﻿608 
  Mr. 
  T. 
  S. 
  Taylor 
  on 
  tie 
  Retardation 
  of 
  

  

  centimetres 
  o£ 
  the 
  respective 
  sheets. 
  Column 
  3 
  has 
  the 
  air- 
  

   equivalents 
  of 
  the 
  sheets 
  as 
  measured 
  directly 
  when 
  the 
  sheets 
  

   were 
  nearest 
  the 
  source 
  o£ 
  rays. 
  Column 
  4 
  contains 
  the 
  

   ratios 
  of 
  the 
  air-equivalents 
  to 
  the 
  thickness 
  of 
  the 
  respective 
  

   metals. 
  The 
  last 
  three 
  lines 
  of 
  the 
  table 
  will 
  be 
  referred 
  to 
  

   later. 
  The 
  air-equivalents 
  of 
  the 
  sheets 
  given 
  in 
  column 
  1, 
  

   Table 
  I., 
  as 
  determined 
  by 
  an 
  improved 
  method 
  for 
  any 
  

   position 
  of 
  the 
  sheets 
  are 
  given 
  in 
  Table 
  II. 
  

  

  Table 
  IT. 
  

  

  Range 
  in 
  cms. 
  

  

  

  1 
  

  

  

  

  

  

  of 
  entering 
  A 
  Al. 
  

  

  B 
  Al. 
  

  

  C 
  Al. 
  D 
  Al. 
  

  

  AAu. 
  

  

  BAu. 
  

  

  CAu. 
  

  

  DAu. 
  

  

  a-particle. 
  

  

  

  

  

  

  

  

  1 
  

  

  5-7 
  0-f97 
  

  

  1-209 
  

  

  1-803 
  

  

  2-672 
  

  

  0-719 
  

  

  0-980 
  

  

  1-375 
  

  

  1-900 
  1 
  

  

  5-3 
  

  

  0-597 
  

  

  1-206 
  

  

  1-792 
  

  

  2-659 
  

  

  0-706 
  

  

  0-966 
  

  

  1-352 
  

  

  1-869 
  1 
  

  

  4-9 
  

  

  0-597 
  

  

  1-202 
  

  

  1-781 
  

  

  2-644 
  

  

  0-693 
  

  

  0947 
  

  

  1-328 
  

  

  1-837 
  i 
  

  

  4-5 
  

  

  0-597 
  

  

  1-198 
  

  

  1-769 
  

  

  2-628 
  

  

  0-6^0 
  

  

  0-929 
  

  

  1-S03 
  

  

  1-802. 
  

  

  4-1 
  

  

  0-597 
  

  

  1193 
  

  

  1-757 
  

  

  2-608 
  

  

  0-668 
  

  

  0-9i0 
  

  

  1-276 
  

  

  1-763 
  

  

  3-7 
  

  

  0-597 
  

  

  1-187 
  

  

  1-742 
  

  

  2-582 
  

  

  0-657 
  

  

  0-889 
  

  

  1-248 
  

  

  1-7201 
  

  

  3-3 
  

  

  0-596 
  

  

  1-178 
  

  

  1-724 
  

  

  ... 
  

  

  0-644 
  

  

  0-866 
  

  

  1-214 
  

  

  1-659 
  ! 
  

  

  2-9 
  

  

  0-595 
  

  

  1-168 
  

  

  1-705 
  

  

  

  0-630 
  

  

  0-837 
  

  

  1-178 
  

  

  1-598 
  1 
  

  

  2-5 
  

  

  0592 
  

  

  1-152 
  

  

  ... 
  

  

  

  0-616 
  

  

  0-805 
  

  

  1-127 
  

  

  i 
  

  

  2-1 
  0-584 
  

  

  M31 
  

  

  

  ... 
  

  

  0-600 
  

  

  0-757 
  

  

  

  

  1-7 
  0570 
  

  

  ... 
  

  

  ... 
  

  

  ... 
  

  

  0-582 
  

  

  

  

  

  1-3 
  0-555 
  

  

  1 
  

  

  

  

  

  

  

  

  1 
  

  

  Range 
  in 
  cms. 
  

  

  

  

  

  

  

  

  1 
  

  

  of 
  entering 
  

  

  ASn. 
  

  

  BSn. 
  

  

  APb. 
  

  

  B 
  Pb. 
  C 
  Pb. 
  

  

  Pap 
  

  

  pr. 
  

  

  Celloidin, 
  | 
  

  

  a-particle. 
  

  

  

  

  

  

  

  5-7 
  

  

  1-011 
  

  

  1-995 
  

  

  M04 
  

  

  1-396 
  

  

  2-325 
  

  

  1-0 
  

  

  20 
  

  

  0-520 
  

  

  5-3 
  

  

  1-002 
  

  

  1-980 
  

  

  1-085 
  

  

  1-371 
  

  

  2-296 
  

  

  

  

  1 
  

  

  4-9 
  

  

  0-993 
  

  

  1-960 
  

  

  1-064 
  

  

  1-343 
  

  

  2-260 
  

  

  

  

  

  1 
  

   1 
  

  

  4-5 
  

  

  0-984 
  

  

  1-938 
  

  

  1042 
  

  

  1-320 
  

  

  2-220 
  

  

  

  

  

  

  4-1 
  

  

  0-971 
  

  

  1-914 
  

  

  1-020 
  

  

  1-289 
  

  

  2-180 
  

  

  

  

  

  

  3-7 
  

  

  0-957 
  

  

  1-884 
  

  

  0-999 
  

  

  1-263 
  

  

  2-124 
  

  

  

  

  

  

  3-3 
  

  

  0-941 
  

  

  1-845 
  

  

  0-977 
  

  

  1-232 
  

  

  2-046 
  

  

  

  

  

  

  2-9 
  

  

  0-923 
  

  

  1-7951 
  0-950 
  

  

  1-2C0| 
  

  

  ;; 
  

  

  

  

  

  2-5 
  

  

  0-902 
  

  

  ... 
  \ 
  0-923 
  

  

  1-163 
  

  

  

  

  

  

  2-1 
  

  

  0-882 
  

  

  ... 
  ' 
  0-888 
  i 
  

  

  

  

  

  

  1-7 
  

  

  0-853 
  

  

  1 
  

  

  

  

  

  

  1-3 
  

  

  

  

  1 
  

  

  

  1 
  

  

  The 
  aluminium 
  foil 
  over 
  the 
  radium 
  to 
  prevent 
  the 
  escape 
  

   of 
  the 
  emanation 
  cut 
  down 
  the 
  range 
  of 
  the 
  alpha-particles 
  

   0*46 
  cm. 
  The 
  height 
  of 
  the 
  plug 
  containing 
  the 
  radium 
  was 
  

   0*9 
  cm. 
  above 
  the 
  radium. 
  Therefore 
  the 
  maximum 
  avail- 
  

   able 
  range 
  of 
  the 
  alpha-particles 
  entering 
  the 
  sheet 
  is 
  5*70. 
  

   The 
  values 
  of 
  the 
  air-equivalents 
  for 
  each 
  of 
  the 
  metal 
  sheets 
  

   in 
  Table 
  II. 
  represent 
  the 
  average 
  results 
  obtained 
  from 
  a 
  

   series 
  of 
  from 
  six 
  to 
  ten 
  separate 
  determinations, 
  the 
  details 
  

   of 
  which 
  have 
  been 
  omitted 
  for 
  the 
  sake 
  of 
  brevity. 
  

  

  