Aristotle took all knowledge as his province and proceeded to map it out for further investigation. It is impossible even to enumerate all his extant writings here, and they are only a small part of what he wrote. For scientific method he wrote on Logic and Dialectic, and here he was the discoverer of the syllogism and distinguished the inductive and deductive methods of reasoning. For literature he dissected Poetry and Rhetoric, laying down principles which all subsequent critics have been compelled to follow. In his Ethics he defines the nature of virtue in a sense that is truly Hellenic. Virtues are the mean between two vices. Thus liberality is the virtue of which prodigality and parsimony are the extremes; courage is the mean between foolhardiness and cowardice. For Natural Science he wrote the first treatise on zoology, enumerating about 500 different species. It was the first time in the history of the world when men had thought it worth while to observe the world around them. Most of this scientific work was beyond the reach of mankind, and remained so for two thousand years. The Romans studied him, but scarcely advanced a step. In the Dark Ages Europe lost even the power to follow him, and much of his teaching was recovered from the wise men of Arabia. The mediæval schoolmen were content with abridged translations for their scientific knowledge. It was not until the fifteenth and sixteenth centuries that Europe came again to be able to study and understand him. In the seventeenth and eighteenth men like Bacon and Newton began to make some advance. Even now he is our master in Logic, in Criticism, and above all in Politics. Plato had treated Political Science in three great dialogues, the greatest of which is “The Republic.” The ostensible object of this work is to define the nature of Justice, and in order to do so Socrates and his friends set out to construct an [Illustration: PLATE LXXXVIII. THE VICTORY OF SAMOTHRACE _Alinari_]