﻿produced 
  in 
  Gases 
  by 
  Ultra- 
  Violet 
  Light. 
  569 
  

  

  the 
  three 
  variables 
  is 
  to 
  take 
  a 
  number 
  of 
  values 
  of 
  - 
  and 
  — 
  

  

  P 
  V 
  

   determined 
  over 
  large 
  ranges, 
  and 
  see 
  whether 
  the 
  points 
  

  

  whose 
  coordinates 
  are 
  - 
  and 
  — 
  lie 
  on 
  a 
  curve. 
  All 
  the 
  

  

  a 
  P 
  P 
  

  

  values 
  of 
  — 
  (derived 
  from 
  the 
  experimental 
  determinations) 
  

  

  are 
  marked 
  on 
  the 
  accompanying 
  diagrams, 
  p 
  being 
  measured 
  

  

  in 
  millimetres 
  of 
  mercury, 
  and 
  X 
  in 
  volts 
  per 
  centimetre. 
  

  

  It 
  is 
  evident 
  that 
  a 
  curve 
  runs 
  through 
  the 
  set 
  of 
  points 
  

  

  belonging 
  to 
  each 
  gas. 
  Each 
  point 
  is 
  numbered 
  in 
  order 
  to 
  

  

  show 
  from 
  which 
  table 
  of 
  observations 
  the 
  value 
  of 
  a 
  was 
  

  

  ■\r 
  

  

  calculated. 
  The 
  range 
  of 
  values 
  of 
  — 
  and 
  - 
  are 
  so 
  large 
  that 
  

   & 
  p 
  p 
  © 
  

  

  it 
  was 
  found 
  necessary 
  to 
  have 
  two 
  diagrams 
  on 
  different 
  

   scales. 
  From 
  these 
  curves 
  it 
  is 
  possible 
  to 
  obtain 
  the 
  value 
  

   of 
  a 
  for 
  any 
  force 
  and 
  any 
  pressure. 
  

  

  6. 
  The 
  properties 
  of 
  the 
  curves 
  are 
  interesting 
  in 
  many 
  

   ways, 
  and 
  are 
  in 
  accordance 
  with 
  what 
  we 
  should 
  expect 
  from 
  

   simple 
  considerations. 
  

  

  When 
  an 
  ion 
  travels 
  through 
  a 
  gas 
  under 
  an 
  electric 
  force, 
  

   it 
  makes 
  a 
  number 
  of 
  collisions 
  with 
  the 
  molecules 
  which 
  is 
  

   proportional 
  to 
  the 
  pressure. 
  If 
  the 
  velocity 
  of 
  the 
  ion 
  is 
  

   sufficiently 
  great, 
  the 
  effect 
  of 
  a 
  collision 
  will 
  be 
  to 
  produce 
  

   two 
  new 
  ions. 
  The 
  free 
  paths 
  of 
  the 
  ion 
  between 
  the 
  

   collisions 
  are 
  of 
  various 
  lengths 
  which 
  are 
  inversely 
  pro- 
  

   portional 
  to 
  the 
  pressure. 
  The 
  velocity 
  acquired 
  in 
  a 
  path 
  of 
  

   length 
  x 
  is 
  proportional 
  to 
  \/X 
  . 
  x 
  s 
  so 
  that 
  the 
  velocities 
  of 
  

  

  X 
  X 
  

  

  the 
  ions 
  must 
  depend 
  on 
  the 
  quantity 
  — 
  . 
  The 
  value 
  of— 
  

  

  must 
  be 
  large 
  in 
  order 
  that 
  the 
  ion 
  may 
  acquire 
  a 
  velocity 
  

   along 
  the 
  shorter 
  paths 
  which 
  will 
  be 
  sufficiently 
  great 
  to 
  

   produce 
  new 
  ions 
  on 
  collision. 
  When 
  this 
  effect 
  is 
  obtained 
  

   further 
  increases 
  in 
  X 
  cannot 
  give 
  rise 
  to 
  larger 
  values 
  of 
  a 
  y 
  

   as 
  new 
  ions 
  will 
  be 
  produced 
  at 
  every 
  collision. 
  The 
  maximum 
  

  

  value 
  of 
  - 
  represents 
  the 
  total 
  number 
  of 
  collisions 
  that 
  an 
  

   p 
  

  

  ion 
  can 
  make 
  in 
  going 
  through 
  one 
  centimetre 
  of 
  a 
  gas 
  at 
  a 
  

  

  millimetre 
  pressure. 
  

  

  The 
  curves 
  show 
  that 
  — 
  approaches 
  a 
  maximum 
  as 
  — 
  

  

  P 
  . 
  P 
  

  

  increases, 
  and, 
  as 
  we 
  should 
  expect, 
  this 
  value 
  is 
  larger 
  

  

  for 
  carbonic 
  acid 
  than 
  for 
  air, 
  and 
  larger 
  for 
  air 
  than 
  for 
  

   hydrogen. 
  

  

  