﻿Distribution 
  oj 
  Energy 
  in 
  the 
  Spectra 
  of 
  Gases. 
  803 
  

  

  over 
  the 
  space 
  of 
  one 
  day, 
  is 
  a 
  practical 
  impossibility. 
  The 
  

   electrodes 
  emit 
  and 
  re-absorb 
  various 
  gases, 
  and 
  are 
  on 
  this 
  

   account 
  a 
  continual 
  source 
  of 
  trouble. 
  

  

  We 
  may 
  say 
  a 
  few 
  words 
  here 
  as 
  to 
  the 
  comparative 
  

   merits 
  of 
  thermal 
  and 
  photometric 
  methods 
  of 
  measurement. 
  

   The 
  great 
  advantage 
  of 
  the 
  latter 
  method 
  is 
  that 
  very 
  

   much 
  smaller 
  amounts 
  of 
  radiant 
  energy 
  can 
  be 
  compared. 
  

   On 
  the 
  other 
  hand, 
  the 
  thermal 
  method, 
  especially 
  the 
  

   thermopile, 
  gives 
  an 
  immediate 
  effect 
  proportional 
  to 
  the 
  

   energy 
  received. 
  There 
  are 
  no 
  sources 
  of 
  error 
  such 
  as 
  

   comparison 
  standards, 
  personal 
  equation, 
  &c. 
  Further, 
  the 
  

   setting 
  of 
  a 
  photometric 
  apparatus 
  is 
  an 
  operation 
  requiring 
  

   far 
  more 
  time 
  than 
  a 
  thermopile 
  reading. 
  It 
  is 
  true 
  that 
  the 
  

   best 
  thermal 
  measuring-instruments 
  are 
  as 
  yet 
  unable 
  to 
  give 
  

   measurable 
  readings 
  for 
  any 
  but 
  the 
  very 
  strong 
  lines 
  in 
  the 
  

   spectra 
  of 
  gases, 
  but 
  improvements 
  in 
  this 
  direction 
  are 
  

   possible. 
  

  

  2. 
  Summary 
  of 
  Previous 
  Work 
  on 
  the 
  Subject. 
  

  

  Investigations 
  on 
  the 
  radiations 
  from 
  gases 
  in 
  discharge- 
  

   tubes 
  have 
  been 
  made 
  by 
  the 
  following, 
  among 
  others 
  : 
  — 
  

  

  Greenwich 
  Observations. 
  1887. 
  

  

  o 
  

  

  Angstroii. 
  Ann. 
  der 
  Phys. 
  vol. 
  xlviii. 
  pp. 
  493-531 
  (1893). 
  

   J. 
  J. 
  Thomson. 
  Proc. 
  Roy. 
  Soc. 
  vol. 
  lviii. 
  p. 
  244 
  (1895). 
  

   Kalahne. 
  Ann. 
  der 
  Phys. 
  vol. 
  lxv. 
  pp. 
  815-848 
  (1898). 
  

   Ferry. 
  Ann. 
  der 
  Pkys. 
  1899, 
  vol. 
  lxix. 
  pp. 
  398-425; 
  Plivs. 
  

  

  Review, 
  1898, 
  vol. 
  vii. 
  pp. 
  1-9 
  (1898). 
  

   Lewis. 
  Ann. 
  der 
  Phys. 
  vol. 
  lxix. 
  pp. 
  398-425 
  (1899). 
  

   Langenbach. 
  Ann. 
  der 
  Phys. 
  vol. 
  x. 
  pp. 
  789-815 
  (1903). 
  

   Berndt. 
  Ann. 
  der 
  Phys. 
  vol. 
  xii. 
  pp. 
  1101-1114 
  (1903). 
  

   \Vaetzmann. 
  Ann. 
  der 
  Phys. 
  vol. 
  xiv. 
  pp. 
  772-790 
  (1904). 
  

   Geiger. 
  Ann. 
  der 
  Phys. 
  vol. 
  xxii. 
  pp. 
  973-1007 
  (1907). 
  

   Pfluger. 
  Ann. 
  der 
  Phys. 
  vol, 
  xxiv. 
  pp. 
  515-526 
  (1907). 
  

   Paschen. 
  Ann. 
  der 
  Phys. 
  vol. 
  xxvii. 
  pp. 
  537-570 
  (1908). 
  

   Ladenburg. 
  Verh. 
  d. 
  B. 
  Ges. 
  vol. 
  x. 
  pp. 
  550-561 
  (1908) 
  ; 
  Ann. 
  

  

  der 
  Phys. 
  vol. 
  xxxviii. 
  pp. 
  249-318 
  (1912). 
  

   Nutting 
  & 
  Tugman. 
  ' 
  Nature,' 
  vol. 
  lxxxi. 
  p. 
  189 
  (1909) 
  ; 
  Astroph. 
  

  

  Journal, 
  vol. 
  xxxi. 
  pp. 
  62-75 
  (1910). 
  

  

  The 
  results 
  obtained 
  by 
  the 
  experimenters 
  mentioned 
  

   above 
  do 
  not 
  at 
  first 
  sight 
  appear 
  to 
  form 
  a 
  consistent 
  

   whole. 
  But 
  it 
  must 
  be 
  remembered 
  that 
  the 
  experiments 
  

   described 
  refer 
  to 
  almost 
  every 
  conceivable 
  method 
  of 
  pro- 
  

   ducing 
  a 
  discharge, 
  and 
  that 
  the 
  other 
  conditions 
  varied 
  

   much 
  in 
  the 
  work 
  of 
  the 
  different 
  observers. 
  There 
  seems 
  

   no 
  doubt 
  that 
  the 
  energy 
  of 
  the 
  total 
  radiation, 
  and 
  there- 
  

   fore 
  the 
  energy 
  of 
  any 
  line, 
  in 
  the 
  spectra 
  of 
  the 
  permanent 
  

  

  312 
  

  

  