﻿316 
  Prof. 
  E. 
  Rutherford 
  and 
  Mr. 
  T. 
  Royds 
  on 
  the 
  

  

  strong 
  discharge 
  to 
  get 
  rid 
  of 
  most 
  of 
  the 
  hydrogen 
  from 
  

   the 
  electrodes. 
  About 
  the 
  same 
  quantity 
  o£ 
  pure 
  emanation 
  

   as 
  in 
  the 
  first 
  experiment 
  was 
  condensed 
  in 
  the 
  tube. 
  After 
  

   sealing 
  off 
  the 
  tube, 
  the 
  spectrum 
  was 
  photographed, 
  visual 
  

   observations 
  being* 
  made 
  at 
  the 
  same 
  time. 
  

  

  The 
  same 
  general 
  effect 
  as 
  in 
  the 
  first 
  experiment 
  was 
  

   observed 
  when 
  the 
  emanation 
  was 
  condensed 
  on 
  the 
  side 
  

   tube. 
  In 
  this 
  case, 
  however, 
  the 
  hydrogen 
  spectrum 
  was 
  

   relatively 
  much 
  feebler. 
  On 
  condensing 
  the 
  emanation, 
  the 
  

   tube 
  became 
  very 
  hard 
  and 
  showed 
  the 
  characteristic 
  green 
  

   coloration 
  of 
  the 
  cathode-ray 
  vacuum. 
  It 
  was 
  thus 
  clear 
  

   that 
  the 
  methods 
  employed 
  had 
  been 
  fairly 
  successful 
  in 
  

   getting 
  rid 
  of 
  the 
  hydrogen 
  from 
  the 
  electrodes. 
  The 
  photo- 
  

   graph 
  of 
  the 
  spectrum 
  in 
  this 
  case 
  (photograph 
  3) 
  showed 
  

   only 
  the 
  hydrogen 
  line 
  H/3, 
  although 
  H 
  a 
  also 
  was 
  observed 
  

   visually. 
  In 
  the 
  second 
  photograph, 
  already 
  referred 
  to, 
  the 
  

   stronger 
  lines 
  of 
  the 
  compound 
  line 
  spectrum 
  of 
  hydrogen 
  

   had 
  been 
  photographed*. 
  The 
  photograph 
  3 
  is 
  reproduced 
  

   in 
  Plates 
  X. 
  and 
  XL, 
  magnification 
  3'7 
  times. 
  Plate 
  X. 
  was 
  

   exposed 
  to 
  bring 
  out 
  clearly 
  the 
  strong 
  lines 
  of 
  the 
  spectrum 
  

   only. 
  It 
  will 
  be 
  seen 
  that 
  the 
  stronger 
  lines 
  in 
  Plate 
  XI. 
  are 
  

   somewhat 
  overexposed 
  in 
  order 
  to 
  bring 
  out 
  some 
  of 
  the 
  less 
  

   intense 
  lines 
  in 
  the 
  spectrum. 
  This 
  photograph 
  is 
  somewhat 
  

   better 
  for 
  reproduction 
  purposes 
  than 
  photograph 
  2, 
  but 
  does 
  

   not 
  show 
  quite 
  the 
  same 
  number 
  of 
  faint 
  lines. 
  

  

  The 
  measurements 
  of 
  the 
  wave-lengths 
  of 
  the 
  lines 
  common 
  

   to 
  the 
  two 
  plates 
  agreed 
  within 
  the 
  limits 
  of 
  experimental 
  

   error. 
  We 
  shall 
  consequently 
  only 
  give 
  the 
  measurement 
  

   of 
  photograph 
  2, 
  since 
  the 
  hydrogen 
  lines 
  present 
  in 
  this 
  

   spectrum 
  serve 
  as 
  an 
  indication 
  of 
  the 
  accuracy 
  of 
  the 
  

   measurements. 
  It 
  will 
  be 
  seen 
  that 
  the 
  error 
  of 
  measure- 
  

   ment 
  is 
  certainly 
  not 
  greater 
  than 
  half 
  an 
  Angstrom 
  unit. 
  

   The 
  lines 
  given 
  in 
  the 
  Table 
  are 
  common 
  to 
  both 
  photographs. 
  

   It 
  has 
  not 
  been 
  thought 
  necessary 
  to 
  give 
  the 
  weaker 
  lines 
  

   observed, 
  for 
  the 
  identity 
  of 
  these 
  with 
  the 
  emanation 
  spectrum 
  

   requires 
  further 
  confirmation. 
  

  

  In 
  the 
  Table 
  the 
  lines 
  observed 
  visually 
  are 
  given 
  in 
  a 
  

   separate 
  column. 
  In 
  photograph 
  3, 
  when 
  the 
  hydrogen 
  was 
  

   far 
  less 
  prominent, 
  the 
  relative 
  intensity 
  of 
  some 
  of 
  the 
  

   emanation 
  lines 
  differed 
  from 
  that 
  observed 
  in 
  photograph 
  2. 
  

  

  * 
  No 
  trace 
  of 
  the 
  carbon-dioxide 
  spectrum 
  was 
  observed 
  in 
  either 
  

   experiment. 
  The 
  occurrence 
  of 
  this 
  spectrum 
  in 
  the 
  electrodeless 
  dis- 
  

   charge 
  in 
  nearly 
  pure 
  emanation 
  (see 
  paper, 
  loc. 
  cit.) 
  was 
  without 
  doubt 
  

   due 
  to 
  a 
  trace 
  of 
  organic 
  matter 
  on 
  the 
  surface 
  of 
  the 
  mercurv. 
  

  

  