SEQUEL TO THE EPOCH OF GALILEO. 57 



Galileo's belief in the near approximation of the 

 curve described by a cannon-ball or musket-ball to 

 the theoretical parabola, was somewhat too obse- 

 quiously adopted by succeeding practical writers on 

 artillery. They underrated, as he had done, the 

 effect of the resistance of the air, which is in fact 

 so great as entirely to change the form and proper- 

 ties of the curve. Notwithstanding this, the para- 

 bolic theory was employed, as in Anderson's Art of 

 Gunnery; (1674;) and Blondel, in his Art de Jeter 

 les Bombes, (1683,) not only calculated Tables on 

 this supposition, but attempted to answer the objec- 

 tions which had been made respecting the form of 

 the curve described. It was not till a later period, 

 (1740,) when Robins made a series of careful and 

 sagacious experiments on artillery, and when some 

 of the most eminent mathematicians calculated the 

 curve, taking into account the resistance, that the 

 Theory of Projectiles could be said to be verified 

 in fact. 



The Third Law of Motion was still in some con- 

 fusion when Galileo died, as we have seen. The 

 next great step made in the school of Galileo was 

 the determination of the Laws of the motions of 

 bodies in their Direct Impact, so far as this impact 

 affects the motion of translation. The difficulties of 

 the problem of Percussion arose, in part, from the 

 heterogeneous nature of Pressure (of a body at rest), 

 and Momentum (of a body in motion) ; and, in part, 

 from mixing together the effects of percussion on 



