MORTAR

Mortars are used in the attack of a fortified place, by sea, to discharge shells or carcases amongst the buildings. The shell is a great hollow ball, filled with powder, which, falling into the works of a fortification, &c. destroys the most substantial buildings by its weight; and, bursting asunder, creates the greatest disorder and mischief by its splinters.

The chambers of mortars' are extremely different in their figures, and each of those figures is defended by better or worse arguments. Thus they are spherical, cylindrical, conical, bottled, or concave. In reality, nothing appears to be less determined upon true principles or experiments than the proportions of the several 'parts of a mortar [Muller's Artillery].

As the sea-mortars, or those which are fixed in the bomb-vessels, are generally fixed at a much greater distance from the object than is ever required ashore, they are made somewhat longer, and much heavier, than the land-mortars.

Plate VI. fig. 7. represents a sea-mortar, the principal parts of which are, A, the chace; B, the reinforce; C, the breech ; and D, the trunnions. The interior part, comprehended between the dotted lines, is called the bore, wherein the bomb is lodged; and the inner part of the bore, which is diminished towards the breech, and contains the powder, is termed the chamber.

Plate VI

Mr. Muller, in his Treatise of Artillery, very justly observes, that the breech of our 1 inch sea- mortars is loaded with an unnecessary weight of metal. The chamber thereof contains 32 pounds of powder, and at the same time they are never charged with more than 12 or 15 pounds, by the most expert officers, because the bomb vessel is unable to bear the violent shock of their full charge. Thus the action of the powder is diminished by the vacancy left in the chamber, which is never above half filled. As a charge of 12 or 15 pounds of powder at most is therefore sufficient, it is evidently proved, by the theory of powder, that this will produce the greatest effect when discharged from a mortar with a cylindrical chamber, represented by fig. 8. He also proves, by a variety of experiments made by Captain Desaguliers and himself, that the conical chamber, now used, is consider-ably inferior to the cylindrical one with the last charge of powder.

To facilitate the use of the mortar, it is placed in a solid carriage of timber, called the bed, whose different parts are strongly bolted together. By means of this it is firmly secured in its situation, so that the explosion of the powder may not alter its direction. In the middle of the upper side of this Carriage, plate VI. fig. 9. are two semi-circular notches, to receive the trunnions; over these are fixed two very strong bands of iron, called the cap-squares, a, the middle of which is bent into a semi-circle, to embrace the trunnions, and keep them fast in the mortar-bed. The cap squares are confined to the timber-work by strong pins of iron, called the eye-bolts, b, into whose upper ends are driven the keys, chained beneath them. On the fore-part of the bed a piece of timber is placed transversely, upon which rests the belly of the mortar, or that part which contains the chamber. The elevation of this piece, which is called the bed-bolster, is represented by fig. 13. and the plan by fig. 12. it is used to elevate and support the mortar whilst firing.

Reference Works