It should have been stated, that all an• gles projecting outward from the body of the place, are called saliant angles : for instance, a, B, t, of bastion 3, and e, o, e, of the raveline N : while such angles as point inwards towards the body of the place are designated re-entering angles ; such as t, u, VI, on the lines of defence of the centre face: When an angle re-enters at such a position in the outworks, that its apex or point cannot be seen, and con sequently cannot be defended from the body of the place, it is called a dead an gle. Such cannot easily take place, where the smallest attention is paid to the most ordinary rules ; but, wherever found, should be exploded from the defences, either by cutting off a large part of the pinch, or narrowest part, and substituting a curtain, or by new modelling-the de fences in that part. It may be proper to observe in this place, that works intended for mutual defence should never exceed an angle of 120 degrees, nor be less than 60. The medium, i. e. 90, which forms a. right angle, generally considered, is indis putably the best for the above purpose. Where batteries stand at such an open ing, that their direct fire, that is immedi ately to their own front, is parallel with the front of the part they flank, it is call ed a razant, or grazing fire ; but when the angle is less than 90, so that the direct fire would strike upon the face of the work to be defended, it is termed fish. ant, or plonging : both have their uses, but the latter is rarely adopted, except from necessity, because a direct fire, at right angles, may be made to plonge, by givingthe cannon an inclination more pa rallel with the side of the embrasure, which being angular, allows a deviation of many degrees from the direct fire.
When two lines form a very acute an gle with each other, they no longer are defences ; for in case the enemy should carry either of them, he would be able to work its battery against the other line ; and though the fire would be plonging, and that too at a great disadvantage, yet, as many shots would light within the em. brasures, the parapet would speedily be destroyed. The revetement, or masonry, in the/front of the line, so plunged, would not be much hurt, as it would turn off the shots.
Before we proceed farther, it is expedi ent that the reader should examine the line of the principal, following along A, o, S, r, B, t, v, C, b, z, to, D ; in all which he will perceive, that every part is made to flank some other. The rave lines 0, N, K, will be found to give great security to their several curtains, a r, v a, and y while at the same time they would enfiladewhatever approaches might be made towards the saliant angles of the bastions. In examining these circum stances, all the other outworks must be exempted from consideration ; our view must be confined to the manlier in which the gates in the curtain are protected ; the flanks of the bastions concealed from every part but the line of their direct fire ; and the spaces opposite the saliant angles subjected to a heavy cross fire. The ravelines, themselves, stand at too wide an angle to absolutely flank each other, but they are capable of scouring the glacis reciprocally, and would, as be fore remarked, subject the besieger to a dangerous enfilade, or flanking fire, were he to proceed without due attention to their obnoxious positions. In works of more sides, where the angles of the bas tons are necessarily more obtuse, the ra velines are thrown more towards a right angle with each other, and afford mutual support, even in cases of assault.
The communications with the raveli nes are effected by the aid of bridges, when wet ditches are in question, as may be seen in the third face, y z, where the bridge V is carried over from the curtain to the counterscarp, or outer face of the ditch, so as to afford access to the rave line K, in which is the intrenched redoubt L. The double lines, T, represent a channel of about fourteen feet broad, and about six or seven feet deep, made in all ditches that are at any time filled with water. These channels are called cunettes, or cuvettes ; they are usually lined with masonry, and kept full, so as to prevent a surprise : when the water is allowed to fill the whole of the ditch, which should generally be to the depth of nine or ten feet, or at all events so as not to be fordable, the cunette proves a for midable obstacle.
The bridges have barriers at their cuter ends, and towards their inner ends generally a draw-bridge, besides one that lifts immediately under the gateway, to which it gives additional strength. The very small compass allowed for the exhi biting of such figures as are indispensably necessary towards the right understand ing of the subject, absolutely precludes the possibility of showing the dimensions of the ramparts, &c. and occasions the omission of many particulars in the plate, which must be therefore described. The foregoing impediment prevents us from showing the berm, which is a space, al ways left, between the cordon that runs along the inner brink, or scarp of the ditch, and the foot of the ramparts. Its use is to prevent the latter, when batter ed, from falling into the ditch ; and it af fords likewise a very good line of com munication all round the works. The breadth of the berm is very uncertain ; it should never be less than six feet, even where the works are scarped from the solid rock, and not subject to let fall much rubbish when battered. In the common mode of building ramparts with a revetement of masonry, the berm should be at least ten or twelve feet ; and where only turf facing is used, or that the soil with which the rampart is filled, between the outer and inner faces of masonity, is of a loose nature, the berm should then be full twenty feet broad. The bulk of the rampart should, however, be consi dered also , whether it be much exposed or not ; for on these points much will depend as to the probable quantity of battered rubbish to be sustained. There used to be a work, called the fausse braye, carried all round the principal and the edge of the berm : its intention was to defend the ditch, and its fire was in deed highly destructive ; but the facility with which it could be enfiladed, for it was necessarily low, evinced its inutility in general : the immense number of splin ters falling from the rampart, immedi ately above, was another formidable ob jection. The fausse-braye is, therefore, out of repute ; though in some fortifica tions, a substantial parapet supplies its place, generally of masonry, more for the purpose of stopping the rubbish of a battered rampart, than for the means of sheltering troops. Perhaps the strong hedge, adopted in many instances, may be preferable ; to say the least, it is far cheaper, and stands to more advan tage on the berm, than a heavy range of masonry.