r of the work of Aristarchus was Eratosthenes of
Alexandria.

ERATOSTHENES, "THE SURVEYOR OF THE WORLD"

An altogether remarkable man was this native of Cyrene, who came to
Alexandria from Athens to be the chief librarian of Ptolemy Euergetes.
He was not merely an astronomer and a geographer, but a poet and
grammarian as well. His contemporaries jestingly called him Beta the
Second, because he was said through the universality of his attainments
to be "a second Plato" in philosophy, "a second Thales" in astronomy,
and so on throughout the list. He was also called the "surveyor of the
world," in recognition of his services to geography. Hipparchus said
of him, perhaps half jestingly, that he had studied astronomy as a
geographer and geography as an astronomer. It is not quite clear whether
the epigram was meant as compliment or as criticism. Similar phrases
have been turned against men of versatile talent in every age. Be that
as it may, Eratosthenes passed into history as the father of scientific
geography and of scientific chronology; as the astronomer who first
measured the obliquity of the ecliptic; and as the inventive genius
who performed the astounding feat of measuring the size of the globe
on which we live at a time when only a relatively small portion of
that globe's surface was known to civilized man. It is no discredit to
approach astronomy as a geographer and geography as an astronomer if the
results are such as these. What Eratosthenes really did was to approach
both astronomy and geography from two seemingly divergent points of
attack--namely, from the stand-point of the geometer and also from that
of the poet. Perhaps no man in any age has brought a better combination
of observing and imaginative faculties to the aid of science.

Nearly all the discoveries of Eratosthenes are associated with
observations of the shadows cast by the sun. We have seen that, in the
study of the heavenly bodies, much depends on the measurement of angles.
Now the easiest way in which angles can be measured, when solar angles
are in question, is to pay attention, not to the sun itself, but to
the shadow that it casts. We saw that Thales made some remarkable
measurements with the aid of shadows, and we have more than once
referred to the gnomon, which is the most primitive, but which long
remained the most important, of astronomical instruments. It is believed
that Eratosthenes invented an important modification of the gnomon