MORTARS are pieces of ordnance which, compared with guns, are very short, and which are employed to throw shells or carcasses at con siderable elevations (generally at 45°, but sometimes as much as 70°), in order that the missile may range to a great distance, and, by falling nearly vertically upon the object (a barrack, magazine, or casemate), may crush it by the momentum acquired in descending. Mortars are either of iron or brass; they rest upon solid beds, and the trunnions or cylinders upon which they turn, in giving the required elevation, are placed at the lower extremity of the piece. A mortar platform, in a battery, should be very strong, in order that it may bear the great recoil or shock of the piece when fired ; and it should be carefully laid in a horizontal position.
The calibres of mortars in the British service are 45, 51, 8, 10, and 13 inches. All these different kinds of mortars are used on land, and the two last are also employed in the navy ; but in this latter service the pieces are about 16 inches longer than the land-service pieces of the same calibre, and are much heavier, the sea-service 13 in. weighs 101 cwt. and the land-aerviee 36 cwt. The two first-mentioned are sometimes called royal mortars.
By varying the charge of ponder in the same mortar, it has been found that there is a particular elevation which, with each charge, gives a longer range than is obtained from an equal charge at any other elevation. It has also been found that the elevations which give the longest ranges differ much in two mortars of different calibres, but of like proportions, even when charged with quantities of powder bearing the same proportion to the weights of the shells, but for the sake of simplicity they are all generally fired at 45°, and the tables are all arranged for that elevation.
It has been supposed that mortars were employed in the year 1495, at the siege of the castle of Naples, but on no other ground than a statement that artillery of considerable magnitude was conveyed into Italy with the army of Charles VIII. In 1588, however, the use of
mortars must have been well known, since, the Appendix to the Colloquies of Tartaglia,' which was published in that year, the method of filling and projecting carcasses is fully described : and it appears that in the some year shells were thrown from ordnance at the siege of 1Vachtendonk. [Boma.] Red-hot shot were thrown from mortars at the siege of Bremen, by the Swedes, in 1663.
The first artillerists were somewhat capricious in the formation of their great ordnance; and among the various kinds which they devised may be mentioned what were called Partridge mortars. These had one great central bore for the reception of the shell; and about it, on the face of the muzzle, were sunk thirteen chambers, each of which contained a grenade. The shell and grenades were discharged at the same time, and in the air they must have appeared like a flight of birds ; from which circumetanco, no doubt, the name of mortar was taken.
The Dutch engineer Coehorn invented a small mortar for throwing grenades into the covered-ways of places. They were capable of being carried about and served by one man; consequently they could be readily brought up to a convenient spot, and rapidly tired when it wap intended to drive the defenders from behind the parapets. In the French service Pierriers (small mortars loaded with stones) are still employed for the same purpose.
In the year 1771 an experiment was tried at Gibraltar on the dis charge of atones from an excavation in the rock. The figure of the excavation is a parabolic conoid, whose axis is 4 feet long, and whose diameter at the muzzle is 3 feet. It was charged with 27 lbs. of powder stones ; and, on the explosion taking place, nearly one-fourth of the stones were projected to the distance of 100 yards. There are several rock-mortars, as they are called, at Malta, and such may on many occasions be very useful both in the defence and in the attack of a fortified place.