﻿342 
  Mr. 
  W. 
  Sutherland 
  on 
  

  

  Phillips, 
  it 
  removes 
  all 
  necessity 
  for 
  ascribing 
  varying 
  com- 
  

   plexity 
  to 
  that 
  ion. 
  Wellisch 
  (* 
  Nature/ 
  Ixxix. 
  1908, 
  p. 
  148) 
  

   has 
  already 
  shown 
  by 
  reasoning 
  which 
  is 
  not 
  supported 
  by 
  

   the 
  present 
  investigation, 
  that 
  by 
  considering 
  the 
  electric 
  

   force 
  of 
  an 
  ion 
  in 
  the 
  same 
  way 
  as 
  cohesional 
  force 
  in 
  the 
  

   theory 
  of 
  gaseous 
  viscosity, 
  it 
  becomes 
  no 
  longer 
  necessary 
  

   to 
  hold 
  that 
  the 
  linear 
  dimensions 
  of 
  the 
  smallest 
  ions 
  in 
  

   gases 
  betoken 
  a 
  complex 
  structure 
  for 
  them. 
  But 
  in 
  the 
  

   larger 
  ions 
  formed 
  by 
  spraying 
  electrolytic 
  solations 
  into 
  

   flames 
  and 
  hot 
  gases 
  we 
  find 
  on 
  a 
  more 
  elaborate 
  scale 
  just 
  

   such 
  a 
  variable 
  gaseous 
  ion 
  as 
  the 
  simplest 
  has 
  hitherto 
  been 
  

   supposed 
  to 
  be. 
  As 
  an 
  extreme 
  case 
  of 
  this 
  type 
  we 
  have 
  

   the 
  large 
  ion 
  discovered 
  by 
  Langevin 
  in 
  the 
  atmosphere. 
  

   Of 
  this 
  ion 
  we 
  know 
  little 
  more 
  than 
  its 
  small 
  mobility 
  

   except 
  the 
  demonstration 
  by 
  Pollock 
  (Austr. 
  Assoc, 
  for 
  the 
  

   Adv. 
  of 
  Sci. 
  1909) 
  that 
  this 
  mobility 
  varies 
  considerably 
  

   with 
  the 
  humidity 
  of 
  the 
  atmosphere. 
  Premising 
  that 
  the 
  

   mobility 
  of 
  an 
  ion 
  is 
  its 
  velocity 
  in 
  cm. 
  per 
  second 
  under 
  an 
  

   electric 
  force 
  of 
  a 
  volt 
  per 
  cm. 
  we 
  shall 
  for 
  convenience 
  

   divide 
  gaseous 
  ions 
  into 
  three 
  classes, 
  those 
  having 
  at 
  about 
  

   15° 
  C. 
  mobilities 
  of 
  the 
  order 
  of 
  magnitude 
  2, 
  0-02, 
  and 
  002. 
  

   No 
  doubt 
  these 
  types 
  merge 
  continuously 
  each 
  into 
  the 
  next. 
  

   'They 
  can 
  be 
  specified 
  more 
  accurately 
  according 
  to 
  the 
  

   following 
  definitions. 
  Let 
  the 
  ion 
  formed 
  of 
  atom 
  and 
  

   ^electron 
  be 
  called 
  a 
  nucleolus, 
  such 
  an 
  ion 
  surrounded 
  by 
  

   molecules 
  forming 
  a 
  solid 
  or 
  liquid 
  mass 
  be 
  called 
  a 
  nucleus, 
  

   :and 
  let 
  a 
  collection 
  of 
  molecules 
  in 
  the 
  form 
  of 
  a 
  vapour 
  

   xound 
  a 
  nucleus 
  or 
  nucleolus 
  be 
  called 
  an 
  envelope 
  ; 
  then 
  the 
  

   three 
  types 
  of 
  gaseous 
  ion 
  are 
  (1) 
  nucleolus 
  alone, 
  (2) 
  

   nucleolus 
  and 
  envelope, 
  and 
  (3) 
  nucleus 
  and 
  envelope. 
  The 
  

   ihird 
  type 
  merges 
  into 
  the 
  visible 
  drop 
  of 
  fog 
  and 
  rain, 
  

   though 
  it 
  is 
  probably 
  distinguished 
  from 
  these 
  by 
  the 
  fact 
  

   that 
  the 
  majority 
  of 
  the 
  molecales 
  in 
  the 
  nucleus 
  and 
  

   envelope 
  are 
  more 
  directed 
  by 
  central 
  electric 
  force 
  from 
  the 
  

   electron 
  than 
  by 
  the 
  mutual 
  cohesional 
  forces. 
  The 
  present 
  

   theory 
  will 
  be 
  divided 
  into 
  three 
  sections, 
  each 
  devoted 
  to 
  

   one 
  of 
  these 
  types 
  of 
  ion 
  with 
  a 
  reference 
  to 
  theories 
  of 
  

   condensation 
  and 
  a 
  summary. 
  

  

  1. 
  The 
  Ion 
  formed 
  hy 
  Atom 
  or 
  Radical 
  with 
  Electron. 
  

  

  Let 
  the 
  ion 
  of 
  charge 
  e 
  move 
  with 
  velocity 
  u 
  in 
  the 
  direc- 
  

   tion 
  X 
  under 
  uniform 
  fall 
  of 
  potential 
  whose 
  rate 
  is 
  d^/da:^ 
  

   then, 
  if 
  the 
  viscous 
  resistance 
  of 
  the 
  gas 
  to 
  its 
  motion 
  with 
  

   unit 
  velocity 
  is 
  F 
  

  

  Fu^ed'E^ldx 
  (1) 
  

  

  