﻿THE 
  

   LONDON, 
  EDINBURGH, 
  and 
  DUBLIN 
  

  

  PHILOSOPHICAL 
  MAGAZINE 
  

  

  AND 
  

  

  JOURNAL 
  OF 
  SCIENCE. 
  

  

  [SIXTH 
  SERIES.] 
  

  

  AUGUST 
  1913. 
  

  

  

  

  *\ 
  

  

  <* 
  

  

  XVI. 
  0?i 
  Me 
  Velocities 
  of 
  Delta 
  Rays. 
  - 
  

   By 
  H. 
  A. 
  Bumstead, 
  Yale 
  University 
  *.' 
  ? 
  

  

  §i- 
  

  

  I^HE 
  name 
  " 
  delta 
  rays 
  " 
  was 
  given 
  by 
  Sir 
  J. 
  J. 
  Thomson 
  

   in 
  1905 
  to 
  the 
  slow 
  electrons 
  which 
  he 
  found 
  to 
  be 
  

   emitted 
  by 
  polonium, 
  and 
  which 
  had 
  previously 
  masked 
  the 
  

   positive 
  charge 
  of 
  the 
  a-rays. 
  Shortly 
  afterward, 
  and 
  inde- 
  

   pendently, 
  Rutherford 
  discovered 
  a 
  similar 
  emission 
  from 
  

   radium 
  and 
  showed 
  that 
  it 
  was 
  not 
  confined 
  to 
  the 
  source 
  

   of 
  a-rays, 
  but 
  took 
  place 
  from 
  any 
  body 
  which 
  was 
  struck 
  by 
  

   them. 
  Some 
  writers 
  have 
  made 
  a 
  distinction 
  between 
  these 
  

   two 
  phenomena, 
  restricting 
  the 
  name 
  delta 
  rays 
  to 
  those 
  

   which 
  are 
  emitted 
  by 
  the 
  source 
  of 
  a-rays 
  and 
  calling 
  the 
  

   others 
  secondary 
  rays. 
  There 
  appears, 
  however, 
  to 
  be 
  little 
  

   ground 
  for 
  this 
  distinction; 
  there 
  is 
  no 
  appreciable 
  difference 
  

   between 
  the 
  two 
  kinds 
  of 
  rays, 
  and 
  everything 
  goes 
  to 
  show 
  

   thai 
  Rutherford 
  was 
  right 
  in 
  his 
  original 
  suggestion 
  that 
  all 
  

   S-ravs 
  are 
  secondary 
  phenomena, 
  due 
  to 
  the 
  impact 
  of 
  a-rays 
  

   upon 
  matter. 
  In 
  the 
  present 
  paper, 
  therefore, 
  the 
  name 
  will 
  

   be 
  used 
  in 
  this 
  sense. 
  

  

  The 
  question 
  of 
  the 
  velocity 
  of 
  the 
  $Vrays 
  has 
  been 
  attacked 
  

   by 
  a 
  number 
  o£ 
  investigators 
  f- 
  They 
  have 
  all 
  agreed 
  that 
  a 
  

   large 
  proportion 
  of 
  the 
  rays 
  have 
  velocities 
  which 
  are 
  small, 
  

  

  * 
  ('rirmiunicatpfl 
  by 
  the 
  Author. 
  

  

  f 
  ] 
  ■'■ 
  ir 
  mi 
  historical 
  sketch 
  of 
  the 
  subject 
  see 
  Campbell, 
  Jahrb, 
  d. 
  Radio- 
  

   aktivitat 
  und 
  EUktronik, 
  ix. 
  p. 
  419 
  (1912). 
  

  

  Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  26. 
  X«». 
  152. 
  Aug. 
  1 
  ( 
  M:\. 
  K 
  

  

  