 
  when 
  the 
  twist 
  is 
  large. 
  

  

  To 
  illustrate 
  these 
  observations, 
  the 
  readings 
  in 
  experiments 
  

   14 
  and 
  16 
  are 
  given 
  in 
  detail 
  in 
  Table 
  II. 
  The 
  first 
  column 
  

   gives 
  the 
  azimuth, 
  that 
  is, 
  the 
  angle 
  between 
  the 
  initial 
  plane 
  

   of 
  polarization 
  and 
  an 
  arbitrary 
  radius 
  of 
  the 
  glass 
  cylinder; 
  

   the 
  last 
  column 
  the 
  mean 
  of 
  the 
  preceding 
  tive 
  readings 
  in 
  

   units 
  of 
  the 
  instrumental 
  scale. 
  The 
  irregularity 
  in 
  the 
  read- 
  

   ings 
  for 
  a 
  constant 
  azimuth 
  is 
  due 
  to 
  the 
  opacity 
  and 
  lack 
  of 
  

   homogeneity 
  of 
  the 
  cylinder, 
  which 
  made 
  the 
  setting 
  of 
  the 
  

   compensator 
  somewhat 
  rough, 
  and 
  the 
  variation 
  in 
  different 
  azi- 
  

   muths 
  is 
  due 
  to 
  double 
  refraction. 
  Although 
  there 
  are 
  these 
  

   large 
  variations 
  I 
  think 
  the 
  final 
  means 
  have 
  a 
  qualitative 
  

   value. 
  The 
  diameter 
  of 
  this 
  glass 
  cylinder 
  was 
  7*55'"'°. 
  

  

  Glass 
  is 
  an 
  unsatisfactory 
  material 
  for 
  these 
  experiments 
  

   since 
  it 
  breaks 
  easily 
  and 
  usually 
  shows 
  double 
  refraction, 
  so 
  

   that 
  observations 
  are 
  difficult. 
  Agar 
  agar, 
  gum 
  sandarach, 
  

   gum 
  Arabic, 
  Burgundy 
  pitch, 
  borax 
  glass 
  and 
  gelatine 
  were 
  

   carefully 
  tried, 
  but 
  gelatine 
  alone 
  was 
  found 
  satisfactory. 
  

  

  Square 
  glass 
  plates 
  were 
  cemented 
  to 
  the 
  ends 
  of 
  moderately 
  

   heavy 
  but 
  soft 
  rubber 
  tubes 
  a 
  few 
  centimeters 
  long 
  and 
  12"""^ 
  

   external 
  diameter- 
  Gelatine 
  was 
  reduced 
  to 
  a 
  jelly 
  by 
  adding 
  a 
  

   suitable 
  quantity 
  of 
  water, 
  with 
  gentle 
  heat, 
  and 
  poured 
  into 
  

   these 
  tubes 
  through 
  a 
  slit 
  in 
  the 
  side 
  and 
  allowed 
  to 
  cool. 
  One 
  

   of 
  these 
  square 
  glass 
  caps 
  was 
  placed 
  in 
  a 
  square 
  aperture 
  at 
  

   one 
  end 
  of 
  a 
  rigid 
  frame. 
  Over 
  the 
  other 
  glass 
  plate 
  was 
  

   slipped 
  a 
  circular 
  wooden 
  disk 
  with 
  an 
  opening 
  in 
  the 
  center 
  

   slightly 
  larger 
  than 
  the 
  glass 
  cap. 
  The 
  jelly 
  tubes 
  were 
  

   twisted 
  by 
  turning 
  this 
  wooden 
  disk 
  in 
  the 
  frame. 
  When 
  the 
  

   proper 
  torsion 
  had 
  been 
  secured 
  the 
  disk 
  was 
  clamped 
  and 
  the 
  

   position 
  of 
  the 
  analyzer 
  read 
  for 
  sixteen 
  different 
  azimuths 
  of 
  

   the 
  frame 
  relative 
  to 
  the 
  initial 
  plane 
  of 
  polarization. 
  The 
  

   edge 
  of 
  the 
  disk 
  was 
  graduated 
  and 
  enabled 
  one 
  to 
  determine 
  

   quite 
  accurately 
  the 
  angle 
  of 
  torsion. 
  The 
  jelly 
  was 
  examined 
  

   with 
  a 
  polari 
  meter, 
  the 
  polarizer 
  of 
  which 
  was 
  a 
  reflecting 
  sur- 
  

   face 
  of 
  black 
  glass 
  and 
  the 
  analyzer 
  a 
  Nicol 
  mounted 
  on 
  a 
  

   graduated 
  circle. 
  A 
  biquartz 
  giving 
  the 
  sensitive 
  tint 
  was 
  

   placed 
  above 
  the 
  polarizing 
  surface, 
  and 
  the 
  substance 
  to 
  be 
  

   examined 
  between 
  the 
  biquartz 
  and 
  the 
  Nicol. 
  The 
  jelly 
  must 
  

   be 
  supported 
  in 
  flexible 
  tubes 
  of 
  considerable 
  stiffness. 
  Inde- 
  

   pendent 
  cylinders 
  of 
  jelly 
  were 
  tried, 
  and 
  jelly 
  in 
  thin 
  rubber 
  

   tubes, 
  but 
  the 
  weight 
  of 
  the 
  jelly 
  and 
  its 
  freedom 
  of 
  motion 
  

   produced 
  such 
  double 
  refraction 
  that 
  no 
  observations 
  were 
  

   possible. 
  The 
  independent 
  cylinders 
  of 
  jelly 
  cracked 
  under 
  

   very 
  slight 
  torsion. 
  Thin 
  paper 
  tubes 
  were 
  tried 
  but 
  found 
  

   unsatisfactory. 
  

  

  