﻿PHENOMENA 
  OF 
  THE 
  ZODIACAL 
  LIGHT. 
  495 
  

  

  although 
  such 
  an 
  effect 
  might 
  be 
  produced 
  by 
  a 
  periodical 
  alteration 
  in 
  the 
  size 
  

   and 
  general 
  lustre 
  of 
  the 
  body, 
  still 
  the 
  supposition 
  of 
  such 
  a 
  rapid 
  material 
  change 
  

   in 
  so 
  large 
  a 
  member 
  of 
  the 
  solar 
  system, 
  is 
  extremely 
  improbable: 
  whilst 
  this 
  

   body's 
  revolving 
  may 
  be 
  held 
  to 
  be 
  necessary 
  according 
  to 
  the 
  principles 
  of 
  gravi- 
  

   tation 
  ; 
  for 
  otherwise 
  the 
  component 
  particles 
  would 
  speedily 
  fall 
  into 
  the 
  sun 
  ; 
  and 
  

   that 
  some 
  portions 
  are 
  brighter 
  than 
  others, 
  follows 
  partly 
  as 
  a 
  consequence 
  of 
  the 
  

   observed 
  unequal 
  size 
  of 
  the 
  two 
  sides. 
  Were 
  the 
  light 
  stationary, 
  then 
  the 
  

   greatest 
  and 
  least 
  lengths 
  and 
  brightnesses 
  should 
  occur 
  at 
  the 
  same 
  time 
  in 
  suc- 
  

   cessive 
  years, 
  because 
  on 
  arriving 
  again 
  at 
  the 
  same 
  points 
  of 
  its 
  orbit, 
  the 
  earth 
  

   should 
  again 
  see 
  the 
  same 
  parts 
  of 
  the 
  zodiacal 
  light 
  pointing 
  to 
  the 
  same 
  direc- 
  

   tion 
  in 
  space 
  ; 
  but, 
  as 
  already 
  stated, 
  the 
  contrary 
  to 
  this 
  has 
  been 
  observed. 
  

  

  The 
  greatest 
  elongation 
  observed 
  was 
  79°, 
  and 
  the 
  least 
  50°, 
  but 
  from 
  the 
  

   varying 
  circumstances 
  and 
  positions 
  in 
  which 
  the 
  observations 
  were 
  made, 
  the 
  

   short 
  period 
  of 
  time 
  over 
  which 
  they 
  extend, 
  together 
  with 
  the 
  small 
  number 
  of 
  

   favourable 
  opportunities, 
  and 
  the 
  distance 
  of 
  the 
  place 
  from 
  the 
  equator, 
  which 
  

   these 
  conditions 
  afforded, 
  no 
  numerical 
  results 
  of 
  much 
  accuracy 
  can 
  be 
  derived 
  

   from 
  them 
  alone 
  ; 
  but 
  some 
  advantage 
  may 
  be 
  gained 
  by 
  comparing 
  them 
  with 
  

   the 
  results 
  of 
  former 
  observers. 
  

  

  The 
  number, 
  however, 
  of 
  these, 
  i. 
  e., 
  of 
  actual 
  observers, 
  is 
  comparatively 
  

   small, 
  and 
  they 
  are 
  all 
  very 
  recent 
  ; 
  for, 
  strange 
  to 
  say, 
  no 
  notice 
  of 
  the 
  zodiacal 
  

   light 
  is 
  found 
  amongst 
  the 
  writings 
  of 
  astronomers 
  or 
  natural 
  philosophers 
  until 
  

   1661. 
  And 
  indeed, 
  when 
  we 
  consider 
  that 
  this 
  phenomenon 
  may 
  be 
  generally 
  

   described 
  as 
  a 
  broad 
  and 
  tall 
  light 
  seen 
  in 
  the 
  western 
  sky 
  after 
  sunset, 
  and 
  in 
  

   the 
  eastern 
  before 
  sunrise, 
  with 
  a 
  length 
  of 
  about 
  60°, 
  a 
  breadth 
  of 
  20°, 
  combining 
  

   with 
  a 
  brightness 
  nearly 
  equal 
  to 
  that 
  of 
  the 
  milky 
  way, 
  a 
  regular 
  mathematical 
  

   figure, 
  which 
  makes 
  it 
  far 
  more 
  remarkable, 
  and 
  rising, 
  as 
  it 
  does, 
  at 
  a 
  greater 
  

   angle 
  to 
  the 
  horizon, 
  so 
  as 
  to 
  be 
  better 
  seen 
  in 
  countries 
  nearer 
  the 
  equator 
  than 
  

   ourselves, 
  and 
  being 
  probably 
  of 
  as 
  great 
  antiquity 
  as 
  the 
  sun 
  itself, 
  — 
  truly 
  it 
  is 
  

   astonishing 
  that 
  all 
  these 
  notabilia 
  should 
  have 
  been 
  passed 
  over 
  in 
  the 
  earlier 
  

   ages 
  of 
  the 
  world, 
  when 
  civilization 
  flourished 
  more 
  to 
  the 
  south, 
  and 
  the 
  men 
  of 
  

   ancient 
  Athens 
  and 
  Babylon 
  lived 
  under 
  a 
  clear 
  sky, 
  in 
  a 
  genial 
  climate, 
  which 
  

   invited 
  rather 
  than 
  forbade 
  the 
  contemplation 
  of 
  the 
  firmament 
  by 
  night. 
  It 
  re- 
  

   mained, 
  however, 
  for 
  the 
  inhabitants 
  of 
  these 
  cloud- 
  vexed 
  northern 
  islands 
  to 
  be 
  

   the 
  first 
  to 
  take 
  notice 
  of 
  the 
  phenomenon, 
  and 
  so 
  supply 
  another 
  instance 
  of 
  the 
  

   indomitable 
  perseverance 
  of 
  an 
  iron 
  race 
  overcoming 
  all 
  the 
  untoward 
  obstacles 
  

   of 
  an 
  unpropitious 
  position, 
  and 
  rising 
  superior 
  to 
  other 
  races 
  revelling 
  in 
  the 
  

   most 
  luxurious 
  advantages 
  of 
  nature. 
  

  

  Claims 
  have 
  been 
  put 
  up 
  for 
  Kepler 
  and 
  Descartes, 
  as 
  being 
  the 
  original 
  

   discoverers 
  of 
  the 
  zodiacal 
  light 
  ; 
  but 
  the 
  passages 
  in 
  their 
  respective 
  works* 
  

  

  * 
  Kepler's 
  Epit. 
  Astron. 
  Copernicanae, 
  t. 
  i., 
  p. 
  57 
  ; 
  and 
  t. 
  ii., 
  p. 
  893 
  ; 
  Descartes, 
  Principes, 
  iii., 
  

   Art. 
  136, 
  and 
  137- 
  

  

  