mending the text of Homer, and to whom we are indebted for the tolerably
correct state of the great poet's works, which had become faulty through
the carelessness of the copiers. Zenodotus was soon followed by other
critics in this task of editing Homer. But their labours were not
approved of by all; and when Aratus asked Timon which he thought the
best edition of the poet, the philosopher shrewdly answered, "That which
has been least corrected."

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.