nomena  render  the  transition  almost  insensible ;  as  in  the  theory
of  the  Tides.  But  it  is  evident  that  the  whole  reality  of  celestial
mechanics  consists  in  its  having  issued  from  the  exact  knowledge
of  true  movements,  furnished  by  celestial  geometry.  It  was  for
want  of  this  point  of  departure  that  all  attempts  before  the  time
of  Newton,  even  Descartes',  however  valuable  in  other  ways,  failed
to  establish  systems  of  celestial  mechanics.  This  division  of  the
science  into  two  parts  has  therefore  nothing  arbitrary  in  it,  nor
even  scholastic ;  it  is  deiived  from  the  nature  of  the  science,  and
is  at  once  historical  and  dogmatic.  As  for  the  subdivisions,  we
need  not  trouble  ourselves  with  them  now.
In  regard  to  the  point  of  view  from  which  the  science  should  be
regarded,  Lacaille  thought  it  would  simplify  matters  extremely  to
place  his  observer  on  the  surface  of  the  sun.  And  so  it  would,  if
the  thing  could  be  done  in  accordance  with  positive  knowledge ;
but  undoubtedly  the  solar  station  should  be  the  ultimate  and  not
the  original  one,  under  a  rational  system  of  astronomical  study.
And  when,  as  in  the  case  of  this  work,  the  object  is  the  analysis  of
the  scientific  method,  and  the  observation  of  the  logical  filiation  of
the  leading  scientific  ideas,  it  matters  less  to  obtain  a  clearer  expo-
sition of  general  results  than  to  adhere  to  the  positive  method.
