XXIV ADDITIONAL NOTES.
moon's phases, thus foreshadowing the modern discovery that
gravitation is a universal force. (Tarn, Hellenistic Civilisation, 2nd
edition, p. 270.)
P. 194. Aristotle's wind-points
In Aristotle's scheme the wind-points were arranged at uniform
intervals of three to each right angle. It has been ingeniously
explained by D'Arcy Thompson (Classical Review, 1918, pp. 49-
56), that this division was suggested by the apparent solstitial and
equinoctial positions of the rising and setting sun in Mediterranean
latitudes, which lie apart at distances of approximately thirty
degrees.
Pp. 196, 197, Erosion by rivers
In recognising the erosive power of rivers Polybius was in advance
of Herodotus, who believed that the Vale of Tempe (along which
the river Peneus gradually ground a bed for itself through a lime-
stone cliff) had been caused by an earthquake (7. 129).
P. 197,1. 13, and n. 3. Posidonius' visit to Britain
The late author who is quoted here as evidence for a journey
by Posidonius to Britain was almost certainly in error. Since
Posidonius' travels in western Europe were anterior to Caesar's
invasion of Britain, a visit to the Thames estuary on his part would
have been a notable voyage of discovery. Yet Strabo, who quotes
profusely from Posidonius, gives no hint of such a visit.
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P. 209,1. 12. Polybius' journeys in Libya
On Polybius' exploration of the West African coast, see p. 106
of the text. This voyage was made after the destruction of Carthage
in 146 B.C., at the instance of its captor, Scipio Aemilianus. It had
no enduring consequences.
P. 209,1. 19. Polybius' passage over the Alps
Polybius was probably the first Greek to obtain a tolerably
correct idea of the general trend of the Alps, and of their magnitude.
Apollonius Rhodius (following Ephorus or Timaeus) imagined
that the Argonauts could row through the Alpine chain from Italy
to Gaul (4. 625-629). He had heard of' stormy lakes' hard by the
*Hetrcynian Rock' (i.e. the Alps), but he had no clear knowledge
of their relation to the river-system of Europe.