When the season came for the overflow of the Nile, in the first summer after the destruction of the temples, the waters happened to rise more slowly than usual; and the Egyptians laid the blame upon the Christian emperor, who had forbidden their sacrificing the usual offerings in honour of the river-god. [Illustration: 250.jpg MANFALOOT, SHOWING THE HEIGHT OF THE NILE IN SUMMER] The alarm for the loss of their crops carried more weight in the religious controversy than any arguments that could be brought against pagan sacrifices; and the anger of the people soon threatened a serious rebellion. Evagrius the prefect, being disturbed for the peace of the country, sent to Constantinople for orders; but the emperor remained firm; he would make no change in the law against paganism, and the fears of the Egyptians and Alexandrians were soon put an end to by a most plenteous overflow. Since the time of Athanasius, and the overthrow of the Arian party in Alexandria, the learning of that city was wholly in the hands of the pagans, and was chiefly mathematical. Diophantus of Alexandria is the earliest writer on algebra whose works are now remaining to us, and has given his name to the Diophantine problems. Pappus wrote a description of the world, and a commentary on Ptolemy's _Almagest_, beside a work on geometry, published under the name of his _Mathematical Collections_. Theon, a professor in the museum, wrote on the smaller astrolabe--the instrument then used to measure the star orbits--and on the rise of the Nile, a subject always of interest to the mathematicians of Egypt, from its importance to the husbandman. From Theon's astronomical observations we learn that the Alexandrian astronomers still made use of the old Egyptian movable year of three hundred and sixty-five days only, and without a leap-year. Paul the Alexandrian astrologer, on the other hand, uses the Julian year of three hundred and sixty-five days and a quarter, and he dates from the era of Diocletian. His rules for telling the day of the week from the day of the month, and for telling on what day of the week each year began, teach us that our present mode of dividing time was used in Egypt. Horapollo, the grammarian, was also then a teacher in the schools of Alexandria. He wrote in the Koptic language a work in explanation of the old hieroglyphics, which has gained a notice far beyond its deserts, because it is the only work on the subject that has come down to us.