﻿892 
  Prof. 
  McLennan 
  and 
  Mr. 
  Keys 
  on 
  the 
  Electrical 
  

  

  the 
  effect 
  would 
  be 
  to 
  reduce 
  the 
  effective 
  area 
  o£ 
  the 
  

   opening. 
  This 
  would 
  result 
  in 
  the 
  values 
  of 
  the 
  mobilities 
  

   deduced 
  as 
  above 
  being 
  smaller 
  than 
  they 
  really 
  should 
  be. 
  

   However, 
  one 
  would 
  scarcely 
  expect 
  the 
  reduction 
  from 
  

   values 
  calculated 
  on 
  the 
  basis 
  of 
  the 
  inverse 
  pressure 
  law 
  to 
  be 
  

   so 
  great 
  as 
  that 
  indicated 
  by 
  the 
  numbers 
  given 
  in 
  Table 
  VII. 
  

  

  A 
  circumstance 
  which 
  seemed 
  to 
  point 
  to 
  diffusion 
  exerting 
  

   an 
  influence 
  on 
  the 
  readings 
  was 
  a 
  time 
  effect 
  which 
  was 
  

   observed 
  especially 
  when 
  low 
  fields 
  were 
  used. 
  With 
  fields 
  

   below 
  60 
  volts 
  a 
  centimetre 
  this 
  was 
  particularly 
  marked, 
  

   and 
  it 
  occurred 
  with 
  both 
  positive 
  and 
  negative 
  fields. 
  

   Where 
  such 
  fields 
  vs 
  ere 
  applied 
  after 
  the 
  various 
  parts 
  of 
  

   the 
  apparatus 
  had 
  remained 
  uncharged 
  for 
  some 
  time, 
  a 
  

   gradual 
  diminution 
  in 
  the 
  intensity 
  of 
  the 
  current 
  was 
  

   always 
  observed 
  in 
  taking 
  a 
  series 
  of 
  successive 
  readings. 
  

  

  It 
  required 
  about 
  half 
  an 
  hour 
  to 
  elapse 
  after 
  the 
  field 
  was 
  

   applied 
  before 
  the 
  current 
  reached 
  a 
  limiting 
  value, 
  and 
  the 
  

   diminution 
  in 
  current 
  amounted 
  to 
  from 
  12 
  to 
  20 
  per 
  cent. 
  

   With 
  fields 
  above 
  60 
  volts 
  a 
  centimetre 
  the 
  effect 
  gradually 
  

   disappeared, 
  and 
  when 
  fields 
  of 
  250 
  volts 
  a 
  centimetre 
  

   and 
  higher 
  were 
  applied 
  no 
  diminution 
  in 
  the 
  current 
  was 
  

   observed. 
  This 
  effect 
  would 
  seem 
  to 
  indicate 
  that 
  the 
  walls 
  

   of 
  the 
  opening 
  in 
  the 
  ebonite 
  plate 
  gradually 
  became 
  

   charged 
  by 
  ions 
  diffusing 
  to 
  them. 
  One 
  effect 
  of 
  this 
  action 
  

   would 
  be 
  to 
  produce 
  a 
  partial 
  neutralization 
  of 
  the 
  field, 
  and 
  

   this 
  in 
  turn 
  would 
  account 
  for 
  the 
  falling 
  off 
  in 
  the 
  current. 
  

  

  As 
  this 
  effect 
  was 
  absent 
  when 
  the 
  higher 
  fields 
  were 
  

   applied 
  it 
  is 
  not 
  clear 
  why 
  such 
  small 
  values 
  were 
  obtained 
  

   for 
  the 
  mobilities. 
  It 
  may 
  be 
  added 
  that 
  the 
  readings 
  given 
  

   in 
  Table 
  VII. 
  were 
  all 
  taken 
  immediately 
  after 
  the 
  application 
  

   of 
  the 
  field. 
  

  

  It 
  was 
  the 
  intention 
  of 
  the 
  writers 
  to 
  use 
  the 
  apparatus 
  to 
  

   determine 
  the 
  mobilities 
  of 
  the 
  ions 
  produced 
  in 
  liquid 
  air 
  

   by 
  alpha 
  rays, 
  but 
  in 
  view 
  of 
  the 
  small 
  values 
  obtained 
  with 
  

   it 
  for 
  &j 
  and 
  k 
  2 
  in 
  air 
  at 
  the 
  particular 
  pressure 
  of 
  116 
  atmo- 
  

   spheres 
  it 
  seemed 
  advisable 
  to 
  defer 
  these 
  measurements 
  until 
  

   more 
  extended 
  observations 
  were 
  made 
  on 
  the 
  mobilities 
  of 
  

   the 
  ions 
  in 
  air 
  at 
  a 
  series 
  of 
  high 
  pressures. 
  The 
  polonium- 
  

   coated 
  plate 
  used 
  above 
  was 
  of 
  rather 
  small 
  dimensions, 
  but 
  

   it 
  was 
  all 
  that 
  was 
  available 
  at 
  the 
  time 
  the 
  experiments 
  

   were 
  made. 
  With 
  a 
  larger 
  plate 
  the 
  effects 
  of 
  diffusion 
  

   should 
  be 
  lessened. 
  

  

  The 
  experiments 
  made 
  so 
  far 
  show 
  that 
  there 
  should 
  be 
  no 
  

   great 
  difficulty 
  in 
  finding 
  the 
  mobilities 
  of 
  ions 
  produced 
  in 
  

   air 
  up 
  to 
  and 
  even 
  beyond 
  150 
  atmospheres. 
  The 
  difficulty 
  

   in 
  determining 
  the 
  mobilities 
  in 
  liquid 
  air 
  will 
  be 
  largely 
  

   one 
  of 
  getting 
  rid 
  of 
  the 
  formation 
  of 
  air-bubbles 
  in 
  the 
  field 
  

  

  