﻿On 
  the 
  Principle 
  of 
  Relativity. 
  039 
  

  

  radioactive 
  substances 
  do 
  not 
  emit 
  secondary 
  radiations 
  to 
  an 
  

   abnormal 
  extent. 
  It 
  is 
  clear 
  that 
  there 
  is 
  a 
  sharp 
  line 
  o£ 
  

   distinction 
  between 
  the 
  emission 
  of 
  an 
  electron 
  from 
  an 
  atom 
  

   as 
  a 
  primary 
  ft 
  ray, 
  and 
  the 
  emergence 
  of 
  an 
  electron 
  from 
  

   an 
  atom 
  as 
  a 
  secondary 
  /9 
  ray. 
  On 
  oar 
  hypothesis 
  the 
  origin 
  

   of 
  the 
  distinction 
  is 
  simply 
  that 
  in 
  the 
  former 
  case 
  the 
  

   electron 
  was 
  part 
  of 
  the 
  atom 
  which 
  ejected 
  it 
  ; 
  in 
  the 
  latter 
  

   case, 
  it 
  was 
  no 
  part 
  of 
  the 
  atom 
  : 
  it 
  came 
  in 
  with 
  the 
  exciting 
  

   ray. 
  All 
  the 
  experimental 
  evidence 
  accords 
  with 
  this 
  view. 
  

   We 
  come 
  very 
  close 
  to 
  the 
  complete 
  realization 
  of 
  an 
  antici- 
  

   pation 
  made 
  twelve 
  months 
  ago 
  (Trans. 
  Roy. 
  Soc. 
  of 
  S.A., 
  

   May 
  7, 
  1907, 
  pp. 
  81, 
  85) 
  : 
  " 
  All 
  secondary 
  radiation, 
  other 
  

   than 
  the 
  h 
  rays, 
  seems 
  to 
  be 
  in 
  general 
  a 
  rough 
  reflexion 
  or 
  

   scattering 
  of 
  the 
  primary. 
  . 
  . 
  . 
  The 
  only 
  cases 
  in 
  which 
  a 
  

   secondary 
  radiation 
  appears, 
  that 
  is 
  neither 
  8 
  radiation 
  nor 
  

   reflected 
  primary 
  rays, 
  are 
  those 
  in 
  which 
  j3 
  rays 
  are 
  

   produced 
  at 
  the 
  impact 
  of 
  X- 
  or 
  <y 
  rays, 
  and 
  in 
  which 
  X-rays 
  

   are 
  produced 
  by 
  cathode 
  rays. 
  ... 
  Jt 
  may 
  well 
  be 
  that 
  

   further 
  research 
  will 
  bring 
  these 
  cases 
  into 
  better 
  agreement 
  

   with 
  the 
  rest. 
  - 
  " 
  On 
  the 
  neutral-pair 
  hypothesis 
  the 
  exceptions 
  

   mentioned 
  here 
  practically 
  disappear. 
  There 
  remains 
  a 
  broad 
  

   generalization, 
  which, 
  with 
  all 
  the 
  faults 
  natural 
  to 
  its 
  kind, 
  

   seems 
  to 
  us 
  to 
  be 
  applicable 
  to 
  every 
  case 
  of 
  which 
  we 
  have 
  

   knowledge, 
  and 
  to 
  be 
  an 
  important 
  principle 
  of 
  the 
  theory 
  of 
  

   secondary 
  radiation. 
  

  

  ^ 
  LXXIX. 
  On 
  the 
  Principle 
  of 
  Relativity. 
  

   A 
  Reply 
  to 
  Mr. 
  E. 
  Cunningham. 
  By 
  A. 
  H. 
  Bucherer*. 
  

  

  NOTWITHSTANDING 
  my 
  objections 
  Mr. 
  Cunningham, 
  

   in 
  the 
  September 
  number 
  of 
  this 
  Magazine, 
  still 
  

   asserts 
  that 
  my 
  principle 
  of 
  relativity 
  leads 
  to 
  the 
  same 
  

   forces 
  as 
  the 
  Lorentz-Einstein 
  principle. 
  Mr. 
  Cunningham 
  

   seems 
  not 
  to 
  have 
  noticed 
  that 
  the 
  forces 
  on 
  moving 
  electrons 
  

   are 
  quite 
  different. 
  Take 
  the 
  concrete 
  case 
  realized 
  in 
  ex- 
  

   periments, 
  and 
  let 
  Becquerel 
  rays 
  traverse 
  a 
  uniform 
  magnetic 
  

   field. 
  The 
  force 
  on 
  the 
  electron, 
  according 
  to 
  my 
  principle, 
  

   is 
  

  

  e&u 
  sin 
  a. 
  

  

  1 
  ^COS" 
  a 
  

  

  v 
  2 
  

  

  whereas 
  according 
  to 
  Lorentz 
  the 
  force 
  is 
  

  

  eHit 
  sin 
  a. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  