(697) 
for, the Ball, going from Weft to Eaft, hath indeed two impulfes^, 
one from the Earth, and another from the Fire 5 but this impulfe 
from the Earth is alfo common to the mark, and therefore the 
Ball hits the mark only with that fimple impulfe, received from 
the Fire., as it doth being fhot towards the North or Souths as, 
Angeii doeth excellently illuftrate by familiar examples of 
Motion. 
loRiccioli his third Argument AngeUtifiN£ttth\ defiling him 
to prove the fequel of his Major, which Riccioli doeth, fuppofing 
the curve, in which the heavy body defcends^ to be com poled of 
many fmall right lines ^ and proving^ that the motion is almoft 
always equal in thefe lines-, and after fome debate, concerning 
the equality of motion in thefe right lines, Angeii anfwers, that 
the equality of motion is not fufficient to prove the equality ' of 
percuftiw and found., but that there is neceuary alfo equal angles 
of incidence $ which in this cafe he proveth to be very unequal. To 
illultrate thrsmor^ let us prove ; that,other things being a!ike,the 
proportion of tWopercuffions is compofed of the dired proportion 
of their 'velocities, and of the dired proportions of the Sines of 
their angles of incidence. Supponamus ant em fequensprincipium, > 
'nen^e, quod per cu^siones ( uteris paribus,) fwt in dire5ia proper-* 
tkriecuMvilociMibus, quibus mobile appropinquat planum rcfiftens 9 > 
Viz* z fa. " Sit planum CF : fmtque duo mobilia omni modo &qualia y & 
$mtlia y qu& motu aquali accedant a puntto A. ad planum CF, in ' 
rectis AD, AF; dico,percufsionem in puntfoD adpercufsionem in 
pwn$tolc> ejfe in ratione compoftta ex ratione velocitatis in re£ta A D, 
ad velocitatmin AF, ex ratione (inus anguli AT>E- ad finum 
anguli AFE« Expuncto A in planum CF, {it recta AE normalise 
fitque retta AC aqualis retta. AJF, & AB aqualis recta AD & 
pianum3GH x parallelum piano CF: fupponamus mobile, prioribus 
§mik$* aquale, moveri aqualiter in reffia AC, eadem vclocitate» 
\qua moveturmobile in reBa AD: quomam plana BGH,CF ? y##£ 
farallela, & metits in recta AC<? (I «qualis, Igitur mobile eadem ve- 
locitate accedit ad planum BH ? qua ad planum CF, &_ proinde per- 
cufsiones in punStis B,C,/#/^ aquales^ atque percufsio in pmfto 
D, eft adpercufsioneminpunBo B, #tf recta AE ad reBa?n AH } fen 
■(*b Aquales rectos AD, AB)ut ftnus anguli ADE ad [mum anguli 
ABH, quod fie probo^ velocity moklis in retfa AD 7 eft *quali$ 
