IX.] PARALLELS OF LATITUDE. IJJ
surprised, when we consider that here the reports of voyagers
were the only source of information; and, as regards the rest of
the computation, what strikes us most is its approximate accuracy.
In a lesser degree the same remark applies to the continuation of
the same parallel through the Asiatic continent, for the two first
points through which it was drawn—Thapsacus on the Euphrates
and the Pylae Caspiae—are nearly in the same latitude with the
gulf of Issus, and the third—the foot of the Paropamisus range—
is at no extravagant distance to the southward of it; while the
remainder of the line is deflected towards the south-east, since it
was supposed to follow the course of the Himalaya as far as the
Eastern Ocean. Eratosthenes, also, as we have seen, placed the
Arctic circle in Thule; and towards the south he
drew another parallel through Meroe. The latitude
of this place had been determined by a Greek
called Philon, who had travelled in Aethiopia, and had calculated
the number of days before the summer solstice when the sun
became vertical there, and had also observed the shadow of the
gnomon1. Other places, the latitudes of which were known at
this time, were Syene, which was on the tropic, Alexandria, which
had been measured by Eratosthenes, and Massilia by Pytheas:
but as the gnomon, which was the sole instrument available for
this purpose, was not in common use, the number of observations
was very limited. Other measurements, indeed, were taken by
noticing the length of the longest days and nights at certain
points—which according to Strabo was done for the parallel
through Gades and Rhodes*; but since this must have been
accomplished as a rule by residents in those places, because an
explorer would not necessarily be on the spot on the longest day,
they could not have been numerous.
A marked development of the theory of parallels of latitude,
especially from the point of view of scientific carto- Tfae Climata
graphy, was made by the astronomer Hipparchus of Hipparcims
in his system of climata^ or belts of latitude. He ctrc> *** B"C"
took for his starting-point Eratosthenes' calculation of 250,000
1 Strabo, 2. i. 20.
2 a. 5. 14; ffvi*4>wea> yap Kol ra wpo07«nr«a *al rouj dvtfMus (pad rotft
^opota xai ra /MJKTJ r£v /