﻿441 
  Lord 
  Rayleigh 
  on 
  Reflexion 
  from 
  

  

  the 
  state 
  of 
  rest, 
  the 
  effective 
  part 
  of 
  the 
  kinetic 
  potential 
  is 
  

  

  L 
  = 
  -|°J^>MrfS-^„(T-T 
  ). 
  . 
  . 
  . 
  (18) 
  

  

  Finally, 
  if 
  there 
  is 
  vortex 
  motion 
  the 
  existence 
  of 
  a 
  function 
  

   corresponding 
  to 
  pressure 
  is 
  dependent 
  on 
  the 
  vortex 
  equations 
  

  

  being 
  satisfied. 
  The 
  integral 
  p 
  dr 
  may 
  continue 
  to 
  behave 
  

  

  as 
  a 
  kinetic 
  potential, 
  though 
  possibly 
  the 
  character 
  of 
  the 
  

   latter 
  may 
  be 
  modified 
  by 
  the 
  conditions 
  for 
  the 
  existence 
  of 
  

   a 
  pressure-function. 
  

  

  XXXVIII. 
  On 
  Reflexion 
  from 
  Glass 
  at 
  the 
  Polarizing 
  Angle. 
  

   By 
  Lord 
  Rayleigh, 
  O.M., 
  Pres.R.S* 
  

  

  ACCORDING 
  to 
  Fresnel's 
  theory 
  the 
  polarization 
  is 
  

   complete 
  when 
  light 
  is 
  reflected 
  at 
  the 
  Brewsterian 
  

   angle 
  (tan 
  -1 
  /a) 
  or, 
  as 
  we 
  may 
  put 
  it, 
  light 
  vibrating 
  in 
  the 
  

   plane 
  of 
  incidence 
  is 
  not 
  reflected 
  at 
  all 
  at 
  the 
  angle 
  in 
  

   question. 
  It 
  has 
  long 
  been 
  known 
  that 
  this 
  conclusion 
  is 
  

   but 
  approximately 
  correct. 
  If 
  we 
  attempt 
  to 
  extinguish 
  

   with 
  a 
  nicol 
  sunlight 
  reflected 
  from 
  ordinary 
  glass, 
  we 
  find 
  

   that 
  at 
  no 
  angle 
  of 
  incidence 
  and 
  reflexion 
  can 
  we 
  succeed. 
  

   It 
  is 
  difficult 
  even 
  to 
  fix 
  upon 
  an 
  angle 
  of 
  minimum 
  reflexion 
  

   with 
  any 
  precision. 
  

  

  The 
  interpretation 
  of 
  these 
  deviations 
  from 
  Fresnel's 
  laws 
  

   is 
  complicated 
  by 
  uncertainties 
  as 
  to 
  the 
  nature 
  of 
  surfaces 
  

   of 
  transition 
  from 
  one 
  medium 
  to 
  another. 
  It 
  is 
  certain 
  that 
  

   many, 
  if 
  not 
  all, 
  surfaces 
  attract 
  to 
  themselves 
  films 
  of 
  

   moisture 
  and 
  grease 
  from 
  the 
  surrounding 
  atmosphere, 
  and 
  

   the 
  opinion 
  has 
  been 
  widely 
  held 
  that 
  even 
  in 
  the 
  absence 
  of 
  

   moisture 
  and 
  grease 
  solid 
  bodies 
  are 
  still 
  coated 
  with 
  films 
  

   of 
  condensed 
  air. 
  Other 
  complications 
  depend 
  upon 
  possible 
  

   or 
  probable 
  residues 
  of 
  the 
  polishing 
  material 
  used 
  in 
  the 
  

   preparation 
  of 
  optical 
  surfaces. 
  It 
  was 
  mainly 
  for 
  these 
  

   reasons 
  that 
  I 
  gave 
  much 
  attention 
  some 
  years 
  ago 
  t 
  to 
  the 
  

   case 
  of 
  reflexion 
  from 
  water, 
  where 
  at 
  any 
  rate 
  there 
  was 
  no 
  

   question 
  of 
  a 
  polishing 
  powder 
  and 
  atmospheric 
  moisture 
  

   could 
  introduce 
  no 
  complication. 
  It 
  was 
  found 
  that 
  Jamin's 
  

   results, 
  up 
  to 
  that 
  time 
  considered 
  standard, 
  were 
  entirely 
  

   vitiated 
  by 
  films 
  of 
  grease. 
  Special 
  operations 
  are 
  necessary 
  

   to 
  remove 
  these 
  films. 
  When 
  proper 
  precautions 
  are 
  taken, 
  

   the 
  intensity 
  of 
  reflexion 
  at 
  the 
  polarizing 
  angle 
  may 
  be 
  less 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  Phil. 
  Mag-, 
  xxxiii. 
  p. 
  1 
  (1892) 
  ; 
  Scientific 
  Papers, 
  iii. 
  p. 
  496. 
  

  

  