﻿694 
  Prof. 
  Bragg 
  and 
  Mr. 
  Madsen 
  on 
  the 
  Quality 
  

  

  heterogeneous, 
  and 
  consists 
  of 
  rays 
  of 
  various 
  velocities. 
  

   According 
  to 
  H. 
  W. 
  Schmidt 
  there 
  are 
  a 
  certain 
  number 
  of 
  

   groups, 
  each 
  homogeneous 
  in 
  itself 
  (Ann. 
  der 
  Pliys. 
  Nov. 
  

   1906). 
  It 
  is 
  conceivable 
  that 
  the 
  effect 
  of 
  varying 
  the 
  

   atomic 
  weight 
  of 
  the 
  radiator 
  might 
  depend 
  on 
  the 
  velocity 
  

   of 
  the 
  (3 
  particle, 
  and 
  that 
  the 
  smaller 
  atomic 
  weights 
  might 
  

   return 
  a 
  relatively 
  small 
  amount 
  of 
  fast 
  primary 
  rays. 
  

   Assuming 
  the 
  velocity 
  of 
  the 
  secondary 
  rays 
  to 
  be 
  of 
  the 
  

   order 
  of 
  that 
  of 
  the 
  primary, 
  it 
  would 
  then 
  follow 
  that 
  the 
  

   constitution 
  of 
  a 
  heterogeneous 
  primary 
  beam 
  would 
  be 
  

   altered 
  by 
  scattering, 
  the 
  alteration 
  depending 
  on 
  the 
  atomic 
  

   weight 
  of 
  the 
  scattering 
  substance 
  or 
  radiator, 
  and 
  being 
  of 
  

   the 
  nature 
  indicated 
  by 
  experiment. 
  Crowther 
  (Phil. 
  Mag. 
  

   Oct. 
  1906) 
  has 
  described 
  an 
  experiment 
  which 
  appears 
  to 
  

   show 
  a 
  considerable 
  effect 
  of 
  this 
  kind. 
  He 
  found 
  that 
  the 
  

   secondary 
  ionization 
  due 
  to 
  the 
  ft 
  rays 
  of 
  UrX 
  was 
  much 
  

   more 
  nearly 
  proportional 
  to 
  atomic 
  weight 
  than 
  in 
  the 
  case 
  

   of 
  radium, 
  as 
  studied 
  by 
  McClelland, 
  and 
  he 
  has 
  suggested 
  

   that 
  the 
  difference 
  "may 
  be 
  due 
  to 
  to 
  the 
  presence 
  in 
  the 
  

   radium 
  radiation 
  of 
  comparatively 
  slowly-moving 
  /3 
  rays." 
  

   On 
  the 
  other 
  hand, 
  H. 
  W. 
  Schmidt 
  has 
  recently 
  found 
  (Ann, 
  

   der 
  Phys. 
  Bd. 
  xxiii. 
  1907) 
  that 
  the 
  behaviour 
  of 
  substances 
  

   under 
  radiation 
  from 
  the 
  ft 
  rays 
  of 
  UrX 
  is 
  not 
  very 
  different 
  

   to 
  that 
  found 
  by 
  McClelland 
  in 
  the 
  case 
  of 
  radium. 
  As 
  it 
  

   was 
  important 
  to 
  settle 
  this 
  point, 
  if 
  we 
  were 
  to 
  find 
  the 
  true 
  

   interpretation 
  of 
  our 
  own 
  experiments, 
  we 
  put 
  together 
  the 
  

   apparatus 
  of 
  the 
  form 
  used 
  by 
  Crowther, 
  and 
  repeated 
  his 
  

   experiments 
  with 
  UrX, 
  using 
  also 
  radium 
  and 
  actinium. 
  

   The 
  apparatus 
  is 
  not 
  very 
  well 
  suited, 
  as 
  Schmidt 
  points 
  out, 
  

   for 
  obtaining 
  accurately 
  the 
  proportion 
  between 
  secondary 
  

   and 
  primary 
  ; 
  but 
  it 
  gives 
  a 
  ready 
  answer 
  to 
  the 
  question 
  

   as 
  to 
  whether 
  or 
  no 
  the 
  speed 
  of 
  the 
  (3 
  particle 
  has 
  any 
  

   effect. 
  

  

  Subtracting 
  the 
  effects 
  of 
  the 
  carbon 
  plate 
  from 
  all 
  the 
  

   others, 
  and 
  setting 
  lead 
  equal 
  to 
  200, 
  we 
  obtained 
  the 
  following 
  

   results 
  : 
  — 
  

  

  Pb. 
  Sn. 
  Ag. 
  Zn. 
  Cu. 
  Fe. 
  Al. 
  (X 
  

  

  Ac 
  200 
  158 
  147 
  110 
  102 
  91 
  37 
  

  

  UrX 
  200 
  160 
  147 
  110 
  102 
  87'5 
  36 
  

  

  Eal 
  200 
  155 
  145 
  106-5 
  99'5 
  865 
  345 
  

  

  Ka2 
  200 
  152 
  5 
  141 
  1015 
  94-5 
  79 
  31 
  O 
  

  

  Ea3 
  200 
  152 
  145 
  99 
  82 
  68 
  25-5 
  

  

  Ea4 
  200 
  132-5 
  123 
  88 
  82-5 
  73 
  27'5 
  G 
  

  

  