Before the appearance of Aristotle, the phenomena of nature had not been studied by the aid of acute observation, and for their interpretation they were surrendered to obscure guesses and arbitrary hypotheses. But in the new age which succeeded, much more careful attention to empirical analysis was manifested. Facts were sifted, and synthetical results obtained. The securer road of induction was opened, and speculations in natural philosophy assumed more and more the form and worth of practical knowledge. An ardent desire to study facts succeeded the power and passion to amass them, and a science was born of nobler aspect than a merely spiritless and empty erudition. The peculiar character of Ptolemean scholasticism preserved itself until near the fall of the western empire, and formed an all-prevailing element in Roman science. Much assistance was derived from the great collections originally in the museum at Alexandria, and the two libraries at Bruchium and at Rhacotis. Connected with the first was a large body of learned men, whose diversified talents and universal knowledge enabled them to generalize all the elements that had been agglomerated for the advantage of a yet more critical age. The library of Bruchium was the oldest, and suffered at the burning of the fleet in the time of Julius Cæsar. The library of Rhacotis made a part of the Serapeum, where it was united to the museum. The collection of Pergamus was, by the generosity of Anthony, incorporated with the library of Rhacotis. Doubtless the germ of all subsequent progress in the natural sciences was to be found in Plato's high regard for the development of a mathematical mode of thought, and in the system which Aristotle set forth respecting all organized beings. These were the guiding-stars which conducted all great masters of learning amid fanatical errors for many centuries, and prevented the utter loss of a scientific method. Step by step the progress went forward. Eratosthenes of Cyrene projected a systematic "Universal Geography;" and, outstripping the "System of Floodgates," by Strato of Lampsacus, followed the rush of waters through the Dardanelles, and went forth in thought beyond the Pillars of Hercules to attempt the solution of the problem concerning the similarity of the level of the ocean around all the continents. A corresponding illustration of the intellectual activity of the age appeared in the attempt to determine, by approximation, the circumference of the earth. The data arrived at by Bematist, were indeed incomplete; but the device to raise himself from the narrow segment of his native land, measure adjacent degrees, and finally obtain a knowledge of the size of the entire globe, is a striking index to the Augustan age.