﻿Gaseous 
  Ionization 
  and 
  Pressure. 
  

  

  883 
  

  

  cement 
  fluid. 
  Sealing-wax 
  was 
  tried 
  and 
  abandoned 
  as 
  it 
  

   cracked 
  with 
  the 
  flexure 
  of 
  the 
  apparatus. 
  

  

  A 
  Dolezalek 
  electrometer 
  was 
  used, 
  which 
  gave 
  at 
  2 
  metres 
  

   about 
  5000 
  mms. 
  deflexion 
  for 
  a 
  volt. 
  The 
  earth 
  connexion 
  

   to 
  the 
  central 
  plate 
  of 
  the 
  ionization-chamber 
  was 
  made 
  or 
  

   broken 
  through 
  a 
  calcium-chloride 
  solution 
  key. 
  The 
  radium 
  

   was 
  placed 
  opposite 
  one 
  of 
  the 
  faces 
  of 
  the 
  chamber 
  at 
  a 
  

   distance 
  which 
  gave 
  a 
  convenient 
  leak. 
  In 
  addition 
  to 
  the 
  

   7 
  mm. 
  aluminium 
  wall 
  the 
  y 
  rays 
  passed 
  through 
  about 
  1 
  cm. 
  

   of 
  brass 
  before 
  they 
  entered 
  the 
  chamber. 
  The 
  electrometer 
  

   was 
  shielded 
  from 
  the 
  radium 
  by 
  a 
  heavy 
  composite 
  lead- 
  

   iron 
  screen. 
  

  

  Measurements. 
  

  

  To 
  obtain 
  some 
  information 
  as 
  to 
  stray 
  ionization, 
  obser- 
  

   vations 
  were 
  made, 
  in 
  the 
  case 
  of 
  air, 
  at 
  pressures 
  less 
  than 
  

   atmospheric 
  down 
  to 
  the 
  vacuum 
  produced 
  by 
  a 
  charcoal 
  

   tube 
  in 
  liquid 
  air. 
  We 
  found 
  there 
  was, 
  in 
  spite 
  of 
  all 
  

   shielding 
  precautions, 
  a 
  small 
  quantity 
  of 
  residual 
  ionization 
  

   in 
  a 
  zinc 
  box 
  which 
  surrounded 
  the 
  key. 
  The 
  amount 
  of 
  this 
  

   was 
  applied 
  as 
  a 
  correction 
  to 
  all 
  the 
  readings. 
  

  

  Saturation 
  Current. 
  — 
  We 
  first 
  determined 
  the 
  saturation 
  

   field 
  for 
  the 
  highest 
  pressures 
  used. 
  The 
  values 
  below, 
  taken 
  

   from 
  our 
  curves, 
  oive 
  the 
  order 
  of 
  magnitude 
  of 
  the 
  field 
  

   required 
  for 
  air. 
  The 
  values 
  of 
  the 
  current 
  for 
  the 
  two 
  sets 
  

   of 
  pressures 
  are 
  not 
  comparable. 
  

  

  Pressure 
  8 
  

  

  itmo 
  spheres. 
  

  

  ield 
  in 
  yolts, 
  cm. 
  

  

  Current 
  

  

  100 
  

  

  18-5 
  

  

  500 
  

  

  20-2 
  

  

  1000 
  

  

  21-7 
  

  

  1500 
  

  

  22-0 
  

  

  2000 
  

  

  22-0 
  

  

  Pressure 
  15 
  atmospheres. 
  

  

  500 
  

  

  -12-0 
  

  

  1000 
  

  

  44'3 
  

  

  1500 
  

  

  46-0 
  

  

  2000 
  

  

  47-3 
  

  

  2500 
  

  

  47-9 
  

  

  3000 
  

  

  48-0 
  

  

  3500 
  

  

  48*1 
  

  

  3 
  M 
  

  

  