40 MECHANICS. 



large stone rolls down a mountain, it first moves slow- 

 ly, but afterward bounds with rapidity, sweeping be- 

 fore it all smaller obstacles. Hail-stones, although 

 small, acquire such velocity as to break windows ; and 

 but for the resistance of the air, they Avould be much 

 more destructive. The blow of a sledge-hammer is 

 more severe as it is lifted to a greater height. New- 

 ton was first led to the examination of the laws of 

 gravity by observing, when sitting under an apple-tree, 

 that the fruit struck his hand with greatest severity 

 when it fell from the top of the tree. 



It is not an unusual error to suppose that a large 

 body will fall more rapidly than a small one. Some 

 can scarcely believe that a fifty-six pound weight will 

 not drop with a greater velocity than a small nail, not 

 remembering that a proportionately greater force is re- 

 quired to overcome the inertia and set the larger body 

 in motion. Tliis error existed for many centuries, from 

 the time of Aristotle until G-alileo first questioned its 

 correctness. The celebrated experiment which estab- 

 lished the truth on this subject, and led to the discov- 

 ery of the laws of falHng bodies just explained, and 

 which formed an era in modern philosophy, was per- 

 formed from the top of the leaning tower of Pisa. 

 Gralileo was a philosophical teacher, and, being a man 

 who thought for himself, soon discovered, by reasoning, 

 the errors that had been received without a doubt for 

 more than twenty centuries. AU the learning of the 

 age and the wisdom of the universities were against 

 him, and in favor of this time-honored error, the truth 

 of which no one had ever thought of submitting to ex-. 

 periment. The hour of trial arrived, when he, an ob- 



