SHELLS, called in earlier times bombs, consist of hollow vessels of metal, containing gunpowder 'or other explosive compound, so arranged that it shall explode at a certain point, and spread destruction around by the forcible' dispersion of its fragments. The invention of this murderous missile cannot be accurately traced. Shells were employed in 1480 A.D. by the sultan of Gujerat, and by the Turks at the siege of Rhodes, in 1522. The Spaniards and Dutch both used them during the war of Dutch independence; and they, appear to have been generally adopted by about 1634. As shells required mortars (q.v.) for their projection, they were not used in naval warfare until the French con structed special bomb-vessels in 1681; but since that period, shell-guns, being cannon of large bore, have been introduced, and. shells are now employed by all ships of war.
Until within a feW years, every shell was a hollow sphere of cast-iron, varying in thickness from half an in. to 2 in., and in diameter from 5i in. to 13 inches. The sphere had a fuse-hole (like a botr-hole) an inch across, through which the charge was inserted consisting of•pieces of metal and powder to burst the shell. The hole was plugged by a fuse, which was a tube of slow-burning powder, timed to communicate fire to the charge after the lapse of a certain number of seconds. This fuse might either be kindled by hand the moment before the mortar was fired, or its ignition might be effected by the act of firing itself: The Shrapnel] shell, introduced by col. Shrapnell of the royal artillery, about 1803, contained a number of bullets, and being fired at bodies of men, it was timed to explode about 100 yards before reaching them, when the shell burst, 'and the bullets with the fragments continued their course, diverging• continually- as they. went, until they reached their object in a death-cloud. The concussion shell, or percus sion shell, is one in which the charge . is fired by the dethation of a cap on striking an object. If sufficiently delicate to explode on touching a soft object, and at the same time not to be exploded by the resistance of the air to its rapid flight, this form of shell is the most certain in execution.
Since the introduction of rifled ordnance, the shell has becotbe the commonest former of projectile. It has ceased to be spherical, and is usually in the shape of an elongated
bolt. Several rival shells at present divide public favor, and compete for adoption into war service. Without noticing the numerous varieties which arc in course of trial on the continent and in America, the following are the principal British competitors: Tho Armstrong shell is a pointed bolt of iron (usually percussion), containing an inner "seg ment shell," made up of 49 segments of cast-iron. Seven of these segments form a circle, or ring, and 7 circles give the necessary length. A coating of lead affords a soft medium for fitting into the grooves of the gun. The shell thus made somewhat resem ides a bottle without a neck. The necessary charge having been inserted, the rear-end is plugged with lead, the fuse is sereWed into the front, and the shell is ready for action. This projectile has a great and accurate range, and its segments cannot fail, on explosion, to do great damage. The principal drawback has been found in the lead casing which is often thrown off in parts soon after the shell leaves the gun, and which time falls among the foremost ranks of the army using it,.sometimes inflicting severe woundS. The 1V7titworto shell is an elongated hexagonal bolt of iron or steel, cast in one piece, and whit a bursting charge at the rear end. It explodes on percussion; but the space allowed for the burster is deemed insufficient to produce the full effect which the length and correctness of the weapon's range give cause to expect. The Lancaster shell is oval, to fit the bore of the Lancaster gun (q.v.). Martin's shell is charged with molten iron, which sets on fire all combustible matter on which it can he thrown. The Dia phragm shell, invented by col. Boxer, R. A. , has an iron division or diaphragm to sepa rate the powder in the shell from any balls or slugs, in order that the friction of the latter may not prenaturely cause the powder to explode. A six-pounder diaphragm shell con tains 30 carbine-balls, an eight-inch shell, 322 musket-balls. The Palliser shell. which is now employed in the British service, is chiefly remarkable for the hardness imparted to its fire-point by a process of "chilling" during casting. This gives it a great power of penetration into iron plates, etc.