﻿606 
  ]\tr. 
  T. 
  S. 
  Taylor 
  on 
  the 
  Retardation 
  of 
  

  

  greater 
  when 
  the 
  diaphragm 
  was 
  completely 
  open 
  than 
  it 
  was 
  

   when 
  the 
  diaphragm 
  just 
  limited 
  the 
  beam. 
  However, 
  the 
  

   difference 
  between 
  the 
  ionization 
  in 
  the 
  two 
  cases 
  was 
  a 
  

   constant 
  value 
  for 
  all 
  positions 
  of 
  the 
  metal 
  sheets 
  above 
  the 
  

   source 
  of 
  rays. 
  This 
  difference 
  would 
  not 
  be 
  a 
  constant 
  

   quantity 
  if 
  the 
  scattering 
  of 
  the 
  rays 
  was 
  the 
  occasion 
  of 
  the 
  

   increase 
  in 
  the 
  ionization 
  produced 
  by 
  moving 
  the 
  metal 
  

   sheets 
  away 
  from 
  the 
  source 
  of 
  the 
  rays. 
  On 
  the 
  contrary, 
  

   the 
  difference 
  between 
  the 
  ionizations 
  with 
  and 
  without 
  the 
  

   diaphragm 
  limiting 
  the 
  geometrical 
  beam 
  of 
  rays 
  would 
  be 
  

   greater 
  when 
  the 
  sheet 
  is 
  far 
  away 
  from 
  the 
  source 
  of 
  rays 
  

   than 
  when 
  it 
  is 
  near 
  the 
  source 
  of 
  rays 
  if 
  scattering 
  of 
  the 
  

   rays 
  by 
  the 
  foils 
  was 
  the 
  cause 
  of 
  the 
  increase 
  in 
  the 
  ioni- 
  

   zation. 
  The 
  fact 
  that 
  the 
  ionization 
  was 
  greater 
  with 
  the 
  

   diaphragm 
  open 
  than 
  when 
  it 
  just 
  limited 
  the 
  cone 
  of 
  rays 
  

   signifies 
  that 
  more 
  alpha-particles 
  get 
  into 
  the 
  ionization- 
  

   chamber 
  in 
  the 
  former 
  than 
  in 
  the 
  latter 
  case, 
  and 
  therefore 
  

   confirms 
  the 
  existence 
  of 
  the 
  scattering 
  of 
  the 
  rays 
  by 
  metal 
  

   foils 
  as 
  found 
  by 
  Geiger 
  *. 
  

  

  These 
  two 
  methods 
  of 
  investigation, 
  although 
  in 
  the 
  case 
  

   of 
  the 
  latter 
  showing 
  the 
  existence 
  of 
  the 
  scattering 
  of 
  the 
  

   rays, 
  seem 
  to 
  be 
  sufficient 
  to 
  preclude 
  scattering 
  as 
  an 
  

   explanation 
  for 
  the 
  so-called 
  decrease 
  in 
  the 
  air- 
  equivalents 
  

   of 
  the 
  metal 
  sheets 
  as 
  they 
  are 
  moved 
  away 
  from 
  the 
  polonium. 
  

   By 
  measuringthe 
  ionizations 
  with 
  and 
  without 
  the 
  diaphragms 
  

   limiting 
  the 
  cone 
  of 
  rays 
  when 
  there 
  was 
  not 
  a 
  metal 
  sheet 
  

   over 
  the 
  source 
  of 
  rays, 
  it 
  was 
  found 
  that 
  the 
  ionization 
  was 
  

   greater 
  in 
  the 
  latter 
  than 
  in 
  the 
  former 
  case, 
  which 
  shows 
  

   that 
  the 
  rays 
  are 
  scattered 
  by 
  air 
  as 
  w^ell 
  as 
  by 
  metals. 
  These 
  

   methods, 
  however, 
  are 
  not 
  particularly 
  suitable 
  for 
  measuring- 
  

   the 
  amount 
  of 
  the 
  scattering, 
  and 
  hence 
  no 
  comparison 
  as 
  to 
  

   how 
  much 
  each 
  metal 
  scatters 
  the 
  rays 
  was 
  attempted. 
  The 
  

   important 
  fact 
  is 
  that 
  the 
  effect 
  under 
  consideration 
  is 
  not 
  

   influenced 
  by 
  the 
  scattering 
  of 
  the 
  rays. 
  

  

  Continuation 
  of 
  the 
  Experiments. 
  

   In 
  the 
  first 
  experiments 
  polonium 
  had 
  been 
  used 
  as 
  the 
  

   source 
  of 
  rays, 
  but 
  in 
  order 
  to 
  extend 
  the 
  study 
  to 
  alpha- 
  

   particles 
  of 
  higher 
  range, 
  radium 
  C 
  has 
  been 
  used 
  in 
  the 
  

   present 
  experiments. 
  This 
  made 
  it 
  possible 
  to 
  use 
  foils 
  of 
  

   greater 
  thickness 
  than 
  had 
  been 
  previously 
  used. 
  A 
  thin 
  

   aluminium 
  foil 
  covered 
  with 
  a 
  thin 
  coating 
  of 
  lacquer 
  was 
  

   put 
  directly 
  over 
  a 
  capsule 
  containing 
  a 
  thin 
  film 
  of 
  pure 
  

   radium 
  bromide 
  in 
  order 
  to 
  prevent 
  escape 
  of 
  the 
  emanation. 
  

   The 
  hole 
  in 
  the 
  brass 
  plug 
  over 
  the 
  radium 
  bromide 
  was 
  of 
  

  

  * 
  Proceedings 
  of 
  the 
  Eoyal 
  Society, 
  Series 
  A, 
  vol, 
  Ixxxi. 
  no, 
  A 
  546 
  

   p. 
  174. 
  

  

  