﻿THE 
  

  

  AMERICAN 
  JOURNAL 
  OF 
  SCIENCE 
  

  

  [FOURTH 
  SERIES.] 
  

  

  Art. 
  XI. 
  — 
  On 
  the 
  Velocities 
  of 
  Delta 
  Bays 
  ; 
  by 
  H. 
  A. 
  

  

  BlJMSTEAD. 
  

  

  The 
  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 
  independently, 
  Ruth- 
  

   erford 
  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 
  every- 
  

   thing 
  goes 
  to 
  show 
  that 
  Rutherford 
  was 
  right 
  in 
  his 
  original 
  

   suggestion 
  that 
  all 
  8-rays 
  are 
  secondary 
  phenomena, 
  due 
  to 
  the 
  

   impact 
  of 
  a-rays 
  upon 
  matter. 
  In 
  the 
  present 
  paper, 
  therefore, 
  

   the 
  name 
  will 
  be 
  used 
  iii 
  this 
  sense. 
  

  

  The 
  question 
  of 
  the 
  velocity 
  of 
  the 
  S-rays 
  has 
  been 
  attacked 
  

   by 
  a 
  number 
  of 
  investigators.* 
  They 
  have 
  all 
  agreed 
  that 
  a 
  

   large 
  proportion 
  of 
  the 
  rays 
  have 
  velocities 
  which 
  are 
  small, 
  as 
  

   electronic 
  velocities 
  go, 
  not 
  very 
  different, 
  in 
  fact, 
  from 
  those 
  

   which 
  are 
  observed 
  in 
  the 
  photo-electric 
  effect. 
  The 
  estimates 
  

   by 
  different 
  observers 
  of 
  the 
  maximum 
  velocity 
  of 
  the 
  rays 
  

   have 
  been 
  discordant 
  ; 
  they 
  have 
  varied 
  from 
  zero 
  to 
  3*9 
  

  

  cm 
  

   X 
  10 
  8 
  — 
  , 
  the 
  latter 
  corresponding 
  to 
  a 
  fall 
  of 
  potential 
  of 
  

   sec 
  

  

  about 
  42 
  volts. 
  

  

  *For 
  a 
  historical 
  sketch 
  of 
  the 
  subject 
  see 
  Campbell, 
  Jahrb. 
  d. 
  Eadio- 
  

   aktivitat 
  trad 
  Elektronik, 
  ix, 
  p. 
  419, 
  1912. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Yol. 
  XXXV, 
  No. 
  212.— 
  August, 
  1913. 
  

  

  7 
  

  

  