﻿PHENOMENA 
  OF 
  THE 
  ZODIACAL 
  LIGHT. 
  501 
  

  

  emanation, 
  or 
  an 
  enlargement 
  of 
  its 
  dimensions 
  ; 
  and 
  whether 
  this 
  be 
  any 
  con- 
  

   comitant 
  symptom 
  with 
  the 
  appearance 
  of 
  spots 
  on 
  the 
  sun, 
  or 
  magnetical 
  dis- 
  

   turbances 
  on 
  the 
  earth, 
  — 
  are 
  matters 
  still 
  to 
  be 
  determined 
  by 
  observation. 
  

  

  The 
  physical 
  constitution 
  of 
  the 
  zodiacal 
  light 
  seems 
  also 
  well 
  worthy 
  of 
  being 
  

   inquired 
  into. 
  The 
  most 
  probable 
  supposition 
  is, 
  that 
  which 
  makes 
  it 
  consist 
  of 
  

   innumerable 
  small 
  planetary 
  particles 
  revolving 
  about 
  the 
  sun, 
  and 
  shining 
  by 
  

   reflected, 
  or 
  not 
  impossibly 
  by 
  direct 
  light. 
  Not 
  impossibly, 
  because 
  while, 
  on 
  

   the 
  one 
  hand, 
  the 
  occasional 
  crossing 
  of 
  the 
  earth's 
  orbit 
  by 
  the 
  extremer 
  portions 
  

   of 
  the 
  zodiacal 
  light, 
  has 
  been 
  by 
  many 
  held 
  to 
  be 
  the 
  origin 
  of 
  the 
  shooting 
  stars 
  ; 
  

   and 
  many 
  of 
  them 
  have 
  been 
  found 
  to 
  be, 
  at 
  the 
  time 
  of 
  their 
  incandescence, 
  

   several 
  hundred 
  miles 
  above 
  the 
  earth's 
  surface, 
  and 
  thus 
  far 
  above 
  the 
  limits 
  of 
  

   the 
  atmosphere, 
  whose 
  friction 
  might 
  have 
  imparted 
  such 
  a 
  degree 
  of 
  heat 
  to 
  a 
  

   body 
  at 
  a 
  lower 
  altitude, 
  moving 
  with 
  a 
  velocity 
  of 
  1000 
  miles 
  per 
  minute 
  ; 
  — 
  on 
  

   the 
  other 
  hand, 
  M. 
  Mathieson 
  has 
  recently 
  made 
  some 
  most 
  interesting 
  experi- 
  

   ments, 
  in 
  which 
  the 
  thermomultiplier 
  shewed 
  evident 
  indications 
  of 
  radiant, 
  and 
  

   therefore 
  direct 
  heat, 
  proceeding 
  from 
  the 
  zodiacal 
  light.* 
  

  

  But 
  in 
  its 
  present 
  stage, 
  the 
  subject 
  can 
  only 
  be 
  profitably 
  and 
  successfully 
  

   prosecuted 
  in 
  other 
  climates, 
  in 
  countries 
  where 
  the 
  twilight 
  is 
  shorter, 
  where 
  the 
  

   ecliptic 
  makes, 
  all 
  through 
  the 
  year, 
  a 
  larger 
  angle 
  with 
  the 
  horizon 
  than 
  here, 
  

   and 
  where 
  there 
  are 
  clearer 
  skies, 
  and 
  a 
  more 
  transparent 
  atmosphere. 
  

  

  As 
  such 
  conditions 
  are 
  well 
  commanded 
  by 
  some 
  of 
  the 
  magnetical 
  and 
  me- 
  

   teorological 
  observatories 
  which 
  have 
  been 
  lately 
  established 
  on 
  a 
  similar 
  foot- 
  

   ing 
  to 
  that 
  of 
  Makerstoun, 
  in 
  connection 
  with 
  the 
  Royal 
  Society 
  of 
  Edinburgh 
  ; 
  

   and 
  as 
  the 
  species 
  of 
  phenomenon 
  is 
  one 
  that 
  belongs 
  eminently 
  to 
  those 
  de- 
  

   partments, 
  — 
  we 
  might 
  expect 
  ere 
  long 
  to 
  enjoy 
  much 
  more 
  intimate 
  and 
  exact 
  

   knowledge 
  of 
  the 
  laws 
  and 
  relations 
  of 
  this 
  wondrous 
  and 
  extensive 
  member 
  of 
  

   the 
  solar 
  system, 
  if 
  the 
  Royal 
  Society 
  were 
  to 
  give 
  its 
  testimony 
  that 
  the 
  pheno- 
  

   menon 
  was 
  one 
  of 
  a 
  nature 
  worthy 
  of 
  scientific 
  investigation 
  ; 
  as 
  well 
  as 
  that 
  all 
  

   that 
  has 
  been 
  done 
  hitherto 
  is 
  insufficient, 
  except 
  for 
  mere 
  approximative 
  pur- 
  

   poses, 
  and 
  has 
  been 
  labouring 
  under 
  geographical 
  disadvantages, 
  which 
  need 
  not 
  

   by 
  any 
  means 
  continue 
  to 
  shackle 
  observation 
  in 
  the 
  present 
  day. 
  

  

  * 
  Comptes 
  Rendus, 
  t. 
  xvi., 
  p. 
  687 
  : 
  Ap. 
  1843. 
  

  

  VOL. 
  XX. 
  PART 
  III. 
  6 
  T 
  

  

  