﻿4:06 
  E. 
  A. 
  Hill— 
  Argon, 
  Front's 
  

  

  out 
  by 
  Thomson, 
  Maxwell, 
  and 
  others, 
  we 
  need 
  only 
  postulate 
  

   particles 
  in 
  motion, 
  and 
  a 
  mutual 
  action 
  between 
  them, 
  tending 
  

   to 
  reverse 
  that 
  motion 
  when 
  they 
  approach 
  within 
  certain 
  

   small 
  distances 
  of 
  each 
  other, 
  in 
  order 
  to 
  arrive 
  at 
  all 
  the 
  

   ordinary 
  conclusions 
  of 
  the 
  kinetic 
  theory 
  of 
  gases 
  ; 
  which 
  in 
  its 
  

   simplest 
  form 
  does 
  not 
  depend 
  on 
  any 
  assumptions 
  whatever 
  

   as 
  to 
  the 
  exact 
  nature 
  of 
  the 
  process 
  by 
  which 
  the 
  motion 
  is 
  

   reversed. 
  It 
  is 
  only 
  when 
  Boyle's 
  law 
  no 
  longer 
  holds, 
  that 
  is 
  

   w 
  T 
  hen 
  because 
  of 
  reduced 
  volume 
  the 
  molecules 
  are 
  within 
  the 
  

   sphere 
  of 
  their 
  mutual 
  actions 
  for 
  an 
  appreciable 
  time, 
  that 
  the 
  

   theory 
  has 
  to 
  deal 
  with 
  the 
  nature 
  of 
  the 
  encounter, 
  as 
  in 
  the 
  

   case 
  of 
  viscosity, 
  and 
  for 
  those 
  conditions 
  where 
  we 
  make 
  use 
  

   of 
  Yan 
  der 
  Waals' 
  equation 
  instead 
  of 
  the 
  more 
  simple 
  form,. 
  

   PY=HT. 
  But 
  this 
  ratio 
  of 
  the 
  two 
  specific 
  heats 
  in 
  Argon, 
  

   was 
  determined 
  under 
  ordinary 
  conditions 
  of 
  pressure 
  and 
  

   temperature, 
  for 
  which 
  the 
  gas 
  obeys 
  Boyle's 
  law, 
  hence 
  in 
  ex- 
  

   plaining 
  this 
  ratio 
  we 
  can 
  without 
  going 
  counter 
  to 
  the 
  ordi- 
  

   nary 
  kinetic 
  theory 
  of 
  gases, 
  make 
  any 
  assumptions 
  we 
  please 
  as 
  

   to 
  the 
  nature 
  of 
  the 
  encounter 
  and 
  the 
  constitution 
  of 
  the 
  

   molecule, 
  not 
  at 
  variance 
  with 
  known 
  facts 
  and 
  the 
  fundamen- 
  

   tal 
  postulate 
  of 
  moving 
  particles 
  and 
  reversed 
  motion 
  at 
  small 
  

   distances. 
  Whenever 
  we 
  reach 
  problems 
  in 
  any 
  way 
  condi- 
  

   tioned 
  by 
  the 
  nature 
  of 
  the 
  encounter, 
  the 
  ordinary 
  kinetic 
  

   theory 
  fails. 
  Evidently 
  the 
  nature 
  of 
  the 
  encounter 
  is 
  by 
  it 
  

   not 
  properly 
  taken 
  into 
  account. 
  Maxwell, 
  in 
  order 
  to 
  test 
  the 
  

   theory 
  as 
  to 
  viscosity 
  found 
  that, 
  assuming 
  the 
  molecules 
  to 
  be 
  

   hard 
  elastic 
  balls 
  only 
  acting 
  on 
  each 
  other 
  when 
  in 
  actual 
  con- 
  

   tact, 
  viscosity 
  should 
  be 
  proportional 
  to 
  the 
  square 
  root 
  of 
  

   absolute 
  temperature, 
  but 
  assuming 
  them 
  to 
  be 
  systems 
  repell- 
  

   ing 
  each 
  other 
  with 
  a 
  force 
  varying 
  inversely 
  as 
  the 
  5th 
  power 
  

   of 
  distance, 
  it 
  should 
  be 
  proportional 
  to 
  the 
  absolute 
  tempera- 
  

   ture. 
  As 
  shown, 
  however, 
  by 
  Barus 
  and 
  others, 
  viscosity 
  varies 
  

   more 
  rapidly 
  than 
  required 
  by 
  the 
  first 
  hypothesis, 
  and 
  more 
  

   slowly 
  than 
  required 
  by 
  the 
  second. 
  Hence 
  the 
  encounter 
  is 
  

   not 
  a 
  mere 
  collision 
  involving 
  an 
  actual 
  contact. 
  Sutherland, 
  

   says 
  Thomson, 
  concludes 
  that 
  the 
  molecules 
  act 
  without 
  contact 
  

   by 
  a 
  repulsive 
  force 
  varying 
  inversely 
  with 
  the 
  fourth 
  power 
  

   of 
  distance, 
  and 
  Pickering 
  in 
  his 
  theory 
  of 
  solutions, 
  represents 
  

   chemical 
  attraction 
  to 
  be 
  due 
  to 
  charges 
  on 
  the 
  surfaces 
  of 
  the 
  

   attracting 
  matter, 
  but 
  inalienable 
  from 
  the 
  matter, 
  owing 
  to 
  a 
  

   repulsive 
  force 
  between 
  the 
  atoms 
  similar 
  to 
  that 
  which 
  pro- 
  

   duces 
  elasticity, 
  preventing 
  the 
  atoms 
  ever 
  coming 
  close 
  enough 
  

   together 
  to 
  allow 
  of 
  the 
  charges 
  combining 
  by 
  actual 
  contacts. 
  

   Now 
  if 
  we 
  suppose 
  the 
  atom 
  endowed 
  with 
  such 
  a 
  force 
  of 
  

   repulsion, 
  varying 
  inversely 
  say 
  as 
  the 
  fourth 
  power 
  of 
  distance 
  

   (following 
  Sutherland) 
  and 
  combine 
  this 
  with 
  the 
  force 
  of 
  

   gravitation, 
  then 
  as 
  the 
  atom 
  is 
  approached 
  the 
  repulsive 
  force 
  

  

  