Antipodes, a word of Greek origin, signifying, literally, those who have their feet over against each other. Thus Trevisa, in 1398, says that 'in Ethiopia are the Antipodes, men that have their feet against our feet.' As applied in geography, the term means the inhabitants of any two opposite points of the globe, or, in other words, the dwellers at the opposite extremities of any diameter of the earth. From this primary relation there necessarily arise many secondary relations. Antipodes must be on one and the same meridional circle, separated from each other by half the circumference. Being on one and the same meridional circle, they must differ in longitude exactly 180°, with the exception of the poles themselves, as having no longitude at all; and being separated from each other by half the circumference, they must be equidistant from the equator in opposite directions. Take, as an example, London, in 51° 30' N. lat., and 0° 5' W. long. Its antipodes must be in 51° 30' S. lat., and in 180° 5' W. long., or rather 179° 55' E.—coinciding pretty nearly with Antipodes Island (49° 48' S.; 178° 20' E.), an uninhabited rocky islet, about 5 miles long, with smaller rocks around it, lying to the south-east of New Zealand.
Between antipodes in general there necessarily exist also other secondary relations. With reference to the earth's daily rotation, the noon of the one side must be the midnight of the other; while, with regard to its annual revolution, the summer and the autumn of the one side must be the winter and the spring of the other. The midnight corresponds to the noon on the other side, either of the day before or the day after, according as one has reached the antipodes sailing from the east or from the west. In going eastward—that is, in meeting the sun—one, from day to day, anticipates every noon and every midnight in the proportion of 4' of time to 1° of long., or of 12 hours of time to 180° of long. In going westward, again, one postpones every noon and every midnight in the same proportion.