Dr.  W.  Huggins  on  the  Spectrum  ofEncke's  Comet.       381 
fainter  nebulosity,  of  which  the  boundary  on  the  eastern  side  ap- 
peared to  form  a  line  at  right  angles  to  the  axis  of  the  comet. 
I  suspected  a  very  minute  stellar  nucleus  just  within  the  eastern 
extremity  of  the  brighter  condensed  part,  and  to  a  small  extent 
north  of  the  comet's  axis. 
Nov.  8.  The  description  given  yesterday  is  applicable  to  the  comet 
tonight.  The  brighter  part  appears  more  denned  and  in  stronger 
contrast  to  the  fainter  outlying  nebulosity.  The  nucleus  is  now 
visible  with  certainty.  On  the  western  preceding  side  of  the  comet, 
the  side  towards  the  sun,  the  cometary  light  becomes  gradually  fainter 
and  more  extended  until  it  is  lost  to  view. 
On  this  evening  the  light  of  the  comet  was  examined  by  the 
spectroscope.  The  larger  part  of  the  light  was  resolved  by  the 
prism  into  a  bright  band  in  the  green  part  of  the  spectrum.  The 
band  was  denned  at  its  less  refrangible  limit,  and  gradually  faded 
towards  the  blue.  The  micrometer  gave  5160  millionths  of  a  milli- 
metre as  the  wave-length  of  the  less  refrangible  boundary  of  the 
band.  Two  other  bright  bands  were  occasionally  suspected ;  one 
of  them  appeared  to  be  about  two  thirds  of  the  distance  from  the 
bright  band  towards  D,  the  other  a  little  distance  beyond  F.  No 
continuous  spectrum  could  be  detected.     The  nucleus  was  probably 
T 
6 
^      E 
1         1         § 
D 
I     i     «     t     5    *    f    f     I     f    t     I 
O 
I 
much  too  minute  and  faint  to  give  a  continuous  spectrum  that  could 
be  seen. 
No  difference  in  the  spectrum  was  seen  when  the  slit  was  moved 
over  the  comet  in  different  directions,  as  far  as  its  feeble  light  per- 
mitted. 
The  spectrum  of  a  hydrocarbon,  giving  the  bands  which  appear 
to  be  due  to  carbon,  was  then  reflected  into  the  instrument,  and  ob- 
served simultaneously  with  that  of  the  comet.  The  band  in  the  green 
was  found  to  be  identical  in  position  with  the  brightest  of  the  bands 
of  carbon,  and  to  be  similar  in  gradation  of  brightness  from  its  less 
refrangible  limit. 
Nov.  9.  The  observations  of  yesterday  were  confirmed.  The 
second  more  refrangible  band,  which  was  then  caught  only  by 
glimpses,  was  found  to  be  coincident  with  the  third  band  in  the  car- 
bon spectrum.  The  wave-length  of  the  less  refrangible  limit  was 
about  4/35mm.  The  least  refrangible  of  the  three  cometary  bands 
could  be  seen  only  occasionally. 
Nov.  12.  The  observations  on  this  evening  contain  no  new  facts. 
Nov.  13.  To-night  the  nucleus  appears  as  a  minute,  well-defined 
stellar  point. 
