1911 Encyclopædia Britannica/Antipodes

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ANTIPODES (Gr. ἀντί, opposed to, and πόδες, feet), a term applied strictly to any two peoples or places on opposite sides of the earth, so situated that a line drawn from the one to the other passes through the centre of the globe and forms a true diameter. Any two places having this relation—as London and, approximately, Antipodes Island, near New Zealand— must be distant from each other by 180° of longitude, and the one must be as many degrees to the north of the equator as the other is to the south, in other words, the latitudes are numerically equal, but one is north and the other south. Noon at the one place is midnight at the other, the longest day corresponds to the shortest, and mid-winter is contemporaneous with midsummer. In the calculation of days and nights, midnight on the one side may be regarded as corresponding to the noon either of the previous or of the following day. If a voyager sail eastward, and thus anticipate the sun, his dating will be twelve hours in advance, while the reckoning of another who has been sailing westward will be as much in arrear. There will thus be a difference of twenty-four hours between the two when they meet. To avoid the confusion of dates which would thus arise, it is necessary to determine a meridian at which dates should be brought into agreement, i.e. a line the crossing of which would involve the changing of the name of the day either forwards, when proceeding westwards, or backwards, when proceeding eastwards. Mariners have generally adopted the meridian 180° from Greenwich, situated in the Pacific Ocean, as a convenient line for co-ordinating dates. The so-called “International Date Line,” which is, however, practically only due to American initiative, is designed to remove certain objections to the meridian of 180° W., the most important of which is that groups of islands lying about this meridian differ in date by a day although only a few miles apart. Several forms have been suggested; these generally agree in retaining the meridian of 180° in the mid Pacific, with a bend in the north in order to make the Aleutian Islands and Alaska of the same time as America, and also in the south so as to bring certain of the South Sea islands into line with Australia and New Zealand.