﻿726 
  Prof. 
  E. 
  Rutherford 
  and 
  Mr. 
  H. 
  Robinson 
  on 
  the 
  

  

  velocity 
  of 
  the 
  particle 
  in 
  terms 
  of 
  the 
  velocity 
  of 
  light 
  : 
  this 
  

   is 
  calculated 
  from 
  the 
  value 
  of 
  Up 
  with 
  the 
  aid 
  of 
  the 
  Lorentz- 
  

   Einstein 
  formula 
  

  

  m/m 
  =(l-/3 
  2 
  )-*; 
  . 
  

   e/m 
  is 
  taken 
  as 
  1*772 
  x 
  10 
  7 
  cm. 
  units. 
  

  

  Column 
  V. 
  gives 
  the 
  total 
  energy 
  of 
  the 
  electron, 
  calculated 
  

   from 
  the 
  Lorentz-Einstein 
  formula 
  

  

  e 
  \ 
  V1-/3 
  2 
  / 
  

  

  where 
  c 
  is 
  the 
  velocity 
  of 
  light. 
  

  

  The 
  energy 
  is 
  expressed 
  in 
  terms 
  of 
  e 
  in 
  order 
  to 
  avoid 
  

   any 
  assumption 
  with 
  regard 
  to 
  the 
  accuracy 
  of 
  any 
  particular 
  

   value 
  of 
  the 
  electronic 
  charge. 
  

  

  Radium 
  B 
  Groups. 
  

  

  A 
  diagrammatic 
  representation 
  of 
  the 
  lines 
  from 
  radium 
  B 
  

   is 
  shown 
  in 
  fig. 
  2 
  (PL 
  XII.). 
  Using 
  an 
  emanation 
  tube 
  as 
  a 
  

   source, 
  no 
  lines 
  above 
  Hp 
  = 
  2450 
  were 
  observed 
  which 
  could 
  be 
  

   definitely 
  ascribed 
  to 
  radium 
  B. 
  It 
  would 
  no 
  doubt 
  be 
  difficult 
  

   to 
  detect 
  very 
  faint 
  lines 
  in 
  higher 
  fields 
  on 
  account 
  of 
  the 
  

   masking 
  action 
  of 
  the 
  strong 
  photographic 
  effect 
  of 
  the 
  rays 
  

   from 
  the 
  radium 
  C 
  groups. 
  Both 
  H. 
  W. 
  Schmidt* 
  and 
  

   Fajans 
  and 
  Makowerf 
  have 
  observed 
  that 
  radium 
  B 
  emits 
  

   some 
  fairly 
  penetrating 
  /3 
  radiation, 
  If 
  this 
  radiation 
  be 
  

   due 
  to 
  some 
  groups 
  of 
  comparatively 
  high 
  velocity, 
  it 
  is 
  to 
  

   be 
  expected 
  that 
  their 
  photographic 
  intensity 
  would 
  be 
  small, 
  

   and 
  consequently 
  difficult 
  to 
  detect 
  in 
  experiments 
  with 
  » 
  

   source 
  containing 
  radium 
  B 
  and 
  C 
  together. 
  In 
  addition 
  to 
  

   the 
  lines 
  recorded, 
  a 
  number 
  of 
  faint 
  groups 
  were 
  observed 
  

   between 
  H/o 
  = 
  1392 
  and 
  H^ 
  = 
  950. 
  These 
  apparently 
  con- 
  

   sisted 
  of 
  two 
  or 
  more 
  lines 
  close 
  together, 
  but 
  it 
  was 
  difficult 
  

   to 
  measure 
  their 
  position 
  with 
  accuracy. 
  

  

  The 
  measurements 
  of 
  most 
  of 
  the 
  strong 
  lines 
  are 
  in 
  fair 
  

   agreement 
  with 
  those 
  given 
  by 
  Danysz 
  (loc. 
  cit.) 
  in 
  the 
  

   photographs 
  obtained 
  with 
  radium 
  B 
  + 
  C 
  together. 
  

  

  It 
  may 
  be 
  remarked 
  that 
  in 
  a 
  few 
  cases 
  lines 
  due 
  to 
  

   radium 
  B 
  and 
  radium 
  C 
  are 
  exactly, 
  or 
  very 
  nearly, 
  co- 
  

   incident. 
  This 
  occurs 
  in 
  the 
  case 
  of 
  the 
  complex 
  groups 
  

   Up 
  836-861, 
  914-950, 
  in 
  the 
  low 
  velocity 
  part 
  of 
  the 
  spectrum. 
  

  

  * 
  A. 
  W. 
  Schmidt, 
  Ann. 
  d. 
  Phys. 
  xxi. 
  p. 
  609 
  (1906). 
  

   f 
  Fajans 
  and 
  Makower, 
  Phil. 
  Mag. 
  xxiii. 
  p, 
  292 
  (1912). 
  

  

  