This period marks the commencement of European civilisation. Owing to the excellent government adopted by Ptolemy, large numbers of Arabians, Jews, and Greeks were induced to take up their residence at Alexandria, which quickly became the centre of learning and first commercial city of the whole known world, and the resort of people of all nationalities. The celebrated museum, which was commenced by Ptolemy Soter and completed by his successor, Ptolemy Philadelphus, contained a library, which grew so largely that 400,000 volumes were soon acquired by it, and a daughter library, containing 300,000 volumes, built at the Serapion, or Temple of Serapis. Books were freely bought, transcribers engaged, apartments set aside, at the king’s expense, for the residence of Greek philosophers and students, and four faculties established, for literature, mathematics, astronomy, and medicine, including natural history. There were also in connection with the university botanical and zoological gardens, an astronomical observatory, with spheres, globes, parallactic rules, etc., and an anatomical theatre for the dissection of dead bodies. It was here that Euclid produced his celebrated geometrical demonstrations, which are at this day used in our schools. Here also Archimedes proclaimed his method for the determination of specific gravities, and invented the theory of the lever. Here Eratosthenes daily taught that the earth was a globe, and determined the interval between the tropics. The earth was described as possessing imaginary poles, axis, equator, arctic and antarctic circles, equinoxial points, solstices, climate, etc. Hipparchus taught the precession of the equinoxes, catalogued the stars, and adopted lines of latitude and longitude in describing the situations of places. Thus science progressed under the wise and beneficent rule of the Ptolemies.