﻿368 
  Mr. 
  W. 
  Sutherland 
  on 
  

  

  Further 
  experiments 
  must 
  elucidate 
  many 
  o£ 
  the 
  points 
  

   raised 
  in 
  the 
  foregoing 
  sketch 
  of 
  a 
  theory. 
  According 
  to 
  the 
  

   theory 
  the 
  experimental 
  values 
  of 
  the 
  velocities 
  found 
  

   hitherto 
  for 
  the 
  large 
  Langevin 
  ion 
  ought 
  to 
  be 
  doubled 
  for 
  

   the 
  same 
  reason 
  as 
  that 
  for 
  doubling 
  the 
  ionic 
  experimental 
  

   mobilities 
  discussed 
  in 
  section 
  2. 
  Very 
  interesting 
  questions 
  

   present 
  themselves 
  as 
  to 
  the 
  equilibrium 
  of 
  these 
  three 
  orders 
  

   of 
  the 
  ion 
  in 
  the 
  atmosphere. 
  Radioactive 
  substances 
  

   generate 
  the 
  small 
  ions, 
  most 
  of 
  which 
  disappear 
  through 
  re- 
  

   combination 
  in 
  such 
  a 
  way 
  as 
  nearly 
  to 
  keep 
  the 
  number 
  of 
  

   small 
  ions 
  constant 
  under 
  a 
  given 
  set 
  of 
  conditions. 
  But 
  

   some 
  of 
  the 
  small 
  ions 
  will 
  gather 
  envelopes 
  round 
  them 
  and 
  

   so 
  build 
  up 
  the 
  ion 
  of 
  the 
  intermediate 
  type. 
  This 
  will 
  be 
  

   liable 
  to 
  destruction 
  through 
  neutralization 
  oE 
  its 
  charge 
  by 
  a 
  

   small 
  ion. 
  The 
  difficulties 
  of 
  building 
  up 
  the 
  large 
  Langevin 
  

   ion 
  must 
  be 
  great, 
  but 
  once 
  it 
  is 
  formed, 
  the 
  following 
  

   principle 
  will 
  act 
  favourably 
  to 
  its 
  permanence. 
  The 
  

   ionizing 
  power 
  of 
  water 
  comes 
  into 
  play. 
  Consider 
  a 
  very 
  

   small 
  drop 
  of 
  water 
  in 
  which 
  there 
  is 
  one 
  molecule 
  of 
  NaCl. 
  

   This 
  will 
  be 
  ionized 
  into 
  Na# 
  and 
  CI 
  (7, 
  which 
  will 
  be 
  driven 
  

   as 
  far 
  apart 
  as 
  possible 
  by 
  the 
  ionizing 
  action 
  of 
  the 
  water, 
  

   whose 
  tendency 
  is 
  favourable 
  to 
  the 
  splitting 
  of 
  the 
  drop 
  into 
  

   two 
  parts 
  charged 
  with 
  the 
  opposite 
  ions. 
  Thus 
  then 
  the 
  

   nucleus 
  of 
  a 
  large 
  Langevin 
  ion 
  by 
  its 
  ionizing 
  action 
  will 
  

   tend 
  to 
  keep 
  its 
  charge 
  unneutralized 
  by 
  opposite 
  ionic 
  

   charges. 
  So 
  we 
  can 
  account 
  for 
  the 
  permanent 
  existence 
  of 
  

   the 
  Langevin 
  ion 
  in 
  the 
  atmosphere. 
  These 
  large 
  ions 
  some- 
  

   times 
  carry 
  50 
  times 
  as 
  much 
  electricity 
  as 
  the 
  small 
  ions 
  in 
  

   the 
  atmosphere 
  at 
  the 
  same 
  time. 
  Lusby 
  has 
  shown 
  that 
  

   when 
  the 
  Langevin 
  ions 
  are 
  removed 
  from 
  air, 
  22 
  minutes 
  

   are 
  required 
  for 
  the 
  formation 
  of 
  the 
  same 
  number. 
  If 
  the 
  

   large 
  ion 
  contains 
  a 
  nucleus 
  of 
  quasi-liquid 
  H2O, 
  its 
  structure 
  

   merges 
  into 
  that 
  of 
  the 
  drop 
  of 
  water 
  in 
  cloudy 
  condensa- 
  

   tions. 
  Something 
  similar 
  to 
  the 
  large 
  ion 
  ought 
  to 
  appear 
  in 
  

   the 
  condensation 
  of 
  HgO 
  on 
  small 
  ions, 
  and 
  in 
  the 
  evaporation 
  

   of 
  a 
  drop 
  surrounding 
  an 
  ion. 
  The 
  theory 
  of 
  large 
  ions 
  is 
  

   closely 
  connected 
  with 
  that 
  of 
  cloudy 
  condensation. 
  Now 
  

   J. 
  J. 
  Thomson 
  in 
  ' 
  Conduction 
  of 
  Electricity 
  through 
  Gases'' 
  

   and 
  Langevin 
  (Bloch, 
  Ann, 
  de 
  Ch. 
  et 
  de 
  Ph. 
  [8] 
  iv. 
  1905, 
  

   p. 
  25) 
  have 
  given 
  a 
  theory 
  of 
  cloudy 
  condensation 
  upon 
  ions, 
  

   which 
  in 
  both 
  cases 
  seems 
  to 
  furnish 
  a 
  remarkably 
  successful 
  

   explanation 
  of 
  the 
  experimental 
  fact 
  that 
  fourfold 
  saturation 
  

   is 
  needed 
  in 
  vapour 
  of 
  HgO 
  to 
  produce 
  cloudy 
  condensation 
  

   on 
  small 
  ions. 
  But 
  they 
  use 
  quite 
  different 
  expressions 
  from 
  

   those 
  developed 
  here 
  concerning 
  the 
  potential 
  energy 
  of 
  an 
  

   electron 
  and 
  surrounding 
  molecules. 
  It 
  seems 
  to 
  me 
  that 
  

  

  