﻿66 
  Mr. 
  W. 
  G. 
  Hormell 
  on 
  the 
  

  

  will 
  reveal 
  the 
  fact 
  that 
  in 
  every 
  case 
  there 
  is 
  a 
  gradual 
  

   increase 
  as 
  the 
  wave-length 
  decreases, 
  even 
  including 
  the 
  

   light-wave. 
  These 
  results 
  certainly 
  indicate 
  the 
  analogous 
  

   behaviour 
  of 
  electrical 
  and 
  light 
  waves. 
  A 
  comparison 
  of 
  

   the 
  dielectric 
  constants 
  of 
  the 
  different 
  paraffins 
  shows 
  that 
  

   these 
  constants 
  increase 
  with 
  the 
  melting-point. 
  From 
  these 
  

   experiments 
  it 
  seems 
  necessary, 
  therefore, 
  in 
  tabulating 
  the 
  

   dielectric 
  constant 
  of 
  paraffin 
  to 
  give 
  its 
  density, 
  its 
  melting- 
  

   point, 
  and 
  the 
  wave-length 
  for 
  which 
  the 
  constant 
  was 
  ob- 
  

   tained. 
  The 
  third 
  decimal 
  place 
  is 
  bracketed 
  because 
  the 
  

   accuracy 
  of 
  measurements 
  does 
  not 
  warrant 
  its 
  unqualified 
  

   use, 
  and 
  yet 
  the 
  quantities 
  of 
  which 
  the 
  tabulated 
  numbers 
  

   are 
  the 
  average 
  are 
  of 
  such 
  uniformity 
  that 
  some 
  credence 
  

   must 
  be 
  given 
  to 
  this 
  third 
  place. 
  

  

  Light-Index 
  of 
  Refraction. 
  

  

  The 
  light-index 
  of 
  refraction 
  was 
  obtained 
  by 
  means 
  of 
  an 
  

   Abbe 
  * 
  refractometer. 
  This 
  is 
  constructed 
  upon 
  the 
  principle 
  

   of 
  total 
  reflexion, 
  and 
  is 
  graduated 
  to 
  read 
  directly 
  the 
  index 
  

   of 
  refraction 
  of 
  the 
  Dj 
  line 
  of 
  any 
  transparent 
  liquid 
  or 
  solid 
  

   which 
  can 
  be 
  placed 
  between 
  its 
  prisms. 
  Films 
  of 
  paraffin 
  

   were 
  easily 
  procured 
  by 
  floating 
  bits 
  of 
  wax 
  on 
  hot 
  water 
  

   and 
  allowing 
  the 
  melted 
  wax 
  to 
  solidify. 
  In 
  order 
  to 
  ensure 
  

   close 
  contact, 
  both 
  the 
  film 
  and 
  the 
  prisms 
  were 
  gently 
  heated 
  

   before 
  the 
  wax 
  was 
  placed 
  between 
  the 
  prisms. 
  The 
  refracto- 
  

   meter 
  gave 
  data 
  also 
  from 
  which 
  by 
  means 
  of 
  a 
  table 
  one 
  could 
  

   calculate 
  the 
  dispersion-factor 
  between 
  the 
  D 
  1 
  and 
  the 
  F 
  

   lines. 
  

  

  Having 
  the 
  index 
  of 
  refraction 
  for 
  two 
  lines 
  in 
  the 
  spectrum, 
  

   one 
  may 
  apply 
  Cauchy's 
  formula, 
  and 
  thus 
  obtain 
  the 
  index 
  

   for 
  infinitely 
  long 
  waves. 
  When 
  the 
  constants 
  A 
  and 
  B 
  of 
  

   this 
  formula 
  are 
  eliminated 
  it 
  takes, 
  according 
  to 
  Gordon 
  f. 
  the 
  

   following 
  form 
  : 
  — 
  

  

  /JlX 
  2 
  — 
  fJLiXi 
  2 
  

  

  where 
  /t/. 
  A=x 
  = 
  index 
  of 
  refraction 
  for 
  infinitely 
  long 
  -waves, 
  

   jju 
  = 
  , 
  } 
  „ 
  a 
  given 
  long 
  wave, 
  

  

  Hi 
  — 
  „ 
  „ 
  a 
  shorter 
  wave, 
  

  

  X 
  and 
  \ 
  x 
  represent 
  the 
  corresponding 
  wave-lengths. 
  

  

  * 
  Physikalischer 
  Fraktikum, 
  Wiedemann-Ebert. 
  

   t 
  Phil. 
  Trans, 
  pt. 
  i. 
  p. 
  441 
  (1879). 
  

  

  