As might be expected from the friendship that existed between Alexander, Ptolemy, and Aristotle, the Aristotelian philosophy was the intellectual corner-stone on which the Museum rested. King Philip had committed the education of Alexander to Aristotle, and during the Persian campaigns the conqueror contributed materially, not only in money, but otherwise, toward the "Natural History" then in preparation. The essential principle of the Aristotelian philosophy was, to rise from the study of particulars to a knowledge of general principles or universals, advancing to them by induction. The induction is the more certain as the facts on which it is based are more numerous; its correctness is established if it should enable us to predict other facts until then unknown. This system implies endless toil in the collection of facts, both by experiment and observation; it implies also a close meditation on them. It is, therefore, essentially a method of labor and of reason, not a method of imagination. The failures that Aristotle himself so often exhibits are no proof of its unreliability, but rather of its trustworthiness. They are failures arising from want of a sufficiency of facts. ETHICAL SCHOOL OF THE MUSEUM. Some of the general results at which Aristotle arrived are very grand. Thus, he concluded that every thing is ready to burst into life, and that the various organic forms presented to us by Nature are those which existing conditions permit. Should the conditions change, the forms will also change. Hence there is an unbroken chain from the simple element through plants and animals up to man, the different groups merging by insensible shades into each other. The inductive philosophy thus established by Aristotle is a method of great power. To it all the modern advances in science are due. In its most improved form it rises by inductions from phenomena to their causes, and then, imitating the method of the Academy, it descends by deductions from those causes to the detail of phenomena. While thus the Scientific School of Alexandria was founded on the maxims of one great Athenian philosopher, the Ethical School was founded on the maxims of another, for Zeno, though a Cypriote or Phoenician, had for many years been established at Athens. His disciples took the name of Stoics. His doctrines long survived him, and, in times when there was no other consolation for man, offered a support in the hour of trial, and an unwavering guide in the vicissitudes of life, not only to illustrious Greeks, but also to many of the great philosophers, statesmen, generals, and emperors of Rome.