The  occasions  of  life,  however,  are  often  reasons
for  men  going  quicker  or  slower,  but  in  the  incor-
ruptible nature  of  the  stars,  it  is  not  possible  that
any  cause  can  be  alleged  of  quickness  and  slow-
ness. Whereupon  they  propounded  this  question,
how  the  phenomena  might  be  represented  by
equable  and  circular  motions."

These  conjectures  and  assumptions  led  natu-
rally to  the  establishment  of  the  various  parts  of
the  Theory  of  Epicycles.  It  is  probable  that  this
theory  was  adopted  with  respect  to  the  planets
at  or  before  the  time  of  Plato.  And  Aristotle
gives  us  an  account  of  the  system  thus  devised7.
"Eudoxus,"  he  says,"  "attributed  four  spheres  to
each  Planet :  the  first  revolved  with  the  fixed  stars
(and  this  produced  the  diurnal  motion) ;  the  second
gave  the  planet  a  motion  along  the  ecliptic  (the
mean  motion  in  longitude) ;  the  third  had  its  axis
perpendicular8  to  the  ecliptic  (and  this  gave  the
inequality  of  each  planetary  motion) ;  the  fourth
produced  the  oblique  motion  transverse  to  this
(the  motion  in  latitude)."  He  is  also  said  to  have
attributed  a  motion  in  latitude  and  a  correspond-

7  Metaph.  xi.  8.
a  Aristotle  says  "  has  its  poles  in  the  ecliptic,"  but  this  must
be  a  mistake  of  his.  He  professes  merely  to  receive  these  opinions
from  the  professed  astronomers  "e'/c  T^  olK.eioTa.Tris  <pt\o(ro(f)ia<;


180  THE  GREEK  ASTRONOMY.
