( 8S9 ) 
An Account of two Books : 
ITraitUe U PERCUSSION on CHO^ Des CORPS, ^s. 
par Monpur Mariotte, de tAcademk Rojale des Sckmes. A 
Paris, 1673. 12°. 
THis Mathematical Author begins this Book with fome 
De^nitions , neceffary for the underftanding of fonie 
- ternis frequently ufedby hira. Of$e is that of a Springy Body, 
by which he underftands fuchanone, as having changed its 
figure by the percuffion of another body , retakes of it felf 
its former figure. An other is that of a Body not S/>ri;sg/, which, 
rohim, isfuchanone, as having taken a new figure by the 
preflure of another body, conferves that figure , as Wax, &€. 
The UJl Definition is that of the rejpe^ive Velocity of two 
bodies, by which he means that, whereby they approach to, 
or are removed from, one another, whatever be their own velo- 
cities. ^ 
Next he lays down certain Suppojitions ^vtrrtd by divers in- 
telligent Geometricians 3 and grounded upon fundry confide- 
rable Experiments. Thefe Suppoficions ase, j. That a Body 
being put in motion, will always continue that motion the fanie 
way with the fame velocity, if it be not hindred or diverted 
by *the encounter of another body, or fome other caufe, 
2. That the Bodies that are impelled upwards by different 
forces, are raifed to different heights, and that ihefe heights 
have the fame proportion to one another, as the fquares of the 
velocities, wherewith thefe bodies began to be raifed : And 
reciprpcally', that the bodies which fall by their own v/eight 
from^different Altitudes upon one and the fame Horrzonral 
iWace, doencounter that furface with different celerities, of 
which the Squares are to one another as their Alti- 
tudes. 3* That, if a body, (as B '^) fufpended -^" ^i^. 
at a ftring AB. is perpendicularly impelled up- 
ward, and raifed to a certain height, as BD ; that 
body when it is ftruck horizontally, fo as to begin its motion 
with the fame velocity , will be raifed to ^he fame height in C, 
bj 
