The communication between the lunette and the cover ed way, is by means of caponniers ; but lest these should be occupied by the enemy, a subterraneous passage from the counterscarpe of the covered way, to the gorge of the lunette, is preferable. If the communication is not co vered, it enters the gorge by steps ; if it is subterrancous, the gorge is straight, and the steps arc in the middle of the lunette. if the terre-plein of the lunette is not higher than the ground, the gorge must be protected by a wall, with loop-holes, at least 6i feet high, and 12 to 20 inches thick. The covered way and glacis round the lunettes, are constructed in the same way as before the enceinte.
A horn work is represented by ABCD, Fig. 2, and is constructed as follows. From the saliant E produce the capital, making EF from 450 to 500 feet. Through F draw a perpendicular BC, making BF, CF each from 300 to 350 feet, and on this line construct a Front, as on the ex terior side of the polygon. Then draw the faces BA, CD directed to a point, about 30 fe,et from the shoulder of the bastion. if a ravelin a b c is constructed before the horn work, its faces ought to be 200 feet. The ditch round horn works is about 72 feet. Various entrenchments, as G and 11, have been used to strengthen crown works, but none of them have been of much advantage.
Horn works arc placed sometimes before the curtain, and sometimes before the bastion. In the former position, they do not appear to be of advantage, as, in case of their being taken, the enemy becomes master of the whole front. Before the bastion they may be very useful ; but in every situation they are liable to strong objections. They require a great number of men to defend them—they form a saliant that is not easily supported by other works—they present a straight front to the enemy, which is always weak, and they are very much exposed to an assault on their wings or faces.
Crown-works differ from horn-works in having a bastion in the middle, as Plate CCLVIII. Fig. 3. In other re spects, they are the same, and constructed in the same way. They are, however, liable to still stronger objec tions than horn-works. They are more expensive, and more difficult to defend. They are therefore seldom used, unless it be to cover some large and important position near the fortress.
Detached and isclated works are such as are completely unconnected with the body of the place, and intended to protect or attack some distant position. Their form and
magnitude differ with circumstances ; but they are always similar to some one or other of the works already des cribed.
Of the works placed in the ditches, or used as coupures and entrenchments, the most remarkable are I1Iontalem bert's casemated caponniers, angular towers, and ravelins with ailerons. The caponniers are large stone buildings, with two or three rows of guns above one another, and be tween these rows loop-holes, through which the soldiers may fire with musquetry. One half of the caponniers may be used as casemates, as the smoke is easily carried off. The whole is covered with a shell-proof covering. The angular towers, or tours angulaires, are round buildings, with a stair in the middle, and places all about it for men and guns. The sides are pierced with embrasures and loop-boles, and the whole covered as the caponniers are, with a shell-proof covering. On the top is sometimes erected a watch-tower. Under the same denomination of works may be classed the English martello towers, con sisting sometimes of several stories, with embrasures and loop-holes. The communication between these stories is by means of ladders. On the top is placed one gun, and sometimes more, the carriage of which moves on a pivot. The ravelins, with ailerons, or orillons, do not differ from common ravelins, except that they are smaller, and have the orillons. The latter are sometimes constructed of stone, but more frequently of earth, and are separated from the ravelin by a small ditch. These orillons are of great use in covering the shoulders of the bastion, when the ravelin is too small for that purpose. But in every case it would be better to have a large ravelin without the orillons, than a small one with them. The orillons are in fact a sort of places of arms, which when taken, give the enemy the command of the ravelin.
Of all the means of defence, none perhaps can be turn ed to greater advantage than water, when it can be readily commanded. An inundation, well directed, is not only a defence to the besieged, but may even be converted into a powerful means of annoyance, by suddenly destroying the enemy's last and most important works in the fosses. It is no small recommendation, too, of this method of defence, that it can be used without much expense, either of labour or ammunition.