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  PROFESSOR 
  PIAZZI 
  SMYTH 
  ON 
  THE 
  

  

  zodiacal 
  light," 
  no 
  idea 
  except 
  the 
  visible 
  fact 
  itself 
  is 
  included. 
  But 
  to 
  call 
  it 
  

   the 
  " 
  Sun's 
  atmosphere," 
  is 
  taking- 
  for 
  granted 
  a 
  supposed 
  fact 
  which 
  has 
  never 
  

   been 
  proved, 
  and 
  is 
  imagining 
  the 
  body 
  to 
  obey 
  peculiar 
  laws, 
  to 
  which 
  it 
  may 
  not 
  

   really 
  be 
  subject. 
  Moreover, 
  as 
  in 
  the 
  case 
  of 
  a 
  phenomenon 
  which 
  is 
  so 
  extremely 
  

   faint 
  as 
  scarcely 
  to 
  be 
  seen 
  at 
  all, 
  a 
  person 
  may 
  too 
  easily 
  persuade 
  himself 
  that 
  

   he 
  sees 
  it 
  as 
  he 
  ought 
  to 
  see 
  it, 
  — 
  so 
  there 
  seemed 
  to 
  be 
  much 
  necessity 
  for 
  making 
  

   further 
  observations, 
  which 
  though 
  they 
  might 
  prove, 
  after 
  all, 
  to 
  be 
  not 
  entirely 
  

   free 
  from 
  errors 
  of 
  judgment 
  and 
  idea, 
  yet 
  would 
  probably 
  not 
  be 
  affected 
  in 
  the 
  

   same 
  way 
  as 
  those 
  of 
  other 
  observers. 
  

  

  The 
  circumstances 
  in 
  which 
  I 
  was 
  placed 
  were 
  very 
  favourable, 
  so 
  far 
  as 
  the 
  

   clearness 
  of 
  the 
  sky, 
  the 
  purity 
  of 
  the 
  atmosphere, 
  and 
  the 
  advantage 
  of 
  geogra- 
  

   phical 
  position 
  were 
  concerned 
  ; 
  but 
  being 
  engaged 
  in 
  the 
  active 
  duties 
  of 
  a 
  trigo- 
  

   nometrical 
  survey, 
  sometimes 
  on 
  the 
  top 
  of 
  high 
  mountains 
  and 
  sometimes 
  in 
  the 
  

   plains 
  below, 
  the 
  different 
  character 
  of 
  the 
  stations 
  exercised 
  too 
  great 
  an 
  influence 
  

   on 
  the 
  phenomenon 
  to 
  be 
  observed, 
  to 
  allow 
  of 
  strict 
  comparison 
  being 
  made 
  be- 
  

   tween 
  the 
  observations 
  at 
  the 
  various 
  places. 
  But 
  there 
  was 
  at 
  least 
  the 
  possibi- 
  

   lity 
  of 
  being 
  able 
  to 
  determine 
  a 
  good 
  method 
  of 
  making 
  the 
  observations, 
  by 
  en- 
  

   deavouring 
  to 
  reduce 
  to 
  practice 
  some 
  plan 
  by 
  which 
  the 
  results 
  should 
  be 
  expressed 
  

   more 
  in 
  numbers 
  than 
  has 
  generally 
  been 
  the 
  case 
  ; 
  and 
  of 
  ascertaining 
  at 
  least 
  

   the 
  degree 
  of 
  accuracy 
  with 
  which 
  observations 
  of 
  place, 
  i. 
  <?., 
  of 
  AR. 
  and 
  Deck, 
  

   could 
  be 
  made, 
  in 
  more 
  or 
  less 
  favourable 
  localities 
  and 
  seasons. 
  

  

  I 
  proposed 
  to 
  myself, 
  therefore, 
  to 
  endeavour 
  to 
  determine 
  each 
  night 
  the 
  AR. 
  

   and 
  Deck 
  of 
  the 
  apex 
  of 
  the 
  light 
  ; 
  though 
  the 
  only 
  method 
  which 
  was 
  then 
  avail- 
  

   able, 
  viz., 
  observing 
  the 
  particular 
  stars 
  amongst 
  which 
  the 
  point 
  was 
  situated, 
  

   was 
  only 
  of 
  use 
  when 
  there 
  were 
  large 
  stars 
  close 
  by 
  ; 
  since 
  even 
  if 
  there 
  had 
  been 
  

   star-maps 
  to 
  refer 
  to 
  in 
  the 
  desert, 
  to 
  identify 
  the 
  smaller 
  ones, 
  the 
  phenomenon 
  

   to 
  be 
  observed 
  was 
  not 
  one 
  that 
  would 
  bear 
  close 
  and 
  direct 
  investigation. 
  It 
  

   was 
  only 
  after 
  having 
  shut 
  the 
  eyes 
  for 
  some 
  little 
  time, 
  or 
  having 
  turned 
  them 
  

   to 
  some 
  dark 
  part 
  of 
  the 
  sky 
  or 
  earth, 
  that 
  on 
  suddenly 
  directing 
  them 
  to 
  the 
  

   region 
  of 
  the 
  zodiacal 
  light, 
  but 
  not 
  exactly 
  to 
  the 
  middle 
  of 
  it, 
  — 
  it 
  was 
  seen 
  

   of 
  a 
  well-defined 
  figure 
  ; 
  for 
  by 
  looking 
  straight 
  at 
  it, 
  and 
  still 
  more 
  by 
  coming 
  

   into 
  contact 
  with 
  any 
  artificial 
  light, 
  the 
  situation 
  of 
  the 
  apex 
  appeared 
  to 
  vary 
  

   many 
  degrees, 
  or 
  could 
  not 
  be 
  decided 
  on 
  at 
  all. 
  At 
  length, 
  therefore, 
  in 
  1844, 
  

   I 
  made 
  a 
  little 
  wooden 
  instrument 
  with 
  equatorial 
  motion, 
  plain 
  sights, 
  and 
  

   roughly 
  divided 
  circles 
  ; 
  which 
  being 
  placed 
  in 
  position 
  in 
  some 
  spot 
  free 
  from 
  

   any 
  artificial 
  light, 
  readily 
  gave 
  the 
  means 
  of 
  determining 
  the 
  object 
  sought. 
  

   Then, 
  by 
  the 
  sort 
  of 
  side 
  glance 
  above 
  described, 
  a 
  good 
  notion 
  of 
  the 
  position 
  

   of 
  the 
  apex 
  being 
  obtained, 
  the 
  plain 
  sights 
  were 
  immediately 
  pointed 
  to 
  the 
  spot, 
  

   the 
  circles 
  read 
  off, 
  and 
  their 
  index 
  error 
  obtained 
  by 
  reference 
  to 
  known 
  stars 
  on 
  

   either 
  side. 
  This 
  was 
  usually 
  done 
  two 
  or 
  three 
  times 
  each 
  night, 
  and 
  the 
  mean 
  

   has 
  been 
  entered 
  in 
  the 
  accompanying 
  table 
  as 
  a 
  single 
  observation. 
  

  

  