﻿336 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  protracted 
  on 
  a 
  trustworthy 
  map 
  of 
  the 
  environs 
  of 
  Goteborg,* 
  are 
  very 
  well 
  

   satisfied 
  by 
  a 
  point, 
  which, 
  from 
  the 
  known 
  latitude 
  and 
  longitude 
  of 
  the 
  Observa- 
  

   tory, 
  I 
  find 
  to 
  be 
  in 
  latitude 
  57° 
  42' 
  57 
  "'3 
  N. 
  and 
  longitude 
  h 
  47 
  m 
  45 
  s 
  -2 
  E.f 
  

  

  So 
  many 
  phenomena 
  occur 
  at 
  the 
  total 
  phase 
  of 
  a 
  solar 
  eclipse, 
  that 
  I 
  wished 
  

   to 
  avoid 
  having 
  my 
  attention 
  distracted 
  by 
  my 
  being 
  obliged 
  to 
  count 
  the 
  beats 
  

   of 
  the 
  chronometer 
  in 
  taking 
  observations 
  for 
  time. 
  I 
  therefore 
  gladly 
  availed 
  

   myself 
  of 
  the 
  assistance 
  of 
  Mr 
  Edward 
  W. 
  Lane, 
  Advocate, 
  of 
  Edinburgh, 
  who 
  

   kindly 
  undertook 
  to 
  read 
  the 
  chronometer, 
  and 
  mark 
  the 
  times 
  at 
  a 
  preconcerted 
  

   signal. 
  His 
  co-operation 
  proved 
  quite 
  invaluable 
  ; 
  and 
  it 
  is 
  with 
  the 
  greatest 
  

   pleasure 
  I 
  avail 
  myself 
  of 
  this 
  opportunity 
  of 
  acknowledging 
  my 
  obligations 
  to 
  

   him. 
  

  

  The 
  telescope 
  I 
  employed 
  in 
  observing 
  the 
  eclipse 
  was 
  furnished 
  by 
  Mr 
  Adie. 
  

   It 
  has 
  a 
  very 
  good 
  object-glass 
  t 
  of 
  about 
  2*3 
  inches 
  aperture, 
  and 
  31 
  -5 
  inches 
  focal 
  

   length, 
  and 
  was 
  mounted 
  on 
  a 
  rough 
  equatorial 
  stand. 
  Of 
  the 
  eye-pieces 
  be- 
  

   longing 
  to 
  this 
  instrument, 
  I 
  chose 
  that 
  of 
  the 
  lowest 
  power, 
  magnifying 
  28 
  

   times, 
  as 
  it 
  was 
  necessary 
  for 
  some 
  of 
  the 
  observations 
  I 
  purposed 
  to 
  make, 
  to 
  

   have 
  the 
  entire 
  disc 
  of 
  the 
  sun 
  within 
  the 
  field 
  of 
  view 
  at 
  once. 
  I 
  also 
  then 
  

   thought, 
  and 
  I 
  am 
  still 
  of 
  the 
  same 
  opinion, 
  that 
  any 
  advantage 
  gained 
  by 
  using 
  

   a 
  higher 
  power 
  would 
  be 
  more 
  than 
  counterbalanced 
  by 
  the 
  time 
  lost, 
  during 
  the 
  

   short 
  duration 
  of 
  the 
  total 
  phase 
  of 
  the 
  eclipse, 
  in 
  directing 
  the 
  telescope 
  from 
  

   point 
  to 
  point 
  of 
  the 
  moon's 
  limb, 
  instead 
  of 
  seeing 
  the 
  whole 
  at 
  once. 
  In 
  effect, 
  

   the 
  power 
  I 
  had 
  chosen 
  proved 
  very 
  convenient, 
  and 
  apparently 
  quite 
  sufficient 
  

   for 
  observing 
  the 
  interesting 
  phenomena 
  of 
  the 
  total 
  phase 
  ; 
  While 
  the 
  definition 
  

   of 
  the 
  corona 
  and 
  the 
  red 
  prominences 
  seemed 
  as 
  perfect 
  as 
  could 
  be 
  wished. 
  

  

  I 
  had 
  prepared 
  some 
  slips 
  of 
  smoked 
  plate-glass, 
  gradually 
  increasing 
  in 
  depth 
  

   of 
  tint 
  from 
  one 
  end 
  to 
  the 
  other, 
  for 
  the 
  purpose 
  of 
  observing 
  the 
  sun 
  before 
  the 
  

   period 
  of 
  total 
  obscuration 
  ; 
  but 
  Professor 
  Chevallier 
  kindly 
  lent 
  me 
  a 
  dark 
  

   glass, 
  by 
  Troughton 
  and 
  Simms, 
  consisting 
  of 
  wedges 
  of 
  coloured 
  glass 
  achroma- 
  

   tised 
  by 
  a 
  colourless 
  prism. 
  § 
  This 
  combination 
  of 
  glasses 
  made 
  the 
  sun 
  appear 
  

   yellow, 
  slightly 
  tinged 
  with 
  green, 
  and 
  I 
  willingly 
  adopted 
  it 
  in 
  preference 
  to 
  

   the 
  smoked 
  glasses, 
  as 
  the 
  definition 
  of 
  the 
  sun 
  was 
  decidedly 
  sharper 
  when 
  it 
  

   was 
  used 
  instead 
  of 
  them. 
  This 
  dark 
  glass 
  slid 
  in 
  a 
  groove 
  in 
  front 
  of 
  the 
  eye- 
  

   piece, 
  so 
  as 
  to 
  admit 
  of 
  being 
  instantly 
  removed. 
  

  

  From 
  the 
  conflicting 
  accounts 
  which 
  were 
  given 
  regarding 
  the 
  red 
  prominences 
  

  

  * 
  This 
  map, 
  published 
  by 
  A. 
  Hahr, 
  is 
  entitled 
  Topografisk 
  Karta 
  ofver 
  Gdtheborgs 
  Omgifning 
  

   Jemte 
  plan 
  ofver 
  Staclen 
  med 
  dess 
  nya 
  Hambyggnad. 
  1844. 
  

  

  \ 
  Since 
  this 
  paper 
  was 
  read, 
  Lieutenant 
  Pettersson 
  has 
  kindly 
  verified 
  my 
  calculation, 
  and 
  assigns, 
  

   as 
  the 
  position 
  of 
  my 
  station, 
  lat. 
  57° 
  42' 
  58"-0 
  N., 
  long. 
  h 
  47™ 
  45s- 
  3 
  E. 
  

  

  J 
  As 
  the 
  value 
  of 
  the 
  following 
  observations 
  must 
  depend 
  greatly 
  on 
  the 
  character 
  of 
  the 
  instru- 
  

   ment 
  with 
  which 
  they 
  were 
  made, 
  I 
  may 
  mention 
  that 
  this 
  telescope 
  shews 
  bright 
  stars, 
  with 
  per- 
  

   fectly 
  round, 
  well-defined 
  discs 
  ; 
  and, 
  with 
  a 
  power 
  of 
  75, 
  the 
  two 
  stars 
  in 
  Castor 
  are 
  seen 
  com- 
  

   pletely 
  separated. 
  

  

  | 
  To 
  Professor 
  Chevallier, 
  and 
  especially 
  to 
  Lieutenant 
  Pettersson, 
  my 
  wannest 
  thanks 
  are 
  

   also 
  due, 
  for 
  their 
  kind 
  assistance 
  and 
  advice. 
  

  

  