), literally a slope
used in the mathematical geography of the Greeks1
with reference to the inclination of various parts of the earth's
surface to the plane of the equator. Before the globular figure of the earth
was known, it was supposed that there was a general slope of its surface
from south to north, and this was called κλίμα
. But as the science of mathematical geography advanced,
the word was applied to different belts of the earth's surface, which were
determined by the different lengths of the longest day at their lines of
demarcation. This division into climates was applied only to the northern
hemisphere, as the geographers had no practical knowledge of the earth south
of the equator.
Hipparchus (about B.C. 160) seems to have been the first who made use of this
division; his system is explained at length by Strabo (ii. p.132
). Assuming the circumference of a
great circle of the earth to be 252,000 stadia, Hipparchus divided this into
360 degrees, of 700 stadia to each; and then, beginning at the parallel of
Meroë, and proceeding northwards, he undertook to describe the
astronomical phenomena observed at each degree of latitude, or every 700
stadia: among these phenomena he observed that the length of the longest day
at Meroë was 13 hours, and at Syene 13 1/2 The observations of
later astronomers and geographers--such as Geminus, Strabo, Pliny, and
Ptolemy--are described in the works cited below. Ukert, in a table, shows
the climates as given by Ptolemy (Geogr.
1.23). There are
nineteen climates, the beginning and middle of which are marked by lines
called parallels, of which the first marks the equator, and the thirty-third
the Arctic circle. The term κλίμα
afterwards applied to the average temperature of each of these regions, and
hence our modern use of the word. (Strab. l.c.;
Dionys. A. R. 1.9
; Plut. Mar. 11
, Aem. Paul. 5,
p. 891; Plb. 7.6.1
e; Gemin. Elem. Astron.
5; Plin. Nat. 2
. §§ 73-77;
Agathem. 1.3; Cellar. Geog.
1.6; Ukert, Geog.
vol. i. pt. 2, pp. 182, &c.)