﻿622 
  Messrs. 
  F. 
  Soddy 
  and 
  A. 
  S. 
  Russell 
  on 
  the 
  

  

  X-ray 
  pulse 
  generated 
  by 
  the 
  expulsion 
  of 
  a 
  /5-ray 
  electron 
  

   from 
  the 
  disintegrating 
  atom, 
  a 
  point 
  of 
  view 
  which 
  has 
  been 
  

   already 
  seriously 
  challenged 
  by 
  the 
  alternative 
  theory 
  advo- 
  

   cated 
  by 
  Bragg. 
  But 
  it 
  is 
  also 
  difficult 
  to 
  accept 
  the 
  ready 
  

   mutual 
  convertibility 
  of 
  /3- 
  into 
  7- 
  rays, 
  and 
  vice 
  versa, 
  which 
  

   Bragg's 
  theory 
  requires, 
  in 
  face 
  of 
  the 
  great 
  similarity 
  in 
  

   nature 
  and 
  great 
  difference 
  in 
  relative 
  intensity 
  which 
  are 
  

   shown 
  by 
  the 
  ff- 
  and 
  7-rays 
  of 
  radium 
  and 
  uranium. 
  The 
  

   most 
  natural 
  conclusion 
  is 
  that 
  the 
  two 
  types 
  are 
  not 
  inter- 
  

   dependent. 
  

  

  The 
  work 
  here 
  described 
  falls 
  under 
  two 
  heads. 
  First, 
  

   the 
  preparation 
  of 
  the 
  uranium 
  X 
  and 
  the 
  comparison 
  of 
  its 
  

   j3- 
  and 
  7-activity 
  with 
  that 
  of 
  radium 
  under 
  defined 
  con- 
  

   ditions 
  will 
  be 
  described. 
  Secondly, 
  an 
  account 
  will 
  be 
  given 
  

   of 
  the 
  absorption 
  of 
  the 
  7-rays 
  of 
  uranium 
  and 
  radium 
  under 
  

   comparable 
  conditions, 
  which 
  has 
  been 
  studied 
  in 
  considerable 
  

   detail. 
  The 
  7-rays 
  are 
  much 
  more 
  difficult 
  to 
  measure 
  ac- 
  

   curately 
  than 
  the 
  less 
  penetrating 
  types, 
  and 
  there 
  is 
  much 
  

   that 
  is 
  mysterious 
  and 
  unexplained 
  in 
  the 
  actions 
  they 
  pro- 
  

   duce. 
  In 
  particular 
  we 
  may 
  mention 
  that 
  the 
  7-ray 
  ioniza- 
  

   tion 
  itself 
  is 
  not 
  in 
  all 
  cases 
  a 
  constant 
  quantity, 
  but 
  may 
  

   suffer 
  a 
  regular 
  progressive 
  increase 
  in 
  amount 
  from 
  a 
  

   minimum 
  to 
  a 
  maximum 
  when 
  consecutive 
  observations 
  with 
  

   the 
  same 
  disposition 
  are 
  made. 
  This 
  variation, 
  which 
  may 
  

   give 
  rise 
  to 
  errors 
  as 
  great 
  as 
  ten 
  per 
  cent, 
  in 
  an 
  observation, 
  

   must 
  be 
  guarded 
  against 
  in 
  all 
  measurements 
  in 
  which 
  the 
  

   7-rays 
  are 
  concerned. 
  So 
  far 
  we 
  have 
  been 
  concerned 
  mainly 
  

   to 
  find 
  a 
  method 
  of 
  working 
  which 
  will 
  eliminate 
  these 
  

   fluctuations, 
  and 
  which 
  will 
  give 
  consistent 
  results. 
  In 
  this 
  

   we 
  have 
  been 
  successful, 
  but 
  the 
  cause 
  of 
  the 
  variation 
  is 
  still 
  

   to 
  be 
  worked 
  out. 
  So 
  far 
  as 
  the 
  determinations 
  of 
  the 
  absorp- 
  

   tion 
  coefficients 
  are 
  concerned 
  they 
  have 
  been 
  done 
  under 
  

   conditions 
  as 
  nearly 
  alike 
  as 
  possible 
  for 
  uranium 
  and 
  radium. 
  

   Not 
  much 
  weight 
  is 
  to 
  be 
  attached 
  to 
  the 
  absolute 
  values 
  of 
  

   the 
  coefficients, 
  for 
  there 
  is 
  necessarily 
  a 
  certain 
  amount 
  of 
  

   arbitrariness 
  in 
  the 
  choice 
  of 
  the 
  experimental 
  disposition. 
  

   We 
  have 
  tried 
  a 
  great 
  variety, 
  and 
  our 
  conclusion 
  is 
  that 
  

   though 
  many 
  give 
  curves 
  which 
  are 
  practically 
  exponential 
  

   within 
  the 
  limits 
  of 
  error, 
  it 
  is 
  difficult 
  to 
  repeat 
  ab 
  initio 
  

   measurements 
  of 
  the 
  absorption 
  coefficient 
  even 
  under 
  any 
  

   one 
  disposition 
  with 
  a 
  variation 
  of 
  less 
  than 
  5 
  percent., 
  while 
  

   the 
  actual 
  value 
  of 
  the 
  coefficient 
  may 
  depend 
  considerably 
  

   on 
  the 
  experimental 
  disposition. 
  

  

  