ARCHYTAS

, of Tarentum, a celebrated mathematician, cosmographer, and Pythagorean philosopher, whom Horace calls ——Maris ac Terræ, numeroque carentis Arenæ Mensorem. He flourished about 400 years before Christ; and was the master of Plato, Eudoxus, and Philolaus. He gave a method of finding two mean proportionals between two given lines, and thence the Duplication of the Cube, by means of the conic sections. His skill in Mechanics was such, that he was said to be the inventor of the crane and the screw; and he made a wooden pigeon that could fly about, when it was once set off, but it could not rise again of itself, after it rested. He wrote several works, though none of them are now extant, particularly a treatise peri\ t<*> *pan<*>o\s, de Universo, cited by Simplicius in Aristot. Categ. It is said he invented the ten categories. He acquired great reputation both in his legislative and military capacity; having commanded an army seven times without ever being defeated. He was at last shipwrecked, and drowned in the Adriatic sea.

ARCTIC Circle, is a lesser circle of the sphere, parallel to the equator, and passing through the north pole of the ecliptic, or distant from the north or arctic pole, by a quantity equal to the obliquity of the ecliptic, which was formerly estimated at 23° 30′, but its mean quantity is now 23° 28′ nearly. This, and its opposite, the antarctic circle, are also called the polar circles, where the longest day and longest night are 24 hours, and within all the space of these circles, at one time of the year, the sun never sets, and at the opposite season he never rises for some days, more or less according as the place is nearer the pole.

Arctic Pole, the north pole of the world, and so called from ark<*>os, ursa, the bear, from its proximity to the constellation of that name.