SECT. I. Of the MORTAR

THE mortar is a ƒort of cannon, made of the like metal, but much ƒhorter, and wider, than the common cannon; the kind of bullet, for the diƒcharge of which this piece is generally uƒed, is called a bomb.
        The name of mortar given to this piece might, perhaps, be taken from its reƒemblance to a common mortar.
        The bomb is a great hollow bullet, concave within, which is filled with powder, and by means of the mortar is diƒcharged upon the place intended to be deƒtroyed.  Theƒe bombs produce two effects, viz. that of ruining the moƒt ƒubƒtantial buildings by their weight, and that of creating great diƒorder by their ƒplinters; for when the powder they are charged with takes fire, its effort breaks or burƒts the bomb, and explodes the ƒlinters on every ƒide with great violence.
        The uƒe of the mortar is very ancient; M. Blondell thinks they have been uƒed as long as other cannon, but is of the opinion they were then employed only in throwing ƒtones, and red-hot bullets; he thinks too that the firƒt bombs were thrown in 1588 at the ƒiege of Wachtendonck, a town in the duchy of Gueldres.  But be this as it may, they were not uƒed in our army till the firƒt ƒeige of La Motte in 1634. Lewis the 13th ƒent for Mr. Maltus, an Engliƒh engineer, from Holland, who made uƒe of bombs in ƒeveral ƒeiges with ƒucceƒs, and was killed at that of Gravelines in 1658.  He had remarked, ƒays M. Blondell, a poƒt where he deƒigned to force the trenches in the night, and being deƒirous to ƒhow the place to the general officer, he leaped into the trenches to reconnoitre the ƒituation; the general officer did the like after him, but not having well reconnoitred the place, he deƒired Maltus to jump in a ƒecond time, to remark it with more exactneƒs; Maltus conƒented, and leaping received in the air a muƒket ƒhot in the head, which made it ƒaid jeƒtingly in the army, that he was kill'd flying.
        The aperture l of the mortar (Plate V, Fig. 2) is called its mouth, the oppoƒite a, its breech; b is its touch-hole, which correƒponds to the inner bottom, or the place that receives its charge of powder; this place is called the chamber of the mortar; the two prominences c c are its trunnions, or the parts by which it is ƒupported on its carriage; d is the aƒtragal of the touch-hole, e the firƒt renfort, fthe platband of the renfort, with the handle by which the mortar is ƒuƒpended and managed, and its mouldings; g is the chace, h the neck aƒtragal, i the firƒt collar or neck, k the rim or moulding of the muzzle; the concave part of the piece, from the mouth to the mouldings of the platband, is called the bore of the mortar, and the chamber is the reƒt of the cavity quite to the breech.
 

SECT. II.  Of  the Carriage of the Mortar

THE mortar is placed upon a carriage, to facillitate the uƒing of it; the design of the carriage is to hold the mortar firmly in the ƒituation it is put into, ƒo that the explosion of the powder it is charged with may not alter its direction.  The carriage of the mortar has no wheels; for a mortar is not, as the cannon, removed from place to place on its carriage.  Several ƒorts of carriages for mortars have been contrived; ƒome have been made of iron, and ƒome of braƒs; but we shall here treat of none but thoƒe commonly uƒed, which are compoƒed of two pieces of wood, more or leƒs long and ƒtrong, according to the ƒize of the mortar; theƒe, as in cannon, are called cheeks, and joined by very thick tranƒoms.  In the middle of the upper ƒide of the cheeks are two ƒemicircular notches, to receive the trunnions; over each of theƒe is placed a very ƒtrong band of iron, called the upper band, the middle of which is bent in a ƒemicircle, to embrace the trunnions, and keep them faƒt to the cheeks of the carriage.  The inward part of each notch, or hollow, is lined alƒo with the like iron band, called from its ƒituation the under band; theƒe bands are made faƒt to the cheeks, by long iron pins of great ƒtrength; the upper band is ƒometimes faƒtened to the cheeks by another band of iron, that covers each of its extremities.  The cheeks are ƒtrengthened before and behind with round bars of iron, which croƒs them from ƒide to ƒide, and ƒerve to unite more firmly one part to the other, and bind the cheeks faƒt to the tranƒoms; theƒe are called pins.  On the front of the cheeks, or carriage, are four iron pegs, or pins, ƒet up perpendicularly; between theƒe is placed a piece of wood, on which reƒts the belly of the mortar, or that part of it which contains its chamber.  This piece of wood ƒerves to ƒupport the mortar while it is fired, and is called the pillow.  Inƒtead of the iron pegs, it is ƒometimes ƒecured in a groove, made on purpoƒe, towards the extremity of the cheeks.  When the mortar is to be elevated, and its inclination on the pillow leƒƒened, the aiming wedge is introduced between the mortar and its pillow, almoƒt in the ƒame manner as in pointing cannon.  For the mortar mounted on its carriage ƒee Plate V. Fig. 3.
 

SECT. III.  Of  the Poƒition of a Mortar proper for firing a Bomb, and the line deƒcribed by the Bomb during its motion.

AS one of the effects of the bomb reƒults from its weight, it is never diƒcharged in the ƒame manner as a ball from the cannon, that is, by directing or pointing the mortar at a certain object; but the mortar is a little inclined to the horizon, ƒo that the bomb being thrown up obliquely, much in the ƒame direction as a tennis ball ƒtruck by the racket, may fall upon the place intended; from whence it appears that a mortar has no point-blank range, or at leaƒt that no uƒe is made of it.
        The mortar being in a fixed ƒituation oblique to the horizon, ƒo as that the line a c, which paƒƒes through the middle of it longitudinally, being continued, would make an angle b a d, which the horizontal line a b, a bomb diƒcharged in the direction of this continued line wou'd deviate from it every inƒtant of its motion by its weight, which inclines it towards the centre of the ƒuperficies of the earth, and by this means it would deƒcribe a kind of curve line a e b, called by Geometricians a parabola. 1
        Weight, or gravity, always operates equally on a falling body; for as it always ƒubƒists in an equal degree, it muƒt alƒo always act with equal force, or, which is the ƒame thing, produce always the ƒame effect at the ƒame time.  So, if in the firƒt inƒtant of falling it communicates to a body a certain force capable of moving it a certain ƒpace, in every following inƒtant it muƒt communicate a force ƒufficient to move it the like ƒpace, and by this means the velocity of a falling body is every moment accelerated; for if it has on degree the firƒt inƒtant, it will have two the ƒecond, three the third, and ƒo on.  From whence it follows, that it muƒt move different ƒpaces every inƒtant, and by that means deƒcribe the curve line juƒt mentioned.
        The line a b is called the extent of the range, or the amplitude of the parabola; and the line a d the line of projection, or direction of the bomb. Pl. V.  Fig. 3.