﻿404 
  Dr. 
  H. 
  S. 
  Allen 
  on 
  Molecular 
  

  

  and 
  passes 
  through 
  the 
  point 
  — 
  i 
  sec 
  «. 
  Now 
  combining 
  (22) 
  

   and 
  (24), 
  the 
  resultant 
  of 
  all 
  the 
  pressures 
  is 
  seen 
  to 
  reduce 
  

   to 
  a 
  couple 
  of 
  moment 
  — 
  \irp 
  sin 
  2 
  a. 
  sin 
  2/3. 
  

   Introducing 
  the 
  velocity 
  and 
  radius, 
  we 
  have 
  

  

  Couple 
  =:-- 
  i777>a 
  2 
  IP 
  sin 
  2 
  a 
  sin 
  2/3. 
  . 
  . 
  (25) 
  

  

  This 
  becomes 
  zero 
  in 
  the 
  case 
  o£ 
  the 
  complete 
  cylinder, 
  

   a 
  = 
  7r, 
  and 
  reduces, 
  in 
  the 
  case 
  of 
  a 
  plane, 
  to 
  

  

  -i7r^ 
  2 
  U 
  2 
  sin2/3, 
  {26) 
  

  

  which 
  are 
  known 
  to 
  be 
  correct 
  results. 
  

  

  §8. 
  In 
  (23) 
  above, 
  it 
  follows 
  that 
  if 
  /#=-, 
  there 
  is 
  no 
  

  

  term 
  in 
  £*. 
  This 
  corresponds 
  to 
  the 
  case 
  in 
  which 
  the 
  

   stream-line 
  T/r 
  = 
  divides 
  at 
  the 
  edge 
  of 
  the 
  lamina. 
  If 
  this 
  

   may 
  be 
  applied 
  to 
  the 
  case 
  of 
  an 
  aeroplane 
  wing, 
  it 
  is 
  seen 
  to 
  

   lead 
  to 
  the 
  conclusion 
  that 
  the 
  entering 
  edge 
  should 
  point 
  

   downwards, 
  at 
  an 
  angle 
  equal 
  to 
  the 
  angle 
  of 
  attack 
  of 
  the 
  

   chord 
  of 
  the 
  (cambered) 
  plane. 
  Observation 
  and 
  photo- 
  

   graphs 
  would 
  seem 
  to 
  show 
  that 
  in 
  practice 
  such 
  a 
  condition 
  

   has 
  been 
  found 
  most 
  favourable. 
  

  

  P.S. 
  — 
  Since 
  the 
  majority 
  of 
  the 
  above 
  results 
  were 
  

   obtained, 
  a 
  paper 
  has 
  appeared 
  (Dr. 
  J. 
  G. 
  Leathern, 
  Phil. 
  

   Mag. 
  (6) 
  xxxv. 
  Jan. 
  1918) 
  in 
  which 
  it 
  is 
  shown 
  by 
  a 
  general 
  

   method, 
  that 
  (14) 
  above 
  is 
  deducible 
  from 
  (6), 
  and, 
  in 
  fact, 
  

   when 
  applied, 
  does 
  give 
  the 
  result 
  (14) 
  obtained 
  indepen- 
  

   dently 
  above. 
  

  

  Loughborough, 
  

   Feb. 
  5th, 
  1918. 
  

  

  XLVI. 
  Molecular 
  Frequency 
  and 
  Molecular 
  Number. 
  Part 
  II. 
  

   The 
  Frequency 
  of 
  the 
  Longer 
  Residual 
  Rays. 
  By 
  

   H. 
  Stanley 
  Allen, 
  M.A., 
  D.Sc, 
  University 
  of 
  London, 
  

   King's 
  College*. 
  

  

  A 
  METHOD 
  of 
  studying 
  the 
  frequency 
  of 
  vibration 
  of 
  

   the 
  atoms 
  in 
  compounds 
  is 
  afforded 
  by 
  the 
  " 
  residual 
  

   rays" 
  obtained 
  by 
  repeated 
  reflexions 
  from 
  the 
  surfaces 
  of 
  

   solids, 
  and 
  studied 
  by 
  Rubens 
  and 
  his 
  collaborators. 
  It 
  may 
  

   be 
  assumed 
  that 
  the 
  frequency 
  of 
  such 
  infra-red 
  radiation 
  

   corresponds 
  with 
  the 
  frequency 
  of 
  vibration 
  of 
  an 
  electrically 
  

   charged 
  ion, 
  and, 
  in 
  certain 
  cases 
  at 
  least, 
  it 
  is 
  to 
  be 
  expected 
  

   that 
  the 
  ion 
  in 
  question 
  may 
  be 
  identified 
  with 
  one 
  of 
  the 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  