﻿1875.] 
  

  

  Spectrum 
  of 
  Coggia's 
  Comet. 
  

  

  157 
  

  

  obtained, 
  together 
  with 
  the 
  known 
  lines 
  of 
  oxygen, 
  when 
  carbonic 
  acid 
  

   and 
  carbonic 
  oxide 
  were 
  employed. 
  

  

  2. 
  The 
  Continuous 
  Spectrum 
  of 
  the 
  Nucleus. 
  

  

  I 
  was 
  not 
  able 
  to 
  satisfy 
  myself 
  of 
  the 
  existence 
  in 
  the 
  continuous 
  

   spectrum 
  of 
  the 
  nucleus 
  of 
  any 
  dark 
  lines, 
  nor 
  of 
  any 
  bright 
  lines, 
  other 
  

   than 
  the 
  three 
  bright 
  bands 
  which 
  have 
  been 
  described. 
  

  

  I 
  found 
  that 
  the 
  presence 
  of 
  the 
  bright 
  bands 
  increased 
  the 
  relative 
  bright- 
  

   ness 
  of 
  the 
  middle 
  part 
  of 
  the 
  linear 
  continuous 
  spectrum, 
  so 
  as 
  to 
  give 
  an 
  

   apparently 
  smaller 
  relative 
  amplitude 
  to 
  the 
  red 
  and 
  violet 
  parts 
  of 
  the 
  spec- 
  

   trum. 
  This 
  was 
  particularly 
  noticed 
  to 
  be 
  the 
  case 
  during 
  the 
  first 
  week 
  of 
  

   July. 
  "When 
  some 
  breadth 
  was 
  given 
  to 
  the 
  spectrum 
  by 
  means 
  of 
  a 
  cylin- 
  

   drical 
  lens, 
  the 
  bright 
  bands 
  were 
  clearly 
  distinguished 
  in 
  it, 
  and 
  then 
  the 
  

   relative 
  brightness 
  of 
  different 
  parts 
  of 
  the 
  continuous 
  spectrum 
  was 
  more 
  

   nearly 
  that 
  of 
  an 
  ordinary 
  incandescent 
  body. 
  The 
  blue 
  end 
  of 
  the 
  con- 
  

   tinuous 
  spectrum 
  appeared 
  to 
  fail 
  abruptly 
  a 
  little 
  beyond 
  G, 
  and 
  I 
  was 
  

   not 
  able 
  to 
  trace 
  the 
  spectrum 
  beyond 
  this 
  point. 
  I 
  took 
  this 
  circum- 
  

   stance 
  at 
  first 
  to 
  show 
  the 
  absence 
  of 
  the 
  violet 
  rays, 
  and 
  consequently 
  

   a 
  low 
  temperature 
  in 
  the 
  nucleus. 
  Afterwards, 
  when 
  the 
  solar 
  spectrum 
  

   was 
  reduced 
  to 
  about 
  the 
  brightness 
  of 
  that 
  of 
  the 
  comet, 
  I 
  observed 
  a 
  

   similar 
  apparent 
  abrupt 
  termination 
  of 
  light 
  at 
  the 
  same 
  part 
  of 
  the 
  

   spectrum, 
  which 
  is 
  therefore 
  a 
  phenomenon 
  due 
  to 
  the 
  eye 
  of 
  the 
  observer. 
  

   Although 
  it 
  is 
  probable 
  that 
  the 
  violet 
  rays 
  are 
  absent, 
  or 
  at 
  least 
  not 
  

   present 
  with 
  any 
  great 
  intensity 
  in 
  the 
  light 
  of 
  the 
  nucleus, 
  this 
  observa- 
  

   tion 
  of 
  the 
  apparent 
  failure 
  of 
  the 
  spectrum 
  a 
  little 
  beyond 
  G- 
  cannot, 
  by 
  

   itself, 
  be 
  accepted 
  as 
  a 
  trustworthy 
  proof 
  that 
  such 
  is 
  really 
  the 
  case. 
  

  

  When 
  the 
  nucleus 
  was 
  examined 
  in 
  the 
  telescope, 
  it 
  appeared 
  as 
  a 
  well- 
  

   defined 
  minute 
  point 
  of 
  light 
  of 
  great 
  brilliancy. 
  I 
  suspected 
  at 
  times 
  

   a 
  sort 
  of 
  intermittent 
  flashing 
  in 
  the 
  bright 
  point. 
  The 
  nucleus 
  sug- 
  

   gested 
  to 
  me 
  an 
  object 
  on 
  fire, 
  of 
  which 
  the 
  substance 
  was 
  not 
  unif 
  orm 
  

   in 
  composition, 
  so 
  that 
  at 
  intervals 
  it 
  burned 
  with 
  a 
  more 
  vivid 
  light. 
  

   On 
  July 
  6th 
  the 
  diameter 
  of 
  the 
  nucleus, 
  when 
  measured 
  with 
  a 
  power 
  of 
  

   800, 
  was 
  1"*8. 
  On 
  July 
  13th 
  the 
  measure 
  was 
  nearly 
  double, 
  viz. 
  3"; 
  

   but 
  at 
  this 
  time 
  the 
  point 
  of 
  light 
  was 
  less 
  defined. 
  On 
  July 
  15th 
  the 
  

   nucleus 
  appeared 
  elongated 
  towards 
  the 
  following 
  side 
  of 
  the 
  comet, 
  at 
  

   an 
  angle 
  of 
  about 
  40° 
  to 
  the 
  comet's 
  axis. 
  

  

  The 
  nucleus 
  appeared 
  of 
  an 
  orange- 
  colour. 
  This 
  may 
  be 
  due 
  in 
  part 
  

   to 
  the 
  effect 
  of 
  contrast 
  with 
  the 
  greenish 
  light 
  of 
  the 
  coma. 
  Sir 
  J 
  ohn 
  

   Herschel 
  described 
  the 
  head 
  of 
  the 
  comet 
  of 
  1811 
  to 
  be 
  of 
  a 
  greenish 
  or 
  

   bluish-green 
  colour, 
  while 
  the 
  central 
  point 
  appeared 
  to 
  be 
  of 
  a 
  pale 
  ruddy 
  

   tint. 
  The 
  elder 
  Struve's 
  representations 
  of 
  Halley's 
  comet, 
  at 
  its 
  appear- 
  

   ance 
  in 
  1835, 
  are 
  coloured 
  green, 
  and 
  the 
  nucleus 
  is 
  coloured 
  reddish 
  

   yellow. 
  He 
  describes 
  the 
  nucleus 
  on 
  October 
  9 
  thus, 
  " 
  Der 
  Kern 
  zeigte 
  

   sich 
  wie 
  eine 
  kleine, 
  etwas 
  ins 
  gelbliche 
  spielende, 
  gluhende 
  Kohle 
  von 
  

   langlicher 
  Form." 
  Dr. 
  Winnecke 
  describes 
  similar 
  colours 
  in 
  the 
  bright 
  

  

  