ZONE

geomotrically, the portion of the surface of a sphere intercepted between two parallel planes. The earth’s climatic Zs. are determined by planes at the Arctic and Antarctic circles, and the tropics of Cancer and Capricorn. The resulting Z’s. are known as the frigid, consisting of the polar caps; the torrid, between the tropics: the temperate, between the frigid and torrid. They merely mark out the incidence of the sun's radiation, and are only useful as determining that factor, rather than as giving any clue to actual climate. Actual thermometric observations have led to the establishment of tyermal zones between certain isotherms, The equatorial or tropic a) regions are marked by climate and vegetation arranged in vertical zones between different heights above sea level. In astronomy, star-catalogues are based on Z's.