MECHANICS AND PHYSICS 201 



axis is equal to the product of the perimeter of the 

 curve and the circumference or portion of circumference 

 described by its centre of gravity. 



The foundations which Aristotle had assigned to 

 mechanics were criticized by Joannes Philoponus, called 

 the Grammarian or the Christian, because he was con- 

 verted from Alexandrian Neo-platonism to Christianity 

 about the year a.d. 520. In his Commentaries on the 

 five later books of Aristotle's Physics, Philoponus dis- 

 putes Aristotle's arguments against the existence of 

 empty space, for " if the medium were solid, it would 

 hinder the movements of bodies, which in order to move 

 would be obliged to divide it ; these bodies nevertheless 

 are in motion. If the medium were empty, what is 

 there to prevent the flight of an arrow, a stone or any 

 other thing, as long as there is an instrument for 

 throwing, a projectile and space ? " x Thus the air, far 

 from sustaining the movement of a projectile, only 

 hinders it. 



The Arabs confined themselves to accepting and 

 commenting on the treatises of mechanics bequeathed 

 to them by antiquity. The Western Middle Ages were 

 more venturesome. The fragments received from 

 Byzantium and from Islamitic science were sufficient to 

 awaken their attention and fertilize their intelligence. 

 From the thirteenth century, perhaps even before, the 

 school of Jordanes opened up paths unknown to 

 antiquity. Jordanes of Nemora, whose real name and 

 nationality are unknown to us, discovered the following 

 law : If a force can raise a certain weight to a certain 

 height, it will be able to raise a weight n times greater 

 to a height n times smaller. 



Another savant worthy of mention is he whom P. 



Duhem calls the forerunner of Leonardo da Vinci. We 



know nothing about him, except that he lived later 



than Jordanes and was a man of genius. Inspired by 



1 Quoted from 13 Duhem, Systime, I, p. 383. 



