s, discovered from the course of the sun, the shadows cast by an
equinoctial gnomon, and the inclination of the heaven that the
circumference of the earth is two hundred and fifty-two thousand stadia,
that is, thirty-one one million five hundred thousand paces, and
observing that an eighth part of this, occupied by a wind, is three
million nine hundred and thirty-seven thousand five hundred paces, they
should not be surprised to find that a single wind, ranging over so wide
a field, is subject to shifts this way and that, leading to a variety of
breezes.

10. So we often have Leuconotus and Altanus blowing respectively to the
right and left of Auster; Libonotus and Subvesperus to the right and
left of Africus; Argestes, and at certain periods the Etesiae, on either
side of Favonius; Circias and Corus on the sides of Caurus; Thracias and
Gallicus on either side of Septentrio; Supernas and Caecias to the right
and left of Aquilo; Carbas, and at a certain period the Ornithiae, on
either side of Solanus; while Eurocircias and Volturnus blow on the
flanks of Eurus which is between them. There are also many other names
for winds derived from localities or from the squalls which sweep from
rivers or down mountains.

11. Then, too, there are the breezes of early morning; for the sun on
emerging from beneath the earth strikes humid air as he returns, and as
he goes climbing up the sky he spreads it out before him, extracting
breezes from the vapour that was there before the dawn. Those that still
blow on after sunrise are classed with Eurus, and hence appears to come
the Greek name [Greek: euros] as the child of the breezes, and the word
for "to-morrow," [Greek: aurion], named from the early morning breezes.
Some people do indeed say that Eratosthenes could not have inferred the
true measure of the earth. Whether true or untrue, it cannot affect the
truth of what I have written on the fixing of the quarters from which
the different winds blow.

[Illustration: DIAGRAM OF THE WINDS (From the edition of Vitruvius by
Fra Giocondo, Venice, 1511)]

12. If he was wrong, the only result will be that the individual winds
may blow, not with the scope expected from his measurement, but with
powers either more or less widely extended. For the readier
understanding of these topics, since I have treated them with brevity,
it has seemed best to me to give two figures, or, as the Greeks say,
[Greek: schemata], at the end of this book: one d