ROCKET

, in Pyrotechny, an artificial firework, usually consisting of a cylindrical case of paper, filled with a composition of certain combustible ingredients; which being tied to a rod, mounts into the air to a considerable height, and there bursts. These are called Sky Rockets. Beside which, there are others called Water Rockets, from their acting in water. |

The composition with which Rockets are filled, consists of the three following ingredients, viz, saltpetre, charcoal, and sulphur, all well ground; and in the smaller sizes, gunpowder dust is also added. But the proportions of all the ingredients vary with the weight of the Rocket, as in the following Table.

When Rockers are intended to mount upwards, they have a long slender rod sixed to the lower end, to direct their motion.

Theory of the Flight of Rockets.—Mariotte takes the rise of Rockets to be owing to the impulse or resistance of the air against the flame. Desaguliers accounts for it thus.

Conceive the Rocket to have no vent at the choke, and to be set on fire in the conical bore; the consequence would be, either that the Rocket would burst in the weakest place, or that, if all parts were equally strong, and able to sustain the impulse of the flame, the Rocket would burn out immoveable. Now, as the force of the flame is equable, suppose its action downwards, or that upwards, sufficient to lift 40 pounds; as these forces are equal, but their directions contrary, they will destroy each other's action.

Imagine then the Rocket opened at the choke; by this means the action of the flame downwards is taken away, and there remains a force equal to 40 pounds acting upwards, to carry up the Rocket, and the stick or rod it is tied to. Accordingly we find that if the composition of the Rocket be very weak, so as not to give an impulse greater than the weight of the Rocket and stick, it does not rise at all; or if the composition be slow, so that a small part of it only kindles at first, the Rocket will not rise.

The stick serves to keep it perpendicular; for if the Rocket should begin to tumble, moving round a point in the choke, as being the common centre of gravity of Rocket and stick, there would be so much friction against the air, by the stick between the centre and the point, and the point would beat against the air with so much velocity, that the reaction of the medium would restore it to its perpendicularity. When the composition is burnt out, and the impulse upwards has ceased, the common centre of gravity is brought lower towards the middle of the stick; by which means the velocity of the point of the stick is decreased, and that of the point of the Rocket is increased; so that the whole will tumble down, with the Rocket end foremost.

All the while the Rocket burns, the common centre of gravity is shifting and getting downwards, and still the faster and the lower as the stick is lighter; so that it sometimes begins to tumble before it is quite burnt out: but when the stick is too heavy, the common centre of gravity will not get so low, but that the Rocket will rise straight, though not so fast.

From the experiments of Mr. Robins, and other gentlemen, it appears that the Rockets of 2, 3, or 4 inches diameter, rise the highest; and they found them rise to all heights in the air, from 400 to 1254 yards, which is about three quarters of a mile. See Robins's Tracts, vol. 2, pa. 317, and the Philos. Trans. vol. 46, pa. 578.