DISCOVERY OF THE LAWS OF MOTION. 47 



very great. Arriaga 14 , who wrote in 1639, is 

 troubled to discover how several flat weights, lying 

 one upon another on a board, should produce a 

 greater pressure together than the lowest one 

 alone produces, since that alone touches the 

 board. Among other solutions, he suggests that 

 the board affects the upper weight, which it does 

 not touch, by determining its uHcation, or rchere- 

 ness. 



Aristotle's doctrine, that a body ten times as 

 heavy as another, will fall ten times as fast, is 

 another instance of the confusion of Statical and 

 Dynamical Forces : the Force of the greater body, 

 while at rest, is ten times as great as that of the 

 other; but the Force as measured by the velocity 

 produced, is equal in the two cases. The two 

 bodies would fall downwards with the same rapid- 

 ity, except so far as they are affected by accidental 

 causes. The merit of proving this by experiment, 

 and thus refuting the Aristotelian dogma, is usually 

 ascribed to Galileo, who made his experiment from 

 the famous leaning tower of Pisa, about 1590. 

 But others about the same time had not overlooked 

 so obvious a fact. F. Piccolomini, in his Liber 

 Scientice de Natura, published at Padua, in 1597, 

 says, "On the subject of the motion of heavy 

 and light bodies, Aristotle has put forth various 

 opinions, which are contrary to sense and expe- 

 rience, and has delivered rules concerning the 



14 Rod. de Arriaga, Cursux Philosophic us. Paris, 1(539. 



