IX.] THEORY OF ZONES. 179
The division of the earth into zones, or belts of temperature,
which was first promulgated by Parmenides1, was
based on a similar division which had already been zone*!* °f
drawn out for the celestial sphere. The scheme of
this philosopher included a torrid zone, which was uninhabitable
on account of the heat, two frigid zones, which were uninhabitable
on account of the cold, and two intermediate zones, which were
of moderate temperature, and fitted for the habitation of man.
The limits, however, which were to be assigned to these belts
were for some time variously estimated, but the habitable area
was gradually extended both towards the north and the south, in
proportion as the knowledge of the remoter tribes that were found
in both those directions increased. Aristotle is
the first writer in whom we find an attempt to view?*0 CS
determine these limits on scientific principles.
He defined the temperate zone as the belt which lay between
the tropic and the arctic circle—a statement, the accuracy of
which must depend on the meaning he attached to the latter of
these terms. The earlier sense which the expression 'arctic
circleJ bore among the Greeks, was that of a circle in the
northern heavens marking the limit in that direction of the
stars which never set. From this point of view, every latitude
had a different arctic circle; and this accounts for the name
' arctic,' because in the latitude of Greece, where it was first used,
the Great Bear just sweeps the sea but does not set—'arctos
oceani metuentes aequore tingi.' According to the modern view,
on the other hand, the arctic circle is fixed at the point on the
earth's surface where during one day of the year the sun does not
rise above the horizon. It is difficult to determine which of
these two senses is the one which Aristotle intended. From his
own brief statement of his opinions, as far as it is intelligible, and
also from Strabo's account of them, we should suppose that he
uses the term in the modem and scientific sense; but the
criticisms which are passed upon him by Posidonius and Strabo
imply that he treated the arctic circle as varying with the latitude
of the place of observation2. At a later period, at all events, the
1 «/. suprat p. 60.
* Ar. MettoroLt a. 5.10; Strabo, 2. 4. 2*
12—2