﻿j'Rai/s 
  of 
  Uranium 
  and 
  Radium. 
  635 
  

  

  about 
  2 
  "5 
  per 
  cent, 
  greater 
  over 
  the 
  whole 
  range 
  for 
  the 
  dispo- 
  

   sition 
  described 
  in 
  detail 
  in 
  section 
  10. 
  For 
  thicknesses 
  less 
  

   than 
  1 
  cm. 
  of 
  lead 
  the 
  curves 
  are 
  no 
  longer 
  exponential, 
  and 
  

   the 
  value 
  of 
  X 
  apparently 
  increases. 
  The 
  study 
  of 
  this 
  part 
  

   of 
  the 
  range 
  forms 
  the 
  subject 
  of 
  a 
  separate 
  communication. 
  

  

  It 
  will 
  be 
  seen 
  that 
  as 
  a 
  general 
  result 
  the 
  experimental 
  

   values 
  of 
  \jd 
  are 
  nearly 
  the 
  same 
  for 
  all 
  substances, 
  the 
  mean 
  

   value 
  being 
  0*0536. 
  The 
  departures 
  of 
  the 
  values 
  of 
  Xjd 
  from 
  

   this 
  mean 
  are, 
  however, 
  greater 
  than 
  should 
  be 
  the 
  case 
  if 
  they 
  

   were 
  due 
  merely 
  to 
  errors 
  of 
  observation. 
  Indeed 
  the 
  varia- 
  

   tions 
  seemed 
  not 
  to 
  be 
  due 
  so 
  much 
  to 
  differences 
  in 
  the 
  

   metals, 
  as 
  different 
  results 
  were 
  obtained 
  for 
  different 
  series 
  

   of 
  observations 
  on 
  the 
  same 
  metals, 
  as 
  to 
  other 
  unexplained 
  

   causes. 
  The 
  extreme 
  values 
  for 
  Xjd 
  vary 
  between 
  '0668 
  and 
  

   •0440, 
  a 
  difference 
  of 
  about 
  20 
  per 
  cent, 
  on 
  either 
  side 
  of 
  the 
  

   mean 
  value. 
  

  

  Beyond 
  a 
  thickness 
  of 
  5 
  cm. 
  of 
  lead, 
  or 
  an 
  equivalent 
  

   thickness 
  of 
  mercury, 
  the 
  absorption 
  appeared 
  to 
  be 
  less 
  than 
  

   the 
  normal. 
  At 
  this 
  range, 
  however, 
  the 
  effects 
  produced 
  

   are 
  of 
  the 
  same 
  order 
  of 
  magnitude 
  as 
  the 
  natural 
  leak 
  of 
  

   the 
  instrument, 
  and 
  are 
  too 
  small 
  to 
  be 
  measured 
  with 
  any 
  

   certainty. 
  Subsequent 
  experiments 
  with 
  the 
  more 
  active 
  

   preparations 
  of 
  the 
  third 
  separation 
  failed 
  to 
  establish 
  beyond 
  

   doubt 
  any 
  alteration 
  in 
  the 
  value 
  of 
  the 
  absorption 
  coefficient. 
  

  

  The 
  disposition 
  employed 
  in 
  this 
  series 
  is 
  a 
  troublesome 
  

   one 
  to 
  work 
  with 
  in 
  practice, 
  but 
  in 
  our 
  opinion 
  the 
  general 
  

   results 
  obtained 
  are, 
  from 
  a 
  theoretical 
  point 
  of 
  view, 
  of 
  

   equal 
  value 
  to 
  those 
  obtained 
  with 
  another 
  disposition 
  detailed 
  

   in 
  section 
  11. 
  

  

  7. 
  Variation 
  of 
  the 
  Ionization 
  produced 
  hy 
  fy-Rays. 
  

  

  In 
  order 
  to 
  compare 
  directly 
  the 
  7-rays 
  of 
  uranium 
  with 
  

   those 
  of 
  radium 
  and 
  to 
  obtain 
  further 
  light 
  on 
  the 
  variations 
  

   referred 
  to, 
  experiments 
  were 
  now 
  undertaken 
  with 
  radium. 
  

   It 
  w^as 
  found, 
  in 
  the 
  first 
  place, 
  that 
  the 
  errors 
  of 
  observation 
  

   were 
  reduced 
  by 
  remo^ang 
  the 
  source 
  of 
  light 
  a 
  considerable 
  

   distance 
  from 
  the 
  electroscope, 
  and 
  interposing 
  a 
  sheet 
  of 
  

   ground 
  glass 
  between 
  it 
  and 
  the 
  electroscope. 
  A 
  thin 
  cardboard 
  

   cover 
  also 
  was 
  placed 
  over 
  the 
  electroscope 
  which 
  was 
  re- 
  

   moved 
  only 
  when 
  the 
  leaf 
  system 
  was 
  being 
  charged. 
  This 
  

   hood 
  had 
  the 
  effect 
  of 
  maintaining 
  a 
  constant 
  temperature 
  

   around 
  the 
  wall 
  of 
  the 
  electroscope 
  while 
  its 
  presence 
  did 
  not 
  

   affect 
  the 
  leak 
  of 
  the 
  instrument. 
  In 
  the 
  second 
  place, 
  a 
  very 
  

   curious 
  effect 
  was 
  noticed, 
  first 
  in 
  working 
  with 
  the 
  more 
  

   powerful 
  7-rays 
  from 
  radium. 
  If 
  the 
  time 
  for 
  the 
  leaf 
  to 
  cross 
  

   the 
  scale 
  was 
  taken 
  and 
  the 
  experiment 
  repeated 
  a 
  number 
  

  

  2U2 
  

  

  