﻿860 
  Mr. 
  F. 
  Soddy 
  on 
  the 
  

  

  is 
  about 
  32 
  days, 
  or 
  5 
  x 
  10"^ 
  in 
  terms 
  oi 
  the 
  other 
  as 
  unity. 
  

   The 
  amount 
  o£ 
  uranium 
  X 
  in 
  equilibrium 
  with 
  a 
  definite 
  

   amount 
  of 
  uranium 
  should 
  produce 
  therefore 
  upon 
  complete 
  

   disintegration 
  about 
  5 
  x 
  10"^ 
  of 
  the 
  amount 
  of 
  the 
  parent 
  of 
  

   radium 
  in 
  equilibrium 
  with 
  the 
  same 
  quantity 
  of 
  uranium. 
  

   The 
  a-activity 
  of 
  this 
  product 
  would 
  therelore 
  be 
  about 
  

   2x10"^ 
  of 
  that 
  of 
  the 
  uranium. 
  In 
  other 
  words, 
  the 
  

   uranium 
  X 
  in 
  equilibrium 
  with 
  1 
  kilogram 
  of 
  uranium 
  

   should 
  thus 
  produce 
  in 
  its 
  complete 
  disintegration 
  a 
  product 
  

   having 
  tlie 
  a-activity 
  of 
  2 
  milligrams 
  of 
  uranium. 
  

  

  The 
  uranium 
  X, 
  after 
  concentration 
  to 
  the 
  greatest 
  possible 
  

   extent 
  j 
  was 
  finally 
  prepared 
  in 
  the 
  form 
  of 
  films 
  in 
  rect- 
  

   angular 
  trays 
  having 
  an 
  area 
  of 
  10 
  sq. 
  cm., 
  which 
  could 
  

   be 
  slipped 
  between 
  the 
  poles 
  of 
  the 
  electromagnet. 
  The 
  

   undeviated 
  radiation 
  entered 
  an 
  electroscope 
  placed 
  above 
  

   the 
  poles 
  provided 
  with 
  an 
  opening 
  in 
  its 
  base 
  covered 
  with 
  

   very 
  thin 
  aluminium-foil. 
  The 
  first 
  attempts 
  were 
  frustrated 
  

   and 
  the 
  first 
  preparations 
  decayed 
  without 
  result, 
  owing 
  to 
  

   the 
  totally 
  unexpected 
  difiiculty 
  in 
  deviating 
  the 
  yS-rays. 
  

   The 
  latter 
  previotisly 
  had 
  been 
  supposed 
  to 
  consist 
  of 
  homo- 
  

   geneous 
  rays 
  having 
  a 
  Value 
  ibr 
  H/3 
  = 
  2000. 
  But 
  it 
  was 
  

   found 
  that 
  a 
  field 
  twice 
  as 
  strong 
  as 
  was 
  necessary 
  completely 
  

   to 
  deviate 
  such 
  rays 
  failed 
  to 
  deviate 
  about 
  5 
  per 
  cent, 
  of 
  

   the 
  total 
  /3-radiation. 
  In 
  the 
  later 
  dispositions 
  the 
  width 
  

   of 
  the 
  gap 
  Was 
  reduced 
  to 
  one-half 
  the 
  former 
  width, 
  and 
  

   the 
  field 
  was 
  sufiicient 
  to 
  deviate 
  completely 
  all 
  rays 
  with 
  a 
  

   value 
  for 
  H/o 
  below 
  8640 
  ; 
  but 
  the 
  leak 
  due 
  to 
  the 
  still 
  

   undeviated 
  y8-radiation, 
  although 
  now 
  proportionately 
  very 
  

   small, 
  was 
  still 
  several 
  times 
  that 
  due 
  to 
  the 
  7-radiation. 
  It 
  

   was 
  still 
  too 
  great 
  in 
  the 
  earlier 
  measurements 
  for 
  the 
  small 
  

   growth 
  of 
  a-radiation^ 
  theoretically 
  to 
  be 
  expected, 
  to 
  be 
  

   within 
  the 
  range 
  of 
  certain 
  detection. 
  In 
  the 
  later 
  experi- 
  

   ments 
  the 
  electroscope 
  \vas 
  filled 
  with 
  hydrogen 
  instead 
  of 
  

   with 
  aif, 
  and 
  this 
  constituted 
  an 
  enormous 
  advance. 
  [Not 
  

   only 
  is 
  the 
  ionization 
  due 
  to 
  the 
  yS- 
  and 
  7-radiation 
  greatly 
  

   reduced 
  and 
  that 
  due 
  to 
  the 
  a-radiation 
  greatly 
  increased, 
  

   but 
  the 
  convection-currents 
  generated 
  in 
  the 
  electroscope 
  by 
  

   the 
  warming 
  up 
  of 
  the 
  magnet 
  are 
  also 
  enormously 
  reduced. 
  

   The 
  readings 
  are 
  far 
  more 
  regular 
  and 
  can 
  be 
  continued 
  for 
  

   a 
  longer 
  time 
  before 
  the 
  leaf 
  begins 
  to 
  be 
  disturbed. 
  In 
  air, 
  

   after 
  half-an-hour's 
  work 
  or 
  less, 
  the 
  leaf 
  commences 
  to 
  wave 
  

   like 
  a 
  flag, 
  and 
  nothing 
  can 
  then 
  be 
  done 
  for 
  eight 
  hours. 
  

   A 
  preparation 
  which 
  gave 
  (in 
  divisions 
  per 
  minute) 
  a 
  leak 
  of 
  

   370 
  divisions 
  bare, 
  and 
  351 
  covered 
  with 
  thin 
  mica 
  (a-rays 
  

   therefore 
  19) 
  when 
  the 
  electroscope 
  w^as 
  filled 
  with 
  air, 
  gave 
  

   in 
  the 
  same 
  apparatus 
  filled 
  with 
  hydrogen^ 
  bare 
  105' 
  2 
  

  

  