﻿880 
  Messrs. 
  T. 
  H. 
  Laby 
  and 
  G. 
  W. 
  C. 
  Kaye 
  on 
  

  

  ures 
  over 
  one 
  atmosphere. 
  Pen-in 
  * 
  found 
  for 
  Rontgen- 
  

   ray 
  ionization 
  that 
  "the 
  quantity 
  of 
  electricity 
  dissociated 
  by 
  

   unit 
  mass 
  (of 
  gas) 
  is 
  independent 
  of 
  the 
  pressure 
  and 
  pro- 
  

   portional 
  to 
  the 
  absolute 
  temperature" 
  f 
  ; 
  or, 
  in 
  other 
  words, 
  

   the 
  ionization 
  in 
  a 
  constant 
  volume 
  of 
  gas 
  is 
  proportional 
  to 
  

   the 
  pressure. 
  

  

  Experimental. 
  

   Some 
  preliminary 
  experiments 
  on 
  the 
  effect 
  of 
  pressure 
  on 
  

   the 
  ionization 
  in 
  air 
  were 
  made 
  using 
  an 
  aluminium 
  ionization 
  

   chamber 
  of 
  cylindrical 
  form 
  with 
  a 
  central 
  wire 
  electrode. 
  

   The 
  results 
  were 
  sufficient 
  fco 
  show 
  that 
  the 
  field 
  necessary 
  to 
  

   produce 
  a 
  saturation 
  current 
  was 
  a 
  strong 
  one 
  — 
  over 
  1000 
  

   Folts 
  per 
  cm. 
  for 
  the 
  higher 
  pressures 
  and 
  the 
  intensity 
  of 
  

   ionization 
  of 
  the 
  experiment. 
  The 
  cylindrical 
  form 
  of 
  

   apparatus 
  was 
  abandoned, 
  for 
  the 
  lack 
  of 
  uniformity 
  in 
  the 
  

   field 
  made 
  it 
  impossible 
  with 
  the 
  voltage 
  available 
  to 
  ensure 
  

   a 
  saturation 
  li< 
  i 
  ld 
  over 
  the 
  whole 
  volume 
  of 
  the 
  gas. 
  For 
  two 
  

   concentric 
  cylinders, 
  with 
  a 
  potential-difference 
  of 
  V 
  volts 
  

  

  y 
  

   between 
  them, 
  the 
  electric 
  field 
  falls 
  from 
  r— 
  - 
  at 
  the 
  

  

  v 
  ( 
  ,,log 
  ^) 
  

  

  inner 
  cylinder 
  to 
  z 
  5 
  at 
  the 
  outer 
  cylinder, 
  where 
  

  

  (Rlog.-) 
  

  

  /• 
  is 
  the 
  radius 
  of 
  the 
  inner 
  cylinder, 
  R 
  that 
  of 
  the 
  

   outer. 
  Thus 
  for 
  complete 
  saturation 
  of 
  all 
  the 
  gas 
  V 
  

  

  not 
  be 
  less 
  than 
  XR 
  . 
  log 
  e 
  — 
  , 
  where 
  X 
  is 
  the 
  least 
  

  

  saturation 
  field 
  for 
  the 
  conditions 
  of 
  the 
  experiment. 
  Thus, 
  

   for 
  example, 
  if 
  R=10r, 
  the 
  field 
  will 
  fall 
  from 
  V/2-3r 
  at 
  

   the 
  inner 
  cylinder 
  to 
  V 
  23r 
  at 
  the 
  outer 
  cylinder. 
  If 
  the 
  

   saturation 
  field 
  be 
  equal 
  to 
  the 
  mean 
  field 
  =V/(R 
  — 
  r) 
  = 
  V/9 
  r, 
  

   then 
  < 
  s 
  <"> 
  per 
  cent, 
  of 
  the 
  gas 
  is 
  subjected 
  to 
  a 
  field 
  less 
  than 
  

   this, 
  and 
  is 
  theref 
  urated. 
  A 
  uniform 
  ionization 
  is 
  

  

  of 
  course 
  assumed. 
  We 
  mention 
  this 
  as 
  showing 
  that 
  this 
  

   form 
  of 
  vessel 
  is 
  unsuitable 
  for 
  experiments 
  in 
  which 
  one 
  of 
  

   the 
  difficulties 
  is 
  to 
  saturate 
  a 
  dense 
  gas 
  at 
  high 
  pressures. 
  

  

  Apparatus. 
  

  

  The 
  apparatus, 
  which 
  was 
  made 
  by 
  the 
  writers, 
  is 
  shown 
  

   in 
  plan 
  in 
  fig. 
  1 
  (PI. 
  XXVI.). 
  It 
  consisted 
  of 
  an 
  ionization 
  

   vessel 
  connected 
  by 
  thick-walled 
  capillary 
  tubing 
  of 
  glass 
  

   to 
  a 
  drying-tube, 
  and 
  to 
  an 
  air-pressure 
  manometer 
  placed 
  

   horizontally. 
  A 
  scale 
  of 
  centimetres 
  was 
  etched 
  on 
  the 
  

  

  * 
  C. 
  R. 
  exxiii. 
  p. 
  878 
  (1896). 
  

  

  + 
  This 
  temperature 
  effect 
  has 
  not 
  been 
  confirmed 
  by 
  later 
  observers. 
  

  

  