ROCKET is a cylindrical vessel or case, of pasteboard or iror, attached to one end of a light rod of wood, and containing a compo sition which, being fired, the vessel and rod are projected through the air by a force arising from the combustion.
Rockets have long been used as a means of making signals for the purpose of communi cation when the parties have been invisible from distance or darkness ; and they have occasionally served the important purpose of determining the difference of longitude between two places. Rockets have also been con structed for the purpose of being used in warfare, and such missiles were so employed for the first time at the battle of Copenhagen, in 1807. Signal rockets are made to weigh half a pound, one pound, or two pounds ; and the one pound rocket is about 16 inches long. The rod is generally attached near the base, on one side of the rocket, and its length is about 8 feet. The composition with which the cylinder is filled consists generally of salt petre, sulphur, and charcoal or gunpowder, and the composition which produces what are called the stars, consists of saltpetre, sulphur, antimony, mewled powder, and isinglass. The latter is dissolved in one quart of vinegar, after which one pint of spirit of wine is added, and then the mewled composition is mixed with the liquid till the whole becomes like a stiff paste. The burning composition acting at the head, and at the opposite end of the rocket, produces impulsive forces in opposite directions ; but sundry perforations at the lower extremity, by allowing the fire to escape there, nearly de stroys the pressure against the lower end, and thus the pressure at the head is almost wholly effective in giving a forward motion to the rocket. The rod serves to guide it in its flight,
the resistance of the air perpendicularly to its length checking any vibrations which may be caused by inequalities in the action of the burning composition.
Rockets whose diameters vary from 1 to 2 inches have been found to ascend vertically lo the height of about 500 yards, and those whose diameters vary from 2 to 3 inches have as cended to the height of 1200 yards. The distances at which rockets can be seen vary from 35 to 40 miles ; and the times of ascent, from 7 to 10 seconds. Rockets, to be employed as military projectiles, were invented by Sir William Congreve, and, in the British artillery service, a body of men, called the Rocket Troop, has been organised expressly for their management. From their form they pene trate to a considerable depth when fired against timber or earth : 12-pounder rockets, after a range of 1260 yards, have been found to enter the ground obliquely as far as 22 feet. As used in pyrotechnic exhibitions, rockets always have pasteboard cases.