﻿496 
  PROFESSOR 
  PIAZZI 
  SMYTH 
  ON 
  THE 
  

  

  are 
  so 
  very 
  meagre 
  and 
  obscure, 
  that 
  they 
  require 
  all 
  the 
  knowledge 
  of 
  the 
  phe- 
  

   nomenon 
  acquired 
  up 
  to 
  the 
  present 
  day, 
  to 
  be 
  applied 
  to 
  make 
  them 
  mean 
  

   anything. 
  Mairan, 
  with 
  whose 
  theory 
  Kepler's 
  fancy 
  seems 
  to 
  agree, 
  when 
  

   discussing, 
  in 
  1754, 
  the 
  history 
  of 
  the 
  phenomenon, 
  gives 
  the 
  German 
  full 
  credit 
  ; 
  

   but 
  Humboldt, 
  in 
  1844, 
  with 
  different 
  theoretical 
  views, 
  dismisses 
  the 
  case 
  of 
  

   his 
  countryman 
  in 
  a 
  very 
  summary 
  way. 
  

  

  An 
  earlier 
  claim 
  still 
  has 
  been 
  brought 
  forward, 
  on 
  account 
  of 
  the 
  mention, 
  

   in' 
  a 
  letter 
  from 
  Rothmaxn 
  to 
  Tycho 
  Brahe, 
  that 
  in 
  the 
  spring 
  the 
  twilight 
  

   ceased 
  not 
  till 
  the 
  sun 
  was 
  24° 
  below 
  the 
  horizon 
  ; 
  and 
  as 
  the 
  true 
  twilight 
  would 
  

   have 
  ceased 
  long 
  before 
  the 
  sun 
  was 
  so 
  low, 
  — 
  it 
  is 
  contended 
  that 
  Rothmaxx 
  

   must 
  have 
  seen 
  the 
  zodiacal 
  light, 
  though 
  without 
  remarking 
  anything 
  peculiar 
  

   in 
  it, 
  or 
  different 
  from 
  the 
  ordinary 
  course 
  of 
  the 
  evening. 
  

  

  So 
  that 
  the 
  first 
  satisfactory 
  and 
  clear 
  description 
  is 
  still 
  that 
  of 
  Childrey 
  in 
  

   1661, 
  already 
  alluded 
  to. 
  " 
  There 
  is 
  another 
  thing," 
  says 
  he, 
  in 
  his 
  Britannia 
  

   Baconica, 
  p. 
  183, 
  " 
  which 
  I 
  recommend 
  to 
  the 
  observation 
  of 
  mathematical 
  men 
  : 
  

   which 
  is, 
  that 
  in 
  February, 
  and 
  for 
  a 
  little 
  before 
  and 
  after 
  that 
  month 
  (as 
  I 
  have 
  

   observed 
  for 
  several 
  years 
  together), 
  about 
  six 
  in 
  the 
  evening, 
  when 
  the 
  twilight 
  

   hath 
  almost 
  deserted 
  the 
  horizon, 
  you 
  shall 
  see 
  a 
  plainly 
  discernible 
  way 
  of 
  the 
  

   twilight, 
  striking 
  up 
  towards 
  the 
  Pleiades, 
  and 
  seeming 
  almost 
  to 
  touch 
  them. 
  It 
  

   is 
  so 
  observed 
  any 
  clear 
  night, 
  but 
  it 
  is 
  best 
  iliac 
  node. 
  There 
  is 
  no 
  such 
  way 
  to 
  

   be 
  observed 
  at 
  any 
  other 
  time 
  of 
  the 
  year. 
  But 
  what 
  the 
  cause 
  of 
  it 
  in 
  nature 
  

   should 
  be, 
  I 
  cannot 
  yet 
  imagine, 
  but 
  leave 
  it 
  to 
  further 
  inquiry." 
  

  

  Here, 
  then, 
  is 
  a 
  clear 
  and 
  simple 
  account 
  of 
  one 
  phase 
  of 
  the 
  phenomenon, 
  

   marking 
  it 
  as 
  a 
  something 
  unusual, 
  as 
  different 
  from 
  ordinary 
  twilight, 
  as 
  con- 
  

   stant 
  in 
  that 
  anomalous 
  difference, 
  and 
  therefore 
  well 
  worthy 
  of 
  being 
  carefully 
  

   inquired 
  into. 
  

  

  In 
  his 
  Travels 
  in 
  Persia 
  in 
  1668,* 
  Chardin 
  mentions 
  having 
  seen 
  the 
  tail 
  of 
  

   the 
  great 
  comet 
  of 
  that 
  year 
  above 
  the 
  western 
  horizon 
  after 
  sunset 
  ; 
  the 
  head 
  

   being 
  visible 
  only 
  in 
  the 
  southern 
  hemisphere. 
  Cassixi 
  and 
  Mairan, 
  writing 
  some 
  

   years 
  after, 
  under 
  the 
  influence 
  of 
  the 
  then 
  new 
  discovery 
  of 
  the 
  zodiacal 
  light, 
  

   asserted 
  that 
  it 
  must 
  have 
  been 
  this 
  which 
  Chardin 
  saw 
  ; 
  and 
  he 
  is 
  even 
  made 
  

   out 
  by 
  Delambre 
  to 
  have 
  been 
  the 
  original 
  discoverer 
  of 
  it. 
  The 
  comet 
  of 
  1668 
  

   having, 
  however, 
  appeared 
  again 
  in 
  1843 
  (that 
  is, 
  they 
  are 
  supposed, 
  with 
  the 
  

   greatest 
  probability, 
  to 
  be 
  identical 
  ; 
  and 
  if 
  not 
  identical, 
  still 
  they 
  are 
  at 
  least 
  

   both 
  specimens 
  of 
  the 
  comet 
  genus), 
  has 
  given 
  us 
  the 
  opportunity 
  of 
  determining 
  

   whether 
  Chardin's 
  description 
  applies 
  to 
  the 
  zodiacal 
  light 
  or 
  to 
  the 
  comet, 
  which 
  

   though 
  so 
  very 
  unlike 
  each 
  other, 
  were 
  not 
  only 
  confounded 
  at 
  the 
  former 
  appa- 
  

   rition, 
  but 
  at 
  the 
  latter 
  also 
  ; 
  when 
  the 
  tail, 
  as 
  before, 
  was 
  the 
  only 
  part 
  visible 
  

   in 
  the 
  northern 
  hemisphere. 
  The 
  slightest 
  glance 
  at 
  the 
  accompanying 
  drawings 
  

  

  * 
  Edit, 
  de 
  Langles, 
  t. 
  iv., 
  p. 
  326 
  ; 
  and 
  t. 
  x., 
  p. 
  97. 
  

  

  