ZONE, the term applied to any portion of the earth's surface bounded by two parallels of latitude, but more particularly applied to fire such zones, the position of which is marked by natural boundaries. These five zones are called the torrid, northern and southern temperate, and northern and southern frigid zones. The torrid zone extends 23;4° north and south of the equator; and twice a year the sun shines vertically on its inhabitants. This zone is bounded, on both sides of the equator, by the two tropics; that is, the circles in which the sun reaches its greatest distance from the equator. As the rays of the sun here are nearly vertical a perpetual summer reigns, and day and night under the equator are always equal; and es en at the tropics the difference is scarcely an boar. Owing to the nature and situation, however. of the countries in this zone the heat is not every where the same. The warmest portions are the sandy deserts of Africa; in the regions nearer the equator where vegetation prevails the heat is less excessive; in the islands of the South Seas a milder climate prevails, and the highest mountains of Peru and equatorial Af rica are covered with perpetual snow. The two temperate zones extend from the tropics to the polar circles. They contain the most popu
lous countries, and the climate is various. As the distance from the tropics increases the heat under similar conditions diminishes, the differ ence of the seasons becomes greater, the days and nights become more unequal until we ar rive at a point where once a year the sun does not appear above the horizon during the 24 hours, and once a year does not set for the same time. The circles passing th these points, parallel to the equator tropics, form the limits of the temperate zones, and arc called the arctic and antarctic circles. The distance from the tropics to the polar cir cles, or the breadth of the temperate zones, both in the northern and southern hemispheres, is 43°. All beyond the polar circles to the poles is called the frigid zones. The distance from the polar circles to the poles is 2354'. The characteristic of the frigid zones is, that day and night are more and more unequal the nearer you approach the poles, and for days. weeks even months the sun is either con stantly above or constantly below the horizon. At the poles the year consists of one day and one night each six months long.