with  a  glass  rod  so  as  to  form  a  thin  even  layer,  and  if  then
a  drop  of  spirit  of  wine  on  the  end  of  a  glass  rod  is  put  in
the  middle  of  the  water,  the  surface  tension  is  lessened  at  this
point,  and  the  molecules  shrink  away  on  all  sides,  like  a  retreat-
ing army,  so  as  to  form  a  ring  round  the  drop,  separated  from  it
by  a  clear  space.  A  drop  of  oil,  placed  on  the  surface  of  the
water  in  a  similar  way,  follows  up  the  retreating  molecules  and
spreads  quickly  over  a  large  surface.  Many  different  and
curious  'cohesion-figures'  may  be  formed  by  dropping  various
liquids,  such  as  ether,  turpentine,  oil  of  cloves,  upon  a  thin  layer
of  water  as  above  described.
59.  Capillary  Attraction  is  only  a  particular  effect  of  cohesion
and  adhesion.     A  tube  with  a  small  bore,  like  a  hair,  is  called  a
capillary  tube,  from  capillus,  the  Latin  word  for  a  hair.     If  the
end  of  such  a  glass  tube  is  dipped  in  water,  the  water  is  seen  to

rise  in  the  tube  above  the
level  of  the  rest  of  the  sur-
face. In  a  series  of  tubes
of  different  diameters,  the
liquid  ascends  highest  in
the  smallest ;  or  the  heights
are  inversely  as  the  diame-
ters. Water  will  be  seen  to
rise  in  a  similar  way  between
two  glass  plates  placed  as  in

the  figure,  with  two  of  the  upright  edges  touching,  and  the  other
two  slightly  apart.  The  sustained  film  rises  higher  as  the
plates  approach,  assuming  the  form  of  a  particular  curve.  The
fluid  rises  also  slightly  on  the  outside  of  the  tubes  and  plates,
and  the  surface  of  the  sustained  column  within  the  tube  is  seen
to  be  hollow  like  a  cup.
