Tredife ^/BODIES. 



hath excellently fet down in his book of Dioptrikes by the ex- 

 ample of a ball ftrucken by a racket ag.iinft the earth, or any 

 refifting body : the fubftance whereof is as followeth. 



In the Rectangle Paral- 

 lelogramme A E, let C E 

 be the fuperficies of the 

 earth : A, the point from 

 which the racket HG, 

 ftriketh the ball by the 

 line A B, to the point B in the fuperficies of the earth : and let 

 us conCder C, to be on the left hand, and E on the right. Now 

 we arc to fhew that the ball will rebound by the line B F, to 

 the point F, in the fame time in which it went from A to B; and 

 fo make the angle ABC equall to the angle FEE. For the 

 eftc6Ung whereofj we muft abftradt, according to the manner 

 of mathematicians, from all Phyficall inequalities, and fuppofe 

 the fuperficies C E, to be mathematically plain, and the force 

 of che racket to continue equally ftrong in B as it is in A- for 

 although in truth, neither of thefe be rigoroufly fb;nererthclefTe, 

 becaufe there is no fenfible defect in any operation that depend- 

 oh on them, it is the fame to our purpofe as if they were ma- 

 thematically fo. We fee then that the racket H G, doth in a 

 certain time drive the ball from A to B that is to fay , from 

 the left hand to the right, as farre as from C to B ; and from 

 above to downwards as ferre as from A to C. We fee again, 

 thas: the fuperficies CE, is not contrary unto this motion of 

 the ball, as ir goeth from the left hand to the right ; for the line 

 C E Jyeth likcwife that way : but is contrary unto it, as it 



goeth from above down- 

 wards; for in that courfc 

 the fuperficies C E cncoun- 

 tercth and puttcth a period 

 to the line A C. And there- 

 fore the motion of the ball 

 Vvhen it meeteth with the fuperficies C E, muft be changed from 

 the line A C, fo much as the fuperficies C E is contrary unco it; 

 that is quite backwards as farre as it depcndeth of that oppofi- 

 tion. Therefore, when the ball is come to B, it muft go from 

 thence in the fame proportion of left hand to right hand, and 

 from below upwards, as it came before from left han J to right 



