Small divisions exterior. The vent, dolphins, vent astragal and fillets, breech ring and ogee, reinforce ring and ogee, reinforce astragal and fillets, muzzle astragal and fillets, muzzle ring and ogee, muzzle moulding, shoulders.
Interior parts. Chamber, bore, mouth, vent.
Chamber in Mortars, is the place where the powder is lodged. There are different sorts, and made variously by different nations. The Spaniards use chiefly the spheric; the French, Germans, and Dutch, the conic, cylindric, and the concave or bottled; the Portuguese at present, the parabolic; and the English make them in the form of a frustrum of a cone. Each nation has its reasons, good or bad, to prefer their make before that of others: among which the English say the concave and cylindric chambers are the best; the French say the frustrum of a cone.
Sea-Mortars; are those which are fixed in the bomb-vessels, for bombarding places by sea: they are made somewhat longer, and much heavier than the land-mortars.
Land-Mortar-Beds, are made of very solid timber, and placed upon very strong timber frames, fixed in the bomb ketch; to which a pintle is attached in such a manner, that the bed may turn round. The fore part of these beds is an arc of a circle, described from the same centre as the pintle-hole. Land-mortar-beds are now made of cast iron.
Stone-Mortars, serve to throw stones into the enemy’s works, when near at hand; such as from the town into the trenches in the covert-way, or upon the glacis; and from these trenches into the town. The bore is terminated by two quadrants of a circle, terminated by the reinforce and lines drawn from the ends of the cylinder, made to lodge the tompions parallel to the axis of the mortar. The bottom of the conic chamber is terminated by an arc of 60 degrees, and the round part of the outside is a semi-circle.
Chambers in Mortars, are of different sorts and dimensions. Mr. Belidor mentions four; namely, the cylindric, the spheric, the conic, and the concave or bottled; to which a fifth may be added, the parabolic, invented by count de Lippe Buckeburg.
Cylindric chambers. Experience demonstrates, that concave chambers will throw the shell farthest of any with the same charge, yet, in this case, where but little powder is required, in the entrance would become too narrow, and consequently inconvenient to clean; whereas, when they are cylindric, the difference between the advantages of the one and the other will be but little, and not attended with any inconveniences.
Conic chambers, are generally made in a circular form at the bottom, so that the sides produced, meet the extremities of the diameter at the mouth.
Spheric chambers, are much inferior to the cylindric or concave; for it is well known by the properties of geometry, that when a cylinder and a frustrum of a cone occupy equal spaces, the surface of the cone is always greater than that of the cylinder. Hence, if the entrance of these chambers be not made very narrow, contrary to practice, as demonstrated by Mr. Muller, in his second edition of Artillery, page 38, of the introduction, and the examples that follow, we conclude that these and the conic chambers are the worst.