﻿154 
  

  

  Dr. 
  W. 
  Huggins 
  on 
  the 
  

  

  [Jan. 
  7, 
  

  

  Butherfurd 
  have 
  shown 
  can 
  be 
  reached 
  by 
  long 
  exposure 
  with 
  the 
  

   present 
  processes). 
  

  

  I 
  cannot 
  but 
  think, 
  moreover, 
  that 
  when 
  the 
  li'ght 
  which 
  the 
  spectro- 
  

   scope 
  has 
  already 
  thrown 
  upon 
  molecular 
  action 
  shall 
  be 
  better 
  known, 
  

   and 
  used 
  as 
  a 
  basis 
  for 
  further 
  inquiry, 
  methods 
  of 
  photography 
  greatly 
  

   exceeding 
  the 
  present 
  one 
  in 
  rapidity, 
  in 
  the 
  less-refrangible 
  portion 
  of 
  

   the 
  spectrum, 
  will 
  be 
  developed 
  and 
  utilized 
  in 
  the 
  research. 
  

  

  The 
  map 
  is 
  being 
  drawn 
  by 
  my 
  assistant, 
  Mr. 
  Baphael 
  Meldola 
  (to 
  

   whom 
  my 
  thanks 
  are 
  due 
  for 
  the 
  skill 
  and 
  patience 
  he 
  has 
  brought 
  to 
  

   bear 
  upon 
  the 
  work), 
  in 
  the 
  first 
  instance, 
  with 
  more 
  especial 
  reference 
  

   to 
  the 
  positions, 
  thicknesses, 
  and 
  individualities 
  of 
  the 
  lines 
  ; 
  the 
  

   final 
  revision 
  will 
  consist 
  of 
  an 
  absolute 
  intensity 
  reproduction 
  of 
  the 
  

   photographs. 
  

  

  II. 
  " 
  On 
  the 
  Spectrum 
  of 
  Coggia's 
  Comet." 
  By 
  William 
  

   Huggins, 
  D.C.L., 
  LL.D., 
  E.B.S., 
  For. 
  Sec. 
  B.A.S. 
  Received 
  

   November 
  13, 
  1874. 
  

  

  [Plate 
  6.] 
  

  

  In 
  the 
  years 
  1866, 
  1868, 
  and 
  1871* 
  I 
  had 
  the 
  honour 
  to 
  communi- 
  

   cate 
  to 
  the 
  Boyal 
  Society 
  some 
  observations 
  with 
  the 
  spectroscope 
  of 
  five 
  

   small 
  comets, 
  including 
  Encke's 
  comet 
  at 
  its 
  return 
  in 
  1871. 
  

  

  These 
  observations 
  showed 
  that 
  a 
  great 
  part 
  of 
  the 
  light 
  of 
  these 
  

   comets 
  was 
  not 
  reflected 
  solar 
  light, 
  but 
  light 
  emitted 
  by 
  the 
  matter 
  of 
  

   the 
  comets. 
  Eurther, 
  the 
  coincidence 
  which 
  was 
  found 
  to 
  exist, 
  in 
  the 
  

   case 
  of 
  three 
  of 
  the 
  comets, 
  between 
  the 
  three 
  bright 
  bands 
  into 
  which 
  

   their 
  light 
  was 
  resolved 
  by 
  the 
  prism 
  and 
  the 
  spectrum 
  of 
  some 
  com- 
  

   pounds 
  of 
  carbon 
  appeared 
  to 
  indicate 
  the 
  presence 
  of 
  that 
  element, 
  in 
  

   some 
  form, 
  in 
  the 
  cometary 
  matter. 
  The 
  comet 
  now 
  visible, 
  which 
  was 
  

   detected 
  by 
  M. 
  Coggia, 
  April 
  17, 
  1874, 
  is 
  the 
  first 
  bright 
  comet 
  to 
  which 
  

   the 
  spectroscope 
  has 
  been 
  applied. 
  The 
  following 
  spectroscopic 
  observa- 
  

   tions 
  of 
  this 
  comet 
  were 
  made 
  from 
  July 
  1 
  to 
  July 
  15. 
  

  

  When 
  the 
  slit 
  of 
  the 
  spectroscope 
  was 
  placed 
  across 
  the 
  nucleus 
  and 
  

   coma, 
  there 
  was 
  seen 
  in 
  the 
  instrument 
  a 
  broad 
  spectrum, 
  consisting 
  of 
  

   the 
  three 
  bright 
  bands 
  which 
  were 
  exhibited 
  by 
  Comet 
  II., 
  1868 
  f, 
  crossed 
  

   by 
  a 
  linear 
  continuous 
  spectrum 
  from 
  the 
  light 
  of 
  the 
  nucleus. 
  

  

  In 
  the 
  continuous 
  spectrum 
  of 
  the 
  nucleus 
  I 
  was 
  not 
  able 
  to 
  distin- 
  

   guish 
  with 
  certainty 
  any 
  dark 
  lines 
  of 
  absorption, 
  or 
  any 
  bright 
  lines 
  

   other 
  than 
  the 
  three 
  bright 
  bands. 
  

  

  Besides 
  these 
  spectra, 
  there 
  was 
  also 
  present 
  a 
  faint 
  broad 
  continuous 
  

   spectrum 
  between 
  and 
  beyond 
  the 
  bright 
  bands. 
  

  

  When 
  the 
  slit 
  was 
  moved 
  on 
  to 
  different 
  parts 
  of 
  the 
  ccma, 
  the 
  bright 
  

  

  * 
  Proc. 
  Eoy. 
  Soc. 
  vol. 
  xvi. 
  p. 
  386, 
  vol. 
  xix. 
  p. 
  490, 
  vol. 
  xx 
  p. 
  45, 
  and 
  Phil. 
  Trans. 
  

   1868, 
  p. 
  555. 
  

  

  t 
  Phil. 
  Trans. 
  1868, 
  plate 
  xxriii. 
  

  

  