﻿TOTAL 
  ECLIPSE 
  OF 
  THE 
  SUN, 
  JULY 
  28, 
  1851. 
  343 
  

  

  granite 
  mountains. 
  Both 
  prominences 
  were 
  remarkably 
  distinct 
  from 
  the 
  co- 
  

   rona, 
  so 
  as 
  almost 
  to 
  appear 
  standing 
  in 
  front 
  of 
  it 
  ; 
  and 
  their 
  outlines 
  seen 
  

   upon 
  it 
  were 
  at 
  least 
  as 
  definite 
  as 
  that 
  of 
  the 
  illuminated 
  edge 
  of 
  a 
  detached 
  

   cumulous 
  cloud 
  projected 
  against 
  the 
  clear 
  blue 
  sky. 
  But 
  as 
  the 
  sharp 
  definition 
  

   of 
  such 
  a 
  cloud 
  is 
  an 
  illusion, 
  depending 
  as 
  much 
  on 
  its 
  distance, 
  as 
  on 
  the 
  density 
  

   of 
  the 
  vapour 
  composing 
  it, 
  I 
  do 
  not 
  mean 
  to 
  draw 
  from 
  this 
  comparison 
  any 
  

   inference 
  regarding 
  the 
  density 
  of 
  the 
  matter 
  composing 
  the 
  red 
  prominences. 
  

   Notwithstanding 
  their 
  definite 
  outlines, 
  they 
  may, 
  like 
  the 
  tails 
  of 
  comets, 
  be 
  of 
  

   extreme 
  rarity, 
  and 
  indeed, 
  as 
  Sir 
  John 
  Herschel 
  remarks,* 
  their 
  faint 
  illumi- 
  

   nation 
  clearly 
  proves 
  them 
  to 
  be 
  " 
  cloudy 
  masses 
  of 
  the 
  most 
  excessive 
  tenuity." 
  

   The 
  colour 
  of 
  the 
  prominences 
  was 
  a 
  full 
  rose-tint, 
  and 
  the 
  light 
  of 
  the 
  corona 
  in 
  

   their 
  neighbourhood 
  seemed 
  brighter 
  than 
  elsewhere, 
  with 
  the 
  exception 
  of 
  the 
  

   brilliant 
  beams 
  already 
  mentioned. 
  

  

  The 
  appearance 
  of 
  the 
  prominences 
  as 
  they 
  were 
  seen 
  shortly 
  after 
  the 
  com- 
  

   mencement 
  of 
  the 
  totality 
  is 
  represented 
  in 
  figure 
  7. 
  By 
  means 
  of 
  the 
  microme- 
  

   ter 
  I 
  determined 
  their 
  positions 
  as 
  well 
  as 
  that 
  of 
  the 
  bright 
  rays 
  to 
  the 
  east 
  of 
  the 
  

   sun's 
  vertex, 
  and 
  then 
  quitted 
  the 
  telescope 
  for 
  a 
  little 
  to 
  make 
  some 
  other 
  ober- 
  

   vations. 
  On 
  returning 
  to 
  the 
  telescope 
  I 
  found 
  that 
  the 
  bright 
  rays 
  to 
  the 
  east 
  of 
  the 
  

   sun's 
  vertex 
  appeared 
  shorter 
  than 
  before, 
  while 
  the 
  red 
  prominences 
  to 
  the 
  west 
  

   had 
  increased 
  sensibly 
  in 
  height 
  ; 
  and 
  while 
  I 
  watched 
  them, 
  they 
  continued 
  to 
  

   increase 
  still 
  more 
  in 
  size, 
  as 
  if 
  rising 
  from 
  behind 
  the 
  moon's 
  limb. 
  I 
  should 
  

   almost 
  say 
  their 
  motion 
  was 
  sensible 
  ; 
  but 
  however 
  doubtful 
  this 
  may 
  be, 
  its 
  

   cumulative 
  effect 
  was 
  strikingly 
  apparent, 
  for 
  before 
  the 
  end 
  of 
  the 
  totality 
  they 
  

   had 
  assumed 
  the 
  appearance 
  presented 
  in 
  figure 
  8. 
  All 
  this 
  was 
  exactly 
  what 
  

   would 
  have 
  happened 
  on 
  the 
  supposition 
  that 
  the 
  prominences 
  belonged 
  to 
  the 
  

   sun 
  ; 
  for 
  objects 
  on 
  the 
  eastern 
  limb 
  would 
  gradually 
  suffer 
  occultation 
  by 
  the 
  ad- 
  

   vancing 
  moon, 
  while 
  those 
  on 
  the 
  western 
  limb 
  would 
  be 
  simultaneously 
  exposed. 
  

  

  While, 
  then, 
  the 
  definite 
  outlines 
  and 
  permanent 
  forms 
  of 
  the 
  prominences 
  

   satisfied 
  me 
  that 
  they 
  were 
  real 
  objects, 
  and 
  not 
  mere 
  optical 
  phenomena, 
  their 
  

   gradually 
  increasing 
  altitude 
  convinced 
  me 
  that 
  they 
  belong 
  to 
  the 
  sun 
  and 
  not 
  

   to 
  the 
  moon. 
  The 
  observed 
  angles 
  of 
  position 
  of 
  the 
  red 
  prominences 
  and 
  spots 
  

   on 
  the 
  sun's 
  disc, 
  referred 
  to 
  the 
  sun's 
  vertex, 
  and 
  also 
  their 
  angles 
  of 
  position 
  

   reckoned 
  eastward 
  from 
  the 
  sun's 
  vertex 
  a,re 
  given 
  in 
  Table 
  II., 
  p. 
  346. 
  The 
  data 
  

   for 
  reducing 
  their 
  positions 
  to 
  the 
  sun's 
  vertex 
  are 
  the 
  known 
  latitude 
  of 
  the 
  

   station, 
  the 
  sun's 
  declination, 
  and 
  the 
  hour 
  angle 
  from 
  apparent 
  noon, 
  assuming 
  

   the 
  observations 
  to 
  be 
  made 
  at 
  the 
  middle 
  of 
  the 
  totality. 
  

  

  The 
  prominences 
  were 
  distinctly 
  visible 
  to 
  the 
  naked 
  eye 
  by 
  the 
  strong 
  red 
  

   tinge 
  they 
  imparted 
  to 
  the 
  adjacent 
  portions 
  of 
  the 
  corona 
  ; 
  but 
  I 
  could 
  neither 
  

   distinguish 
  their 
  outlines 
  nor 
  see 
  them 
  as 
  separate 
  objects. 
  

  

  I 
  wished 
  to 
  compare 
  the 
  shadow 
  cast 
  by 
  the 
  corona 
  with 
  that 
  formed 
  by 
  a 
  

  

  * 
  Outlines 
  of 
  Astronomy, 
  1851, 
  par. 
  395. 
  

   VOL. 
  XX. 
  PART 
  III. 
  5 
  A 
  

  

  