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  XXXIX. 
  Tlie 
  Recomhination 
  of 
  the 
  Io7is 
  in 
  Air 
  at 
  Different 
  

   Temperatures. 
  By 
  Henry 
  A. 
  Erikson, 
  Assistant-Professor 
  

   of 
  Physics, 
  University 
  of 
  Minnesota*. 
  

  

  IN 
  this 
  paper 
  are 
  given 
  the 
  results 
  of 
  an 
  investigation, 
  as 
  

   far 
  as 
  it 
  has 
  progressed, 
  of 
  the 
  recombination 
  of 
  the 
  

   ions 
  produced 
  by 
  the 
  7 
  and 
  p 
  rays 
  of 
  radium 
  in 
  air 
  at 
  

   different 
  temperatures, 
  the 
  density 
  of 
  the 
  air 
  remaining 
  

   constant 
  and 
  equal 
  to 
  that 
  of 
  the 
  normal 
  atmosphere. 
  

  

  It 
  is 
  now 
  known 
  that 
  the 
  previous 
  experimental 
  results 
  

   obtained 
  in 
  this 
  connexion 
  were 
  rendered 
  uncertain 
  by 
  

   diffusion, 
  owing 
  to 
  the 
  fact 
  that 
  the 
  electrodes 
  were 
  too 
  close 
  

   together 
  in 
  the 
  case 
  of 
  some 
  of 
  the 
  densities 
  involved 
  f. 
  

  

  It 
  was 
  shown 
  experimentally 
  by 
  L. 
  L. 
  Hendren 
  J, 
  in 
  

   connexion 
  with 
  his 
  work 
  on 
  recombination 
  at 
  different 
  pres- 
  

   sures, 
  that 
  the 
  effect 
  of 
  diffusion 
  upon 
  the 
  coefficient 
  of 
  

   recombination 
  (a) 
  in 
  the 
  case 
  of 
  air 
  is 
  very 
  small 
  when 
  the 
  

   electrodes 
  are 
  2 
  cm. 
  apart 
  and 
  the 
  density 
  and 
  temperature 
  

   of 
  the 
  air 
  are 
  those 
  of 
  the 
  atmosphere. 
  

  

  It 
  was 
  concluded 
  from 
  this 
  that, 
  with 
  the 
  electrodes 
  4 
  cm. 
  

   apart 
  and 
  a 
  similar 
  density, 
  the 
  effect 
  of 
  diffusion 
  would 
  be 
  

   so 
  small, 
  even 
  at 
  different 
  temperatures, 
  that 
  whatever 
  

   variation 
  was 
  found 
  in 
  a 
  would 
  be 
  mainly 
  due 
  to 
  causes 
  

   other 
  than 
  diffusion. 
  

  

  If 
  the 
  effect 
  of 
  diffusion 
  may 
  be 
  neglected 
  at 
  room-temper- 
  

   ature, 
  it 
  may 
  be 
  neglected 
  with 
  more 
  safety 
  still 
  at 
  lower 
  

   temperatures. 
  At 
  higher 
  temperatures 
  one 
  cannot 
  be 
  so 
  

   certain. 
  

  

  The 
  Ionization- 
  Chamber. 
  

  

  The 
  final 
  form 
  of 
  ionization-chamber 
  decided 
  upon 
  was 
  a 
  

   copper 
  sphere 
  11 
  cm. 
  in 
  diameter, 
  having 
  at 
  its 
  centre 
  a 
  

   sphere 
  3 
  cm. 
  in 
  diameter. 
  This 
  inner 
  sphere, 
  with 
  its 
  

   attached 
  tube, 
  was 
  of 
  glass 
  covered 
  with 
  copper, 
  electrically 
  

   deposited. 
  These 
  two 
  spheres 
  formed 
  the 
  electrodes 
  and 
  

   were 
  therefore 
  4 
  cm. 
  apart. 
  Any 
  irregularity 
  due 
  to 
  the 
  

   connexion 
  with 
  the 
  inner 
  sphere 
  was 
  avoided 
  by 
  means 
  of 
  a 
  

   cone, 
  as 
  shown 
  in 
  fig. 
  1. 
  

  

  The 
  radium 
  was 
  contained 
  in 
  a 
  small 
  glass 
  sphere 
  and 
  

   placed 
  at 
  the 
  centre 
  of 
  the 
  two 
  spheres 
  forming 
  the 
  chamber. 
  

   This 
  makes 
  a 
  very 
  regular 
  arrangement, 
  for 
  which 
  the 
  

  

  * 
  Communicated 
  bj 
  Sir 
  J. 
  J. 
  Thomson. 
  

  

  T 
  Phil. 
  Mag. 
  vol. 
  yi. 
  p. 
  655 
  (1903). 
  

  

  \ 
  Physical 
  EevieW; 
  vol. 
  xxi. 
  p. 
  314 
  (1905). 
  

  

  