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in India ink, invented by Le Prince, a French artist, about themiddle of the last century, who kept his process for a longtime secret, and sold his prints at first as drawings ; he ap-pears, however, to have been acquainted only with the powdergrain, and the common method of stopping out. The printswhich he produced, are still some of the finest specimens ofthe art. Paul Sandby was the first who practised this methodof engraving in England.

ARAEOMETER, an instrument for ascertaining the densityand gravity of fluids, the invention of which is by someattributed to Archimedes , and by others to Hypatia , thedaughter of Theo, about the end of the fourth century.

ARCH, in architecture. The origin of arches is so obscure,and our lights so few, that it is perhaps impossible, at thistime, to determine to whom the invention is due. The Egyp-tians, skilful as they were in architecture, seem unacquaintedwith Arches , their temples being roofed with slabs, laid hori-zontally from column to column, and the openings coveredwith massy lintels. The Chinese were acquainted with the useof Arches at an early period, and an account of some of themis given by Barrow. However, the most ancient Arches , ofwhose erection we have dates, are those in the cloacae ofRome, which were begun by Tarquinius Priscus : there arealso Arches in several Greek theatres; among others, thetheatre of Bacchus, at Athens, erected probably 400 yearsbefore the Christian aera. Yet the method of constructingArches geometrically, Mr. Watkins asserts, was unknown tillthe date of the Macedonian conquest, about 2SO B. C. Thepointed Arch appears in churches so early as the reign ofEdgar : the lancet Arch is the oldest form of Arch known inthe East, and this form of Arch was introduced by Bishop deLacy, in the cathedral of Winchester, about the commence-ment of the thirteenth century. The church of St. Mary, in