178

MATHEMATICAL GEOGRAPHY.

[CHAP.

the Troad, Byzantium, and the mouth of the Borysthenes1. The
accompanying diagram will shew how greatly the latter portion of

N

• Bo

AN True meridian

A Alexandria

R Rhodes

T Troas

B Byzantium

B0 Mouth of Borysthenes

(from Peschel, Geschichte der Erdkundc^ p. 50)

this line deviates from the true meridian. The same criticism
will apply to another meridian which Eratosthenes drew further
to the west, viz. that through Carthage, the Straits of Messina,
and Rome3; for Rome, which is intermediate in longitude
between the other two, is more than two degrees to the east
of Carthage, and more than three degrees to the west of the
Straits. Hipparchus pointed out that the true method of
determining longitudes was by the comparative observation of
eclipses8, but we have no evidence to shew that any such
investigations were instituted by him. Indeed, in this matter,
. even more than in "the determination of the climata to which
certain places were to be assigned, the requisite facilities were not
forthcoming.
1 Strabo, a. 5. 7.
* Ibid., s. i. 40.
8 Ibid., i. 1.1*; d? ft Kallmrapxas fr TOW vpos^paroffB^ faMffxei, Sn
varrt, *ai I&I&TQ K<d T$ 0iXo/ia0oum, TT?S yeuypa<puci)s Irroptas
d&fo&rov \tLpeiv fotu TTJS TW ovfwlw xoi Tijt T«p