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  PROFESSOR 
  PIAZZI 
  SMYTH 
  ON 
  THE 
  

  

  viz., 
  by 
  particles 
  thrown 
  off 
  from 
  the 
  sun, 
  in 
  consequence 
  of 
  the 
  rapidity 
  of 
  his 
  

   rotation 
  ; 
  nor 
  was 
  he 
  very 
  happy 
  in 
  his 
  name 
  of 
  the 
  " 
  Sun's 
  atmosphere," 
  by 
  

   which 
  he 
  led 
  both 
  himself 
  and 
  others 
  to 
  reason 
  upon 
  it, 
  as 
  if 
  it 
  were 
  proved 
  to 
  be, 
  

   and 
  actually 
  was 
  of 
  a 
  kindred 
  nature 
  with 
  the 
  earth's 
  atmosphere. 
  His 
  conclu- 
  

   sions, 
  however, 
  that 
  the 
  whole 
  of 
  the 
  luminous 
  body 
  was 
  of 
  a 
  lenticular 
  form, 
  

   nearly 
  in 
  the 
  plane 
  of 
  the 
  earth's 
  orbit, 
  somewhat 
  excentric 
  with 
  regard 
  to 
  the 
  

   sun, 
  and, 
  indeed, 
  with 
  a 
  rotation 
  about 
  that 
  luminary, 
  seem 
  to 
  be 
  remarkably 
  

   good. 
  And 
  his 
  opinion, 
  so 
  far 
  as 
  the 
  lenticular 
  shape 
  is 
  concerned, 
  is 
  also 
  held 
  

   by 
  Olbers 
  and 
  by 
  Sir 
  J. 
  Herschel, 
  both 
  of 
  them 
  observers. 
  

  

  Olbers 
  in 
  a 
  letter 
  to 
  Humboldt 
  in 
  1833, 
  says, 
  " 
  What 
  you 
  tell 
  me 
  of 
  the 
  

   changes 
  of 
  brightness 
  in 
  the 
  zodiacal 
  light, 
  and 
  the 
  causes 
  to 
  which, 
  in 
  the 
  tropics, 
  

   you 
  ascribe 
  such 
  variations, 
  has 
  excited 
  my 
  interest 
  the 
  more, 
  because 
  I 
  have 
  been 
  

   for 
  a 
  long 
  time 
  past 
  particularly 
  attentive 
  every 
  spring 
  to 
  this 
  phenomenon 
  in 
  our 
  

   northern 
  latitudes. 
  I, 
  too, 
  have 
  always 
  believed 
  the 
  zodiacal 
  light 
  to 
  rotate 
  ; 
  but 
  

   I 
  assumed 
  it 
  (contrary 
  to 
  Poisson's 
  opinion, 
  which 
  } 
  r 
  ou 
  communicate 
  to 
  me), 
  to 
  

   extend 
  the 
  whole 
  way 
  to 
  the 
  sun, 
  increasing 
  rapidly 
  in 
  intensity. 
  The 
  luminous 
  

   circle 
  which 
  in 
  total 
  eclipses 
  shews 
  itself 
  round 
  the 
  darkened 
  sun, 
  I 
  have 
  sup- 
  

   posed 
  to 
  be 
  this 
  brightest 
  portion 
  of 
  the 
  zodiacal 
  light. 
  I 
  have 
  satisfied 
  myself 
  

   that 
  the 
  light 
  is 
  very 
  different 
  in 
  different 
  years, 
  sometimes 
  for 
  several 
  years 
  being 
  

   very 
  bright 
  and 
  extended, 
  and 
  in 
  other 
  years 
  scarcely 
  perceptible. 
  I 
  have 
  not 
  

   myself 
  been 
  able 
  to 
  observe 
  the 
  sudden 
  fluctuations 
  in 
  the 
  light, 
  probably 
  on 
  ac- 
  

   count 
  of 
  the 
  faintness 
  with 
  which 
  it 
  appears 
  to 
  us 
  in 
  this 
  part 
  of 
  the 
  world. 
  You 
  

   are 
  certainly 
  right 
  in 
  ascribing 
  the 
  rapid 
  variations 
  in 
  the 
  light 
  of 
  celestial 
  objects, 
  

   which 
  you 
  have 
  perceived 
  in 
  the 
  climate 
  of 
  the 
  tropics, 
  to 
  changes 
  taking 
  place 
  in 
  

   our 
  atmosphere, 
  and 
  especially 
  in 
  its 
  higher 
  regions. 
  This 
  shews 
  itself 
  in 
  a 
  more 
  

   striking 
  manner 
  in 
  the 
  tails 
  of 
  great 
  comets. 
  Often, 
  and 
  particularly 
  in 
  the 
  

   clearest 
  weather, 
  pulsations 
  in 
  the 
  tails 
  of 
  comets 
  are 
  seen 
  to 
  commence 
  from 
  the 
  

   head 
  or 
  nucleus 
  as 
  the 
  lowest 
  part, 
  and 
  to 
  run 
  in 
  one 
  or 
  two 
  seconds 
  through 
  the 
  

   whole 
  extent 
  of 
  the 
  tail, 
  which, 
  in 
  consequence, 
  appears 
  to 
  lengthen 
  several 
  de- 
  

   grees, 
  and 
  contract 
  again. 
  That 
  these 
  undulations, 
  which 
  engaged 
  the 
  attention 
  

   of 
  Robert 
  Hooke, 
  and 
  in 
  later 
  times 
  of 
  Schroeter, 
  and 
  Chladni, 
  do 
  not 
  take 
  place 
  

   in 
  the 
  cometary 
  tails 
  themselves, 
  but 
  are 
  produced 
  in 
  our 
  atmosphere, 
  appears 
  evi- 
  

   dent 
  if 
  we 
  reflect 
  that 
  the 
  several 
  particles 
  of 
  these 
  cometary 
  tails 
  (which 
  are 
  many 
  

   millions 
  of 
  miles 
  in 
  length) 
  are 
  at 
  very 
  different 
  distances 
  from 
  us, 
  and 
  that 
  the 
  

   light 
  from 
  them 
  can 
  only 
  reach 
  our 
  eyes 
  at 
  intervals 
  of 
  times 
  which 
  differ 
  several 
  

   minutes 
  from 
  each 
  other. 
  I 
  will 
  not 
  attempt 
  to 
  decide, 
  whether 
  what 
  you 
  saw 
  

   on 
  the 
  banks 
  of 
  the 
  Orinoco, 
  not 
  at 
  intervals 
  of 
  seconds, 
  but 
  of 
  minutes, 
  were 
  

   actual 
  coruscations 
  of 
  the 
  zodiacal 
  light, 
  or 
  whether 
  they 
  belonged 
  solely 
  to 
  the 
  

   upper 
  strata 
  of 
  our 
  atmosphere. 
  Nor 
  can 
  I 
  explain 
  the 
  remarkable 
  lightness 
  of 
  

   entire 
  nights, 
  or 
  the 
  anomalous 
  increase 
  and 
  prolongation 
  of 
  this 
  light 
  in 
  the 
  year 
  

  

  