﻿618 
  Mr. 
  T. 
  S. 
  Taylor 
  o?i 
  the 
  Retardation 
  of 
  

  

  and 
  hence 
  tbe 
  ratio 
  of 
  the 
  energy 
  of 
  the 
  alpha-particle 
  con- 
  

   sumed 
  by 
  its 
  passage 
  through 
  a 
  sheet 
  of 
  metal, 
  to 
  the 
  energy 
  

   that 
  would 
  be 
  consumed 
  by, 
  say, 
  1 
  centimetre 
  of 
  air 
  at 
  the 
  

   same 
  point 
  in 
  the 
  path 
  of 
  the 
  particle, 
  decreases 
  as 
  the 
  range 
  

   of 
  the 
  alpha-particle 
  decreases. 
  The 
  behaviour 
  of 
  the 
  metal 
  

   sheets 
  relative 
  to 
  the 
  air 
  is 
  entirely 
  analogous 
  to 
  the 
  behaviour 
  

   of 
  the 
  air, 
  or 
  celloidin 
  relative 
  to 
  hydrogen. 
  Consequently, 
  

   if 
  it 
  were 
  possible 
  to 
  measure 
  the 
  ionization 
  produced 
  by 
  the 
  

   alpha-particle 
  at 
  different 
  points 
  in 
  the 
  path 
  of 
  the 
  rays 
  in 
  

   the 
  metals, 
  and 
  if 
  the 
  ionization-curves 
  were 
  plotted 
  on 
  the 
  

   same 
  scale 
  as 
  those 
  shown 
  for 
  air 
  and 
  hydrogen 
  (fig. 
  2), 
  it 
  is 
  

   probable 
  that 
  the 
  curves 
  for 
  the 
  metals 
  would 
  all 
  present 
  

   some 
  such 
  differences 
  from 
  the 
  air 
  curve 
  as 
  those 
  existing 
  

   between 
  the 
  air 
  and 
  hydrogen 
  curves. 
  Moreover, 
  these 
  

   differences 
  might 
  be 
  expected 
  to 
  be 
  such 
  as 
  to 
  agree 
  with 
  the 
  

   different 
  rates 
  at 
  which 
  the 
  air-equivalents 
  of 
  the 
  different 
  

   metal 
  sheets 
  change. 
  In 
  the 
  upper 
  portion 
  the 
  curve 
  for 
  

   gold 
  would 
  probably 
  lie 
  within 
  the 
  air 
  curve 
  about 
  the 
  same 
  

   amount 
  as 
  the 
  air 
  curve 
  does 
  within 
  the 
  hydrogen 
  curve 
  

   (fig. 
  2) 
  ; 
  and 
  in 
  the 
  lower 
  portion 
  the 
  curve 
  for 
  gold 
  would 
  

   probably 
  lie 
  without 
  the 
  air 
  curve 
  by 
  the 
  same 
  amount 
  as 
  

   the 
  air 
  curve 
  does 
  without 
  the 
  hydrogen 
  curve. 
  At 
  least 
  

   some 
  such 
  differences 
  would 
  be 
  in 
  accordance 
  with 
  the 
  

   square 
  root 
  law, 
  since 
  the 
  square 
  root 
  of 
  the 
  atomic 
  weight 
  

   of 
  air 
  is 
  a 
  mean 
  proportional 
  between 
  the 
  square 
  roots 
  of 
  the 
  

   atomic 
  weights 
  of 
  gold 
  and 
  hydrogen. 
  The 
  curves 
  for 
  the 
  

   other 
  metals 
  would 
  occupy 
  intermediate 
  positions 
  between 
  

   the 
  curves 
  for 
  gold 
  and 
  air. 
  

  

  We 
  have 
  seen 
  that 
  for 
  different 
  metal 
  sheets 
  of 
  abotit 
  the 
  

   same 
  air-equivalents, 
  the 
  rates 
  at 
  which 
  the 
  air-equivalents 
  

   decrease 
  with 
  the 
  speed 
  of 
  the 
  alpha-particle 
  are 
  proportional 
  

   to 
  the 
  square 
  roots 
  of 
  the 
  atomic 
  weights 
  of 
  the 
  respective 
  

   metals. 
  Consequently, 
  the 
  rates 
  of 
  decrease 
  of 
  the 
  ratios 
  of 
  

   the 
  quantities 
  of 
  energy 
  used 
  up 
  in 
  the 
  sheets 
  to 
  the 
  energy 
  

   that 
  would 
  be 
  consumed 
  by 
  a 
  centimetre 
  of 
  air 
  at 
  the 
  same 
  

   positions 
  in 
  the 
  path 
  of 
  the 
  particle 
  decreases 
  also 
  as 
  the 
  

   square 
  roots 
  of 
  the 
  atomic 
  weights 
  of 
  the 
  respective 
  metals. 
  

   On 
  the 
  basis 
  of 
  our 
  hypothesis 
  that 
  for 
  a 
  given 
  speed 
  of 
  the 
  

   alpha-particle 
  the 
  same 
  amount 
  of 
  energy 
  is 
  required 
  to 
  

   produce 
  an 
  ion 
  in 
  all 
  substances, 
  and 
  from 
  the 
  results 
  in 
  our 
  

   experiments, 
  it 
  appears 
  very 
  probable 
  that 
  for 
  the 
  high 
  

   velocities 
  the 
  alpha-particle 
  loses 
  its 
  energy, 
  in 
  going 
  through 
  

   a 
  substance, 
  more 
  rapidly 
  the 
  higher 
  the 
  atomic 
  weight 
  of 
  the 
  

   substance 
  ; 
  but 
  as 
  the 
  speed 
  of 
  the 
  alpha-particle 
  becomes 
  

   less, 
  this 
  changes 
  until 
  for 
  the 
  low 
  velocities 
  the 
  loss 
  of 
  the 
  

   energy 
  of 
  the 
  particle 
  is 
  more 
  rapid 
  the 
  lower 
  the 
  atomic 
  

   weight 
  of 
  the 
  substance. 
  

  

  