- GEM the means of giving a ruby-red color to glass, and artificial rubies were then first made, espe- cially by one John Kunkel, afterward Lowen- stiern, inspector in 1679 of the glass houses in Potsdam. In modern times the art has been wonderfully perfected by the French, chiefly through the genius of M. Donault-Wieland. A glass called strass, of great lustre and per- fectly transparent, of which the ingredients are given in the article GLASS, is prepared as the basis of the composition. It resembles the dia- mond in high refractive power as in its other qualities, except hardness. That it may be free from color its ingredients must be abso- lutely pure; and care must be exercised in selecting crucibles least likely to impart color to the fused mixture. Artificial diamonds are made from pure strass, which is cut directly into brilliants and roses, without the addition of other matter. Other gems are imitated by melting and mixing it with substances having a metallic base, generally oxides, which com- municate the various colors. The researches and experiments of M. Ebelmen are of a higher order of art. He conceived the idea in 1847 of forming various mixtures with some in- gredients volatile at very high heat. By the dispersion of these in the furnace the other ingredients should crystallize, as substances held in solution in liquids crystallize when these are evaporated. He thus proposed to produce the ruby, corundum or sapphire, and other precious stones. The volatile solvents or fluxes he employed were principally boracic acid and borax. The spinelle ruby, among the first minerals he imitated, was obtained by mixing together 30 parts of magnesia, 25 of alumina, 1 of chlorate of potash, and 35 of boracic acid, and subjecting 500 grammes (7,716 grains) of the compound to high tem- perature in the muffle of a furnace for eight days. The crystals measured 0-197 inch on a side. Chrysoberyl was produced in crystals with faces of 0'24 inch, perfectly transparent, and scratching topaz from a mixture of alumi- na 12 grammes, glucine 3'5, carbonate of lime 10, and fused boracic acid 14 grammes. The object of the lime was to form a fusible borate for holding the other ingredients in a condition favorable for crystallization. Chrysolite in well defined crystals resulted from silica 4 5, magnesia 6'15, and boracic acid 6. Transpa- rent crystals of pure alumina, which are sap- phire or corundum, and which presented the same hardness and specific gravity with this mineral, were a product of alumina thus fused with 3 or 4 parts of borax, or of 10 parts of alumina with 4 of silica and 16 of borax. M. Ebelmen employed also as fluxes the salts of phosphorus and the carbonates of potash and of soda, all which are volatile at high temper- atures, and by means of these solvents repro- duced many other minerals, as he announced to the academy in 1851. His death shortly after terminated his interesting researches ; but they have been successfully continued by Deville, GEMtlNDER 665 Eisner, Manross, and others, and numerous arti- ficial minerals have been prepared. The great establishment of M. Bourguignon in Paris was at one time the most famous manufactory of artificial gems in the world. About 100 work- men, besides many women and girls, were constantly employed in preparing and fusing the mixtures, cutting and polishing the stones, and lining the imitation pearls with fish scales and wax. The sand used to furnish the silica is from the forest of Fontainebleau ; and its quality is so highly esteemed that much is ex- ported for similar use elsewhere. The gems are _ such, perfect imitations that they can be distinguished from genuine stones only by the closest scrutiny of those experienced in such matters. The great hardness of the natural stones it is found most difficult to imitate, and there is a want of permanency in the qualities of most of the imitations, which at last causes their true character to appear. See "A Popular Treatise on Gems," by Dr. L. Feuoh- twanger (New York, 1859 ; revised ed., 1867) ; "The Natural History of Gems," by C. W. King (London, 1867) ; " Diamonds and Precious Stones," by Harry Emanuel (London, 1867); and "Diamonds and Precious Stones," trans- lated from the French of Louis Dieulafait by F. Sanford (New York, 1874). GEMINI (the twins), the third constellation in the zodiac, so named from its two brightest stars, to which the names Castor and Pollux are given, and which are about midway be- tween Aldebaran and Regulus. GEMISTIIS, George, surnamed PLETHO, a schol- ar and philosopher of the 15th century, born in Constantinople, and said to have lived to the age of 100. He held a high position at the court of the Palseologi, and at the council of Florence in 1439 opposed the union of the churches of the East and the West. Subse- quently banished from his country, he found an asylum in Italy, and declared himself in favor of the Latins. While the philosophy of Aristotle was still reigning, he became an enthusiastic votary of the Platonic theories in metaphysics and natural theology, and being admitted to the circle of the Medici, prompt- ed Cosmo to found his celebrated Platonic academy. His treatise in praise of Platonism inaugurated the long quarrel between the dis- ciples of the two great masters of antiquity, which produced a profound study of their sys- tems. Gemistus, however, mingled with the Platonic philosophy the notions of the later Alexandrian school and of the spurious wri- tings attributed to Zoroaster and Hermes, and revived in the West that eclecticism, half Christian and half pagan, half oriental and half Greek, which flourished during the de- cline of the Greek philosophy at Alexandria. GEMiJNDER, George, an American violin ma- ker, born at Ingelfingen, Wtirtemberg, April 13, 1816. He was a pupil of Baptiste Vuil- laume in Paris, and removed to the United States in 1847, establishing himself in Boston,
