At the head of the mathematical school was Euclid; who is, however, less known to us by what his pupils have said of him than by his own invaluable work on geometry. This is one of the few of the scientific writings of the ancients that are still in use. The discoveries of the man of science are made use of by his successor, and the discoverer perhaps loses part of his reward when his writings are passed by, after they have served us as a stepping-stone to mount by. If he wishes his works to live with those of the poet and orator, he must, like them, cultivate those beauties of style which are fitted to his matter. Euclid did so; and his Elements have been for more than two thousand years the model for all writers on geometry. He begins at the beginning, and leads the learner, step by step, from the simplest propositions, called axioms, which rest upon metaphysical rather than mathematical proof, to high geometrical truths. The mind is indeed sometimes wearied by being made to stop at every single step in the path, and wishes, with Ptolemy Soter, for a shorter road; but, upon the whole, Euclid's clearness has never been equalled. Ctesibus wrote on the theory of hydrostatics, and was the inventor of several water-engines; an application of mathematics which was much called for by the artificial irrigation of Egypt. He also invented that useful instrument, the water-clock, to tell the time after sunset. [Illustration: 120.jpg AT THE HEAD OF THE RED SEA] Among the best known of the men of letters who came to Alexandria to enjoy the patronage of Philadelphus was Theocritus. Many of his poems are lost; but his pastoral poems, though too rough for the polished taste of Quintilian, and perhaps more like nature than we wish any works of imitative art to be, have always been looked upon as the model of that kind of poetry. If his shepherds do not speak the language of courtiers, they have at least a rustic propriety which makes us admire the manners and thoughts of the peasant. He repaid the bounty of the king in the way most agreeable to him; he speaks of him as one to freemen kind, Wise, fond of books and love, of generous mind; Knows well his friend, but better knows his foe; Scatters his wealth; when asked he ne'er says No, But gives as kings should give. Idyll, xiv. 60. Theocritus boasted that he would in an undying poem place him in the rank of the demigods; and, writing with the pyramids and the Memnonium before his eyes, assured him that generosity towards the poets would do more to make his name live for ever than any building that he could raise.