﻿314 
  Prof. 
  E. 
  Rutherford 
  and 
  Mr. 
  T. 
  Royds 
  on 
  the 
  

  

  50 
  c.mms., 
  provided 
  with 
  fine 
  platinum 
  electrodes, 
  was 
  used. 
  

   This 
  was 
  sealed 
  to 
  the 
  connexion 
  leading 
  to 
  the 
  pump 
  and 
  

   completely 
  exhausted, 
  a 
  discharge 
  being 
  passed 
  to 
  free 
  the 
  elec- 
  

   trodes 
  of 
  hydrogen. 
  When 
  the 
  emanation 
  had 
  been 
  purified 
  

   as 
  completely 
  as 
  possible 
  in 
  the 
  manner 
  outlined, 
  it 
  was 
  con- 
  

   densed 
  in 
  the 
  spectrum-tube 
  by 
  dipping 
  a 
  side 
  tube 
  connected 
  

   with 
  it 
  in 
  liquid 
  air. 
  When 
  the 
  greater 
  part 
  of 
  the 
  emanation 
  

   had 
  been 
  condensed, 
  the 
  spectrum-tube 
  was 
  sealed 
  off 
  and 
  

   removed 
  for 
  observation. 
  

  

  Measurements 
  of 
  the 
  7 
  ray 
  activity 
  showed 
  that 
  the 
  

   amount 
  of 
  emanation 
  in 
  the 
  tube 
  corresponded 
  to 
  130 
  milli- 
  

   grams 
  of 
  radium. 
  Now 
  the 
  volume 
  of 
  the 
  emanation 
  per 
  

   gram 
  of 
  radium 
  is 
  *57 
  cubic 
  mm. 
  Consequently, 
  the 
  volume 
  

   of 
  the 
  pure 
  emanation 
  in 
  the 
  spectrum 
  tube 
  was 
  *074 
  

   cubic 
  mm. 
  Since 
  the 
  volume 
  of 
  the 
  spectrum-tube 
  was 
  

   50 
  cubic 
  muis., 
  this 
  would 
  give 
  a 
  pressure 
  of 
  emanation 
  in 
  

   the 
  tube 
  of 
  1*1 
  mms. 
  of 
  mercury. 
  In 
  order 
  to 
  photograph 
  

   the 
  spectrum, 
  a 
  spectrograph 
  with 
  a 
  glass 
  prism 
  of 
  two 
  inches 
  

   base 
  was 
  used. 
  The 
  length 
  of 
  the 
  spectrum 
  on 
  the 
  plate 
  

   between 
  X 
  5000 
  and 
  \ 
  4000 
  was 
  1*5 
  cms. 
  Arrangements 
  

   were 
  made 
  so 
  that 
  visual 
  observations 
  of 
  the 
  wave-lengths 
  

   could 
  be 
  made 
  by 
  the 
  Hilger 
  spectroscope 
  while 
  the 
  plate 
  

   was 
  being 
  exposed. 
  Two 
  photographs 
  were 
  taken 
  before 
  the 
  

   emanation 
  spectrum 
  ran 
  out. 
  The 
  first 
  (photograph 
  1) 
  showed 
  

   about 
  thirty 
  of 
  the 
  more 
  intense 
  emanation 
  lines. 
  The 
  second 
  

   (photograph 
  2), 
  which 
  had 
  a 
  much 
  longer 
  exposure, 
  showed 
  

   over 
  a 
  hundred 
  lines. 
  A 
  helium 
  tube 
  was 
  used 
  for 
  comparison 
  

   purposes, 
  and 
  its 
  spectrum 
  obtained 
  above 
  and 
  below 
  the 
  

   emanation 
  spectrum. 
  The 
  plates 
  were 
  measured 
  up 
  with 
  the 
  

   aid 
  of 
  a 
  Kayser's 
  measuring 
  machine. 
  The 
  wave-lengths 
  

   were 
  deduced 
  with 
  the 
  aid 
  of 
  the 
  Hartmann 
  dispersion 
  

   formula. 
  

  

  Remarks 
  on 
  Spectrum. 
  

  

  The 
  colour 
  of 
  the 
  discharge 
  through 
  the 
  emanation 
  was 
  

   bluish 
  and 
  not 
  so 
  intense 
  as 
  the 
  helium 
  tube. 
  The 
  spectrum 
  

   observed 
  visually 
  was 
  a 
  brilliant 
  one 
  of 
  bright 
  lines. 
  The 
  

   most 
  noticeable 
  lines 
  were 
  a 
  number 
  of 
  strong 
  lines 
  in 
  the 
  

   green 
  and 
  another 
  group 
  in 
  the 
  violet. 
  The 
  mercury 
  and 
  

   hydrogen 
  lines 
  were 
  also 
  observed. 
  In 
  order 
  to 
  be 
  sure 
  that 
  

   the 
  lines 
  were 
  due 
  to 
  the 
  emanation, 
  the 
  side 
  tube 
  attached 
  to 
  

   the 
  spectrum-tube 
  was 
  immersed 
  in 
  liquid 
  air. 
  At 
  the 
  moment 
  

   of 
  condensation, 
  which 
  was 
  readily 
  noticed 
  by 
  the 
  increased 
  

  

  