As intimated before, Thales of Miletus, was the father of mathematical science, as of Grecian philosophy in general. The discoveries of that early period were of the most elementary kind, but of sufficient importance to give impulse to more dignified researches. His pupil, Pythagoras, made great advancement, and introduced music into his explanations of scientific phenomena. Democritus and Anaxagoras, the friend of Pericles, improved upon the attainments of their predecessors. The latter employed himself in his prison on the quadrature of the circle. Hippocrates, originally a merchant of Chio, became a geometer at Athens, and was the first to solve the problem of a double cube. Archylas, the teacher of Plato, and Eudoxus, one of that great man's scholars, measured cylindrical surfaces, and attained important results by means of conic sections. Thales is reputed to have introduced the sun-dial into Greece, to have observed the obliquity of the ecliptic, and taught that the earth was spherical, and in the centre of the universe. The cycle of nineteen years, called the golden number, invented for the purpose of making the solar and lunar year coincide, was the most important practical result which the astronomy of the Periclean age attained. Meton and Euctemon proposed it for the adoption of the Athenians, by whom it was adopted B.C. 433 years, and is still in use to determine movable feasts. Pythagoras, the cotemporary of Anaxagoras, greatly improved every branch of science. He is said to have been taken prisoner by Cambyses, and thus to have become acquainted with all the mysteries of the Persian Magi. He settled at Crotona, in Italy, and founded the Italian sect. The physical sciences, particularly natural history, and the science of medicine, were created by the Greeks. The writings of Hippocrates and Galen instructed the age of Pericles in the science of anatomy, which, with geometry and numbers, enabled the greatest of the artists to determine his drawing, proportions, and motion. It was genius guided by science that enabled the master to endow his work with life, action, and sentiment. Science in Greece, like life itself, was thoroughly republican and expansive, so long as vital growth was permitted. Their navigation extended even to the Baltic, as the voyage of Pytheas is a proof; they rather surpassed than yielded to the Phœnicians in the activity of their trade, and the wealth as well as extent of their colonies. It was in their superiority of scientific attainments that the Grecian colonists mainly excelled. Carthage, for instance, was at the same time powerful in conquest and commerce, but despite all her intellectual culture, she was inferior to smaller cities planted on the opposite coasts.