﻿448 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  ing 
  motion. 
  Its 
  base 
  was 
  from 
  first 
  to 
  last 
  sharply 
  bounded 
  by 
  the 
  edge 
  of 
  the 
  

   moon." 
  " 
  To 
  my 
  great 
  astonishment," 
  he 
  adds, 
  " 
  this 
  marvellous 
  object 
  con- 
  

   tinued 
  visible 
  for 
  about 
  five 
  seconds, 
  as 
  nearly 
  as 
  I 
  could 
  judge, 
  after 
  the 
  sun 
  began 
  

   to 
  reappear, 
  which 
  took 
  place 
  many 
  degrees 
  to 
  the 
  south 
  of 
  the 
  situation 
  it 
  oc- 
  

   cupied 
  on 
  the 
  moon's 
  circumference. 
  It 
  then 
  rapidly 
  faded 
  away, 
  but 
  it 
  did 
  not 
  

   vanish 
  instantaneously."* 
  

  

  These 
  observations 
  seem 
  quite 
  inexplicable, 
  on 
  the 
  hypothesis 
  that 
  the 
  pro- 
  

   minences 
  result 
  from 
  mirage 
  occasioned 
  by 
  the 
  unequal 
  heating 
  of 
  the 
  air. 
  For 
  

   not 
  only 
  did 
  they 
  preserve 
  their 
  forms 
  unchanged 
  during 
  a 
  period 
  at 
  which 
  little 
  

   or 
  no 
  unequal 
  heating 
  of 
  the 
  air 
  could 
  have 
  taken 
  place 
  ; 
  but 
  according 
  to 
  the 
  

   very 
  important 
  observations 
  of 
  Mr 
  Dawes 
  and 
  Mr 
  Hind, 
  they 
  continued 
  visible, 
  

   apparently 
  without 
  change 
  of 
  form, 
  even 
  after 
  the 
  reappearance 
  of 
  the 
  sun. 
  Now, 
  

   at 
  the 
  reappearance 
  of 
  the 
  sun, 
  the 
  air 
  in 
  the 
  path 
  of 
  light 
  would 
  rapidly 
  pass 
  

   through 
  the 
  three 
  states, 
  of 
  being 
  first 
  entirely 
  protected 
  from 
  the 
  sun's 
  rays, 
  

   then 
  heated 
  on 
  one 
  side 
  at 
  the 
  moment 
  of 
  reappearance, 
  and 
  finally 
  heated 
  on 
  

   both 
  sides. 
  f 
  About 
  that 
  time, 
  then, 
  if 
  phenomena 
  of 
  the 
  nature 
  of 
  mirage 
  ex- 
  

   isted, 
  we 
  might 
  expect 
  the 
  most 
  rapid 
  and 
  conspicuous 
  changes 
  of 
  form 
  to 
  occur 
  ; 
  

   but 
  instead 
  of 
  this 
  being 
  the 
  case, 
  the 
  prominences 
  retained 
  their 
  forms 
  unal- 
  

   tered, 
  until 
  they 
  vanished 
  before 
  the 
  direct 
  light 
  of 
  the 
  sun. 
  On 
  these 
  grounds, 
  

   we 
  must 
  therefore 
  regard 
  the 
  hypothesis 
  which 
  would 
  refer 
  them 
  to 
  the 
  unequal 
  

   heating 
  of 
  the 
  air, 
  as 
  quite 
  untenable. 
  

  

  * 
  Ast. 
  Soc. 
  Notice, 
  p. 
  69 
  ; 
  or 
  Astronomische 
  Nachrichten, 
  No. 
  777. 
  

  

  M. 
  Mayette 
  at 
  the 
  eclipse 
  of 
  1842, 
  saw 
  one 
  of 
  the 
  red 
  prominences 
  after 
  the 
  sun 
  had 
  reappeared 
  

   (quclqucs 
  instantes 
  apres 
  V 
  'emersion 
  du 
  Soldi.) 
  — 
  Annuaire, 
  for 
  1846, 
  p. 
  411 
  ; 
  see 
  also 
  p. 
  421. 
  M. 
  

   Conti 
  saw 
  the 
  prominences 
  for 
  a 
  long 
  time 
  (per 
  lungo 
  tempo), 
  after 
  the 
  reappearance 
  of 
  the 
  sun 
  ; 
  and 
  

   M. 
  Biela 
  for 
  some 
  seconds, 
  pp. 
  428, 
  429. 
  The 
  statement 
  of 
  the 
  latter 
  observer 
  is 
  particularly 
  

   explicit. 
  " 
  Les 
  premiers 
  rayons 
  dn 
  Soled 
  se 
  montrerent 
  en 
  divers 
  points 
  separes. 
  Bieutot 
  ces 
  points 
  

   se 
  reunirents 
  et 
  formerent 
  une 
  lunule 
  tres-deliee. 
  Quclques 
  secondes 
  apres 
  la 
  formation 
  de 
  cette 
  lunule, 
  

   les 
  pyramides 
  rougeatres 
  cesserent 
  de 
  se 
  voir.'' 
  

  

  f 
  May 
  not 
  the 
  unequal 
  heating 
  of 
  the 
  air 
  on 
  the 
  two 
  sides 
  of 
  the 
  path 
  of 
  the 
  solar 
  rays 
  be 
  the 
  

   chief 
  cause 
  of 
  the 
  remarkable 
  fluctuations 
  in 
  the 
  sun's 
  light, 
  which 
  have 
  been 
  observed 
  at 
  the 
  be- 
  

   ginning 
  and 
  end 
  of 
  the 
  total 
  phase 
  of 
  a 
  solar 
  eclipse 
  1 
  M. 
  Savournin, 
  an 
  observer 
  of 
  the 
  eclipse 
  of 
  

   July 
  1842, 
  relates, 
  " 
  On 
  a 
  vu 
  ici 
  des 
  ombres 
  et 
  des 
  taches 
  lumincuses 
  courir 
  les 
  unes 
  apres 
  les 
  

   autres, 
  comme 
  paraissent 
  le 
  faire 
  les 
  ombres 
  produites 
  par 
  de 
  petits 
  nuages 
  qui 
  passent 
  successivement 
  

   sur 
  le 
  Soleil. 
  Ces 
  taches 
  n'etaient 
  pas 
  de 
  la 
  meme 
  couleur 
  ; 
  il 
  y 
  en 
  avait 
  de 
  rouges, 
  de 
  jaunes, 
  

   de 
  bleues, 
  de 
  blanches. 
  Les 
  enfants 
  les 
  poursuivaient 
  et 
  essayaient 
  de 
  mettre 
  la 
  main 
  dessus. 
  Ce 
  

   phenomene 
  extraordinaire 
  fut 
  remarque 
  quelques 
  instants 
  seulement 
  avant 
  la 
  disparition 
  complete 
  

   du 
  Soleil." 
  — 
  Annuaire 
  for 
  1846, 
  p. 
  393. 
  The 
  strata 
  of 
  illuminated 
  and 
  dark 
  air 
  at 
  the 
  surface 
  of 
  

   the 
  moon's 
  shadow, 
  if 
  their 
  temperatures, 
  and 
  consequently 
  their 
  densities 
  differ, 
  cannot 
  fail 
  to 
  

   mingle 
  irregularly, 
  and 
  occasion 
  fluctuating 
  movements 
  in 
  the 
  transmitted 
  rays 
  of 
  light, 
  similar 
  to 
  

   those 
  which 
  cause 
  the 
  dancing 
  motion 
  of 
  objects 
  seen 
  through 
  an 
  ascending 
  current 
  of 
  heated 
  air, 
  

   or 
  through 
  liquids 
  of 
  unequal 
  densities 
  which 
  are 
  in 
  the 
  act 
  of 
  mixing. 
  This 
  may 
  also 
  serve 
  to 
  ex- 
  

   plain 
  the 
  flickering 
  appearance 
  of 
  the 
  prominences 
  noticed 
  by 
  some 
  observers 
  ; 
  which, 
  from 
  the 
  terms 
  

   used 
  in 
  describing 
  it, 
  was 
  evidently 
  not 
  a 
  permanent 
  change 
  of 
  outline, 
  but 
  merely 
  a 
  fluctuation 
  

   of 
  their 
  forms 
  about 
  a 
  mean 
  condition. 
  Thus 
  Mr 
  Dawes 
  and 
  Mr 
  Good, 
  who 
  saw 
  on 
  the 
  moon's 
  

   southern 
  limb 
  a 
  long 
  range 
  of 
  low 
  prominences, 
  both 
  describe 
  it 
  as 
  in 
  motion. 
  Mr 
  Dawes, 
  however, 
  

   says, 
  its 
  irregularities 
  appeared 
  permanent, 
  and 
  he 
  ascribes 
  its 
  undulation 
  to 
  our 
  own 
  atmosphere. 
  

  

  