﻿452 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  Mr 
  Dunkin 
  and 
  Mr 
  Snow, 
  who 
  were 
  both 
  stationed 
  near 
  the 
  observatory 
  in 
  

   Christiania, 
  differ 
  by 
  20° 
  in 
  their 
  observations 
  of 
  the 
  same 
  remarkable 
  object. 
  

   Lieutenant 
  Pettersson, 
  Mr 
  Adie, 
  Mr 
  Airy, 
  and 
  myself, 
  were 
  all 
  situated 
  within 
  

   a 
  circle 
  of 
  about 
  two 
  miles 
  radius, 
  yet 
  while 
  Lieutenant 
  Pettersson's 
  observation 
  

   of 
  the 
  hook-shaped 
  prominence 
  agrees 
  almost 
  exactly 
  with 
  mine, 
  Mr 
  Adie, 
  and 
  Mr 
  

   Airy 
  differ 
  from 
  us 
  by 
  1 
  3 
  D 
  and 
  22° 
  respectively. 
  Here 
  then, 
  where, 
  even 
  on 
  the 
  

   hypothesis 
  that 
  the 
  prominences 
  are 
  merely 
  optical 
  phenomena, 
  we 
  should 
  expect 
  

   identity 
  of 
  position, 
  we 
  meet 
  with 
  alarming 
  discrepancies. 
  

  

  On 
  the 
  other 
  hand, 
  although 
  Mr 
  Dawes 
  was 
  stationed 
  above 
  100 
  miles 
  from 
  

   Goteborg, 
  the 
  position 
  he 
  assigns 
  to 
  the 
  hook-shaped 
  prominence, 
  agrees 
  almost 
  

   exactly 
  with 
  that 
  given 
  by 
  Lieutenant 
  Pettersson 
  and 
  by 
  me 
  ; 
  and 
  Mr 
  Hind 
  also, 
  

   who 
  was 
  near 
  Mr 
  Dawes, 
  differs 
  from 
  us 
  by 
  less 
  than 
  8°. 
  Now, 
  as 
  Goteborg 
  was 
  

   near 
  the 
  middle 
  of 
  the 
  moon's 
  shadow, 
  while 
  Ravel 
  sberg, 
  where 
  Mr 
  Hind 
  and 
  Mr 
  

   Dawes 
  observed, 
  was 
  near 
  the 
  southern 
  edge 
  of 
  the 
  shadow, 
  the 
  eclipse 
  was 
  seen 
  

   at 
  the 
  two 
  stations 
  under 
  widely 
  different 
  circumstances; 
  and 
  on 
  the 
  optical 
  

   hypothesis, 
  we 
  might 
  expect 
  great 
  discrepancy 
  in 
  the 
  angles 
  of 
  position. 
  The 
  

   coincidence 
  in 
  the 
  observations 
  is 
  therefore 
  strongly 
  in 
  favour 
  of 
  the 
  view 
  that 
  

   the 
  prominences 
  are 
  material 
  objects 
  ; 
  and 
  this 
  conclusion 
  is 
  strengthened, 
  when 
  

   it 
  is 
  borne 
  in 
  mind 
  that 
  the 
  hook-shaped 
  prominence 
  being 
  seen 
  near 
  one 
  of 
  

   Mr 
  Dawes's 
  cross- 
  wires, 
  its 
  position 
  could 
  be 
  estimated 
  with 
  great 
  accuracy, 
  

   and 
  my 
  angles 
  of 
  position 
  were 
  actually 
  measured 
  ; 
  so 
  that 
  the 
  close 
  agreement 
  of 
  

   our 
  observations 
  is 
  by 
  no 
  means 
  to 
  be 
  attributed 
  to 
  chance. 
  The 
  only 
  other 
  person, 
  

   so 
  far 
  as 
  I 
  am 
  at 
  present 
  aware, 
  who 
  has 
  determined 
  the 
  position 
  of 
  the 
  hook- 
  

   shaped 
  prominence 
  by 
  actual 
  measurement, 
  is 
  M. 
  Wichmann, 
  who 
  observed 
  the 
  

   eclipse 
  with 
  the 
  Konigsberg 
  heliometer. 
  He 
  states 
  his 
  determination 
  as 
  some- 
  

   what 
  doubtful 
  ; 
  but 
  it 
  agrees 
  so 
  well 
  with 
  that 
  of 
  Mr 
  Dawes, 
  and 
  with 
  my 
  own, 
  

   as 
  to 
  render 
  it 
  highly 
  probable 
  that 
  the 
  positions 
  of 
  that 
  prominence, 
  as 
  seen 
  

   from 
  stations 
  nearly 
  400 
  miles 
  distant, 
  were 
  identical. 
  The 
  following 
  table 
  con- 
  

   tains 
  the 
  observations 
  to 
  which 
  I 
  have 
  now 
  referred 
  ; 
  and 
  I 
  have 
  added 
  those 
  

   of 
  the 
  spots 
  on 
  the 
  sun, 
  in 
  order 
  that 
  it 
  may 
  be 
  seen 
  that 
  the 
  discrepancies 
  

   in 
  the 
  observed 
  positions 
  of 
  the 
  prominence 
  scarcely 
  exceed 
  those 
  in 
  the 
  positions 
  

   of 
  the 
  spots. 
  As 
  the 
  spots 
  are 
  objects 
  which, 
  while 
  they 
  last, 
  have 
  their 
  positions, 
  

   if 
  not 
  permanent, 
  at 
  least 
  subject 
  only 
  to 
  small 
  and 
  slow 
  changes, 
  we 
  cannot 
  

   attribute 
  the 
  variations 
  in 
  their 
  observed 
  positions 
  to 
  change 
  of 
  place. 
  We 
  must 
  

   therefore 
  refer 
  these 
  discrepancies 
  to 
  errors 
  of 
  observation 
  ; 
  from 
  which 
  it 
  follows 
  

   inevitably, 
  that 
  the 
  variations 
  in 
  the 
  observed 
  positions 
  of 
  the 
  prominence, 
  as 
  they 
  

   scarcely 
  exceed 
  those 
  in 
  the 
  positions 
  of 
  the 
  spots, 
  are 
  also 
  within 
  the 
  limits 
  of 
  

   errors 
  of 
  observation 
  

  

  The 
  agreement 
  of 
  the 
  measured 
  angles 
  of 
  position 
  of 
  that 
  object 
  appear, 
  in- 
  

   deed, 
  sufficiently 
  close, 
  when 
  we 
  advert 
  to 
  the 
  circumstance 
  that 
  it 
  must 
  have 
  

  

  * 
  Astron., 
  Naclirichten, 
  No. 
  787, 
  p. 
  323. 
  

  

  