. Fuses are employed in ordnance for explod ing shell and they may, consist of a compressed core of gunpowder enclosed in a tube of wood or metal, or of a fulminating composition or of both. They are known as °nose fuses" when put in the front end or anose" of the conical pointed shell, or abase fuses" when inserted in the lower end or base of the shell. they are known as lime fuses." when they are planned to burn a certain length of time after they have become ignited, before they set fire to the ex plosive charge in the shell; °percussion fuses" when they are set in operation by the impact of the shell against an object after it has been projected from the gun. They may act in stantaneously in firing the charge in the shell,.
or there may be a column of compressed powder interposed between the charge of explosive in the shell and the fulminating composition which is fired by impact. As sometimes a second or more intervenes between the striking and the bursting of the shell, these are styled *delayed action fuses.° They may be used with armor piercing shells designed to penetrate armor and burst within the ship. In time fuses, used with spherical shell, the powder in the fuse used to be ignited from the flame of the burning charge with which the shell was propelled from the gun. In modern time fuses there is a metal cylinder which serves as a hammer placed within the fuse case and held in place by brittle pegs of metal, or by a number of small balls. When the shell containing such fuses is fired, the inertia causes the hammer to strip from the pegs and set back toward the base of the shell, or, if it be a shell from a rifled gun, the centrif ugal force causes the balls to fly outward and release the hammer. When the shell strikes, and is arrested in its flight, the hammer moves forward, strikes a percussion cap and fires the charge.
*Chemical fuses* have been used in firing gunpowder mines and torpedoes. As an exam ple of these we cite the mixture of cane sugar and potassium chlorate used in the Harvey tor pedo. Above a column of this mixture was placed a small glass bulb filled with concen trated sulphuric acid, the whole being enclosed by a soft copper cover projecting from the torpedo. When this cap was struck, it collapsed and broke the glass bulb, and, as the sulphuric acid came in contact with the mixture of sugar and chlorate, the latter burst into flame and ignited the powder in the torpedo. Such fuses have been used by anarchists in infernal ma chines and they have ascertained the rate at which the acid would eat through sheets of bibulous paper so that by interposing a suffi cient number of sheets of paper they could set the train in operation and get safely out of the way before the machine exploded. Fuses, con sisting of columns of compressed gunpowder composition, are used in pyrotechny by which to ignite the charges in rockets, bombs, roman candles and other devices. By their use the operator is enabled to get to a safe distance after igniting the device before it functions fully.
Fuses are used in *electrical installations,* but these are of an entirely different character from the above. They consist of strips of metal of low fusibility which are interposed, in elec tric lighting and other circuits, between the gen erator and the lamp, or other device, to prevent damage to the device by an excess of current. When the load is greater than is desired the current heats the fuse to its fusion point, when it melts and cuts out the circuit. See GUN POWDER; EXPLOSIVES.