This Egyptian dynasty extended its protection and patronage to literature as well as to science. Thus Philadelphus did not consider it beneath him to count among his personal friends the poet Callimachus, who had written a treatise on birds, and honourably maintained himself by keeping a school in Alexandria. The court of that sovereign was, moreover, adorned by a constellation of seven poets, to which the gay Alexandrians gave the nickname of the Pleiades. They are said to have been Lycophron, Theocritus, Callimachus, Aratus, Apollonius Rhodius, Nicander, and Homer the son of Macro. Among them may be distinguished Lycophron, whose work, entitled Cassandra, still remains; and Theocritus, whose exquisite bucolics prove how sweet a poet he was. [Sidenote: The writings of Apollonius.] To return to the scientific movement. The school of Euclid was worthily represented in the time of Euergetes by Apollonius Pergæus, forty years later than Archimedes. He excelled both in the mathematical and physical department. His chief work was a treatise on Conic Sections. It is said that he was the first to introduce the words ellipse and hyperbola. So late as the eleventh century his complete works were extant in Arabic. Modern geometers describe him as handling his subjects with less power than his great predecessor Archimedes, but nevertheless displaying extreme precision and beauty in his methods. His fifth book, on Maxima and Minima, is to be regarded as one of the highest efforts of Greek geometry. As an example of his physical inquiries may be mentioned his invention of a clock. [Sidenote: The writings of Hipparchus.] [Sidenote: The theory of epicycles and eccentrics.]