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344 DYER DYRRHACHIUM intimate associate of Charles Lamb. In 1830 he lost his eyesight. He was joint editor of Valpy's combination of the Delphin, Bipont, and Variorum editions of the Latin classics, and published a " History of the University and Colleges of Cambridge" (2 vols., 1814), < l The Privileges of the University of Cambridge " (2 vols., 1824), and "Academic Unity " (1827). DYER, John, an English poet, born at Aber- glasney, Carmarthenshire, in 1700, died July 24, 1758. He was educated at Westminster, and after a short study of painting he rambled over England as an itinerant artist. In 1727 he published his " Grongar Hill," a poem marked by warmth of sentiment and an ele- gant simplicity of description. He travelled in Italy to pursue his studies as a painter, but the best result of his observations was his poem entitled "The Ruins of Rome" (1740). On his return he entered holy orders. In 1758 appeared his longer poem of " The Fleece," in which he attempted to treat the subject of wool in a poetical manner, and which is one of the most successful imitations of Virgil's " Georgics." All the poems of Dyer abound in happy and careful pictures of nature, and in appropriate and gentle moral sentiments. They were published collectively in 1761. DYER, Mary, a victim to the persecution which befell the Quakers in the early history of Massachusetts, hanged on Boston common, June 1, 1660. The government of Massachu- setts banished Quakers and sentenced to death any one of them who should be guilty of a sec- ond visit to the colony. The statute was con- strued as an invitation instead of a menace by those against whom it was directed. Mary Dyer had departed from their jurisdiction upon the enactment of the law, but soon after re- turned on purpose to offer up her life. She was arrested and sent to prison, was re- prieved after being led forth to execution, and was against her will conveyed out of the col- ony. She speedily returned and suffered as a willing martyr. DYMOND, Jonathan, an English author, born in Exeter in 1796, died May 6, 1828. The son of a linen draper, and himself engaged in the business, he composed his books amid the pressure of other occupations. He was a member of the society of Friends. He pub- lished in 1823 an "Inquiry into the Accord- ance of War with the Principles of Christian- ity," a work which attracted much attention. His fame rests chiefly on his "Essays on the Principles of Morality," published in 1829, soon after the death of the author. DYNAMICS. See MECHANICS. DYNAMITE. See EXPLOSIVES. DYNAMOMETER (Gr. <5{>m/?, force, and pirpov, a measure), an instrument originally designed to ascertain the strength of men and animals, of the limbs of the body, the fingers, &c. Its application was afterward extended to the de- termination of the power exerted by machines, or of any portions of them, and the instrument has hence come into use as a meter of the power of engines. The principle of the earlier contrivances was to weigh the force exerted by the amount of compression or of deflection produced upon an elliptical steel spring ; this in the former case being drawn together by the application of the power and of the resist- ance at the two opposite ends, and in the lat- ter separated by the force and resistance being applied upon the opposite sides of the spring, on the line of the minor axis of the ellipse; an index upon a graduated arc attached to the spring showed the amount of deflection. Another contrivance was a spiral spring en- closed in a tube, the force being applied in the direction of compression. By such means the greatest power exerted by one impulse was indicated ; but as in most instances the power is not constant for any determinate time, the index must fluctuate in such a manner that the mean effort it should represent cannot be as- certained. If known, its amount multiplied by the time of continuance of the operation would give as a result the value of the whole power exerted. Instruments have been de- vised by MM. Poncelet, Morin, and others, which register upon papers, made to pass by a clockwork movement under the index, curved lines from which the whole power is directly calculated from the areas enclosed ; the ordi- nates of the curves representing the power exerted, and the abscissas the length of time, or in some instances the space run over. The apparatus might be fixed to a carriage, the length of the index paper in this instance bear- ing a certain proportion to the length of the road gone over. A great number of different forms of this instrument have been devised by eminent engineers of France, England, and the United States. One by Watt, improved by Macknaught, gives the force exerted by the piston of a steam engine against a spiral spring, a style attached to the piston inscribing a line representing its position during the unrolling of the paper which moves at an even rate against it. In the Dictionnaire des arts et manufac- tures the subject is fully treated in the article Dynamometre, by M. Laboulaye. The descrip- tions of the various forms of the apparatus are made intelligible by many illustrations. In Appleton's "Dictionary of Mechanics," also, many forms of the apparatus are figured and described; and the following simple contri- vance, applicable in some instances, is pro- posed: A cylinder of some material heavier than water is suspended in this fluid by a rope passing over a pulley. As power is applied to this rope to draw the cylinder out of the water, the increasing weight of this, as more is raised into the air, will at last cause the resistance to equal the force applied, the cylinder being sufficiently large and long. By means of a scale properly arranged, the amount of the power applied may be accurately measured. DYRRHACHIUM, a city of ancient Illyricum, on the coast of the Adriatic, occupying very