ECCENTRIC, from two Greek words, meaning literally "out from the centre," and thus used to connote generally any deviation from the normal. In ancient astronomy the word denotes a circle round which a body revolves, but whose centre is displaced from the visible centre of motion. In early times the ellipses in which the planets revolve around the sun as focus could not be distinguished from circles, but the unequal angular motion due to ellipticity was observed. A point, however, can be found on the major axis of the ellipse (namely the empty focus) such that the angular velocity of the planet about it is nearly constant. It was therefore supposed that the deferent of the epicycle of the planet moved uniformly in a circle about this point. For eccentric angle see ELLIPSE.
In engineering, an eccentric is a disc mounted out of centre on a shaft, to give reciprocating movement to a lever; it is an agent much used in steam-engines and other mechanisms. It is fixed with a key or screw on to the crankshaft and moves the valve-rod to and fro to control the flow of steam and the exhaust. Using two eccentrics with link-motion, the engine can be reversed, and the steam used expansively, e.g., in locomotives, when a good rate of speed has been reached. A reversing eccentric is one with a slotted fitting whereby it can be moved in relation to the shaft, thus reversing the action of the valve to run the engine in the opposite direction. This is but little used, however, the link motion having preference. Eccentrics are also fitted on the popu lar drop-valve steam-engines, being located then on a shaft run ning parallel with the cylinder. An eccentric is often employed to work a pump, and operate the slides of certain machines, such as those for shearing and punching. Eccentrics are used to work the jaws of powerful rock- and stone-crushers, and to close quick acting clamps and safety mechanisms that check slipping. ECCHELLENSIS (or ECHELLENSIS), ABRAHAM (c. 1600-1664), a learned Maronite, was born at Eckel, Syria. Edu cated at Rome, he became professor of Arabic and Syriac in the college of the Propaganda at Rome, and in 1646 professor at the College de France. Invited to take part in the preparation of an Arabic version of the Bible, Ecchellensis returned in 1652 to Rome, where he died. Of his Latin translations of Arabic works, the most important was the Chronicon Orientate of Ibnar-Rahib (Paris, 1653), a history of the patriarchs of Alexandria. With Giovanni Borelli he wrote a Latin translation of the 5th, 6th and 7th books of the Conics of Apollonius of Perga (1661). He also published Eutychius vindicates, sive Responsio ad Seldeni Origines (Rome, 1660. To Le Jay's polyglot Bible he contributed the Ara bic and Latin version of Ruth and the Arabic version of the third book of Maccabees.