﻿278 
  

  

  Dr. 
  A. 
  S. 
  Eve 
  on 
  P 
  

  

  nmary 
  

  

  Bragg 
  has 
  published 
  about 
  a 
  dozen 
  readings 
  o£ 
  this 
  

   character. 
  I 
  find 
  that, 
  for 
  reasons 
  subsequently 
  stated, 
  the 
  

   product 
  of 
  the 
  extreme 
  is 
  nearly 
  equal 
  to 
  the 
  product 
  of 
  the 
  

   mean 
  readings. 
  

  

  The 
  plates 
  used 
  in 
  the 
  experiments 
  measured 
  about 
  

   17 
  X 
  21 
  cm., 
  and 
  their 
  respective 
  thickness 
  is 
  stated 
  — 
  

  

  Lead 
  1*7 
  mm. 
  

  

  Silver 
  4-6 
  

  

  Tin 
  4-0 
  

  

  Zinc 
  0-45 
  

  

  Copper 
  305 
  

  

  Iron, 
  steel 
  1"83 
  mm, 
  

  

  ,, 
  wrought 
  . 
  . 
  6-00 
  

  

  Aluminium 
  .... 
  1*72 
  

  

  Carbon 
  15-0 
  

  

  The 
  zinc 
  and 
  aluminium 
  plates 
  were 
  rather 
  too 
  thin, 
  so 
  a 
  

   few 
  were 
  clamped 
  together 
  as 
  required. 
  

  

  Effect 
  of 
  Reversing 
  Plates 
  and 
  D. 
  

  

  When 
  7 
  rays 
  pass 
  through 
  the 
  electroscope 
  and 
  when 
  the 
  

   back 
  plates 
  C 
  and 
  D 
  alone 
  are 
  varied, 
  the 
  resulting 
  changes 
  

   in 
  the 
  rate 
  of 
  discharge 
  of 
  the 
  electroscope 
  depend 
  simply 
  on 
  

   the 
  atomic 
  weight 
  of 
  the 
  substance 
  at 
  C, 
  provided 
  that 
  plate 
  

   is 
  one 
  or 
  two 
  millimetres 
  thick. 
  For 
  the 
  plate 
  D, 
  unless 
  

   very 
  thick, 
  does 
  not 
  send 
  back 
  through 
  C 
  sufficient 
  secondary 
  

   radiation 
  to 
  affect 
  the 
  ionization 
  in 
  the 
  electroscope 
  to 
  a 
  

   noticeable 
  extent. 
  If 
  the 
  plate 
  D 
  were 
  several 
  centimetres 
  

   thick 
  it 
  would, 
  of 
  course, 
  send 
  back 
  through 
  C 
  secondary 
  

   7 
  rays, 
  the 
  additive 
  effect 
  of 
  which 
  could 
  be 
  detected. 
  

  

  In 
  the 
  actual 
  experiments, 
  keeping 
  at 
  A 
  and 
  B 
  any 
  plates 
  

   of 
  a 
  definite 
  material, 
  and 
  using 
  at 
  S 
  screens 
  of 
  iron 
  2 
  cm.,, 
  

   or 
  lead 
  0*6 
  cm., 
  or 
  lead 
  2 
  cm., 
  the 
  effects 
  of 
  varying 
  C 
  are 
  

   shown 
  in 
  the 
  following 
  table 
  and 
  in 
  curve 
  I. 
  (fig. 
  2). 
  

  

  Table 
  I. 
  

  

  Plate 
  C. 
  

  

  Atomic 
  

   Weight. 
  

  

  Ionization 
  Current. 
  

  

  Iron 
  21. 
  

  

  Pb 
  0-6. 
  

  

  Pb 
  2-0. 
  

  

  Mean. 
  

  

  Pb 
  

  

  206-9 
  

   107-9 
  

   65-4 
  

   63-6 
  

   65-9 
  

   27-1 
  

   12-0 
  

  

  100 
  

   93 
  

  

  88-3 
  

   87-6 
  

   86-9 
  

   81-8 
  

   78-0 
  

  

  100 
  

   92-8 
  

  

  89-5 
  

   890 
  

   87-8 
  

   83-0 
  

   80-7 
  

  

  100 
  

  

  89 
  

   87 
  

   87 
  

   81 
  

   78 
  

  

  100 
  

   92-9 
  

  

  88-9 
  

   88-3 
  

   87-3 
  

   82-4 
  

   79-3 
  

  

  Aff 
  

  

  Zn 
  

  

  Cu 
  

  

  Fe 
  

  

  Al 
  

  

  

  

  

  