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  Prof. 
  E. 
  Rutherford 
  and 
  Mr. 
  H. 
  Robinson 
  on 
  the 
  

  

  that 
  in 
  some 
  cases 
  it 
  was 
  very 
  difficult 
  to 
  decide 
  whether 
  

   these 
  complex 
  groups 
  belonged 
  to 
  radium 
  B 
  or 
  radium 
  C. 
  

   Danysz, 
  in 
  his 
  last 
  paper, 
  gave 
  values 
  for 
  eight 
  lines 
  between 
  

   11^ 
  = 
  2947 
  and 
  Hp 
  = 
  (5073 
  which 
  are 
  due 
  to 
  radium 
  C. 
  For 
  

   most 
  of 
  these 
  lines 
  there 
  is 
  a 
  fair 
  agreement 
  with 
  the 
  values 
  

   found 
  by 
  him. 
  

  

  It 
  should 
  be 
  remarked 
  that 
  all 
  of 
  the 
  groups 
  of 
  j3 
  rays 
  

   from 
  radium 
  C 
  appear 
  to 
  be 
  very 
  closely 
  homogeneous. 
  The 
  

   lines 
  on 
  the 
  photographs 
  were 
  in 
  all 
  cases 
  sharply 
  marked, 
  

   and 
  there 
  was 
  no 
  evidence 
  of 
  widening 
  of 
  the 
  band 
  to 
  indi- 
  

   cate 
  that 
  the 
  group 
  contained 
  electrons 
  of 
  velocities 
  varying 
  

   between 
  small 
  limits. 
  The 
  strong 
  lines 
  due 
  to 
  radium 
  B 
  are 
  

   always 
  diffuse 
  on 
  the 
  inner 
  side 
  when 
  obtained 
  with 
  an 
  

   a-ray 
  tube. 
  This 
  no 
  doubt 
  is 
  partly 
  due 
  to 
  an 
  alteration 
  of 
  

   the 
  velocities 
  in 
  escaping 
  through 
  the 
  walls 
  of 
  the 
  glass 
  tube. 
  

   At 
  the 
  same 
  time 
  there 
  is 
  some 
  evidence 
  from 
  the 
  experiments 
  

   with 
  active 
  wires 
  that 
  the 
  velocities 
  in 
  the 
  strong 
  groups 
  are 
  

   variable 
  over 
  comparatively 
  narrow 
  limits. 
  

  

  General 
  Considerations. 
  

  

  On 
  the 
  theory 
  of 
  the 
  origin 
  of 
  /3 
  and 
  7 
  rays 
  proposed 
  by 
  

   one 
  of 
  the 
  authors 
  (loc. 
  cit.). 
  it 
  is 
  to 
  be 
  expected 
  that 
  the 
  

   differences 
  between 
  the 
  energies 
  of 
  the 
  j3 
  particles 
  in 
  dif- 
  

   ferent 
  groups 
  should 
  be 
  expressed 
  by 
  an 
  integral 
  number 
  of 
  

   one 
  or 
  more 
  constants. 
  These 
  constants 
  occurring 
  represent 
  

   the 
  energy 
  abstracted 
  from 
  the 
  /3 
  particle 
  in 
  passing 
  through 
  

   certain 
  regions 
  of 
  the 
  atom, 
  which 
  are 
  converted 
  into 
  energy 
  

   of 
  the 
  7-ray 
  form. 
  It 
  is 
  not 
  proposed 
  at 
  this 
  stage 
  to 
  enter 
  

   into 
  a 
  discussion 
  of 
  the 
  groups 
  from 
  radium 
  B, 
  as 
  the 
  ex- 
  

   periments 
  of 
  Rutherford 
  and 
  Richardson 
  (loc. 
  cit.) 
  have 
  

   shown 
  that 
  the 
  7 
  radiation 
  from 
  this 
  substance 
  is 
  very 
  com- 
  

   plex, 
  consisting 
  of 
  three 
  distinct 
  types 
  widely 
  differing 
  from 
  

   one 
  another 
  in 
  penetrating 
  power. 
  Before 
  the 
  theory 
  can 
  

   be 
  adequately 
  applied 
  in 
  this 
  case, 
  the 
  velocity 
  of 
  each 
  group 
  

   must 
  be 
  known 
  with 
  greater 
  precision 
  than 
  it 
  is 
  at 
  present. 
  

   On 
  the 
  other 
  hand, 
  the 
  same 
  authors 
  have 
  observed 
  that 
  the 
  

   7 
  radiation 
  from 
  radium 
  consists 
  essentially 
  of 
  one 
  pene- 
  

   trating 
  type, 
  and 
  it 
  is 
  consequently 
  to 
  be 
  expected 
  that 
  if 
  

   any 
  simple 
  relation 
  exists 
  between 
  the 
  lines, 
  it 
  should 
  be 
  

   most 
  obvious 
  amongst 
  the 
  higher 
  velocity 
  electrons 
  ejected 
  

   from 
  radium 
  C. 
  There 
  seems 
  to 
  be 
  fairly 
  definite 
  evidence 
  of 
  

   a 
  relation 
  of 
  this 
  character, 
  at 
  any 
  rate 
  between 
  29 
  lines 
  given 
  

   in 
  the 
  table 
  for 
  radium 
  0. 
  Taking 
  the 
  value 
  of 
  this 
  differ- 
  

   ence 
  as 
  E 
  : 
  = 
  0-4284 
  10 
  18 
  <?, 
  it 
  is 
  seen 
  that 
  all 
  the 
  lines 
  observed 
  

   from 
  Nos. 
  1 
  to 
  29 
  fall 
  closely 
  into 
  position. 
  For 
  the 
  higher 
  

   velocity 
  groups, 
  the 
  average 
  difference 
  is 
  twice 
  this 
  value, 
  

  

  