﻿Polarized 
  Light 
  by 
  Fluorescent 
  Gases. 
  189 
  

  

  much 
  of 
  the 
  energy 
  o£ 
  the 
  gas 
  to 
  rotation 
  of 
  the 
  molecule. 
  

   Another 
  possible 
  depolarizing 
  factor 
  is 
  what 
  may 
  be 
  termed 
  

   secondary 
  fluorescence, 
  or 
  fluorescence 
  excited, 
  not 
  by 
  the 
  

   primary 
  ray 
  but 
  by 
  the 
  resonance 
  radiation 
  of 
  the 
  gas. 
  Lord 
  

   fiayleigh 
  has 
  considered 
  the 
  possibility 
  of 
  an 
  analogous 
  action 
  

   in 
  his 
  treatment 
  of 
  the 
  theory 
  of 
  the 
  colour 
  of 
  the 
  sky 
  and 
  

   its 
  polarization. 
  The 
  fluorescent 
  light 
  is 
  of 
  course 
  rather 
  

   feeble 
  in 
  comparison 
  with 
  the 
  exciting 
  light, 
  but 
  it 
  must 
  be 
  

   remembered 
  that 
  its 
  frequencies 
  are 
  just 
  right, 
  and 
  the 
  

   radiation 
  from 
  one 
  molecule 
  would 
  without 
  doubt 
  be 
  able 
  to 
  

   excite 
  vibrations 
  in 
  a 
  neighbouring 
  one. 
  

  

  The 
  discovery 
  of 
  the 
  polarization 
  of 
  light 
  by 
  fluorescing 
  

   gases 
  will 
  perhaps 
  give 
  us 
  a 
  satisfactory 
  theory 
  of 
  the 
  solar 
  

   corona. 
  

  

  The 
  radial 
  polarization 
  of 
  the 
  corona 
  amounts 
  to 
  about 
  

   11 
  per 
  cent., 
  its 
  spectrum 
  is 
  continuous, 
  though 
  some 
  observers 
  

   have 
  found 
  faint 
  indications 
  of 
  the 
  Fraunhofer 
  lines, 
  and 
  it 
  

   appears 
  to 
  be 
  cold, 
  that 
  is 
  no 
  deflexions 
  are 
  obtained 
  with 
  the 
  

   bolometer. 
  Polarization 
  is 
  usually 
  ascribed 
  to 
  scattering 
  by 
  

   small 
  particles, 
  the 
  continuous 
  spectrum 
  to 
  an 
  emission 
  by 
  

   larger 
  particles 
  (white 
  hot), 
  while 
  the 
  apparent 
  absence 
  of 
  

   radiant 
  heat 
  cannot 
  very 
  well 
  be 
  reconciled 
  with 
  the 
  presence 
  

   o£ 
  white-hot 
  particles. 
  If 
  we 
  regard 
  the 
  corona 
  as 
  a 
  cloud 
  

   of 
  mixed 
  metallic 
  vapours 
  fluorescing 
  under 
  the 
  terrific 
  

   radiation 
  from 
  the 
  sun, 
  there 
  seem 
  to 
  be 
  fewer 
  contradictions. 
  

   The 
  polarization 
  is 
  just 
  about 
  what 
  we 
  should 
  expect, 
  a 
  

   continuous 
  spectrum, 
  at 
  least 
  with 
  all 
  resolving 
  powers 
  which 
  

   can 
  be 
  brought 
  to 
  bear, 
  would 
  be 
  almost 
  certain, 
  and 
  there 
  is 
  

   no 
  inherent 
  difficulty 
  in 
  explaining 
  the 
  absence 
  of 
  radiant 
  

   heat. 
  The 
  presence 
  of 
  faint 
  traces 
  of 
  the 
  Fraunhofer 
  lines 
  

   could 
  be 
  ascribed 
  to 
  light 
  from 
  the 
  sky, 
  which 
  is 
  largely 
  due 
  

   to 
  light 
  from 
  the 
  exposed 
  edge 
  of 
  the 
  sun. 
  The 
  so-called 
  

   coronium 
  line, 
  and 
  other 
  bright 
  lines 
  peculiar 
  to 
  the 
  corona, 
  

   may 
  be 
  merely 
  fluorescent 
  lines 
  of 
  well-known 
  elements. 
  As 
  

   I 
  have 
  shown 
  already, 
  the 
  fluorescent 
  lines 
  of 
  sodium 
  bear 
  no 
  

   relation 
  to 
  any 
  of 
  the 
  lines 
  excited 
  by 
  other 
  means. 
  It 
  

   appears 
  to 
  me 
  to 
  be 
  even 
  possible 
  that 
  the 
  Fraunhofer 
  lines 
  

   are 
  produced 
  by 
  the 
  absorption 
  of 
  this 
  outlying 
  cloud 
  of 
  

   vapour 
  rather 
  than 
  by 
  a 
  comparatively 
  shallow 
  layer 
  as 
  is 
  

   usually 
  supposed, 
  These 
  are 
  of 
  course 
  questions 
  that 
  can 
  be 
  

   more 
  intelligently 
  discussed 
  by 
  those 
  engaged 
  in 
  work 
  upon 
  

   solar 
  physics, 
  and 
  I 
  am 
  merely 
  drawing 
  attention 
  to 
  a 
  new 
  

   factor 
  that 
  may 
  possibly 
  be 
  introduced 
  to 
  advantage. 
  

  

  