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  PROFESSOR 
  PIAZZI 
  SMYTH 
  ON 
  COMETARY 
  PHYSICS. 
  

  

  most 
  forked 
  about 
  the 
  perihelion, 
  both 
  on 
  account 
  of 
  the 
  greater 
  absorption 
  and 
  reflection 
  of 
  light 
  

   in 
  passing 
  through 
  the 
  denser 
  anterior 
  half, 
  and 
  on 
  account 
  of 
  the 
  greater 
  ratio 
  which 
  the 
  difference 
  

   of 
  distance 
  of 
  the 
  anterior 
  and 
  posterior 
  ends 
  bear 
  to 
  that 
  of 
  the 
  former 
  and 
  the 
  sun 
  ; 
  and 
  at 
  a 
  

   distance 
  from 
  the 
  perihelion, 
  the 
  effects 
  being 
  reversed, 
  we 
  might 
  expect 
  to 
  see 
  less 
  phase, 
  a 
  less 
  dark 
  

   axis 
  in 
  the 
  tail, 
  and 
  something 
  of 
  a 
  convergence 
  in 
  the 
  limbs 
  of 
  it. 
  Now, 
  both 
  of 
  these 
  phenomena 
  

   were 
  distinctly 
  and 
  markedly 
  observable 
  in 
  the 
  great 
  comet 
  of 
  1843 
  ; 
  near 
  the 
  perihelion 
  the 
  tail 
  

   being 
  forked, 
  the 
  axis 
  almost 
  as 
  dark 
  as 
  the 
  sky 
  round 
  about, 
  and 
  the 
  limbs 
  intensely 
  bright 
  and 
  

   sharp 
  ; 
  but 
  long 
  before 
  it 
  was 
  lost 
  on 
  its 
  retreat 
  to 
  aphelion, 
  the 
  oval 
  darkness 
  was 
  almost 
  obliterated, 
  

   the 
  whole 
  tail 
  was 
  diffuse, 
  and 
  the 
  posterior 
  portion 
  for 
  fully 
  one-third 
  of 
  the 
  whole 
  visible 
  length 
  

   shewed 
  a 
  convei'gence 
  inwards. 
  

  

  But 
  the 
  notable 
  phenomenon 
  is 
  still 
  to 
  come 
  ; 
  allowing 
  the 
  above 
  increase 
  of 
  phase 
  in 
  approach- 
  

   ing 
  perihelion, 
  it 
  is 
  also 
  evident, 
  that 
  if 
  the 
  perihelion 
  distance 
  be 
  very 
  small, 
  the 
  sun 
  may 
  present 
  a 
  

   very 
  large 
  angle 
  as 
  viewed 
  from 
  the 
  comet 
  ; 
  and 
  in 
  this 
  way 
  rays 
  of 
  light 
  may 
  reach 
  every 
  part 
  of 
  the 
  

   external 
  coats 
  of 
  the 
  body, 
  and 
  these 
  may 
  be 
  also 
  illumined 
  to 
  that 
  intense 
  degree, 
  that 
  as 
  with 
  the 
  

   sunrise 
  and 
  sunset 
  clouds 
  already 
  referred 
  to, 
  no 
  phase 
  may 
  be 
  seen 
  ; 
  so 
  that, 
  with 
  such 
  comets 
  the 
  

   maximum 
  of 
  phase 
  will 
  occur 
  a 
  short 
  distance 
  on 
  either 
  side 
  of 
  the 
  perihelion, 
  at 
  and 
  very 
  close 
  to 
  it 
  

   there 
  will 
  be 
  little 
  or 
  none. 
  

  

  As 
  the 
  comet 
  of 
  1843 
  almost 
  touched 
  the 
  sun's 
  surface 
  in 
  passing 
  round 
  it, 
  it 
  must 
  have 
  pre- 
  

   sented 
  as 
  satisfactory 
  and 
  conclusive 
  a 
  proof 
  as 
  man 
  could 
  have 
  wished 
  for. 
  But 
  although 
  it 
  must 
  

   have 
  been 
  visible 
  to 
  the 
  naked 
  eye, 
  and 
  to 
  nearly 
  the 
  whole 
  world, 
  in 
  this 
  critical 
  part 
  of 
  its 
  orbit, 
  no 
  

   mortal 
  man 
  is 
  known 
  to 
  have 
  seen 
  it. 
  Rather 
  a 
  melancholy 
  fact 
  of 
  the 
  imperfection 
  of 
  the 
  astrono- 
  

   mical 
  watching 
  of 
  the 
  present 
  age 
  ; 
  and 
  it 
  appears 
  all 
  the 
  stronger, 
  from 
  Arago 
  having, 
  in 
  his 
  report 
  

   to 
  the 
  Academy, 
  descriptive 
  of 
  the 
  discovery 
  of 
  a 
  small 
  comet, 
  enlarged 
  on 
  the 
  perfection 
  of 
  the 
  

   system 
  of 
  search 
  organized 
  at 
  the 
  Parisian 
  Obseiwatory 
  ; 
  by 
  which 
  it 
  appeared 
  that 
  nothing 
  could 
  escape 
  

   detection 
  ; 
  for 
  the 
  assistant 
  who 
  made 
  the 
  discovery, 
  having 
  purposely 
  kept 
  silence 
  when 
  he 
  was 
  

   relieved 
  in 
  his 
  watch 
  by 
  another 
  person, 
  this 
  one 
  discovered 
  the 
  same 
  comet 
  before 
  having 
  been 
  an 
  

   hour 
  at 
  his 
  post. 
  But 
  to 
  return 
  to 
  the 
  comet 
  of 
  1843, 
  it 
  was 
  seen 
  while 
  still 
  not 
  very 
  far 
  from 
  the 
  

   perihelion, 
  when 
  the 
  sun 
  was 
  still 
  subtending 
  a 
  very 
  large 
  angle, 
  viz., 
  on 
  February 
  28, 
  the 
  perihelion 
  

   passage 
  being 
  February 
  27, 
  1843 
  ; 
  but 
  then 
  only 
  by 
  three 
  persons, 
  or 
  rather 
  parties, 
  and 
  none 
  of 
  

   them 
  have 
  given 
  sufficiently 
  accurate 
  accounts 
  of 
  what 
  they 
  saw, 
  or 
  have 
  attempted 
  what 
  would 
  have 
  

   been 
  so 
  invaluable, 
  if 
  effectually 
  and 
  faithfully 
  executed, 
  a 
  drawing 
  of 
  the 
  appearances 
  ; 
  but 
  their 
  

   statements, 
  as 
  far 
  as 
  they 
  go, 
  decidedly 
  confirm 
  the 
  views 
  above 
  enumerated. 
  The 
  first 
  of 
  these 
  

   happy 
  three, 
  with 
  whose 
  account 
  I 
  became 
  acquainted, 
  was 
  a 
  person 
  at 
  the 
  Cape 
  of 
  Good 
  Hope, 
  who 
  

   (decidedly 
  no 
  scientific 
  person, 
  and 
  having 
  no 
  prejudice 
  in 
  favour 
  of 
  any 
  theory), 
  described 
  the 
  comet 
  

   as 
  he 
  and 
  his 
  shepherd 
  boy 
  saw 
  it 
  at 
  noonday, 
  a 
  bright 
  hazy 
  star, 
  with 
  the 
  hazy 
  matter 
  streaming 
  off 
  

   on 
  one 
  side, 
  and 
  collected 
  into 
  a 
  focus 
  about 
  two 
  feet 
  behind 
  it. 
  Allowing 
  him 
  to 
  have 
  estimated 
  the 
  

   sun's 
  diameter 
  at 
  one 
  foot, 
  the 
  apparent 
  length 
  of 
  the 
  comet's 
  tail 
  is 
  well 
  given 
  ; 
  and 
  the 
  comet 
  itself 
  

   being 
  spoken 
  of 
  as 
  a 
  bright 
  star 
  in 
  the 
  hazy 
  matter, 
  which 
  streamed 
  off, 
  and 
  collected 
  into 
  a 
  focus 
  at 
  

   a 
  certain 
  distance 
  behind 
  the 
  head 
  ; 
  this 
  certainly 
  may 
  be 
  interpreted 
  into 
  a 
  somewhat 
  symmetrical 
  

   elliptic 
  figure, 
  having 
  the 
  nucleus 
  in 
  the 
  focus 
  nearest 
  the 
  sun. 
  

  

  The 
  next 
  testimony 
  is 
  from 
  the 
  ship 
  Owen 
  Glendower, 
  the 
  crew 
  and 
  passengers 
  of 
  which 
  ship, 
  

   when 
  off 
  the 
  Cape 
  on 
  February 
  28, 
  saw 
  the 
  comet 
  plainly 
  about 
  sunset, 
  " 
  as 
  a 
  short 
  dagger-like 
  

   object 
  close 
  to 
  the 
  sun." 
  This 
  is 
  not 
  particularly 
  explicit, 
  but 
  yet 
  we 
  may 
  certainly 
  conclude 
  from 
  

   it, 
  that 
  the 
  comet 
  was 
  broad 
  in 
  the 
  middle 
  of 
  its 
  length, 
  and 
  pointed 
  towards 
  each 
  end, 
  and 
  had 
  

   little 
  or 
  no 
  axial 
  darkness, 
  which 
  sufficiently 
  conforms 
  with 
  our 
  idea 
  of 
  the 
  perfect 
  shape 
  of 
  the 
  

   envelope 
  of 
  a 
  comet 
  seen 
  under 
  such 
  circumstances. 
  

  

  The 
  last 
  witness 
  is 
  from 
  the 
  United 
  States, 
  where 
  Mr 
  Clarke, 
  of 
  Portland, 
  saw 
  the 
  comet 
  at 
  3 
  h 
  

   p.m., 
  on 
  the 
  same 
  day, 
  and 
  examined 
  it 
  telescopically, 
  and 
  describes 
  it 
  in 
  these 
  words 
  : 
  — 
  " 
  The 
  

   nucleus, 
  and 
  also 
  evei'y 
  part 
  of 
  the 
  tail, 
  were 
  as 
  well 
  defined 
  as 
  the 
  moon 
  on 
  a 
  clear 
  day. 
  The 
  

   nucleus 
  and 
  tail 
  bore 
  the 
  same 
  appearance, 
  and 
  resembled 
  a 
  perfectly 
  pure 
  white 
  cloud 
  without 
  any 
  

   variation, 
  except 
  a 
  slight 
  change 
  near 
  the 
  head, 
  just 
  sufficient 
  to 
  distinguish 
  the 
  nucleus 
  from 
  the 
  

   tail 
  at 
  that 
  point." 
  The 
  first 
  sentence 
  well 
  describes 
  the 
  increase 
  of 
  density 
  and 
  definition 
  we 
  have 
  

   already 
  insisted 
  on 
  as 
  a 
  consequence 
  of 
  so 
  near 
  an 
  approach 
  to 
  the 
  sun 
  ; 
  and 
  the 
  second 
  paragraph 
  

   as 
  perfectly 
  describes 
  the 
  absence 
  of 
  axial 
  darkness, 
  a 
  consequence 
  partly 
  of 
  the 
  increased 
  brightness 
  

   of 
  the 
  illumination 
  of 
  all 
  the 
  external 
  portion, 
  and 
  partly 
  of 
  its 
  being 
  seen 
  in 
  daylight, 
  and 
  so 
  close 
  

   to 
  the 
  sun 
  ; 
  for 
  then, 
  as 
  every 
  one 
  knows, 
  even 
  the 
  darkest 
  shadows 
  amongst 
  the 
  mountains, 
  and 
  in 
  

   the 
  craters 
  of 
  the 
  moon, 
  those 
  which 
  appear 
  absolutely 
  black 
  at 
  night, 
  are, 
  under 
  those 
  circumstances, 
  

   barely 
  distinguishable 
  from 
  the 
  brightest 
  portions. 
  As 
  to 
  the 
  shape, 
  Mr 
  Clarke 
  says, 
  — 
  that 
  the 
  

  

  