Cavaliers are of singular use on many other occasions, to which their form should be accommodated : that in the bastion c of the crown-work is, from its shape, termed, a horseshoe ; the flat ness of its front is applicable to the situa tion it there holds, because it opposes a direct fire towards the point (17 ; but its circular tendency gives its front a bias towards the inner parts of the faces of the ravelines, while its flanks pre sent a direct fire into the ravelines themselves, and give an oblique fire into the opposite ditches, whereby the assault of breaches in the salient angles of the demibastions L b, would become very hazardous.
The proportions of a crown-work must depend greatly on the purposes for which it is erected, but, whatever be its object, the whole of its defences should be commanded by the works of the principal in so complete a manner, that no part whatever should offer an asylum to the enemy after carrying it ; and consequently that none of its bat teries should be able to play into any other of the defences. For the loss of so large a limb, and of the many ser viceable cannon, platforms, &c. which in such case, are invariably and actively employed against the body of the place, is a very serious concern, and requires the utmost exertion to oppose even for a time. On this account it is highly necessary to have mines under all those parts which can prove serviceable in the smallest degree to the enemy, and to blow them up, whenever a favourable moment may present itself.
From what has been stated as to the purposes Hof crown works, it will be seen by reference to that laid down in the plate, that much attention is re quisite to give them every defensive property, while on the other hand they should prove of little value to a success ful assailant. The only work in our plan affected by such a circumstance would be, that the counterguard 7 would be untenable as a battery, though it might retain some small utility as a casement. But by mining all the inner part of the flank, which commands the counterguard, even that evil would be lessened : if, however, an enemy should be able to carry the raveline N, and to maintain his ground therein, notwith standing the tremendous fires from the faces of the bastions 3 and 4, and from the curtain u v, (all of them direct) but little hope could remain of a success ful resistance, and the counterguard would be, comparatively, no sacrifice. We, however, see from this, that a tenaille on the lines of defence, r, u, as shewn at P, between the bastions. 2
and 3, must prove highly serviceable, especially if mounting such heavy metal as would destroy any works thrown up in the raveline N.
The entrenchments, f f, cut the ram parts of the flanks of the crown-work through all but the revetement, and they are carried as far forward as pos sible, so as barely to be flanked by a barbet battery in the salient angle of the raveline, that the bastions of the crown work may be perfectly commanded by musquetry. The cavalier in C, is sup posed to be mined and destroyed, else it would prove very disadvantageous to the defence of the raveline, which it would partly command.
We have already observed, that many out-works might be shewn, in addition to those given to the faces of the crown work, such as lunettes, tenailles, te naillons, fleches, advanced lunettes, re doubts, bonnets, &c. but we apprehend the reader will, from the foregoing de tails, and the plate to which they refer, be able to supply to his imagination the almost endless continuation of outworks, which the limits we are compelled to draw around this branch of science pre. elude us from enlarging upon.
I, The bonnet, mentioned in the pre ceding paragraph, is nothing more than an angle made parallel to a raveline, and not far removed from it, so that the faces of the latter command the faces of the bonnet. This out-work comes down to the lunettes, by which it is flanked.
We now have to treat of those im portant parts, the glacis, and the covert way. The former is a gradual slope, commencing at a distance from the ex terior of the out-works, seldom less than fifty yards, and when within five toises of the ditch, stops abruptly, oc casioning a sudden fall, never less than seven, nor should it be more than nine feet. Here it is supported by a revetement, and is partly met by a ban quette of turfed soil, which is raised high enough to come within four feet and a half of the crest, or highest part of the glacis. At the foot of the revetement, at such distance as tmay prevent an enemy jumping over, say from two to three feet off, a row of palisades is fixed ; these are strong pales, nine feet in length, of which one-third is buried in the banquette, while the long horizontal rails, to which the pali sades are firmly nailed, are at every ten feet morticed into square posts. The lower rails are one foot from the ban quette, and the upper ones are just level with the crest of the glacis, so that the soldiers may fire through the top inter vals between the pales, resting their pie ces on the upper rail.