DIALLAGE. 199 DIAMOND. tain varieties, especially those possessing a char- aeteristie lustre, have been cut and polished. The name dialla^e is also applied to Ihe min- «>ral enstatile and its ferriferous variety, broiiz- ite. DIALOGUE (Lat. dialogus, Gk. ihdf.oyoc, diulmjos, speech, from (!«i, di«, through + Xrfjof, loijos, speech, from /Jyeci; leycin, to speak). A couvorsatiou between two or more jiersons, im- plying, however, greater unity of subject and formality than an ordinary conversation. The Socratic dialogue is a conversation in the form of question and answer, so contrived that the person questioned is led himself to originate those ideas that the questioner wishes to bring before him. The dialogues of Plato are, as it were, philosophical dramas, in which the Socratic rocthod of investigation is brought to bear upon speculative sul)jccls. And in general among the ancients the dialogue was a favorite form for didactic literature. Aristotle employed it, but in less dramatic form than Plato: and Cicero chose the Aristotelian dialogue for his philosophi- cal works. Liician employs it for purposes aj)- proaching those of the drama. Of the more eminent modern writers in this form, we may mention Erasmus in I-atin: Hutten, Lessing, Herder, Wieland, and Schelling among the Ger- mans: Petrarch and Maechiavelli in Italy: Fcne- lon, Fontanelle, and Voltaire in France: and Berkeley, Hurd, and Harris in England. Lan- dor"s Imaginanj Conrersatioiin also are a happy effort of this kind. When dialogue is combined with action, we have the drama. On the ancient dialnsxie^ consult Hirzel, Der Dialog (Leipzig, isn.-,). DIALOGUE OF DEATH. A religious work by William liullein. written and published dur- ing the London Plague (ir)C4-r).5) and professing to be "a goodly regimente against the fever Pestilence." DIAMAGNETISM (from Gk. Ad, dia, tlinnigli -t- (;<i; r;/f, iiiiifjncfs. magnet, from May- vr/f, Mnijiii's, Magnesian, from Majvi/ala, Maij- 'lU'sia, a city of Thessaly. in Greece, where mag- netic stones abounded). A name given certain magnetic phenomena observed in the case of bis- muth and some other substances. If a small piece of bismuth is brought near one pole of a strong magnet, it will be seen to be repelled. This is owing to two things: (1) the magnetic field at the end of the magnet is not uniform, being strong near the magnet and feeble at a distance: (2) the surrounding medium is air. If the field of magnetic force Aere uniform, there would lie neither repulsion nor attraction, the piece of bis- muth would simply turn and take up a definite position. Further, Faraday has shown that the question of attraction or repulsion depends not on the body itself, but on its magnetic properties with reference to those of the surrounding me- diums, (See ilAGNKTlSM.) Faraday sliowed that the following substances and a few others were diamagnetie when placed in air: bismuth, antimony, tin, zinc, cadmium, mercury, silver, ropper. gold, lead, sulphur, sugar, wood, water, alcohol. DIAMANTE, deVi-miin'tIi, .TfAX B.wtist.v fe.ir,20.c.l(ifmi. A Spanish dramatist. He was born in Madrid, where about one-half of the fifty plays written by him and still extant were pub- lished in book-form (2 vols.. IfiTO and 1(179). His best work is the tragedy entitled Kl hoiirador de su padre. Among his other pieces La jiidia dv Toledo has probably enjoyed the greatest popularity. He was a knight "of Saint John of Jerusalem and probably, like Caldcron, Lope de Vega, and several other celebrated poets, spent the closing years of his life in the midst of his brotherhood. DIAMANTINA, de'a-man-te'na. An epis- copal cily in the State of Jlinas Geraes, Brazil, situated 140 miles northeast of Oiro Preto, and 4000 feet above sea-level (Map: Brazil, J 7). It is the centre of a diamond-producing district, and has diamond-cutting and goldsmiths' estab- lishments, as well as cotton and leather manu- factures, and a trade in diamonds amounting almost to $1,000,000 annually, Diamantina was founded in 1730, It formerly bore the name Tejuco, Population, in 1800, 14,000. DI'AME'NIA. A genus of elapine venomous snakes of Australia, See Gbay-Skake. DIAM'ETEK (Lat. diametros, from Gk. (5m- hl"":, iliameter, from did, dia, through + nirpov, mctron, measure). A diameter of a conic section (q.v.) is any chord which connects the points of contact of parallel tangents. In the circle, ellipse, and hyperbola, all diameters pass through the centre (see Cikves) and are bisected by it. Only the circle has all diameters equal, and each bisects the chords perpendicular to it. In the ellipse only the diameters called the minor and major axis bisect the chords per- pendicular to them. In the parabola all di- ameters are parallel to the axis. (For conjugate diameters, see Conjugate.) Certain solid bod- ies also have diameters. In the sphere and the ellipsoid, the lines passing through the centre are called diameters and are bisected by the centre. See Axis. DIAMOND (OF., Fr. diamant. It., Sp. dia- inantc, from Lat." udamas, adam.int, diamond, from Gk. aSa/iag, adnman. adamant, from d, a priv. -f- iafidv, daman, Skt. (f«TO, to subdue) . A precious stone composed of pure carbon, remark- able for hardness, lustre, and flash of color. It crystallizes in the isometric system, usually in octahedrons, or in combinations of several forms, including the octahedron, cube, rhombic dode- cahedron, trisoctahedron, and hexoctahcdron ; the faces and edges of the crystals frequently are curved. It has a very perfect cleavage, by which the primary form of the octahedron may be derived. The diamond is not acted >ipon by acids or alkalies, but if heated to a high temperature in the presence of oxygen it burns to carbon dioxide. Its brilliant lustre and display of prismatic colors are due to the property of re- fracting and dispersing the light-rays, a property possessed in the higliest degree by colorless stones. The specific gr.avity of the dianumd is 3Sy2 : its hardness, which is assumed to be 10 on the mineral scale, exceeds that of any other known substance. By friction it becomes phosphorescent and positively electric. The diamond has a great variety of natural colorings: white, yellow, and brown specimens are the most common, but pure white and fine shades of brown and yellow an- quite rare and conunand high prices. Red in rich, deep tints is perhaps the most prized of all colors, while blue and green are also highly val- ued owing to their beauty and rarity. The amorphous steel-gray to black diamond, known
