392  Royal  Society:— -Mr.  D.  M'Farlane  on  the 
which  was  suspected  at  the  eastern  extremity  of  the  fan  is  not  marked 
in  the  figure. 
Fig.  2.  November  8,  7  p.m.— The  fan  was  now  brighter  and  more 
denned  in  form.  The  nucleus,  as  a  minute  bright  point,-  appeared 
to  be  situated  not  at  the  extreme  western  point,  but  a  little  within 
it,  towards  the  north. 
The  sides  of  the  fan  were  slightly  curved,  suggesting  an  approach 
to  a  parabolic  form. 
The  fan  was  brighter  on  the  southern  side.  The  eastern  edge  of 
the  faint  light  by  which  the  comet  was  surrounded  still  preserved  a 
right  line  from  north  to  south. 
Fig.  3.  November  14,  6.40  p.m. — The  appearance  of  the  comet 
was  essentially  the  same  as  on  Nov.  8. 
The  bounding  lines  of  the  fan  were  perhaps  less  curved ;  they 
enclosed  an  angle  of  from  85°  to  90°. 
The  nucleus  bad  become  brighter,  and  now  appeared  to  form  the 
extreme  eastern  point  of  the  fan. 
No  prolongation  of  the  eastern  boundary,  where  the  tail  is  usually 
formed,  was  seen. 
Fig.  4.  December  5,  5.30  p.m. — Thin  mist  in  the  atmosphere 
allowed  the  brighter  parts  only  of  the  comet  to  be  satisfactorily  ob- 
served. 
The  condensation  of  light  was  now  much  stronger  at  the  eastern 
end,  but  a  denned  nucleus  was  not  detected. 
The  fan  form  was  less  marked ;  the  brighter  part  of  the  comet 
more  resembled  a  brush-like  flame.  . 
The  atmospheric  haze  nearly  concealed  the  faint  light  surrounding 
the  comet,  but,  by  glimpses,  a  tail  was  now  seen  to  project  towards 
the  east ;  it  was  traced  to  a  distance  of  about  twice  the  length  of 
the  bright  brush. 
The  tail  appeared  to  come  from  the  northern  side  of  the  longer 
axis  of  the  comet,  and  to  consist  of  a  faint  ray  with  sides  nearly 
parallel. 
As  I  am  at  present  without  a  suitable  micrometer,  I  was  not  able 
to  take  measures  of  the  comet. 
Jan.  11,  1872.— George  Biddell  Airy,  C.B.,  President,  in  the  Chair. 
The  following  communication  was  read  : — 
"Experiments  made  to  determine  Surface-conductivity  for  Heat 
in  Absolute  Measure."     By  Donald  M'Farlane. 
The  experiments  described  in  this  paper  were  made  in  the 
Physical  Laboratory  of  the  University  of  Glasgow,  under  the  direc- 
tion of  Sir  William  Thomson,  during  the  summer  of  1871.  A  set 
of  similar  experiments  were  made  in  1865  ;  but  being  merely  prelimi- 
nary, carried  on  by  different  individuals,  and  embracing  only  a  limited 
Tange  of  temperatures,  it  is  thought  unnecessary  to  allude  further 
to  them  here*. 
*  These  experiments  consisted  of  two  series,  one  with  the  air  moist  by  a  little 
water  placed  in  the  interior  of  the  vessel,  the  other  having  the  air  dried  by 
