﻿1875.] 
  

  

  Spectrum 
  of 
  Coggia's 
  Comet. 
  

  

  155 
  

  

  bands 
  and 
  the 
  faint 
  continuous 
  spectrum 
  were 
  observed 
  to 
  vary 
  in 
  relative 
  

   intensity. 
  

  

  When 
  the 
  slit 
  was 
  brought 
  back 
  past 
  the 
  nucleus 
  on 
  to 
  the 
  commence- 
  

   ment 
  of 
  the 
  tail, 
  the 
  gaseous 
  spectrum 
  became 
  rapidly 
  fainter, 
  until, 
  at 
  a 
  

   short 
  distance 
  from 
  the 
  nucleus, 
  the 
  continuous 
  spectrum 
  predominated 
  

   so 
  strongly 
  that 
  the 
  middle 
  band 
  only, 
  which 
  is 
  the 
  brightest, 
  could 
  be 
  

   detected 
  on 
  it. 
  

  

  We 
  have 
  presented 
  to 
  us, 
  therefore, 
  by 
  the 
  light 
  of 
  the 
  comet 
  three 
  

   spectra 
  : 
  — 
  

  

  1. 
  The 
  spectrum 
  of 
  bright 
  bands. 
  

  

  2. 
  The 
  continuous 
  spectrum 
  of 
  the 
  nucleus. 
  

  

  3. 
  The 
  continuous 
  spectrum 
  which 
  accompanies 
  the 
  gaseous 
  spectrum 
  

   in 
  the 
  coma, 
  and 
  which 
  represents 
  almost 
  entirely 
  the 
  light 
  of 
  the 
  tail. 
  

  

  1. 
  The 
  Spectrum 
  of 
  Bright 
  Bands. 
  

  

  The 
  three 
  bright 
  bands 
  were 
  obviously 
  similar 
  in 
  position 
  and 
  character 
  

   to 
  those 
  which 
  were 
  observed 
  in 
  Comet 
  II., 
  1868. 
  In 
  that 
  comet 
  the 
  

   bands 
  could 
  not 
  be 
  resolved 
  into 
  lines 
  ; 
  but 
  in 
  the 
  spectrum 
  of 
  the 
  comet 
  

   now 
  under 
  observation, 
  on 
  some 
  occasions, 
  especially 
  during 
  the 
  early 
  

   part 
  of 
  July, 
  the 
  three 
  bands 
  were 
  partially 
  resolved 
  into 
  lines. 
  The 
  

   resolution 
  of 
  the 
  bands 
  was 
  seen 
  most 
  distinctly 
  at 
  the 
  boundary 
  of 
  the 
  

   coma, 
  where 
  the 
  continuous 
  spectrum 
  was 
  very 
  faint. 
  

  

  The 
  bands 
  appeared 
  to 
  me 
  to 
  be 
  brighter 
  relatively 
  to 
  the 
  continuous 
  

   spectrum 
  during 
  the 
  early 
  part 
  of 
  the 
  time 
  that 
  the 
  comet 
  was 
  under 
  

   observation. 
  

  

  On 
  July 
  7, 
  the 
  bands 
  were 
  compared 
  directly 
  with 
  the 
  spectrum 
  of 
  the 
  

   induction-spark 
  taken 
  in 
  a 
  current 
  of 
  olefiant 
  gas. 
  I 
  suspected 
  a 
  

   small 
  shift 
  of 
  all 
  three 
  bands 
  towards 
  the 
  more-refrangible 
  end 
  of 
  the 
  

   spectrum. 
  

  

  July 
  8. 
  — 
  I 
  made 
  some 
  measures 
  of 
  the 
  want 
  of 
  coincidence 
  of 
  the 
  less- 
  

   refrangible 
  edge 
  of 
  the 
  middle 
  and 
  brightest 
  band 
  with 
  the 
  correspondiug 
  

   part 
  of 
  the 
  band 
  in 
  the 
  spectrum 
  of 
  the 
  blue 
  part 
  of 
  a 
  small 
  oil-flame. 
  

   Afterwards 
  I 
  found 
  that 
  the 
  collimating 
  lens 
  had 
  shifted 
  during 
  the 
  

   taking 
  of 
  the 
  measures. 
  I 
  repeated 
  the 
  observations 
  on 
  July 
  13. 
  On 
  

   this 
  day 
  I 
  estimated 
  the 
  shift 
  of 
  the 
  brightest 
  band 
  to 
  be 
  about 
  | 
  of 
  the 
  

   distance 
  of 
  b 
  2 
  to 
  6 
  3 
  . 
  The 
  other 
  bands 
  appeared 
  to 
  be 
  similarly 
  displaced 
  

   in 
  relation 
  to 
  the 
  bands 
  of 
  the 
  terrestrial 
  spectrum. 
  The 
  estimation 
  of 
  

   the 
  amount 
  of 
  displacement 
  was 
  rendered 
  more 
  difficult 
  by 
  the 
  circum- 
  

   stance 
  that 
  the 
  cometary 
  band 
  was 
  not 
  so 
  bright 
  at 
  the 
  less-refrangible 
  

   limit 
  as 
  was 
  the 
  band 
  in 
  the 
  spectrum 
  of 
  the 
  oil-flame. 
  With 
  this 
  

   exception, 
  the 
  relative 
  brightness 
  of 
  the 
  different 
  parts 
  of 
  the 
  bands 
  

   agreed 
  with 
  the 
  corresponding 
  parts 
  of 
  the 
  bands 
  in 
  the 
  terrestrial 
  

   spectrum. 
  

  

  On 
  the 
  supposition 
  of 
  the 
  identity 
  of 
  the 
  comet's 
  bands 
  with 
  those 
  of 
  

   the 
  spectrum 
  of 
  carbon, 
  the 
  shift 
  which 
  was 
  observed 
  would 
  indicate 
  a 
  

  

  