Part 115

_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.

=Rohilcund.= A region of Northeast India; was conquered by the Rohillas, an Afghan tribe, who settled here about 1747. After aiding the sovereign of Oude to overcome the Mahrattas, they were treated with much treachery by him, and nearly exterminated. Rohilcund was ceded to the British in 1801. After the great mutiny Rohilcund was tranquillized in July, 1858.

=Rohillas.= An East Indian tribe of Afghans inhabiting the country north of the Ganges, as far to the north as Oude.

=Roi d’Armes= (_Fr._). King-at-arms, an officer formerly of great authority in armies; he directed the heralds, presided at their chapters, and had the jurisdiction of armories.

=Roleia=, or =Rolica=. A village in Portugal, where on August 17, 1808, a British force under Sir Arthur Wellesley defeated a French army under Gen. Laborde.

=Roll.= A term of varied signification in reference to military matters. Thus, to _roll_ is to continue one uniform beat of the drum, without variations for a certain length of time.

=Roll, Long.= A prolonged roll of the drums, as a signal of an attack by the enemy, and for the troops to arrange themselves in line.

=Roll, Muster-.= See MUSTER-ROLL.

=Roll of Arms.= A heraldic record of arms, either verbally blazoned or illuminated, or both, on a long strip of vellum, rolled up, instead of being folded into leaves.

_Rolls of Arms_ are the most important and most authentic materials for the history of early heraldry. In England they go back to the reign of Henry III., the oldest being a copy of a roll of that reign, containing a list of the arms borne by the sovereign, the princes of the blood, and the principal barons and knights between 1216 and 1272, verbally blazoned without drawings.

=Roll, Squad.= Is a list containing the names of each particular squad in a company, etc.

=Roll, Size.= In the British service, is a list containing the names of all the men belonging to a troop or company, with the height or stature of each specifically marked.

=Roll-call.= The act or time of calling over a list of names; as, tattoo roll-call. _To call the roll_, to call off or recite a list or roll of names of soldiers belonging to a company or troop, in order to ascertain, from the responses, who are present and who are absent.

=Rollers, Friction.= See ORDNANCE, CARRIAGES FOR, SEA-COAST CARRIAGES.

=Rolling Barrels.= See CAKING.

=Rolling Fire.= A discharge of musketry by soldiers in line, in quick succession, and in the order in which they stand. See FIRE.

=Rolling-hitch.= Pass the end of a rope round a piece of timber; take it round a second time, riding the standing part; then carry it across and up through the bight.

=Romagna.= A province of the Papal States, comprised in the legations of Forli and Ravenna. It was conquered by the Lombards; but taken from them by Pepin, and given to the pope, 753. Cæsar Borgia held it as a duchy in 1501, but lost it in 1503. In 1859 the Romagna threw off the temporal authority of the pope, and declared itself subject to the king of Sardinia, who accepted it in March, 1860. It now forms part of the kingdom of Italy.

=Romainville and Belleville=. Heights near Paris, where Joseph Bonaparte, Mortier, and Marmont were defeated by the allies after a vigorous resistance, March 30, 1814. The next day Paris capitulated.

=Roman Candles.= See PYROTECHNY.

=Roman Walls.= One was erected by Agricola (79 to 85) to defend Britain from the incursions of the Picts and Scots; the first wall extended from the Tyne to the Solway Frith (80 miles); the second from the Frith of Forth, near Edinburgh, to the Frith of Clyde, near Dumbarton (36 miles). The former was renewed and strengthened by the emperor Adrian (121) and by Septimus Severus (208). It commenced at Bowness, near Carlisle, and ended at Wallsend, near Newcastle. It had battlements and towers to contain soldiers. The more northern wall was renewed by Lollius Urbicus in the reign of Antoninus Pius, about 140. Many remains of these walls still exist, particularly of the southern one.

=Romans.= See ROME.