56 HISTORY OF MECHANICS. 



physical reasons against its motion were invalid. 

 This restriction enabled Riccioli and other writers 

 on the geocentric side to involve the subject in 

 metaphysical difficulties ; but the conviction of men 

 was not permanently shaken by these, and the 

 Second Law of Motion was soon assumed as un- 

 questioned. 



The Laws of the Motion of Falling Bodies, as 

 assigned by Galileo, were confirmed by the reason- 

 ings of Gassendi and Fermat, and the experiments 

 of Riccioli and Grimaldi ; and the effect of resist- 

 ance was pointed out by Mersenne and Dechales. 

 The parabolic motion of Projectiles was more espe- 

 cially illustrated by experiments on the jet which 

 spouts from an orifice in a vessel full of fluid. This 

 mode of experimenting is well adapted to attract 

 notice, since the curve described, which is transient 

 and invisible in the case of a single projectile, be- 

 comes permanent and visible when we have a con- 

 tinuous stream. The doctrine of the motions of 

 fluids has always been zealously cultivated by the 

 Italians. Castelli's treatise, Delia, Misura delVA cque 

 Corrente, (1638,) is the first work on this subject, 

 and Montucla with justice calls him " the creator of 

 a new branch of hydraulics 3 ; although he mis- 

 takenly supposed the velocity of efflux to be as the 

 depth of the orifice from the surface. Mersenne 

 and Torricelli also pursued this subject, and after 

 them, many others. 



3 Mont. ii. 201. 



