PRELUDE TO THE EPOCH OF GALILEO. 13 



of the reasoning, the weight was supposed to be 

 proportional to the descent in the vertical direc- 

 tion. It is obvious, in all this, that though the 

 author had adopted the false Aristotelian prin- 

 ciple, he had not settled in his own mind whether 

 the motions of which it spoke were actual or 

 virtual motions ; motions in the direction of the 

 inclined plane, or of the intercepted parts of the 

 vertical, corresponding to these ; nor whether the 

 "descending force" of a body was something dif- 

 ferent from its weight. We cannot doubt that, if 

 he had been required to point out, with any exact- 

 ness, the cases to which his reasoning applied, he 

 would have been unable to do so ; not possessing 

 any of those clear fundamental Ideas of Pressure 

 and Force, on which alone any real knowledge on 

 such subjects must depend. The whole of Jor- 

 danus's reasoning is an example of the confusion 

 of thought of his period, and of nothing more. It 

 no more supplied the want of some man of genius, 

 who should give the subject a real scientific foun- 

 dation, than Aristotle's knowledge of the propor- 

 tion of the weights on the lever superseded the 

 necessity of Archimedes's proof of it. 



We are not, therefore, to wonder that, though 

 this pretended theorem was copied by other writers, 

 as by Tartalea, in his Quesiti et Inventioni Di- 

 versi, published in 1554, no progress was made 

 in the real solution of any one mechanical problem 

 by means of it. Guido Ubaldi, who, in 1577, 



