346       REMARKS  ON  THE  COHESION  FIGURES  OF  LIQUIDS. 
constant  is  their  behaviour  in  the  production  of  a  characteristic 
cohesion  figure. 
Fig.  8  is  a  portion  of  the  Balsam  of  Copaiba  figure.  I  had 
only  three  specimens  of  this  balsam  to  operate  on.  The  first, 
which  is  two  or  three  years  old,  from  a  wholesale  house  in  the 
city,  gives  a  splendid  figure,  consisting  of  large  iridescent  disks 
apparently  growing  out  from  under  each  other  and  quickly  sub- 
siding into  a  colorless  disk  with  a  sharp  well-defined  edge,  just 
within  which  appears  a  string  of  very  minute  bosses,  which  it 
requires  a  sharp  eye  to  detect.  In  the  course  of  ten  or  fifteen 
minutes  the  film  does  not  open  into  holes,  as  many  films  do,  but 
becomes  dotted  over  with  pit-like  depressions,  which  enlarge, 
and  gradually  the  base  of  each  pit  opens  into  a  minute  network. 
These  particulars  I  did  not  stop  to  describe  at  the  meeting,  but 
they  are  given  in  my  original  description  of  the  figure. 
A  second  specimen,  of  a  brownish  color,  gave  a  very  good 
figure,  though  not  quite  so  large  as  that  of  the  first,  but  it  be- 
haved in  all  respects  like  it.  A  third  specimen,  much  more 
fluid  than  the  above,*  shot  out  rapidly  with  much  less  develop- 
ment of  color,  and  often  without  any  color  at  all.  The  film 
was  large,  the  bosses-  at  the  edge  larger  and  flatter  than  in  the 
two  former  specimens,  and  not  so  well  defined.  A  fourth  was 
a  specimen  of  the  essential  oil  of  copaiba.  It  opened  with  a 
sudden  flash  of  colored  rings,  forming  a  colorless  disk  over  the 
whole  surface  with  no  bosses  at  the  edge. 
On  thinning  down  the  second  specimen  with  oil  of  turpentine 
a  colorless  film  was  produced  similar  to  that  of  the  third. 
The  second  specimen  was  also  mixed  with  J,  ^,  and  nearly  § 
castor  oil,  (No.  1  castor  oil  in  my  twelve  specimens  being  used), 
and  in  all  cases  a  film  entirely  devoid  of  color  was  produced. 
The  splendid  iridescent  disks  of  the  balsam,  and  the  rainbow- 
rings  of  the  castor  were  entirely  absent  in  the  mixture  of  the 
two,  in  consequence  of  the  increased  thickness  of  the  resulting 
*  The  specimens  Nos.  2  and  3  were  in  long  narrow  bottles,  nearly  full. 
A  rough  measure  may  be  given  of  their  comparative  viscidity  when  it  is 
stated  that  on  inverting  No.  2,  the  bubble  of  air  under  the  cork  reached 
the  other  end  while  8  was  counted;  in  No,  3  it  travelled  through  the 
liquid  while  counting  2. 
