﻿500 
  PROFESSOR 
  PIAZZI 
  SMYTH 
  ON 
  THE 
  

  

  one 
  of 
  peculiar 
  beauty, 
  when 
  a 
  small 
  fleecy 
  cloud 
  is 
  projected 
  against 
  the 
  zodiacal 
  

   light, 
  and 
  detaches 
  itself 
  picturesquely 
  from 
  the 
  illuminated 
  back-ground. 
  A 
  

   passage 
  in 
  my 
  journal 
  during 
  a 
  voyage 
  from 
  Lima 
  to 
  the 
  West 
  Coast 
  of 
  Mexico, 
  

   notices 
  such 
  a 
  picture. 
  ' 
  For 
  the 
  last 
  three 
  or 
  four 
  nights 
  (between 
  10 
  D 
  and 
  14° 
  of 
  

   north 
  latitude), 
  the 
  zodiacal 
  light 
  has 
  appeared 
  with 
  a 
  magnificence 
  which 
  I 
  have 
  

   never 
  before 
  seen. 
  Judging 
  also 
  from 
  the 
  brightness 
  of 
  the 
  stars 
  and 
  nebulae, 
  the 
  

   transparency 
  of 
  the 
  atmosphere 
  in 
  this 
  part 
  of 
  the 
  Pacific 
  must 
  be 
  extremely 
  great. 
  

   From 
  the 
  14th 
  to 
  the 
  19th 
  of 
  March, 
  during 
  a 
  very 
  regular 
  interval 
  of 
  three 
  

   quarters 
  of 
  an 
  hour 
  after 
  the 
  disc 
  of 
  the 
  sun 
  had 
  sunk 
  below 
  the 
  horizon, 
  no 
  trace 
  

   of 
  the 
  zodiacal 
  light 
  could 
  be 
  seen, 
  although 
  the 
  night 
  was 
  perfectly 
  dark 
  ; 
  but 
  

   an 
  hour 
  after 
  sunset, 
  it 
  became 
  suddenly 
  visible, 
  extending 
  in 
  great 
  brightness 
  

   and 
  beauty, 
  between 
  Aldebaran 
  and 
  the 
  Pleiades, 
  and, 
  on 
  the 
  18th 
  of 
  March, 
  at- 
  

   taining 
  an 
  altitude 
  of 
  39° 
  5'. 
  Long 
  narrow 
  clouds, 
  scattered 
  over 
  the 
  lovely 
  azure 
  

   of 
  the 
  sky, 
  appeared 
  low 
  down 
  on 
  the 
  horizon, 
  as 
  if 
  in 
  front 
  of 
  a 
  golden 
  curtain, 
  

   while 
  bright 
  varied 
  tints 
  played 
  from 
  time 
  to 
  time 
  on 
  the 
  higher 
  clouds 
  : 
  it 
  seemed 
  

   a 
  second 
  sunset. 
  Towards 
  that 
  side 
  of 
  the 
  heavens 
  the 
  light 
  diffused 
  appeared 
  

   almost 
  equal 
  to 
  that 
  of 
  the 
  moon 
  in 
  her 
  first 
  quarter. 
  Towards 
  ten 
  o'clock, 
  in 
  

   this 
  part 
  of 
  the 
  Pacific, 
  the 
  zodiacal 
  light 
  usually 
  becomes 
  very 
  faint, 
  and 
  at 
  mid- 
  

   night 
  I 
  could 
  only 
  see 
  a 
  trace 
  of 
  it 
  remaining. 
  On 
  the 
  16th 
  of 
  March, 
  when 
  its 
  

   brightness 
  was 
  greatest, 
  a 
  mild 
  reflected 
  glow 
  was 
  visible 
  in 
  the 
  east.' 
  " 
  

  

  He 
  describes 
  also 
  several 
  anomalous 
  features, 
  as 
  that 
  sometimes 
  it 
  did 
  not 
  

   appear 
  for 
  three-quarters 
  of 
  an 
  hour 
  after 
  sunset, 
  though 
  the 
  twilight 
  had 
  been 
  

   for 
  some 
  time 
  ended 
  ; 
  that 
  then 
  it 
  appeared 
  suddenly, 
  and 
  continued 
  long 
  of 
  very 
  

   great 
  brightness 
  ; 
  that 
  at 
  other 
  times 
  it 
  would 
  continue 
  to 
  shorten 
  and 
  lengthen 
  

   many 
  degrees 
  in 
  a 
  few 
  minutes, 
  and 
  have 
  an 
  undulatory 
  sort 
  of 
  motion. 
  But 
  

   these 
  peculiarities, 
  when 
  not 
  accounted 
  for 
  by 
  the 
  atmospheric 
  circumstances 
  of 
  

   which 
  he 
  himself 
  takes 
  notice, 
  seem 
  rather 
  to 
  be 
  produced 
  in 
  the 
  eye 
  of 
  the 
  ob- 
  

   server 
  by 
  reason 
  of 
  the 
  extreme 
  faintness 
  of 
  the 
  object 
  to 
  be 
  observed 
  ; 
  by 
  the 
  

   length 
  of 
  time 
  that 
  a 
  retina, 
  — 
  which 
  has 
  been 
  initiated 
  by 
  watching 
  the 
  setting 
  

   sun, 
  or 
  even 
  when 
  acted 
  on 
  by 
  ordinary 
  daylight, 
  — 
  requires 
  to 
  recover 
  its 
  full 
  

   degree 
  of 
  sensitivenes 
  ; 
  as 
  well 
  as 
  by 
  the 
  deceptive 
  phantasmagoric 
  effect 
  produced 
  

   on 
  the 
  nerves 
  when 
  strained 
  to 
  a 
  greater 
  extent 
  than 
  they 
  can 
  well 
  bear. 
  

  

  Taking 
  all 
  the 
  above 
  facts 
  into 
  consideration, 
  we 
  are 
  perhaps 
  entitled 
  to 
  con- 
  

   clude, 
  on 
  pretty 
  good 
  foundation, 
  that 
  the 
  zodiacal 
  light 
  is 
  an 
  extremely 
  oblate, 
  

   lenticular, 
  revolving 
  body, 
  nearly 
  in 
  the 
  plane 
  of 
  the 
  sun's 
  equator, 
  rather 
  excen- 
  

   trically 
  situated, 
  of 
  so 
  vast 
  a 
  size 
  as 
  nearly 
  to 
  fill 
  the 
  whole 
  orbit 
  of 
  the 
  earth, 
  

   and 
  sometimes 
  actually 
  to 
  reach 
  it. 
  But 
  whether 
  it 
  does 
  actually 
  at 
  the 
  present 
  

   time 
  correspond 
  exactly 
  with 
  the 
  sun's 
  equator, 
  and 
  if 
  it 
  has 
  always 
  done 
  so, 
  and 
  

   always 
  will; 
  whether 
  the 
  manifest 
  changes 
  in 
  the 
  intrinsic 
  brightness, 
  and 
  the 
  

   form 
  and 
  size 
  of 
  the 
  light 
  that 
  have 
  been 
  observed, 
  be 
  due 
  merely 
  to 
  a 
  rotation 
  of 
  

   the 
  excentric 
  or 
  oval 
  body, 
  or 
  to 
  a 
  real 
  periodical 
  increase 
  of 
  the 
  intensity 
  of 
  its 
  

  

  