The bringing together of facts through observation alone began, to be sure, very early, for it was the motion of the sun, moon, and stars and the relation of the earth to them that first excited interest, and, especially in the countries of the East, led to the accumulation of data as to the motion of the planets, of comets and the occurrence of eclipses. But there was no coördination of these facts and they were so involved in man’s superstition as to be of little value. In passing, however, it is worthy of mention that the Chinese astronomical data accumulated more than two thousand years before the Christian era have in trained hands yielded results of no small significance. Doubtless were full knowledge available as to the science existing in the early civilizations, we should rate it higher than we can at present, but it would probably prove even then to have been developed from within, like the philosophies of the Greeks, and with but minor influence from nature herself. It is indeed remarkable that down to the time with which we are immediately concerned, it was the branches of mathematics, as arithmetic and geometry and later their applications, that were first and most fully developed: in other words those lines of science least closely connected with nature. Of the importance to science of the Greek school at Alexandria in the second and third centuries B. C., there can be no question. The geometry of Euclid (about 300 B. C.) was marvelous in its completeness as in clearness of logical method. Hipparchus (about 160–125 B. C.) gave the world the elements of trigonometry and developed astronomy so that Ptolemy 260 years later was able to construct a system that was well developed, though in error in the fundamental idea as to the relative position of the earth. It is interesting to note that the Almagest of Ptolemy was thought worthy of republication by the Carnegie Institution only a year or two since. This great astronomical work, by the way, had no successor till that of the Arab Ulugh Bey in the fifteenth century, which within a few months has also been made available by the same Institution. To the Alexandrian school also belongs Archimedes (287–212 B. C.), who, as every school boy knows, was the founder of mechanics and in fact almost a modern physical experimenter. He invented the water screw for raising water; he discovered the principle of the lever, which appealed so keenly to his imagination that he called for a ποῦ στῶ, or fulcrum, on which to place it so as to move the earth itself. He was still nearer to modern physics in his reputed plan of burning up a hostile fleet by converging the sun’s rays by a system of great mirrors.