170 E M E E M E 45 miles W.N. VV. of Oldenburg. The town is much intersected by canals, and more than thirty bridges are re quired to connect its different parts. It has a considerable maritime trade, chiefly in corn, butter, cheese, and wood. Its industries are ship-building, tanning, and the manufac ture of paper, cement, and tobacco. Amongst its public buildings may be named the town-house, the orphanage, the poorhouse, the museum, the great Reformed church, the gymnasium, and the deaf and dumb institute. Emdeu belonged originally to East Friesland. From 1595 it was a free town under the protection of Holland until 1744, when, along with East Friesland, it was transferred to Prussia, after which it came into the possession of Holland in 1806, of France in 1809, of Prussia in 1814, and of Hanover in 1815; and finally in 1866 it was, along with Hanover, incorporated with Prussia. The population of Emden in 1875 was 12,874. EMERALD (Greek, oy/.apaySos), a precious stone classed mineralogically with the beryl (see vol. iii. p. 613), from which, however, it differs in having a fine green colour, attributed to the presence in it of chromium sesquioxide : it also never presents the internal striee often seen in the beryl. The chemical composition of the emerald may be represented by the formula 6SiO 2 ,Al.,O 3 ,3G10. It occurs iti six-sided prismatic crystals of the hexagonal system, the edges of which not unfrequently show various modifications. The emerald is transparent or translucent, and has a vitreous, rarely resinous lustre, an uneven and conchoidal fracture, n hardness of 7 5-8, and a specific gravity of 2 - 670 to 2 732. It is brittle and comparatively soft when fresh from the mine, but hardens on exposure to the air. The specific gravity of crystallized emeralds after fusion was found by Greville Williams to be 2 4, 9 per cent, of the original weight having been lost. The emerald is unaffected by acids, but with borax gives before the blowpipe a transparent greenish glass. On friction it becomes electric. Wb hler, Hose, Hofmeister, and Greville Williams have shown that the emerald may be heated to a very high temperature without destruction of its colour, which cannot therefore, as supposed by Lewy, be due to the organic impurities discovered in the stone. Cleavage of the emerald at right angles to the axis of the crystals may be effected without much difficulty, and in the East, previous to about the middle of the 15th century, the stone was generally worn in slices so obtained. The finest emeralds are procured from Muzo, in Colombia (see vol. vi. p. 154). The fossiliferous character of the limestone in which they occur at Muzo. and the presence in them of from 1*65 to 2 15 per cent, of water, led Mr Lewy to the conclusion that they must have been crystallized out of aqueous solution. Other localities are Henbachthal in Salzburg, Oclontchelong in Siberia, and Canjargum in India. The emeralds of Colombia, according to Boussingault, are divided into several classes, the principal of which are the canutillos or the crystallized and more valuable stones, and the morallons or amorphous stones, poor in colour, and of little value. The Hebrew word nojjhech, rendered " emerald " in the English version of the Scriptures, appears to have been the carbuncle. The emerald was highly valued by the ancients (see Pliny, Nat. Hist., xxxvii. 5). Various virtues were formerly ascribed to the gem : it was said to be good for the eyes, to colour water green, to assist women in childbirth, and to drive away evil spirits ; and in the East it is still accredited with talismanic and medicinal properties. One of the most celebrated examples of the emerald is that in the possession of the duke of Devonshire, measuring upwards of 2 inches in length, and across its three diameters 2^, 2|, and 1| inches. Other fine stones are the Hope emerald, weighing 6 oz, and those of the Russian, Saxon, and Papal crowns. Emeralds are cut on a copper wheel with emery, and polished on a tin wheel with rotten-stone. " In a good gem," says Mr Emanuel, " Ihe surface must be perfectly straight and smooth, so as to cast no darkening shadow on any of its particles." The form usually given to emeralds is that of a square table with the edges re placed, the lower surface being cut into facets parallel to their sides. When fine they are always set without a foil; and, as their brilliancy is somewhat impaired by candle light, they are generally surrounded with small diamonds or pearls, which enhance their effect. The gem has been very successfully imitated by manufacturers of paste stones, the colouring matter used being oxide of chromium. As a gem the emerald is reckoned inferior only to the diamond and ruby, but, unlike them, it does not increase in value in proportion to the cube of its weight. What is termed the Oriental emerald is a green variety of corundum, an exceedingly scarce gem. See H. Emanuel, Diamonds and Precious Stones, 1865 ; Greville Williams, "Researches oil Emeralds and Beryls," Proc. Hoi/. Soc xxi. 1872-3, p. 409. EM ERIC-DAVID, TOUSSATNT-BEBNARD (1755-1839), a French archaeologist and writer on art, was born at Aix, in Provence, 20th August 1755. He was destined for the legal profession, and having gone in 1775 to Paris to com plete his legal education, he acquired there a taste for art which influenced his whole future career. After being made advocate, he went to Italy, where he continued his art studies. He soon returned, however, to his native village, and followed for some time the profession of an advocate ; but on the death of his uncle Antoine David in 1787 he succeeded to his printing business. He was elected mayor of Aix in 1791 ; and although he speedily resigned his office, he was in 1793 threatened with arrest, and had for some time to adopt a vagrant life. When danger was past he returned to Aix, sold his printing business, and engaged in general commercial pursuits; but he was not long in renouncing these also, in order to devote himself exclusively to literature and art. From 1809 to 1815 he represented his department in the legislative chamber, and in 1816 he was elected a member of the Institute. He died at Paris, 2d April 1839. fonerie-David was placed in 1825 on the commission appointed to continue L Histoire litteraire dc la France. His principal works are Recherchcs sur I art statuaire, consider^ clwz les anciens et les moderncs, Paris, 1805, a work which obtained the prize of the Insti- tnte ; Suite d etudes calque.es et dessinees d apres cinq tableaux de Raphael, Paris, 1818-21, in 6 vols. fol. ; Jupiter, ou rccherchcs sur cedieu, sur son culte, &c., Paris, 1833, 2 vols. 8vo, illustrated; and Vulcain, Paris, 1837. EMERSON, WILLIAM (1701-1782), an eminent but eccentric mathematician, was born May 14, 1701, at Hurworth, near Darlington, where his father Dudley Emerson, also a mathematician of high attainments, taught a school. From him young Emerson received a thorough mathematical education, and the bequest of a good mathe matical library. For his classical training he was indebted to the curate of Hurworth, who lodged in his father s house. In the earlier part of his life he followed his father s profes sion, but with little success ; and this, coupled with the fact of his having received as an only child a moderate compe tence from his parents, led him to devote himself entirely to studious retirement. Towards the close of 1781 he re linquished his studies and disposed of his library. His death took place soon after, May 20, 1782, at* his native village, in the eighty-first year of his age. Emerson in dress, manners, and appearance was eccentric and indeed clownish, but he possessed remarkable independence of character, and intellectual energy of a very high order. The boldness with which he expressed his opinions on religious subjects led to his being charged with scepticism,
but for this there was no foundation. He invariably shut