﻿Radium 
  Emanation 
  in 
  the 
  Atmosphere. 
  615 
  

  

  lie 
  between 
  12 
  and 
  38 
  near 
  Manchester 
  ; 
  Eve 
  * 
  calculated 
  

   values 
  between 
  1 
  and 
  5 
  for 
  the 
  air 
  over 
  the 
  Atlantic 
  Ocean. 
  

  

  Eve 
  f 
  concluded 
  that 
  the 
  radium 
  emanation 
  in 
  the 
  atmo- 
  

   sphere 
  near 
  the 
  earth 
  fully 
  accounted 
  for 
  the 
  rate 
  of 
  production 
  

   of 
  ions 
  observed 
  in 
  it, 
  but 
  the 
  results 
  above 
  show 
  that 
  although 
  

   the 
  proportion 
  of 
  the 
  natural 
  ionization 
  of 
  the 
  air 
  due 
  to 
  the 
  

   radium 
  emanation 
  and 
  its 
  products 
  is 
  rather 
  uncertain, 
  it 
  

   does 
  not 
  seem 
  likely 
  that 
  the 
  radium 
  emanation 
  and 
  its 
  

   products 
  are 
  responsible 
  for 
  anything 
  like 
  all 
  the 
  natural 
  

   ionization. 
  

  

  Summary. 
  

  

  The 
  amount 
  of 
  radium 
  emanation 
  in 
  the 
  atmosphere 
  near 
  

   the 
  earth* 
  s 
  surface 
  at 
  Cambridge 
  has 
  been 
  measured 
  by 
  two 
  

   methods 
  : 
  — 
  

  

  (1) 
  Absorption 
  by 
  charcoal, 
  

  

  (2) 
  Condensation 
  by 
  liquid 
  air, 
  

  

  and 
  the 
  amounts 
  compared 
  with 
  those 
  given 
  off 
  by 
  a 
  radium 
  

   solution 
  of 
  known 
  strength. 
  The 
  two 
  methods 
  give 
  results 
  

   fairly 
  close 
  agreement. 
  They 
  show 
  that 
  the 
  amount 
  of 
  

   emanation 
  in 
  a 
  cubic 
  metre 
  of 
  air 
  is 
  subjected 
  to 
  considerable 
  

   variation, 
  and 
  is, 
  on 
  the 
  average, 
  equal 
  to 
  that 
  amount 
  which 
  

   would 
  be 
  in 
  radioactive 
  equilibrium 
  with 
  about 
  100 
  x 
  10~ 
  12 
  grm. 
  

   of 
  radium. 
  No 
  very 
  definite 
  correlation 
  could 
  be 
  established 
  

   between 
  the 
  changes 
  in 
  the 
  amount 
  of 
  emanation 
  in 
  the 
  

   atmosphere 
  and 
  changes 
  in 
  the 
  weather 
  and 
  barometer 
  during 
  

   the 
  period 
  through 
  which 
  the 
  experiments 
  were 
  performed. 
  

   I 
  intend 
  to 
  attack 
  this 
  part 
  of 
  the 
  problem 
  again. 
  

  

  The 
  above 
  quantity 
  of 
  radium 
  emanation, 
  together 
  with 
  its 
  

   disintegration 
  products, 
  would 
  produce 
  about 
  3 
  ions 
  per 
  c.c. 
  

   per 
  sec. 
  As 
  the 
  number 
  of 
  ions 
  actually 
  produced 
  per 
  c.c. 
  

   per 
  sec. 
  is 
  about 
  ten 
  times 
  this, 
  it 
  follows 
  that 
  only 
  a 
  small 
  

   proportion 
  of 
  the 
  natural 
  ionization 
  of 
  the 
  air 
  is 
  due 
  to 
  the 
  

   presence 
  of 
  the 
  radium 
  emanation 
  and 
  its 
  products. 
  

  

  In 
  conclusion, 
  I 
  thank 
  Professor 
  J. 
  J. 
  Thomson 
  for 
  per- 
  

   mission 
  to 
  carry 
  out 
  this 
  research 
  in 
  the 
  Cavendish 
  Laboratory 
  

   and 
  for 
  many 
  helpful 
  suggestions. 
  

  

  * 
  Eve, 
  Phil. 
  Mag. 
  Feb. 
  1907. 
  

   t 
  Eve, 
  Phil. 
  Mag. 
  July, 
  1905. 
  

  

  