§ 34. The Earth’s surface is not throughout equally illumined or heated by the Sun; because the Sun’s rays strike some portions of the Earth more perpendicular than others. Our Earth, therefore, is divided into Climates or Zones, which you will understand better from Plate [XII].
You will see from it that the Sun’s rays are perpendicular to the central part of the Earth’s surface; but that toward the extremities of the Earth’s Diameter these rays strike us more and more obliquely. The greatest heat, therefore, must be felt by the people living between the two circles EF and IK. The circle GH, which is exposed to the perpendicular rays, is termed the Equator; and the two circles EF and IK, which are at equal distance from the Equator, are called Tropic Circles. The whole surface included by these two circles is called the torrid Zone. The space between either of the circles CD and EF, or IK and LM, is called a temperate Zone; because the Sun’s rays striking these portions neither perpendicular nor very obliquely, their inhabitants suffer neither great heat nor cold. In one of these Zones are situated the United States of America and the greater portion of Europe. Beyond them, toward the extremities of the Diameter AB, are the two icy or arctic zones. The Sun’s rays strike them very obliquely; which is the cause of their being almost continually covered with ice or snow.
The two circles, CD and LM, are called Polar circles; and the two extremities, A and B, of the Earth’s Diameter, situated in those regions, are called the Poles. A is called the North-Pole and B the South-Pole of the Earth.
§ 35. The different zones of which we have just spoken, are not equal to one another. Plate [XIII], will show their relative extent.
Fig. I represents the surface of the Earth divided proportionally into its three zones: the torrid, the temperate and the arctic. The inner circle represents both the arctic zones; the yellow ring b, which surrounds it, represents the united extent of the two temperate zones; and the outmost red ring, the whole of the two torrid zones.
Fig. II represents separately the whole torrid zone;—Fig. III one of the temperate zones;—Fig. IV one of the arctic zones; and Fig. V the whole extent of land on our globe.
The next Plate, No. XIV, represents the comparative surfaces of these zones, drawn separately in form of squares; and the last figure on that Plate, shows the extent of the five continents, compared to one of the temperate zones.
No. XV.
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.