﻿450 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  spider-lines 
  in 
  the 
  eye-piece, 
  which 
  were 
  carefully 
  adjusted 
  to 
  polar 
  and 
  equatorial 
  

   directions 
  * 
  By 
  this 
  arrangement, 
  the 
  moon's 
  limb 
  could 
  be 
  readily 
  divided 
  into 
  

   four 
  quadrants, 
  so 
  as 
  to 
  facilitate 
  the 
  estimation 
  of 
  angles 
  of 
  position. 
  

  

  I 
  employed 
  a 
  position 
  micrometer, 
  expressly 
  devised 
  for 
  the 
  purpose 
  of 
  re- 
  

   gistering 
  the 
  places 
  of 
  the 
  red 
  prominences;! 
  and 
  although 
  we 
  witnessed 
  the 
  

   eclipse 
  under 
  very 
  different 
  circumstances, 
  and 
  I 
  failed 
  to 
  see 
  a 
  number 
  of 
  promi- 
  

   nences 
  which 
  Mr 
  Dawes 
  has 
  figured, 
  yet 
  our 
  observations 
  of 
  the 
  objects 
  which 
  we 
  

   both 
  saw, 
  agree 
  so 
  closely, 
  as 
  to 
  render 
  it 
  probable, 
  that 
  if 
  some 
  efficient 
  means 
  of 
  

   ascertaining 
  angles 
  of 
  position 
  had 
  been 
  generally 
  adopted, 
  the 
  observations 
  would 
  

   usually 
  have 
  been 
  accordant. 
  

  

  On 
  comparing 
  the 
  different 
  observations, 
  it 
  appears 
  that 
  at 
  least 
  two 
  isolated 
  

   red 
  prominences 
  were 
  seen 
  to 
  the 
  east 
  of 
  the 
  sun's 
  north 
  point 
  ; 
  a 
  long 
  sierra 
  or 
  

   range 
  of 
  red 
  prominences 
  on 
  the 
  sun's 
  southern 
  limb 
  ; 
  two 
  detached 
  prominences 
  

   towards 
  the 
  west 
  of 
  the 
  sun's 
  vertex 
  ; 
  a 
  large 
  hook-shaped 
  prominence 
  also 
  to 
  the 
  

   west 
  ; 
  a 
  small 
  prominence 
  detached 
  from 
  the 
  moon's 
  limb, 
  a 
  little 
  to 
  the 
  south 
  of 
  

   the 
  hook-shaped 
  prominence 
  ; 
  and 
  two 
  prominences 
  between 
  the 
  large 
  one 
  and 
  

   the 
  western 
  end 
  of 
  the 
  sierra. 
  

  

  These 
  objects 
  were 
  by 
  no 
  means 
  equally 
  remarkable 
  in 
  appearance 
  ; 
  and, 
  ac- 
  

   cordingly, 
  they 
  did 
  not 
  all 
  receive 
  the 
  same 
  share 
  of 
  attention. 
  Probably 
  on 
  this 
  

   account, 
  differences, 
  so 
  great, 
  occur 
  among 
  the 
  observed 
  angles 
  of 
  position, 
  in 
  the 
  

   case 
  of 
  some 
  of 
  the 
  less 
  conspicuous 
  prominences, 
  as 
  to 
  render 
  it 
  impossible, 
  in 
  

   some 
  instances, 
  to 
  determine 
  with 
  certainty 
  to 
  which 
  of 
  them 
  the 
  observations 
  

   refer. 
  I 
  think 
  it 
  then 
  sufficient, 
  to 
  select 
  the 
  hook-shaped 
  prominence 
  already 
  

   noticed, 
  as 
  the 
  object 
  which, 
  on 
  the 
  whole, 
  excited 
  most 
  attention, 
  — 
  whose 
  place 
  

   may 
  thus 
  be 
  assumed 
  to 
  have 
  been 
  the 
  best 
  ascertained, 
  — 
  and 
  of 
  which 
  the 
  ob- 
  

   served 
  angles 
  of 
  position 
  are 
  therefore 
  the 
  most 
  likely 
  to 
  throw 
  light 
  on 
  the 
  nature 
  

   of 
  the 
  red 
  prominences. 
  

  

  In 
  the 
  absence 
  of 
  information 
  regarding 
  the 
  manner 
  in 
  which 
  the 
  different 
  ob- 
  

   servers 
  ascertained 
  their 
  angles 
  of 
  position, 
  I 
  have 
  given 
  all 
  the 
  observations 
  equal 
  

   weight 
  ; 
  and 
  the 
  following 
  table 
  exhibits 
  the 
  several 
  positions 
  assigned 
  to 
  the 
  

   hook-shaped 
  prominence, 
  with 
  the 
  difference 
  of 
  each 
  from 
  the 
  mean 
  of 
  the 
  whole. 
  

  

  Such 
  of 
  the 
  angles 
  as 
  were 
  reckoned 
  from 
  the 
  sun's 
  vertex, 
  I 
  have 
  reduced 
  to 
  

   his 
  north 
  point, 
  by 
  means 
  of 
  the 
  latitudes 
  of 
  the 
  stations, 
  and 
  the 
  times 
  of. 
  obser- 
  

   vation, 
  supposing 
  the 
  observations 
  to 
  be 
  made 
  at 
  the 
  middle 
  of 
  the 
  total 
  phase 
  of 
  

   the 
  eclipse. 
  As, 
  however, 
  those 
  data 
  are 
  sometimes 
  only 
  approximately 
  known, 
  

   the 
  reduction 
  of 
  the 
  observed 
  angle 
  is 
  not 
  always 
  quite 
  correct 
  ; 
  yet, 
  I 
  believe, 
  the 
  

   error 
  in 
  no 
  case 
  will 
  be 
  found 
  to 
  amount 
  to 
  1°, 
  so 
  that 
  the 
  comparison 
  of 
  the 
  ob- 
  

   servations 
  is 
  sufficiently 
  exact 
  for 
  the 
  purpose 
  intended. 
  

  

  * 
  Astronomisclie 
  Nachrichten, 
  No. 
  777- 
  f 
  P. 
  337. 
  

  

  