﻿338 
  MR 
  WILLIAM 
  SWAN 
  ON 
  THE 
  

  

  It 
  is 
  evident 
  that 
  if 
  the 
  telescope 
  were 
  mounted 
  equatorially, 
  the 
  level 
  could 
  

   be 
  dispensed 
  with, 
  and 
  the 
  objects 
  might 
  be 
  referred 
  to 
  a 
  parallel 
  of 
  declination, 
  

   by 
  causing 
  a 
  spot 
  on 
  the 
  sun 
  to 
  travel 
  along 
  the 
  wires 
  ; 
  but 
  my 
  stand 
  was 
  too 
  

   rude 
  to 
  allow 
  this 
  method 
  to 
  be 
  adopted 
  with 
  safety.* 
  

  

  In 
  order 
  to 
  ascertain 
  the 
  times 
  of 
  the 
  different 
  phases 
  of 
  the 
  eclipse, 
  I 
  used 
  a 
  

   box 
  chronometer 
  by 
  Adams 
  of 
  London, 
  which 
  was 
  obligingly 
  furnished 
  by 
  Lieute- 
  

   nant 
  Pettersson. 
  It 
  was 
  compared 
  with 
  his 
  standard 
  chronometer 
  about 
  3 
  b 
  15 
  m 
  

   before 
  the 
  commencement 
  of 
  the 
  eclipse, 
  and 
  again 
  the 
  following 
  day 
  after 
  an 
  in- 
  

   terval 
  of 
  24 
  hours. 
  The 
  error 
  and 
  rate 
  of 
  the 
  standard 
  chronometer 
  had 
  been 
  de- 
  

   termined 
  by 
  observations 
  made 
  with 
  a 
  small 
  transit 
  instrument 
  at 
  the 
  Observa- 
  

   tory. 
  

  

  For 
  several 
  days 
  before 
  the 
  eclipse 
  the 
  weather 
  was 
  variable, 
  with 
  little 
  sun- 
  

   shine 
  ; 
  and 
  it 
  became 
  gradually 
  worse, 
  until 
  at 
  length 
  the 
  morning 
  of 
  the 
  28th 
  

   arose 
  as 
  gloomy 
  as 
  the 
  most 
  unfavourable 
  foreboding 
  could 
  have 
  anticipated. 
  

   But 
  about 
  noon, 
  to 
  the 
  great 
  delight 
  of 
  every 
  one, 
  the 
  sun 
  shone 
  brilliantly, 
  and 
  

   the 
  sky 
  soon 
  became 
  nearly 
  cloudless 
  towards 
  the 
  zenith. 
  This 
  state 
  of 
  things, 
  

   however, 
  did 
  not 
  last 
  long 
  ; 
  for 
  shortly 
  after 
  the 
  commencement 
  of 
  the 
  eclipse, 
  an 
  

   extremely 
  thin 
  cirrous 
  cloud 
  began 
  to 
  overspread 
  the 
  sky. 
  I 
  was 
  apprehensive 
  

   that 
  this 
  might 
  interfere 
  with 
  the 
  observation 
  of 
  the 
  eclipse 
  ; 
  but 
  it 
  produced 
  no 
  

   sensible 
  effect 
  in 
  impairing 
  the 
  definition 
  of 
  the 
  sun, 
  which 
  was 
  remarkably 
  good, 
  

   and 
  unusually 
  free 
  from 
  tremulous 
  motion. 
  All 
  the 
  minute 
  spots 
  and 
  faculae, 
  

   which 
  were 
  visible 
  before 
  the 
  cirrous 
  cloud 
  had 
  formed, 
  were 
  seen 
  until 
  they 
  were 
  

   covered 
  by 
  the 
  moon 
  ; 
  and 
  it 
  was 
  only 
  after 
  the 
  total 
  phase 
  of 
  the 
  eclipse 
  had 
  

   passed 
  that 
  the 
  definition 
  was 
  perceptibly 
  injured. 
  Towards 
  the 
  horizon, 
  espe- 
  

   cially 
  in 
  the 
  east, 
  the 
  sky 
  was 
  pretty 
  thickly 
  studded 
  with 
  detached 
  cumulous 
  

   clouds 
  ; 
  and 
  a 
  strong 
  south-west 
  breeze 
  continued 
  to 
  blow 
  during 
  the 
  eclipse, 
  ex- 
  

   cept 
  about 
  the 
  period 
  of 
  the 
  totality, 
  when 
  the 
  wind 
  almost 
  entirely 
  subsided. 
  

  

  I 
  determined 
  the 
  places 
  of 
  the 
  only 
  spots 
  I 
  saw 
  near 
  the 
  sun's 
  limb 
  by 
  means 
  

   of 
  the 
  position 
  micrometer. 
  There 
  was 
  a 
  patch 
  of 
  small 
  spots 
  96° 
  30' 
  to 
  the 
  west 
  

   of 
  the 
  sun's 
  vertex, 
  and 
  about 
  1-5' 
  from 
  its 
  limb; 
  and 
  a 
  considerable 
  spot, 
  evi- 
  

   dently 
  round, 
  but 
  much 
  foreshortened, 
  62° 
  to 
  the 
  east 
  of 
  the 
  vertex, 
  and 
  less 
  than 
  

   1' 
  from 
  the 
  limb 
  of 
  the 
  sun. 
  This 
  spot 
  was 
  surrounded 
  by 
  conspicuous 
  faculse 
  ; 
  

   and 
  after 
  two 
  da}^s, 
  when 
  it 
  had 
  advanced 
  on 
  the 
  sun's 
  disc, 
  it 
  proved, 
  as 
  it 
  had 
  

   seemed 
  at 
  first, 
  to 
  be 
  circular. 
  

  

  At 
  the 
  commencement 
  of 
  the 
  eclipse, 
  my 
  eye 
  was 
  directed 
  to 
  the 
  point 
  at 
  

   which 
  the 
  moon's 
  limb 
  entered 
  the 
  sun's 
  disc 
  ; 
  but, 
  although 
  I 
  distinctly 
  saw 
  the 
  

   first 
  impression 
  of 
  the 
  moon, 
  I 
  did 
  not 
  feel 
  perfectly 
  sure 
  of 
  this 
  until 
  about 
  two 
  

  

  * 
  The 
  chief 
  inconvenience 
  I 
  found 
  in 
  using 
  this 
  instrument, 
  arose 
  from 
  being 
  obliged 
  to 
  point 
  the 
  

   telescope 
  by 
  the 
  hand. 
  A 
  slow 
  rack 
  motion 
  would 
  have 
  been 
  very 
  useful. 
  In 
  observing 
  a 
  total 
  

   solar 
  eclipse, 
  every 
  moment 
  is 
  so 
  valuable, 
  that 
  too 
  much 
  care 
  cannot 
  be 
  bestowed 
  beforehand 
  in 
  

   having 
  everything 
  adapted 
  to 
  save 
  time. 
  From 
  my 
  own 
  experience, 
  I 
  should 
  recommend 
  observers 
  

   to 
  have 
  their 
  telescope 
  mountings 
  as 
  commodious 
  and 
  firm 
  as 
  possible. 
  

  

  