﻿Sjiecial 
  Case 
  of 
  Gaseous 
  Conduction, 
  915 
  

  

  II. 
  Experimental. 
  

  

  3. 
  The 
  experiments 
  about 
  to 
  be 
  described 
  were 
  undertaken 
  

   with 
  the 
  primary 
  object 
  of 
  rinding 
  out 
  something 
  about 
  the 
  

   8 
  rays 
  emitted 
  from 
  the 
  molecules 
  of 
  a 
  gas 
  when 
  it 
  is 
  ionized. 
  

   It 
  was 
  thought 
  that 
  information 
  might 
  be 
  obtained 
  by 
  

   measuring 
  the 
  relation 
  between 
  the 
  current 
  and 
  the 
  field 
  in 
  

   such 
  circumstances 
  that 
  the 
  potential 
  difference 
  necessary 
  to 
  

   obtain 
  a 
  saturation 
  current 
  was 
  not 
  large 
  compared 
  with 
  that 
  

   corresponding 
  to 
  the 
  velocities 
  with 
  which 
  rays 
  are 
  known 
  

   to 
  be 
  emitted 
  from 
  metals. 
  It 
  may 
  be 
  said 
  at 
  once 
  that 
  this 
  

   primary 
  object 
  of 
  the 
  experiments 
  has 
  not 
  been 
  attained. 
  

  

  4. 
  The 
  gas 
  was 
  contained 
  in 
  a 
  parallel 
  plate 
  guard-ring 
  

   condenser. 
  The 
  central 
  portion 
  of 
  the 
  lower 
  plate, 
  which 
  

   was 
  connected 
  to 
  the 
  measuring 
  apparatus, 
  was 
  circular 
  and 
  

   7'5 
  cm. 
  in 
  diameter; 
  it 
  was 
  separated 
  by 
  a 
  gap 
  of 
  1 
  mm. 
  

   from 
  a 
  guard-ring 
  2 
  cm. 
  broad. 
  The 
  distance 
  between 
  the 
  

   plates 
  was 
  in 
  some 
  experiments 
  0*9 
  mm., 
  in 
  others 
  2'6 
  mm. 
  

   The 
  upper 
  plate 
  was 
  pierced 
  by 
  a 
  central 
  hole 
  3 
  cm. 
  in 
  

   diameter 
  ; 
  the 
  plates 
  were 
  of 
  brass, 
  but 
  the 
  lower 
  face 
  of 
  the 
  

   upper 
  plate 
  (including 
  the 
  hole) 
  was 
  covered 
  with 
  aluminium 
  

   leaf. 
  The 
  gas 
  was 
  ionized 
  either 
  by 
  a. 
  rays 
  from 
  a 
  disk 
  

   covered 
  with 
  polonium 
  or 
  ThC 
  placed 
  in 
  the 
  hole 
  in 
  the 
  

   upper 
  plate, 
  or 
  by 
  /3 
  and 
  7 
  rays 
  from 
  Ra, 
  or 
  by 
  X 
  rays 
  

   passing 
  mainly 
  through 
  that 
  hole 
  and 
  through 
  an 
  aluminium 
  

   window 
  in 
  the 
  gas-tight 
  vessel 
  containing 
  the 
  condenser. 
  

  

  The 
  potential 
  difference 
  between 
  the 
  plates 
  was 
  established 
  

   by 
  means 
  of 
  a 
  potentiometer 
  and 
  a 
  cell 
  of 
  which 
  the 
  e.m.f. 
  

   was 
  measured 
  by 
  a 
  Weston 
  Standard 
  Voltmeter. 
  The 
  

   values 
  of 
  V 
  given 
  below 
  are 
  not 
  simply 
  those 
  given 
  by 
  the 
  

   potentiometer. 
  There 
  was 
  a 
  volta 
  difference 
  of 
  potential 
  

   between 
  the 
  plates 
  which 
  could 
  be 
  measured 
  by 
  observing 
  

   what 
  external 
  potential 
  difference 
  had 
  to 
  be 
  applied 
  to 
  the 
  

   plates 
  in 
  order 
  to 
  make 
  the 
  current 
  between 
  them 
  zero. 
  

   The 
  values 
  of 
  Y 
  given 
  are 
  those 
  obtained 
  by 
  subtracting 
  

   from 
  the 
  P.D. 
  given 
  by 
  the 
  potentiometer 
  that 
  necessary 
  to 
  

   make 
  the 
  current 
  zero. 
  

  

  When 
  a 
  or 
  /3 
  rays 
  were 
  used, 
  the 
  current 
  was 
  measured 
  by 
  

   means 
  of 
  a 
  xylol-alcohol 
  resistance, 
  of 
  which 
  the 
  resistance 
  

   was 
  within 
  10 
  per 
  cent, 
  of 
  1'2 
  x 
  10 
  11 
  ohms 
  ; 
  when 
  X 
  rays 
  

   were 
  used 
  the 
  current 
  was 
  measured 
  by 
  the 
  ordinary 
  com- 
  

   pensation 
  method 
  involving 
  the 
  use 
  of 
  a 
  sliding 
  shutter. 
  

  

  The 
  gases 
  used 
  were 
  air, 
  hydrogen, 
  and 
  carbon 
  dioxide 
  ; 
  

   the 
  last 
  two 
  were 
  evolved 
  from 
  Kipps 
  and 
  all 
  were 
  well 
  

   dried. 
  It 
  appeared 
  that 
  no 
  alterations 
  in 
  the 
  results 
  were 
  

  

  3Q2 
  

  

  