﻿463 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  It 
  may 
  be 
  further 
  observed, 
  that 
  if 
  the 
  red 
  prominences 
  are 
  portions 
  of 
  the 
  

   envelope 
  of 
  cloud, 
  thrown 
  upwards 
  by 
  currents 
  in 
  the 
  sun's 
  atmosphere, 
  which 
  

   tend 
  to 
  produce 
  faculse 
  by 
  ultimately 
  rupturing 
  the 
  envelope, 
  the 
  prominences 
  

   will 
  have 
  a 
  physical 
  connexion 
  with 
  the 
  faculse, 
  but 
  no 
  necessary 
  connexion 
  with 
  

   the 
  solar 
  spots. 
  

  

  It 
  is 
  well 
  known, 
  however, 
  that 
  conspicuous 
  faculse 
  often 
  occur 
  in 
  the 
  neigh- 
  

   bourhood 
  of 
  groups 
  of 
  spots 
  ; 
  and 
  the 
  same 
  upward 
  currents 
  in 
  the 
  sun's 
  atmo- 
  

   sphere, 
  which 
  are 
  supposed 
  to 
  occasion 
  the 
  spots, 
  by 
  removing 
  a 
  portion 
  of 
  his 
  lu- 
  

   minous 
  envelope, 
  may 
  also 
  occasion 
  the 
  faculse, 
  by 
  removing 
  a 
  portion 
  of 
  the 
  super- 
  

   incumbent 
  cloudy 
  strata. 
  The 
  occurrence, 
  immediately 
  before 
  an 
  eclipse, 
  of 
  faculse 
  

   near 
  the 
  sun's 
  limb, 
  with 
  or 
  without 
  accompanying 
  spots, 
  ought 
  therefore 
  to 
  indi- 
  

   cate 
  a 
  quarter 
  where 
  red 
  prominences 
  might 
  be 
  expected 
  to 
  appear 
  ; 
  and 
  at 
  least 
  

   one 
  coincidence 
  in 
  the 
  position 
  of 
  spots 
  and 
  red 
  prominences 
  was 
  actually 
  observed 
  

   at 
  the 
  late 
  eclipse. 
  A 
  group 
  of 
  spots 
  was 
  seen 
  by 
  me 
  immediately 
  before 
  the 
  eclipse, 
  

   about 
  l'-5 
  from 
  the 
  sun's 
  limb, 
  and 
  to 
  the 
  west 
  of 
  his 
  vertex. 
  The 
  angle 
  of 
  posi- 
  

   tion 
  of 
  this 
  group, 
  reduced 
  to 
  the 
  sun's 
  north 
  point, 
  was 
  ascertained 
  to 
  be 
  288" 
  47'; 
  

   and 
  the 
  conspicuous 
  hook-shaped 
  prominence, 
  which 
  appeared 
  during 
  the 
  totality, 
  

   was 
  found 
  to 
  be 
  situated 
  at 
  282 
  } 
  8' 
  from 
  the 
  sun's 
  north 
  point. 
  The 
  hook-shaped 
  

   prominence 
  may 
  therefore 
  have 
  been 
  connected 
  with 
  faculse 
  in 
  the 
  neighbourhood 
  

   of 
  the 
  group 
  of 
  spots. 
  The 
  region 
  where 
  spots 
  occur 
  is 
  limited 
  to 
  a 
  zone, 
  extend- 
  

   ing 
  about 
  25° 
  or 
  30° 
  on 
  either 
  side 
  of 
  the 
  sun's 
  equator 
  ; 
  and 
  Mr 
  Lassell 
  observes, 
  

   that, 
  as 
  at 
  the 
  late 
  eclipse 
  " 
  some 
  prominences 
  appeared 
  on 
  parts 
  of 
  the 
  sun's 
  

   limb 
  not 
  usually 
  traversed 
  by 
  spots, 
  the 
  connexion 
  between 
  the 
  two 
  is 
  not 
  made 
  

   out."* 
  This 
  remark, 
  however, 
  does 
  not 
  apply 
  to 
  the 
  supposed 
  occasional 
  relation 
  

   between 
  the 
  prominences 
  and 
  the 
  faculse; 
  for 
  although 
  faculse 
  are 
  seen 
  most 
  

   abundantly 
  in 
  the 
  neighbourhood 
  of 
  spots, 
  they 
  also 
  occur 
  by 
  themselves, 
  and 
  

   have 
  been 
  observed 
  all 
  over 
  the 
  sun's 
  disc 
  ; 
  so 
  that 
  the 
  prominences 
  which 
  are 
  

   supposed 
  to 
  be 
  connected 
  with 
  them 
  might 
  appear 
  at 
  any 
  point 
  in 
  the 
  sun's 
  limb. 
  

  

  5. 
  On 
  the 
  Irregular 
  Illumination 
  of 
  the 
  Corona 
  seen 
  during 
  Total 
  Eclipses 
  of 
  the 
  Sun. 
  

  

  Let 
  us 
  next 
  inquire 
  how 
  the 
  hypothesis 
  of 
  an 
  envelope 
  of 
  cloud 
  surrounding 
  the 
  

   sun's 
  luminous 
  atmosphere, 
  consists 
  with 
  the 
  phenomena 
  of 
  the 
  corona. 
  

  

  There 
  are 
  remarkable 
  appearances 
  in 
  the 
  corona, 
  which 
  seem 
  quite 
  inexpli- 
  

  

  observed 
  a 
  facula 
  projecting 
  beyond 
  the 
  sun's 
  limb 
  (R. 
  Ast. 
  Soc. 
  Notice 
  for 
  April 
  1852). 
  With 
  

   reference 
  to 
  that 
  observation, 
  it 
  may 
  be 
  permitted 
  to 
  remark, 
  — 
  that 
  considering 
  the 
  rapid 
  degrada- 
  

   tion 
  in 
  brightness 
  of 
  the 
  sun's 
  disc 
  towards 
  the 
  edges, 
  — 
  it 
  is 
  evident 
  that 
  the 
  dark 
  glasses 
  used 
  

   in 
  observing 
  the 
  sun 
  may, 
  to 
  some 
  extent, 
  diminish 
  its 
  apparent 
  diameter, 
  the 
  light 
  from 
  the 
  extreme 
  

   edge 
  of 
  the 
  disc 
  being 
  possibly 
  too 
  feeble 
  to 
  be 
  seen 
  through 
  the 
  glass. 
  A 
  portion 
  of 
  the 
  sun's 
  limb 
  

   brighter 
  than 
  the 
  rest 
  would 
  be 
  less 
  encroached 
  on 
  from 
  this 
  cause, 
  and 
  would 
  thus 
  appear 
  to 
  project 
  

   beyond 
  the 
  general 
  outline. 
  Irradiation 
  would 
  also 
  conspire 
  to 
  inci-ease 
  this 
  effect. 
  The 
  action 
  of 
  

   the 
  dark 
  glasses, 
  in 
  diminishing 
  the 
  sun's 
  apparent 
  diameter, 
  may 
  also 
  be 
  one 
  of 
  the 
  causes 
  of 
  the 
  

   anomalous 
  variations 
  in 
  observations 
  of 
  the 
  sun's 
  diameter. 
  

   * 
  R. 
  Ast. 
  Soc. 
  Notice, 
  p. 
  53. 
  

  

  