Dideon’s Formulas. Certain equations relating to the trajectory of a projectile in the air, obtained by Capt. Dideon of Metz by integrating the differential equations of the trajectory under certain assumptions as to the law of the resistance, etc. See [Projectiles, Trajectory, in Air].
Diego. A very strong and heavy sword.
Diest. A town of Belgium, in Southern Brabant, on the Demer. This town was taken by the Duke of Marlborough in 1705, but retaken by the French, and dismantled, in the same year. Since 1830 it has been surrounded with fortifications and made a place of great strength.
Dietary, Military. See [Subsistence] of Armies and [Food].
Dieu et Mon Droit (Fr.). “God and my Right.” The motto of the royal arms of England, first assumed by Richard I., to intimate that he did not hold his empire in vassalage of any mortal. It was afterwards assumed by Edward III., and was continued without interruption to the time of William, who used the motto [Je maintiendray], though the former was still retained upon the great seal. After him Anne used the motto Semper eadem; but ever since her time Dieu et mon droit has continued to be the royal motto.
Differences. In heraldry, are marks introduced into a coat of arms to distinguish brothers and their descendants from the father or head of the house, while he is alive; marks of cadency being used for a similar purpose after his death.
Differential Pulley. A hoisting apparatus consisting of an endless chain and two pulleys of slightly different diameters. The chain winds upon one while unwinding from the other. It is attached to a crane, and used to hoist heavy shot to the muzzle of large cannon.
Dijon. An ancient walled city of France, chief town of the department of Côte-d’Or. It has been several times captured in war. It was attacked by the Germans under Gen. Beyer, October 30, 1870. The heights and suburbs were taken by Prince William of Baden, and the town surrendered October 31.
Dike, or Dyke. A channel to receive water; also a dam or mound, to prevent inundation. Dikes differ from sluices; the former being intended only to oppose the flowing of other water into a river, or to confine the stream by means of strong walls, pieces of timber, or a double row of hurdles, the intervals of which are filled with earth, stones, or pebbles.
Dimachæ. In ancient military affairs, were a kind of horsemen, answering to the dragoons of the moderns.