﻿472 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  occuperaient 
  les 
  images 
  de 
  la 
  troisieme 
  enveloppe 
  ? 
  Peut-etre 
  ces 
  images 
  produi- 
  

   sent-ils 
  les 
  penombres 
  isolees, 
  les 
  penombres 
  sans 
  noyau. 
  Les 
  taches 
  de 
  ce 
  genre 
  

   ne 
  sont 
  pas 
  tres-cornmunes 
  ; 
  jamais 
  leur 
  etendue 
  totale 
  n'est 
  un 
  partie 
  aliquote 
  

   considerable 
  de 
  la 
  surface 
  solaire."* 
  

  

  From 
  these 
  passages, 
  it 
  appears 
  that 
  in 
  M. 
  Arago's 
  opinion, 
  the 
  sun, 
  besides 
  

   being 
  surrounded 
  by 
  a 
  stratum 
  of 
  dark 
  clouds, 
  and 
  a 
  photosphere, 
  has, 
  beyond 
  

   them, 
  and 
  enveloping 
  them, 
  a 
  third 
  atmosphere, 
  in 
  which 
  are 
  floating 
  clouds, 
  

   which, 
  when 
  seen 
  during 
  a 
  total 
  eclipse, 
  form 
  the 
  red 
  prominences. 
  

  

  This 
  is 
  the 
  same 
  view 
  as 
  that 
  stated 
  at 
  the 
  beginning 
  of 
  my 
  paper, 
  on 
  the 
  autho- 
  

   rity 
  of 
  Sir 
  John 
  Heeschel, 
  and 
  to 
  which 
  I 
  have 
  ventured 
  to 
  add 
  the 
  hypothesis 
  

   that 
  the 
  clouds 
  causing 
  the 
  prominences 
  form 
  of 
  themselves 
  a 
  nearly 
  continuous 
  

   envelope, 
  floating 
  in 
  the 
  third 
  atmosphere, 
  and 
  above 
  the 
  photosphere. 
  If, 
  then, 
  a 
  

   formal 
  enumeration 
  of 
  the 
  sun's 
  envelopes 
  were 
  made, 
  according 
  to 
  my 
  view 
  there 
  

   would 
  be/our. 
  1st, 
  The 
  dark 
  clouds 
  below 
  the 
  photosphere. 
  2d, 
  The 
  photosphere 
  

   itself. 
  3d, 
  The 
  envelope 
  of 
  cloud 
  so 
  often 
  referred 
  to 
  ; 
  and, 
  4th, 
  The 
  sun's 
  atmo- 
  

   sphere 
  surrounding 
  all, 
  and 
  in 
  which 
  the 
  other 
  three 
  solar 
  envelopes 
  may 
  be 
  sup- 
  

   posed 
  to 
  float. 
  

  

  That 
  M. 
  Arago 
  does 
  not 
  regard 
  the 
  clouds 
  which 
  occasion 
  the 
  red 
  prominen- 
  

   ces 
  as 
  forming 
  a 
  continuous 
  envelope, 
  appears 
  evident 
  from 
  several 
  considerations. 
  

   In 
  enumerating 
  the 
  envelopes 
  surrounding 
  the 
  sun, 
  he 
  never 
  mentions 
  more 
  

   than 
  three, 
  — 
  viz., 
  the 
  cloudy 
  envelope 
  below 
  the 
  photosphere, 
  the 
  photosphere 
  

   itself, 
  and 
  a 
  third 
  atmosphere 
  surrounding 
  it. 
  This 
  third 
  atmosphere 
  is 
  also 
  

   spoken 
  of 
  as 
  a 
  third 
  envelope, 
  and 
  as 
  an 
  exterior 
  envelope 
  ; 
  but 
  these 
  different 
  

   expressions 
  are 
  evidently 
  employed 
  to 
  denote, 
  as 
  one 
  envelope, 
  the 
  sun's 
  exterior 
  

   atmosphere, 
  along 
  with 
  the 
  clouds 
  floating 
  in 
  it 
  ; 
  for 
  if 
  the 
  atmosphere 
  and 
  the 
  

   clouds 
  were 
  reckoned 
  separately, 
  there 
  would 
  be 
  four 
  envelopes 
  and 
  not 
  three. 
  

   The 
  passage 
  where 
  the 
  third 
  envelope 
  is 
  said 
  to 
  be 
  formed 
  of 
  clouds 
  (formee 
  de 
  

   images) 
  would, 
  indeed, 
  if 
  read 
  by 
  itself, 
  seem 
  to 
  convey 
  the 
  idea 
  of 
  an 
  envelope, 
  

   composed 
  of 
  clouds 
  exclusively 
  ; 
  but 
  other 
  passages 
  sufficiently 
  prove 
  that 
  this 
  is 
  

   not 
  M. 
  Arago's 
  view. 
  Thus 
  the 
  expression, 
  " 
  the 
  clouds 
  of 
  the 
  third 
  envelope" 
  

   indicates 
  the 
  idea 
  that 
  those 
  clouds 
  are 
  not 
  themselves 
  the 
  envelope, 
  but 
  detached 
  

   masses 
  floating 
  in 
  it. 
  Moreover, 
  since 
  the 
  terms, 
  third 
  envelope, 
  third 
  atmosphere, 
  

   and 
  exterior 
  envelope, 
  are 
  obviously 
  all 
  used 
  in 
  the 
  same 
  sense, 
  — 
  the 
  exterior 
  

   envelope 
  or 
  third 
  envelope 
  cannot 
  consist 
  alone 
  of 
  a 
  continuous 
  stratum 
  of 
  clouds 
  

   forming 
  the 
  red 
  prominences 
  ; 
  for 
  it 
  is 
  elsewhere 
  described 
  as 
  causing 
  the 
  white 
  

   corona 
  {couronne 
  blanchatre), 
  which, 
  in 
  the 
  case 
  supposed, 
  would 
  be 
  red, 
  and 
  not 
  

   white. 
  

  

  It 
  seems 
  also 
  highly 
  probable, 
  that 
  if 
  M. 
  Arago 
  had 
  supposed 
  that 
  the 
  clouds 
  

   forming 
  the 
  red 
  prominences 
  also 
  constitute 
  a 
  continuous 
  stratum 
  surrounding 
  

   the 
  sun, 
  the 
  phenomenon 
  of 
  a 
  band 
  of 
  red 
  light 
  seen 
  at 
  the 
  end 
  of 
  the 
  total 
  phase 
  

   of 
  solar 
  eclipses, 
  — 
  which 
  he 
  believes 
  f 
  is 
  caused 
  by 
  the 
  presence 
  of 
  red 
  promi- 
  

  

  * 
  Annuaire 
  for 
  1846, 
  p. 
  465. 
  f 
  Ibid, 
  for 
  1842. 
  p. 
  440, 
  et 
  seq. 
  

  

  