﻿Alpha 
  Rays 
  hy 
  Metals 
  and 
  Gases, 
  609 
  

  

  Experiments 
  were 
  also 
  made 
  with 
  sheets 
  of 
  paper 
  and 
  

   celloidin*. 
  Two 
  sheets 
  o£ 
  paper 
  of 
  about 
  one 
  and 
  two 
  cm. 
  

   air-equivalents 
  respectively, 
  and 
  three 
  sheets 
  of 
  celloidin 
  of 
  

   air-equivalents 
  of 
  the 
  order 
  of 
  0*5, 
  1"0 
  and 
  2*0 
  cm. 
  respec- 
  

   tively 
  were 
  used. 
  For 
  these 
  sheets 
  of 
  paper 
  and 
  celloidin, 
  

   the 
  ionization 
  did 
  not 
  increase 
  as 
  the 
  sheets 
  were 
  moved 
  

   away 
  from 
  the 
  radium 
  but 
  had 
  the 
  same 
  value 
  for 
  all 
  posi- 
  

   tions 
  of 
  the 
  sheets 
  and 
  hence 
  their 
  air-equivalents 
  remained 
  

   constant. 
  

  

  The 
  behaviour 
  of 
  the 
  sheets 
  of 
  paper 
  and 
  celloidin, 
  the 
  

   atomic 
  weights 
  t 
  of 
  which 
  are 
  about 
  the 
  same 
  as 
  that 
  of 
  air, 
  

   suo-D-ested 
  the 
  idea 
  of 
  undertakino- 
  to 
  obtain 
  sheets 
  of 
  some 
  

  

  o 
  

  

  substance 
  such 
  as 
  hydrogen, 
  whose 
  atomic 
  weight 
  is 
  less 
  than 
  

   that 
  of 
  air. 
  For 
  this 
  purpose 
  a 
  ring 
  about 
  one 
  centimetre 
  

   wide 
  was 
  cut 
  from 
  a 
  brass 
  tube 
  six 
  centimetres 
  in 
  diameter 
  

   and 
  two 
  small 
  brass 
  tubes 
  w^ere 
  put 
  in 
  the 
  ring 
  diametrically 
  

   opposite 
  each 
  other. 
  Thin 
  films 
  of 
  celloidin 
  w^ere 
  stretched 
  

   across 
  each 
  side 
  of 
  the 
  ring 
  and 
  held 
  in 
  place 
  by 
  universal 
  

   wax. 
  This 
  formed 
  a 
  cell 
  which 
  could 
  be 
  filled 
  with 
  hydrogen 
  

   and 
  then 
  used 
  in 
  the 
  same 
  manner 
  as 
  the 
  metal 
  foils. 
  To 
  be 
  

   certain 
  that 
  the 
  cell 
  was 
  always 
  full 
  of 
  hydroo-en 
  a 
  slioht 
  

   current 
  of 
  the 
  gas 
  was 
  kept 
  flow^ing 
  through 
  it 
  all 
  the 
  time 
  

   during 
  an 
  experiment. 
  L 
  current 
  of 
  air 
  was 
  kept 
  circulating- 
  

   through 
  the 
  case 
  surrounding 
  the 
  apparatus 
  in 
  order 
  to 
  

   prevent 
  the 
  hydrogen 
  that 
  might 
  possibly 
  leak 
  from 
  the 
  cell 
  

   from 
  entering 
  tlieionization-chamber. 
  The 
  air-equivalent 
  of 
  

   the 
  hydrogen 
  cell, 
  or 
  sheet, 
  when 
  0*9 
  cm. 
  from 
  the 
  radium 
  

   was 
  determined 
  by 
  plotting 
  the 
  ionization-curve 
  first 
  with 
  

   hydrogen 
  and 
  then 
  with 
  air 
  in 
  the 
  cell. 
  The 
  ordinates 
  of 
  the 
  

   latter 
  curve 
  were 
  all 
  increased 
  by 
  the 
  thickness 
  of 
  the 
  cell 
  of 
  

   hydrogen 
  which 
  gave 
  the 
  position 
  of 
  the 
  curve 
  if 
  the 
  cell 
  had 
  

   been 
  evacuated. 
  The 
  difference 
  between 
  the 
  ordinates 
  of 
  the 
  

   two 
  curves 
  corresponding 
  to 
  a 
  given 
  abscissa 
  was 
  the 
  air- 
  

   equivalent 
  of 
  the 
  hydrogen 
  sheet. 
  

  

  When 
  the 
  eel] 
  containing 
  the 
  hydrogen 
  was 
  moved 
  away 
  

   from 
  the 
  radium, 
  which 
  w^as 
  kept 
  at 
  a 
  given 
  position 
  as 
  in 
  the 
  

   previous 
  cases, 
  it 
  was 
  found 
  that 
  the 
  ionization 
  decreased^ 
  

   which 
  signified 
  that 
  the 
  total 
  range 
  in 
  air 
  of 
  the 
  alpha-particle 
  

   was 
  less 
  when 
  the 
  hydrogen 
  sheet 
  was 
  far 
  away 
  from 
  the 
  

   radium 
  than 
  when 
  it 
  was 
  near 
  the 
  radium. 
  Thus 
  the 
  amount 
  

   by 
  which 
  the 
  range 
  of 
  the 
  alpha-particle 
  was 
  cut 
  down 
  

   by 
  its 
  passage 
  through 
  the 
  cell 
  w 
  as 
  greater 
  w^hen 
  the 
  cell 
  

   was 
  at 
  a 
  distance 
  from 
  the 
  radium 
  than 
  it 
  was 
  when 
  it 
  was 
  

   near 
  the 
  radium. 
  Consequently 
  the 
  air-equivalent 
  of 
  the 
  

  

  * 
  Celloidin 
  is 
  a 
  specially 
  pure 
  preparation 
  of 
  collodion, 
  

   t 
  By 
  atomic 
  weight 
  of 
  air, 
  paper, 
  and 
  celloidin 
  is 
  meant 
  the 
  average 
  

   weight 
  of 
  the 
  constituent 
  atoms. 
  

  

  