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  VII. 
  On 
  a 
  New 
  Secondary 
  Radiation 
  of 
  Positive 
  Rays. 
  By 
  

   M. 
  Wolfke, 
  Dr. 
  p/<il, 
  Lecturer 
  at 
  the 
  Federal 
  Technical 
  

   High 
  School 
  and 
  at 
  the 
  University 
  of 
  Zurich, 
  Switzerland* 
  '. 
  

  

  UP 
  to 
  now, 
  two 
  secondary 
  radiations 
  of 
  positive 
  rays 
  

   have 
  been 
  known 
  : 
  the 
  slow 
  electron 
  rays 
  t 
  and 
  the 
  

   very 
  soft 
  X-rays 
  recently 
  discovered 
  by 
  J. 
  J. 
  Thomson 
  J, 
  

   which 
  are 
  probably 
  caused 
  by 
  a 
  retardation 
  of 
  the 
  ions 
  when 
  

   encountering 
  a 
  rigid 
  body. 
  

  

  Some 
  years 
  ago 
  Chad 
  wick 
  § 
  and 
  Russell 
  || 
  showed 
  that 
  

   a-rays 
  are 
  capable 
  of 
  exciting 
  the 
  7-radiation 
  of 
  heavy 
  

   elements. 
  

  

  So 
  far, 
  however, 
  it 
  has 
  not 
  been 
  known 
  whether 
  positive 
  

   rays 
  were 
  capable 
  of 
  producing 
  a 
  similar 
  effect. 
  Now 
  this 
  

   question 
  is 
  of 
  very 
  vital 
  interest, 
  for 
  if 
  it 
  can 
  be 
  proved 
  that 
  

   positive 
  rays 
  are 
  able 
  to 
  excite 
  characteristic 
  rays, 
  it 
  then 
  

   becomes 
  possible 
  to 
  obtain 
  a 
  better 
  insight 
  into 
  the 
  connexion 
  

   between 
  the 
  process 
  of 
  excitation 
  and 
  the 
  chemical 
  nature 
  and 
  

   charge 
  of 
  the 
  exciting 
  particles. 
  And 
  such 
  an 
  investigation 
  

   might 
  throw 
  new 
  light 
  on 
  the 
  questions 
  relating 
  to 
  the 
  

   mechanism 
  of 
  excitation 
  and 
  emission 
  of 
  X-spectra. 
  

  

  These 
  considerations 
  have 
  prompted 
  me 
  to 
  investigate 
  the 
  

   question 
  as 
  to 
  whether 
  positive 
  rays 
  are 
  capable 
  of 
  exciting 
  

   the 
  characteristic 
  X-radiation. 
  

  

  The 
  experimental 
  method 
  was 
  based 
  upon 
  similar 
  principles 
  

   to 
  that 
  employed 
  by 
  Chadwicklf 
  in 
  his 
  investigation 
  of 
  the 
  

   excitation 
  of 
  the 
  characteristic 
  7-radiation 
  of 
  gold 
  by 
  a-rays. 
  

  

  Through 
  a 
  channel 
  of 
  circular 
  section 
  10 
  mm. 
  wide 
  a 
  pencil 
  

   of 
  positive 
  rays 
  was 
  let 
  fall 
  upon 
  a 
  circular 
  opening 
  provided 
  

   in 
  a 
  brass 
  box. 
  This 
  opening 
  is 
  divided 
  into 
  two 
  halves, 
  and 
  

   each 
  of 
  these 
  is 
  covered 
  up 
  by 
  a 
  double 
  foil 
  made 
  up 
  of 
  one 
  

   foil 
  of 
  a 
  heavy 
  metal, 
  say 
  tin 
  or 
  lead, 
  and 
  of 
  a 
  second 
  foil 
  of 
  a 
  

   light 
  metal, 
  say 
  aluminium, 
  laid 
  over 
  the 
  first 
  one. 
  These 
  

   foils 
  are 
  so 
  placed 
  that 
  over 
  one 
  half 
  of 
  the 
  opening 
  the 
  

   heavy-metal 
  foil 
  is 
  on 
  the 
  outside 
  with 
  the 
  aluminium 
  foil 
  

   turned 
  towards 
  the 
  inside 
  of 
  the 
  box, 
  while 
  the 
  second 
  

   similar 
  double 
  foil 
  is 
  so 
  arranged 
  over 
  the 
  other 
  half 
  of 
  the 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  J. 
  J. 
  Thomson, 
  Proc. 
  of 
  Cambr. 
  Phil. 
  Soc. 
  xiii. 
  p. 
  212 
  (1905); 
  

   Ch. 
  Fuchtbauer, 
  Phys. 
  Z. 
  S. 
  vii. 
  p. 
  153 
  (1906) 
  ; 
  L. 
  W. 
  Austin, 
  Phys. 
  Rev, 
  

   xxii. 
  p. 
  312(1906). 
  

  

  I 
  J. 
  J. 
  Thomson, 
  Phil. 
  Mag. 
  [6] 
  xxviii. 
  p. 
  620 
  (1914). 
  

  

  § 
  J. 
  Chadwick, 
  Phil. 
  Mag. 
  [6] 
  xxiv. 
  p. 
  594 
  (1912) 
  ; 
  xxv. 
  p. 
  193 
  (1913). 
  

  

  || 
  J. 
  Chadwick 
  & 
  A. 
  S. 
  Russell, 
  Proc. 
  Roy. 
  Soc. 
  A. 
  lxxxviii. 
  p. 
  217 
  

   (1913) 
  ; 
  A. 
  S. 
  Russell 
  & 
  J. 
  Chadwick, 
  Phil. 
  Mag. 
  [6] 
  xxvii. 
  p. 
  112 
  (1914). 
  

   H 
  J. 
  Chadwick, 
  Phil. 
  Mag. 
  [6] 
  xxv. 
  p. 
  193 
  (1913). 
  

  

  