﻿Transformations 
  of 
  X-Rays. 
  125 
  

  

  The 
  next 
  step 
  was 
  to 
  calculate 
  in 
  some 
  one 
  particular 
  case 
  

   an 
  actual 
  value 
  of 
  k 
  from 
  the 
  data 
  obtained 
  by 
  using 
  a 
  

   suitable 
  pair 
  of 
  secondary 
  and 
  tertiary 
  radiators. 
  A 
  flat 
  

   polished 
  plate 
  of 
  pure 
  copper 
  (3*04 
  cm. 
  x 
  3*03 
  cm.) 
  was 
  

   mounted 
  on 
  a 
  fine 
  aluminium 
  stem 
  and 
  placed 
  in 
  the 
  position 
  

   E2. 
  The 
  ionization-chamber 
  connected 
  to 
  the 
  tertiary 
  elec- 
  

   troscope 
  E3 
  was 
  removed 
  and 
  replaced 
  by 
  the 
  electroscope 
  Eg. 
  

   The 
  distance 
  from 
  the 
  centre 
  of 
  the 
  radiator 
  to 
  the 
  centre 
  of 
  

   the 
  tissue-paper-covered 
  window 
  of 
  Eg 
  was 
  4" 
  7 
  cm., 
  the 
  area 
  

   of 
  the 
  window 
  being 
  the 
  same 
  as 
  in 
  previous 
  experiments. 
  

   The 
  plane 
  of 
  the 
  radiator 
  being 
  vertical 
  with 
  the 
  normnl 
  

   to 
  its 
  surface 
  bisecting 
  the 
  angle 
  between 
  the 
  axis 
  of 
  the 
  

   secondary 
  beam 
  and 
  the 
  normal 
  to 
  the 
  aperture 
  at 
  its 
  centre, 
  

   of 
  the 
  electroscope 
  Eg. 
  

  

  From 
  the 
  relative 
  positions 
  of 
  the 
  tertiary 
  radiator 
  and 
  the 
  

   window 
  of 
  E2 
  (carefully 
  determined) 
  a 
  value 
  of 
  o) 
  was 
  

   calculated 
  and 
  found 
  to 
  be 
  approximately 
  '222, 
  

  

  The 
  ratio 
  of 
  the 
  ionizations 
  in 
  the 
  electroscopes 
  Eg 
  and 
  Ej 
  

   was 
  then 
  determined, 
  allowance 
  being 
  made 
  for 
  the 
  air-effect 
  

   in 
  the 
  manner 
  previously 
  explained, 
  and 
  the 
  mean 
  of 
  several 
  

   readings, 
  none 
  of 
  which 
  differed 
  by 
  more 
  than 
  2 
  per 
  cent, 
  

   from 
  the 
  mean, 
  was 
  found 
  to 
  be 
  '115. 
  

  

  The 
  tertiary 
  radiator 
  was 
  then 
  removed 
  and 
  the 
  electroscope 
  

   Eg 
  was 
  placed 
  with 
  its 
  window 
  perpendicular 
  to 
  the 
  axis 
  of 
  

   the 
  secondary 
  beam, 
  the 
  centre 
  of 
  the 
  window 
  being 
  in 
  the 
  

   position 
  previously 
  occupied 
  by 
  the 
  centre 
  of 
  the 
  tertiary 
  

   radiator. 
  Since 
  the 
  area 
  of 
  the 
  window 
  of 
  Eg 
  was 
  almost 
  

   exactly 
  equal 
  in 
  shape 
  and 
  size 
  to 
  the 
  area 
  of 
  the 
  tertiary 
  

   radiator 
  projected 
  in 
  a 
  plane 
  perpendicular 
  to 
  the 
  axis 
  of 
  the 
  

   secondary 
  beam^ 
  the 
  ionization 
  will 
  correspond 
  to 
  the 
  mean 
  

   intensity 
  over 
  the 
  area 
  of 
  the 
  tertiary 
  radiator 
  in 
  the 
  previous 
  

   part 
  of 
  the 
  experiment. 
  The 
  mean 
  value 
  of 
  the 
  ratio 
  of 
  the 
  

   deflexions 
  in 
  Eg 
  and 
  Ej 
  was 
  now 
  equal 
  to 
  11*48. 
  

  

  Substituting 
  the 
  values 
  of 
  a, 
  /S, 
  Xi 
  and 
  Xg 
  from 
  Table 
  V., 
  

   we 
  find 
  

  

  , 
  -115 
  60*7 
  6*0 
  4'7r 
  ,1^7^ 
  . 
  .oox 
  o/.-. 
  

  

  ^ 
  =11^ 
  ^ 
  1W9 
  ^ 
  9-2 
  >^ 
  -222 
  ^ 
  (1075 
  + 
  488) 
  = 
  361. 
  

  

  The 
  value 
  of 
  Xg 
  was 
  increased 
  by 
  3 
  per 
  cent, 
  to 
  allow 
  for 
  the 
  

   obliquity 
  ; 
  the 
  value 
  of 
  k 
  was, 
  however, 
  affected 
  by 
  less 
  than 
  

   1 
  per 
  cent. 
  

  

  In 
  the 
  series 
  of 
  experiments 
  previously 
  mentioned, 
  in 
  the 
  

   course 
  of 
  which 
  a 
  copper 
  radiator 
  was 
  subjected 
  to 
  secondary 
  

   beams 
  from 
  the 
  group 
  of 
  metals 
  C>r-Ag, 
  we 
  obtained 
  values 
  

   of 
  R^ 
  with 
  arsenic 
  as 
  radiator, 
  and 
  in 
  these 
  cases 
  

  

  qoo^i 
  

  

  R' 
  a 
  A 
  47r, 
  . 
  

  

  