﻿80 
  Scientific 
  Intelligence. 
  

  

  order 
  of 
  8/x 
  2 
  and 
  fx 
  2 
  about 
  100 
  c.g.s. 
  units, 
  so 
  that 
  the 
  contrast 
  i& 
  

   measured 
  by 
  the 
  Napierian 
  base 
  raised 
  to 
  the 
  power 
  -700 
  x. 
  

   Therefore, 
  when 
  x 
  = 
  01 
  mm. 
  the 
  ratio 
  of 
  the 
  intensities 
  at 
  oppo- 
  

   site 
  sides 
  of 
  the 
  discontinuity 
  is 
  about 
  e 
  -7 
  , 
  that 
  is 
  1100 
  : 
  1. 
  In 
  

   practice, 
  de 
  Broglie 
  finds 
  that 
  the 
  unavoidable 
  fogging 
  of 
  the 
  

   photographic 
  plates 
  combined 
  with 
  the 
  masking 
  effect 
  of 
  the 
  

   superposition 
  of 
  more 
  penetrating 
  radiations 
  of 
  higher 
  spectral 
  

   orders 
  requires 
  that 
  the 
  calculated 
  ratio 
  of 
  intensities 
  shall 
  exceed 
  

   2 
  : 
  1 
  in 
  order 
  to 
  give 
  distinct 
  contrast. 
  

  

  To 
  check 
  these 
  deductions 
  experimentally 
  the 
  author 
  made 
  a 
  

   few 
  quantitative 
  tests 
  to 
  find 
  how 
  great 
  a 
  dilution 
  might 
  be 
  used 
  

   without 
  destroying 
  the 
  necessary 
  contrast. 
  For 
  wave-lengths 
  

   inferior 
  to 
  2 
  X 
  10" 
  8 
  cm., 
  the 
  vessel 
  should 
  be 
  made 
  of 
  celluloid, 
  

   since 
  the 
  absorbing 
  power 
  of 
  glass 
  and 
  aluminium 
  is 
  about 
  nine 
  

   times 
  as 
  great 
  as 
  that 
  of 
  celluloid 
  and 
  of 
  water. 
  A 
  solution 
  of 
  

   5 
  grams 
  of 
  barium 
  chloride 
  in 
  a 
  liter 
  of 
  water 
  showed 
  quite 
  dis- 
  

   tinctly 
  the 
  barium 
  band 
  (AO-328 
  X 
  10" 
  s 
  cm.) 
  when 
  the 
  thickness 
  

   of 
  the 
  absorbing 
  layer 
  was 
  3 
  cms. 
  With 
  slightly 
  greater 
  thick- 
  

   nesses, 
  the 
  presence 
  of 
  barium 
  in 
  a 
  solution 
  containing 
  1 
  gram 
  

   of 
  the 
  salt 
  per 
  liter 
  could 
  still 
  be 
  detected. 
  In 
  the 
  last 
  case, 
  the 
  

   mass 
  of 
  barium 
  in 
  the 
  actual 
  path 
  of 
  the 
  beam 
  of 
  X-rays 
  was 
  

   inferior 
  to 
  one 
  milligram. 
  

  

  Having 
  thus 
  shown 
  that 
  the 
  metallic 
  constituents 
  of 
  dilute 
  

   solutions 
  can 
  be 
  detected 
  by 
  X-ray 
  absorption 
  analysis, 
  de 
  Brog- 
  

   lie 
  applied 
  this 
  method 
  to 
  the 
  element 
  radium. 
  The 
  author 
  

   says, 
  in 
  substance: 
  "A 
  solution 
  containing 
  about 
  25 
  mg. 
  of 
  

   radium 
  chloride 
  per 
  cm 
  3 
  , 
  was 
  enclosed 
  in 
  a 
  tube 
  of 
  acetate 
  of 
  

   cellulose, 
  having 
  a 
  diameter 
  of 
  2 
  mm. 
  and 
  thin 
  walls 
  (there 
  being 
  

   20 
  mm 
  3 
  , 
  of 
  solution 
  and 
  about 
  0-5 
  mg. 
  of 
  radium 
  chloride), 
  and 
  

   the 
  region 
  of 
  wave-lengths 
  from 
  0-5 
  X 
  10" 
  8 
  cm. 
  to 
  1-2 
  X 
  10" 
  8 
  cm. 
  

   was 
  then 
  explored. 
  Two 
  characteristic 
  bands, 
  L 
  t 
  and 
  L 
  2 
  , 
  of 
  the 
  

   element 
  radium 
  were 
  discovered, 
  their 
  respective 
  wave-lengths 
  

   being 
  0-802 
  X 
  10 
  8 
  cm. 
  and 
  0-668 
  X 
  10 
  8 
  cm." 
  A 
  weak 
  band 
  of 
  

   uncertain 
  origin 
  was 
  also 
  observed 
  at 
  A 
  0-707 
  X 
  10" 
  8 
  cm. 
  These 
  

   results 
  were 
  confirmed 
  by 
  using 
  another 
  preparation 
  of 
  radium 
  

   chloride 
  which 
  was 
  so 
  much 
  purer 
  than 
  the 
  preceding 
  one 
  that 
  

   the 
  strong 
  band 
  of 
  barium 
  (the 
  chief 
  impurity) 
  had 
  practically 
  

   disappeared. 
  Within 
  the 
  limits 
  of 
  experimental 
  error, 
  the 
  fre- 
  

   quencies 
  for 
  the 
  bands 
  L 
  x 
  and 
  L 
  2 
  conform 
  to 
  Moseley's 
  law 
  and 
  

   the 
  atomic 
  number 
  88, 
  hence 
  the 
  radioactive 
  properties 
  of 
  

   radium 
  seem 
  to 
  have 
  no 
  appreciable 
  influence 
  on 
  the 
  absorption 
  

   of 
  this 
  element 
  for 
  X-rays 
  of 
  the 
  hardness 
  thus 
  far 
  tried. 
  — 
  Jour, 
  

   de 
  Phys., 
  9, 
  31, 
  1919. 
  h. 
  s. 
  u. 
  

  

  8. 
  The 
  Spectra 
  of 
  Isotopes. 
  — 
  In 
  the 
  year 
  1917 
  Aronberg 
  

   made 
  a 
  careful 
  comparison 
  of 
  the 
  line 
  A4058 
  as 
  radiated 
  by 
  ordi- 
  

   nary 
  lead 
  and 
  by 
  uranio-lead 
  obtained 
  from 
  Australian 
  carno- 
  

   tite. 
  He 
  found 
  that 
  the 
  wave-length 
  both 
  of 
  this 
  line 
  and 
  of 
  its 
  

   satellite 
  was 
  greater 
  by 
  about 
  0004 
  Angstrom 
  unit 
  for 
  the 
  

  

  