Congreve’s System.—A Congreve rocket is guided by a long wooden stick attached to its base. If any cause act to turn it from its proper direction, it will be opposed by resistances equal to its moment of inertia and the lateral action of the air against the stick. The effect of these resistances will be increased by placing the centre of gravity near the head of the rocket, and by increasing the surface of the stick. In signal-rockets, where the case is made of paper, the stick is attached to the side, and there is but one large vent, which is in the centre of the case. In war-rockets the stick is attached to the centre of the base, and the large central vent is replaced by several small ones near its circumference. The former arrangement is not so favorable to accuracy as the latter, inasmuch as rotation will be produced if the force of propulsion and the resistance of the air do not act in the same line.
How Fired.—Rockets are generally fired from tubes or gutters; but should occasion require it, they may be fired directly from the ground, care being taken to raise the forward end by propping it up with a stick or stone. As the motion is slow in the first moments of its flight, it is more liable to be deviated from its proper direction at this time than any other; for this reason the conducting-tube should be as long as practicable.
Form of Trajectory.—Take that portion of the trajectory where the velocity is uniform. The weight of the rocket applied at its centre of gravity, and acting in a vertical direction, and the propelling force acting in the direction of its length, are two forces the oblique resultant of which moves the rocket parallel to itself; but the resistance of the air is oblique to this direction, and acting at the centre of figure, a point situated between the centre of gravity and extremity of the guide-stick, produces a rotation which raises the stick, and thereby changes the direction in which the gas acts. As these forces are constantly acting, it follows that each element of the trajectory has less inclination to the horizon than the element of an ordinary trajectory in which the velocity is equal. When the velocity is not uniform, the position of the centre of gravity has a certain influence on the form of the trajectory. To understand this, it is necessary to consider that the component of the resistance of the air which acts on the head of the rocket is greater than that which acts on the side of the stick. It is also necessary to consider that the pressure of the inflamed gas acts in a direction opposite to the resistance of the air, that is to say, from the rear to the front, and that the centre of gravity is near the rear extremity of the case. At the beginning of the trajectory, when the motion of the rocket is accelerated, its inertia is opposed to motion, and being applied at the centre of gravity, which is in rear of the vent, the point of application of the moving force, it acts to prevent the rocket from turning over in its flight. But when the composition is consumed, the centre of gravity is thrown farther to the rear, and the velocity of the rocket is retarded, the inertia acts in the opposite direction, and the effect will be, if the centre of gravity or inertia is sufficiently far to the rear, to cause it to turn over in the direction of its length. If the rocket be directed toward the earth, this turning over will be counteracted by the acceleration of velocity due to the weight, and the form of the trajectory will be preserved.
Effect of Wind.—When the wind acts obliquely to the plane of fire, its component perpendicular to this flame acting at the centre of figure will cause the rocket to rotate around its centre of gravity. As the centre of figure is situated in rear of the centre of gravity, the point will be thrown toward the wind, and the propelling force acting always in the direction of the axis, the rocket will be urged toward the direction of the wind. To make an allowance for the wind in firing rockets, they should be pointed toward the opposite side from which the wind comes, or with the wind instead of against it. If the wind act in the plane of fire from front to rear, it will have the effect to depress the point, and with it the elements of the trajectory in the ascending branch, and elevate them in the descending branch; as the latter is shorter than the former, the effect of a front wind will be to diminish the range. The converse will be true for a rear wind.
Kind Used.—The two sizes of Hale’s rockets in use in the American service are, the 2-inch (interior diameter of case), weighing 6 pounds, and 3-inch (interior diameter of case), weighing 16 pounds. Under an angle of from 4° to 5° the range of these rockets is from 500 to 600 yards. Under an angle of 47° the range of the former is 1760 yards, and the latter 2200.
Rocroy, or Rocroi. A small town of France, in the department of Ardennes, 15 miles northwest from Mézières. It is memorable for the victory gained by the great Condé (then duke of Enghien) over the Spaniards, May 19, 1643. The Spanish army was composed of veteran bands of Walloons, Spaniards, and Italians, and their general, Don Francisco de Mellos, was a commander worthy of his army. The French (22,000) were also good troops, but their general, Condé, was a young and inexperienced officer. At first the battle was unfavorable to the French, but at last the Spaniards were thrown into irretrievable rout. The Count of Fuentes, the commander of the redoubtable infantry, and 10,000 of his men were among the slain; and 5000 men, with all the cannon, many standards, and the baton of the Count de Mellos, were captured. But, far beyond all material losses, the renown of invincibility, first acquired by the Spanish infantry on the field of Pavia (1525), and confirmed at St. Quentin, Gravelines, and Prague, was destroyed.
Rodman Gun. See [Ordnance, Construction of].
Roermond. An old town in the Netherlands, province of Limburg, at the junction of the Roer and Maas. It has often endured the horrors of being besieged and taken.
Rogue River Indians. See [Indians and their Agencies] ([Oregon]).
Rogue’s March. Derisive music performed in driving away a person under popular indignation, or when a soldier is drummed out of a regiment.