A Military Dictionary and Gazetteer / Comprising ancient and modern military technical terms, historical accounts of all North American Indians, as well as ancient warlike tribes; also notices of battles from the earliest period to the present time, with a concise explanation of terms used in heraldry and the offices thereof. The work also gives valuable geographical information. Compiled from the best authorities of all nations. With an appendix containing the Articles of war, etc.

by Thomas Wilhelm

Rock Island. An island in the Mississippi River, the southern extremity of which is nearly opposite the town of Rock Island, Ill. This island is about 3 miles in length, and presents a perpendicular front of limestone 20 or 30 feet high. During the Blackhawk war a garrison was kept on Rock Island, and a part of it was used during the late civil war (1861-65) as a military prison. The U. S. government has a splendid arsenal and armory here.

Rocket. A rocket is a projectile which is set in motion by a force residing within itself; it therefore performs the twofold function of piece and projectile. See [Pyrotechny].

History.—Rockets were used in India and China for war purposes before the discovery of gunpowder; some writers fix the date of their invention about the close of the 9th century. Their inferior force and accuracy limited the sphere of their operations to incendiary purposes, until the year 1804, when Sir William Congreve turned his attention to their improvement. This officer substituted sheet-iron cases for those made of paper, which enabled him to use a more powerful composition; he made the guide-stick shorter and lighter, and removed a source of inaccuracy of flight by attaching the stick to the centre of the base instead of the side of the case. The advantages claimed for rockets over cannon are, unlimited size of projectile, portability, freedom from recoil, rapidity of discharge, and the terror which their noise and fiery trail produce on mounted troops.

Structure.—A rocket is essentially composed of a strong case of paper or wrought iron, inclosing a composition of nitre, charcoal, and sulphur,—the same as gunpowder, except that the ingredients are proportioned for a slower rate of combustion. If penetration and range be required, its head is surmounted by a solid shot; if explosion and incendiary effect, by a shell or spherical case-shot, to which is attached a fuze, which is set on fire when it is reached by the flame of the burning composition. The base is perforated by one or more vents for the escape of the gas generated within, and sometimes with a screw-hole to which a guide-stick is fastened.

Motion.—A rocket is set in motion by the reaction of a rapid stream of gas escaping through its vents. If it be surrounded by a resisting medium, the atmosphere, for instance, the particles of gas as they issue from the vent will impinge against and set in motion certain particles of air, and the force expended on the inertia of these particles will react and increase the propelling force of the rocket. It follows, therefore, that, though a rocket will move in vacuo, its propelling force will be increased by the presence of a resisting medium. Whether the effect will be to accelerate the rocket depends upon the relation between the resistance which the medium offers to the motion of the gas and that which it offers to the motion of the rocket.

Vent.—As the rate of combustion of the composition is independent of the pressure of the gas in the bore, it follows, that if the size of the vent be contracted, the flow of gas through it will be accelerated. The strength of the case, and the friction of the gas, which increases as the vent diminishes, alone limit the reduction of the size of the vent. For vents of the same size, but of different shapes, that one which allows the gas to escape most freely will be most favorable to the flight of the rocket. A conical form of vent, with the larger orifice next to the bore, will allow the gas to escape more rapidly than one of cylindrical form.

Bore.—As the composition of a rocket burns in parallel layers of uniform thickness, the amount of gas generated in a given time, or the velocity of its exit from the case, depends on the extent of the inflamed surface. Experience shows that to obtain the required surface of inflammation, it is necessary to form a long cavity in the mass of the composition. This cavity is called the bore. In all rockets the bore should be concentric with the case; its shape should be made conical to diminish the strain on the case near its head, by reducing the amount of surface where the pressure on the unit of surface is greatest.

Nature of Movement.—Suppose the rocket in a state of rest, and the composition ignited; the flame immediately spreads over the surface of the bore, forming gas which issues from the vent. The escape is slow in the first moments, as the density of the gas is slight; but as the surface of inflammation is large compared to the size of the vent, the gas accumulates rapidly, and its density is increased until the velocity of the escape is sufficient to overcome the resistance which the rocket offers to motion. These resistances are, inertia, friction, the component of weight in the direction of motion, and, after motion takes place, the resistance of the air. The constant pressure on the head of the bore accelerates the motion of the rocket until the resistance of the air equals the propelling force; after this, it will remain constant until the burning surface is sensibly diminished. When the gas ceases to flow, the rocket loses its distinctive character, and becomes, so far as its movement is concerned, an ordinary projectile. The increase in the surface of combustion whereby more gas is developed in the same time, and the diminution in the weight of the remaining composition, cause the point of maximum velocity to be reached with increased rapidity. If the weight of the rocket be increased, the instant of maximum velocity will be prolonged, but the amount will remain the same. A change in the form of the rocket which increases the resistance of the air, will have the effect to diminish the maximum velocity.

Guiding Principle.—The propelling force of a rocket changes its direction with the axis along which it acts; it follows, therefore, that without some means of giving stability to this axis, the path described will be very irregular, so much so, at times, as to fold upon itself; and instances have been known where these projectiles have returned to the point whence they started. The two means now used to give steadiness to the flight of a rocket are, rotation, as in the case of a rifle-ball, and the resistance of the air, as in an arrow.

Hale’s System.—The first is exemplified in Hale’s rocket, where rotation is produced around the long axis by the escape of the gas through five small vents situated obliquely to it. In his first arrangement, the inventor placed the small vents in the base, surrounding the central vent, so that the resultant of the tangential forces acted around the posterior extremity of the axis of rotation. In 1855, this arrangement was changed by reducing the number of the small vents to three, and placing them at the base of the head of the rocket. The rocket thus modified is the one now used by the U. S. government for war purposes. A still later improvement in Hale’s rocket consists in screwing a cast-iron piece into the bottom of the case, which is perforated with three vents. A corresponding side of each vent is surrounded with a fence, the opposite sides being open. The gas in its efforts to expand after issuing from the vents, presses against the fences and rotates the rocket around its long axis.