The science of the Arabians followed the invading track of their literature, which had come into Christendom by two routes--the south of France, and Sicily.

Favored by the exile of the popes to Avignon, and by the Great Schism, it made good its foothold in Upper Italy.

The Aristotelian or Inductive philosophy, clad in the Saracenic costume that Averroes had given it, made many secret and not a few open friends.

It found many minds eager to receive and able to appreciate it.

Among these were Leonardo da Vinci, who proclaimed the fundamental principle that experiment and observation are the only reliable foundations of reasoning in science, that experiment is the only trustworthy interpreter of Nature, and is essential to the ascertainment of laws.