Another notable example of the early Greek philosophy is found in Pythagoras, who asserted that number was the first principle. He and his followers found that the "whole heaven was a harmony of number." The Pythagoreans taught that all comes from one, but that the odd number is finite, the even infinite; that ten was a perfect number. They sought for a criterion of truth in the relation of numbers. Nothing could exist or be formed without harmony, and this harmony depended upon number, that is, upon the union of contrary elements. The musical octave was their best example to illustrate their meaning. The union of the atoms in modern chemistry illustrates in full the principle of number after which they were striving. It emphasized the importance of measurements in investigation. Much more might be said about the elaborate system of the Pythagoreans; but the main principle herein stated must suffice. _The Weakness of Ionian Philosophy_.--Viewed from the modern standpoint of scientific research, the early philosophers of Greece appear puerile and insignificant. They directed their thoughts largely toward nature, but instead of systematic observation and comparison they used the speculative and hypothetical methods to ascertain truth. They had turned from the credulity of ancient tradition to simple faith in the mind to determine the nature and cause of the universe. But this was followed by a scepticism as to the sense perception, a scepticism which could only be overcome by a larger observation of facts. Simple as it appears, this process was an essential transition from the theology of the Greeks to the perfected philosophy built upon reason. The attitude of the mind was of great value, and the attention directed to external nature was sure to turn again to man, and the supernatural. While there is a mixture of the physical, metaphysical, and mystical, the final lesson to be learned is the recognition of reality of nature as external to mind. {220} _The Eleatic Philosophers_.--About 500 B.C., and nearly contemporary with the Pythagoreans, flourished the Eleatic philosophers, among whom Xenophanes, Parmenides, Zeno, and Melissus were the principal leaders. They speculated about the nature of the mind, or soul, and departed from the speculations respecting the origin of the earth. The nature of the infinite and the philosophy of being suggested by the Ionian philosophers were themes that occupied the attention of this new school. Parmenides believed in the knowledge of an absolute being, and affirmed the unity of thought and being. He won the distinction of being the first logical philosopher among the Greeks, and was called the father of idealism.