﻿Alpha 
  Rays 
  hy 
  Metals 
  and 
  Gases. 
  613 
  

  

  successive 
  layers 
  of 
  aluminium 
  foil 
  diminish 
  the 
  range 
  of 
  the 
  

   alpha-particles 
  by 
  equal 
  amounts 
  seem 
  to 
  hold 
  true 
  for 
  thin 
  

   sheets 
  of 
  foil 
  when 
  the 
  range 
  is 
  high 
  ; 
  but 
  when 
  the 
  metal 
  

   sheet 
  is 
  thicker, 
  or 
  for 
  thin 
  sheets 
  when 
  the 
  range 
  is 
  low, 
  it 
  

   does 
  not 
  hold. 
  The 
  slight 
  difference, 
  however, 
  in 
  the 
  air- 
  

   equivalent 
  of 
  the 
  thin 
  foil, 
  when 
  near 
  and 
  far 
  away 
  from 
  the 
  

   polonium, 
  would 
  scarcely 
  be 
  detected 
  by 
  measuring 
  directly 
  

   the 
  air-equivalent 
  in 
  the 
  two 
  positions. 
  This 
  is 
  probably 
  the 
  

   explanation 
  of 
  the 
  above 
  statements 
  by 
  McClung, 
  Levin, 
  and 
  

   Rutherford. 
  

  

  Since 
  the 
  air-equivalent 
  of 
  a 
  metal 
  sheet 
  decreases 
  with 
  

   the 
  speed 
  of 
  the 
  alpha-particle 
  entering 
  it, 
  the 
  ratio 
  of 
  the 
  

   air-equivalent 
  to 
  the 
  thickness 
  of 
  a 
  given 
  sheet 
  of 
  metal 
  

   should 
  be 
  less 
  than 
  the 
  same 
  ratio 
  for 
  a 
  thinner 
  sheet 
  of 
  the 
  

   same 
  metal. 
  This 
  is 
  shown 
  to 
  be 
  true 
  by 
  the 
  last 
  column 
  of 
  

   Table 
  I. 
  For 
  the 
  hydrogen 
  sheets 
  on 
  the 
  contrary 
  the 
  same 
  

   ratio 
  should 
  increase 
  as 
  the 
  thickness 
  of 
  the 
  cell 
  or 
  sheet 
  of 
  

   hydrogen 
  increases. 
  This 
  is 
  also 
  confirmed 
  by 
  the 
  last 
  

   column 
  of 
  Table 
  I. 
  

  

  While 
  the 
  air- 
  equivalent 
  of 
  the 
  sheet 
  of 
  celloidin 
  remains 
  

   constant 
  the 
  hvdrogen-equivalent 
  of 
  the 
  same 
  does 
  not 
  remain 
  

   constant 
  but 
  decreases 
  as 
  the 
  range 
  of 
  the 
  alpha-particle 
  in 
  

   hydrogen 
  decreases. 
  The 
  curve 
  " 
  Celloidin 
  in 
  Hydrogen,'^ 
  

   fig. 
  1, 
  which 
  was 
  plotted 
  from 
  the 
  results 
  recorded 
  in 
  

   Table 
  ly., 
  illustrates 
  this 
  point. 
  It 
  is 
  to 
  be 
  noted 
  also 
  from 
  

   the 
  curve 
  '* 
  A 
  Gold 
  in 
  Hydrogen 
  '^ 
  (fig. 
  1) 
  that 
  the 
  rate 
  at 
  

   which 
  the 
  liydrogen-equivalent 
  of 
  the 
  A 
  gold 
  decreases 
  is 
  much 
  

   greater 
  than 
  the 
  rate 
  at 
  which 
  its 
  air-equivalent 
  decreases. 
  

   The 
  curve 
  designated 
  "A 
  Gold 
  in 
  Air 
  ^' 
  (fig. 
  1) 
  is 
  the 
  portion 
  

   of 
  the 
  ''A 
  Gold^' 
  curve 
  in 
  the 
  same 
  figure 
  that 
  lies 
  to 
  the 
  

   left 
  of 
  the 
  abscissa 
  3"0. 
  The 
  co-ordinates 
  of 
  that 
  portion 
  of 
  

   the 
  curve 
  are 
  magnified 
  about 
  4| 
  times 
  so 
  as 
  to 
  be 
  plotted 
  on 
  

   the 
  same 
  scale 
  as 
  the 
  curves 
  obtained 
  in 
  the 
  hydrogen 
  

   atmosphere. 
  -ii 
  is 
  the 
  ratio 
  of 
  the 
  thickness 
  of 
  a 
  hydrogen 
  

   sheet 
  to 
  its 
  air-equivalent 
  when 
  near 
  the 
  radium. 
  The 
  slope 
  

   of 
  the 
  curve 
  '• 
  A 
  Gold 
  in 
  Air 
  '■' 
  is 
  practically 
  the 
  same 
  as 
  that 
  

   of 
  '' 
  Celloidin 
  in 
  Hydrogen^' 
  as 
  can 
  be 
  seen 
  from 
  the 
  figure. 
  

   The 
  angle 
  which 
  the 
  curve 
  " 
  A 
  Gold 
  in 
  Hydrogen 
  " 
  makes 
  

   with 
  the 
  curve 
  '* 
  A 
  Gold 
  in 
  Air 
  " 
  is 
  about 
  the 
  same 
  as 
  the 
  

   angle 
  which 
  the 
  curve 
  '* 
  Celloidin 
  in 
  Hydrogen 
  '' 
  makes 
  with 
  

   the 
  axis 
  of 
  abscissas. 
  The 
  slope 
  of 
  the 
  curve 
  " 
  A 
  Gold 
  in 
  

   Hydrogen 
  " 
  is 
  nearly 
  3J 
  times 
  the 
  slope 
  of 
  the 
  curve 
  

   " 
  Celloidin 
  in 
  Hydrogen/' 
  But 
  »3J 
  is 
  the 
  ratio 
  of 
  the 
  square 
  

   root 
  of 
  the 
  atomic 
  weight 
  of 
  gold 
  to 
  that 
  of 
  air 
  

  

  [V^'..,.. 
  ]. 
  

  

  