﻿SSS 
  Prop. 
  McLennan 
  and 
  Mr. 
  Keys 
  on 
  the 
  Electrical 
  

  

  Here 
  it 
  will 
  be 
  seen 
  the 
  readings 
  obtained 
  with 
  negative 
  

   fields 
  were 
  considerably 
  higher 
  than 
  those 
  obtained 
  under 
  

   corresponding 
  voltages 
  with 
  positive 
  fields. 
  This 
  no 
  doubt 
  

   arose 
  from 
  the 
  mobility 
  of 
  the 
  positive 
  ion 
  being 
  less 
  than 
  

   that 
  of 
  the 
  negative. 
  With 
  both 
  fields 
  it 
  will 
  be 
  seen 
  

   saturation-currents 
  were 
  obtained 
  with 
  potentials 
  of 
  approxi- 
  

   mately 
  400 
  volts 
  applied 
  to 
  the 
  cylinder. 
  

  

  As 
  the 
  capacity 
  of 
  the 
  measuring 
  system 
  was 
  8142 
  e.s.u.> 
  

   it 
  will 
  be 
  seen 
  from 
  the 
  readings 
  given 
  in 
  the 
  table 
  that 
  the 
  

   maximum 
  conductivity 
  in 
  this 
  case 
  was 
  about 
  16 
  times 
  

   greater 
  than 
  the 
  maximum 
  obtained 
  with 
  the 
  complete 
  

   absorption 
  of 
  the 
  same 
  radiation 
  by 
  air 
  at 
  101 
  atmospheres, 
  

   and 
  consequently 
  about 
  576 
  times 
  greater 
  than 
  the 
  greatest 
  

   conductivity 
  measured 
  when 
  the 
  same 
  radiation 
  was 
  absorbed 
  

   by 
  liquid 
  air. 
  The 
  general 
  results 
  of 
  these 
  measurements 
  

   therefore 
  agree 
  with 
  those 
  obtained 
  by 
  Greinacher 
  with 
  the 
  

   liquids 
  which 
  he 
  used, 
  inasmuch 
  as 
  they 
  show 
  (i.) 
  that 
  it 
  

   is 
  very 
  much 
  more 
  difficult 
  to 
  obtain 
  saturation-currents 
  

   with 
  ionization 
  in 
  liquid 
  air 
  by 
  alpha 
  rays 
  than 
  when 
  the 
  

   ionization 
  was 
  produced 
  by 
  the 
  same 
  radiation 
  in 
  air 
  at 
  

   ordinary 
  pressure, 
  and 
  (ii.) 
  that 
  the 
  currents 
  obtainable 
  with 
  

   a 
  given 
  field 
  under 
  ionization 
  by 
  alpha 
  rays 
  are 
  very 
  much 
  

   less 
  with 
  liquid 
  air 
  than 
  with 
  air 
  at 
  ordinary 
  pressures. 
  

  

  VI. 
  Mobilities 
  of 
  Ions 
  produced 
  by 
  Alpha 
  Rays 
  in 
  Air 
  

   at 
  High 
  Pressures. 
  

  

  In 
  order 
  to 
  clear 
  up 
  if 
  possible 
  the 
  question 
  of 
  the 
  relative 
  

   mobilities 
  of 
  ions 
  produced 
  by 
  alpha 
  rays 
  in 
  air 
  at 
  high 
  

   pressures, 
  the 
  apparatus 
  shown 
  in 
  fig. 
  7 
  was 
  used. 
  

  

  To 
  EL 
  led? 
  omelet" 
  

   To 
  Earth 
  

  

  Fig. 
  7. 
  

  

  A 
  

  

  

  

  B 
  

  

  M 
  

  

  )c* 
  

  

  d[ 
  

  

  N 
  

  

  Q 
  1 
  

  

  

  JH^ 
  

  

  

  To 
  BiaTefv 
  

  

  AB 
  was 
  a 
  brass 
  plate 
  about 
  8 
  cm. 
  long 
  carrying 
  a 
  boss 
  of 
  

   the 
  same 
  metal, 
  CD, 
  about 
  2 
  cm. 
  in 
  diameter. 
  MN 
  was 
  a 
  

   second 
  brass 
  plate 
  attached 
  to 
  AB 
  by 
  insulating 
  supports. 
  

   This 
  plate 
  was 
  provided 
  with 
  a 
  circular 
  opening 
  as 
  shown 
  in 
  

   the 
  diagram 
  and 
  acted 
  as 
  a 
  guard-plate 
  to 
  the 
  boss 
  CD. 
  A 
  

   third 
  brass 
  plate 
  GH 
  carried 
  a 
  polonium-coated 
  plate 
  PQ 
  

   with 
  the 
  coated 
  surface 
  facing 
  the 
  boss 
  CD. 
  EF 
  was 
  a 
  

   plate 
  of 
  ebonite 
  provided 
  with 
  a 
  circular 
  opening 
  and 
  

   inserted 
  between 
  the 
  polonium-coated 
  plate 
  PQ 
  and 
  the 
  

   guard-plate 
  MN 
  and 
  the 
  boss 
  CD. 
  Care 
  was 
  taken 
  in 
  

  

  