﻿424 
  On 
  a 
  Law 
  of 
  Molecular 
  Attraction. 
  

  

  which 
  may 
  be 
  more 
  compactly 
  written 
  

  

  W 
  = 
  * 
  -dr, 
  (2) 
  

  

  where 
  k 
  has 
  been 
  written 
  in 
  place 
  of 
  a/c. 
  

  

  If 
  F 
  denotes 
  the 
  force 
  of 
  attraction 
  between 
  the 
  two 
  mole- 
  

   cules, 
  the 
  " 
  internal 
  " 
  work 
  dW 
  done 
  against 
  molecular 
  

   attraction 
  when 
  the 
  molecules 
  are 
  separated 
  a 
  distance 
  dr, 
  is 
  

  

  dW^Y.dr, 
  (3) 
  

  

  and 
  if 
  the 
  molecules 
  at 
  a 
  distance 
  r 
  x 
  apart 
  are 
  separated 
  to 
  a 
  

   distance 
  r 
  2 
  , 
  

  

  W= 
  y 
  2 
  F 
  .dr 
  (4) 
  

  

  From 
  (2) 
  and 
  (4), 
  

  

  This 
  identical 
  equation 
  in 
  dr 
  allows 
  us 
  to 
  write 
  

  

  F=4; 
  or 
  Foci. 
  

  

  r 
  r 
  

  

  That 
  is 
  to 
  say, 
  the 
  force 
  of 
  attraction 
  between 
  two 
  molecules 
  

   is 
  inversely 
  as 
  the 
  fourth 
  power 
  of 
  the 
  distance 
  between 
  them 
  

   (Sutherland's 
  law). 
  

  

  Van 
  der 
  Waals' 
  assumption 
  that 
  the 
  force 
  of 
  attraction 
  

   between 
  tw 
  r 
  o 
  molecules 
  is 
  inversely 
  proportional 
  to 
  the 
  square 
  

   of 
  the 
  volume 
  occupied 
  by 
  the 
  gas, 
  and 
  Sutherland's 
  law 
  of 
  

   the 
  inverse 
  fourth*, 
  are, 
  therefore, 
  two 
  modes 
  of 
  stating 
  the 
  

   same 
  hypothesis. 
  

  

  I 
  am 
  not 
  aware 
  that 
  this 
  simple 
  relation 
  has 
  been 
  previously 
  

   pointed 
  out. 
  

  

  The 
  Owens 
  College, 
  Manchester. 
  

  

  * 
  Sutherland, 
  Phil. 
  Mag. 
  [5] 
  xxii. 
  p. 
  81 
  (1886). 
  

  

  