ADDITIONAL NOTES. xxiii
P. 172,1. i. Eratosthenes' great circle
There are considerable discrepancies in modern calculations of
Eratosthenes' earth-perimeter, which has been estimated at any-
thing between 20,000 to 25,000 geographical miles (in round
figures). These differences arise partly from a doubt whether
Eratosthenes' own figure was 250,000 or 252,000 stades; but the
chief cause of uncertainty is the length of the stadium in terms of
which he was reckoning. The calculation in the text rests on the
assumption that he used the Attic-Roman stadium, = | of a Roman
mile, This view has the apparent support -of a passage in Pliny,
12. 53, whose meaning, however, is not beyond dispute.
P. 190,1. 18. The return of Eudoxus
The eventual fate of Eudoxus is uncertain. After one false start
he set out again, but all that Posidonius (who was Strabo's in-
formant on this subject) could say about the end of the venture
was that 'they ought to know at Gades and in Spain.' It was
asserted by Mela, 3. 9. 90, and by Pliny, 2. 169, on the authority
of Cornelius Nepos, that Eudoxus accomplished his object. But if
he had really circumnavigated Africa, the effect of his discoveries
in an age when geographic curiosity had been fully awakened must
have been considerable; and Posidonius, who upheld the theory
of a waterway round Africa (Strabo, 2. 3. 5, p. 100), could not
have professed ignorance of them. On the other hand it is^mlikely
that Eudoxus returned to Gades a second time and reported the
definite failure of his expedition. In that case Nepos (who could
easily have made enquiries of Pompey's and Caesar's friend
Cornelius Balbus, a native of Gades), would hardly have stated
as a positive fact that Eudoxus had been successful The most
probable conclusion is that (like the Vivaldi brothers who attempted
to repeat his voyage in 1291 A.D.) he perished on the journey.
P. 191,1. 23. Soundings in the Mediterranean
Sardinia is situated between two marine precipices in which the
sea floor sinks to about 2000 fathoms* In the Ionian Sea measure-
ments of nearly 2500 fathoms have been taken in modern times.
Pp. 192, 193. Observations on the tides
An astronomer of the second century, Seleucus of Babylon,
went on to assume a causal relation between the tides and the