PRELUDE TO THE EPOCH OF GALILEO. 21 



matters. One of his propositions, in the work just 

 mentioned, is (B. i. Prop. 3), " The more a heavy 

 body recedes from the beginning, or approaches the 

 end of violent motion, the slower and more inertly 

 it goes ;" which he applies to the horizontal motion 

 of projectiles. In like manner most other writers 

 about this period conceived that a cannon-ball goes 

 forwards till it loses all its projectile motion, and 

 then falls downwards. Benedetti, who has already 

 been mentioned, must be considered as one of the 

 first enlightened opponents of this and other Aristo- 

 telian errours or puzzles. In his Speculationum 

 Liber, (Venice, 1585,) he opposes Aristotle's mecha- 

 nical opinions, with great expressions of respect, but 

 in a very sweeping manner. His chapter xxiv. is 

 headed, "Whether this eminent man was right in 

 his opinion concerning violent and natural motion." 

 And after stating the Aristotelian opinion just men- 

 tioned, that the body is impelled by the air, he says 

 that the air must impede rather than impel the 

 body, and that 5 " the motion of the body, separately 

 from the mover, arises by a certain natural impres- 

 sion from the impetuosity (ex impetuositate) re- 

 ceived from the mover." He adds, that in natural 

 motions this impetuosity continually increases, by 

 the continued action of the cause, namely, the 

 propension of going to the place assigned it by 

 nature ; and that thus the velocity increases as the 

 body moves from the beginning of its path. This 



5 P . 184. 



