In  order  that  we  may  not  attach  too  much  value
to  the  vague  expressions  of  Cleomedes  and  Sextus  Empi-
ricus, we  may  remark  that  Cleomedes  conceives  such  an
eclipse  as  he  describes  not  to  be  possible,  though  he
offers  an  explanation  of  it  if  it  be  :  (the  fact  must  occur
whenever  the  moon  is  seen  in  the  horizon  in  the  middle
of  an  eclipse)  :  and  that  Sextus  Empiricus  gives  his  sug-
gestion of  the  effect  of  refraction  as  an  argument  why
the  Chaldean  astrology  cannot  be  true,  since  the  con-
stellation which  appears  to  be  rising  at  the  moment  of
a  birth  is  not  the  one  which  is  truly  rising.  The  Chal-
deans might  have  answered,  says  Delambre,  that  the  star
begins  to  shed  its  influence,  not  when  it  is  really  in  the
horizon,  but  when  its  light  is  seen.  (Ast.  Anc.  vol.  i.
p.  281,  and  vol.  ii.  p.  548.)


NOTES   TO    BOOK   If.  117

It  has  been  said  that  Vitellio,  or  Vitello,  whom  we
shall  have  hereafter  have  to  speak  of  in  the  history  of
Optics,  took  his  Tables  of  Refractions  from  Ptolemy.
This  is  contrary  to  what  Delambre  states.  He  says  that
Vitello  may  be  accused  of  plagiarism  from  Alhazen,  and
that  Alhazen  did  not  borrow  his  Tables  from  Ptolemy.
