Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/495

FORTIFICATION 463 inished, tlie difficulty of defending the salient from the flanks is much increased. His great innovation, however, consisted in placing the ravelin and its redoubt in advance of the glacis of the body of the place, and forming in front of them a second or advanced covered-way, the object being to close the main ditch entirely, so that the besiegers bat teries should not he able to fire upon the body of the place through the ditch of the ravelin. The covered-way is made en cremaiUere, and at each bend there is a sort of redoubt, or casemated traverse, not a simple hollow traverse loop- holed, such as those in the detached works of Corfu. It has been objected to Bousmard s system that his advanced works would be speedily taken by turning the gorges both of the ravelin and its redoubt, but it should be remembered that the interior slope of both is replaced by a loopholed wall, being the front of an arched gallery running all round, so that the enemy could not remain within these works exposed to the fire from the galleries, as well as from the body of the place. Without advocating the precise form and disposition of the works recommended by Bousmard, it may be reasonably asserted that in every case of a power ful and well-appointed garrison, the defence will gain by assuming an active character beyond the precincts of the glacis. As already observed, an unmerited indifference has been manifested by many engineers to the merits of Carnot, principally, it may be believed, from his exaggerated esti mate of the effects of a vertical fire of small projectiles. Although he appealed to imagination rather than to calcula tion, when he assumed that by substituting GOO wrought iron balls, weighing each - B>, for the one shell of 150 It), with 6 mortars projecting 3600 balls, he might expect to put hors de combat 20 men at each discharge, or 2000 in 100 discharges, he was right in urging the importance of vertical 6re. Carnot constructed his escarp without a re vetment, but placed a detached loopholed wall in frontof it with a chemin des rondes between, which is one essential feature of his system, the wall being constructed with arched niches in rear so as to shelter the men defending it; the loop holes are in two row r s. He provided arched casemates for mortars on the gorge of his bastion in order to fire upon the capital, and the loopholed wall of an inner curtain, being continued along the retired flanks and in front of these mortar casemates, formed a complete inner retrenchment. Between the tenaille and the ravelin was an earthen cavalier, occupying the position of a redoubt in the ravelin, before the bastion s counterguard, so that the whole of the interior works were masked by these earthen envelopes. There is much ingenuity in these arrangements, and at least as full an appreciation of the value of earthen works as can be found in the writings of any modern writer. Carnot s lead ing principle, however, was, that a successful defence must depend on the active operations of the garrison, and that sorties therefore should be frequent and determined as soon as the enemy had approached close to the fortress. For this purpose he removed the revetment from the counter scarp, and formed it into an easy or countersloping glacis, to admit of the ready advance of the troops from the ditch upon the head of the besiegers sap. He supposed that the overwhelming vertical fire of the 10 mortars in the mortar batteries in the gorges of his bastions would prevent the enemy from accumulating large covering parties in the trenches, and that he should therefore be able to fall upon the working parties and successfully delay the progress of the works. It has been shown that Carnot entertained an exaggerated view of the effects of vertical fire, but the idea of securing his mortars in casemated buildings is good, and has been adopted in the citadel of Ghent, and in several English works at Portsmouth and Plymouth; and it is im possible to study his works without profit. Chasseloup (1754-1835), like Bousmard, placed his ravelin in advance of the glacis, and provided it with a small casemated keep, the flanks of which are pierced for two guns each. The tenaille is also provided with casemated flanks, and in front of it is a casemated redoubt or bastionette to supply the place of the ordinary ravelin, and to flank the salient portion of the face of the bastion, the general face being by him bent into two, so as to place the salient portion in line with the exterior side of the polygon, and thereby secure it from the ricochet fire. Casemated redoubts in the re-entering and salient places of arms, a defensive barrack, and a permanent en trenchment on the bastion are also included in his arrange ments. De Sellon (Memorial de L lnyenieur Militaire) observes, " It would indeed be well to force the besieger to pass through two sieges, if the outworks pushed so far forward -had higher scarps, and were not so easily turned at the gorge, but as the scarp is only 13 feet high, this possibility of attacking the works by the gorge without a previous descent into the ditch presents such serious in conveniences that it is surprising to observe that Bousmard and Chasseloup should have adopted so defective an arrange ment." But notwithstanding this strong condemnation, it is at least doubtful whether such works are not the most suitable for a vigorous defence by a strong garrison, as they would enable the besieged to fall upon the assailants at the most critical moment of their attack with a powerful force ; and it may bo added that a skilful engineer would know how to throw many difficulties in the way of turning these advanced works, whilst the continuance of the besiegers in them might be rendered both difficult and dangerous in the extreme. The most remarkable feature in Dufours modification of the modern system is, that one face of the redoubt in the re-entering place of arms is carried across the ditch, and connected with the coupure of the ravelin, so as completely to close the ditch and cover the face of the bastion from the fire of a battery on the glacis of the salient of the rave lin. Dufour also raised the salient of the ravelin into a high cavalier, so as to secure the faces from ricochet ; and he proposed that the cavalier should be formed of gravel or small stones so that the fire from the body of the place might, by scattering about these natural missiles, cause great damage to the enemy, when attempting to form a lodgment. General Noizet has been already mentioned in connexion with the Modern System, his modification of which is now the normal system adopted at the French military schools. Rejecting Dufour s mode of closing the ditch of the ravelin by carrying across it one face of the redoubt of the re-enter ing place of arms, he effected the same object by placing"a massive mask between the coupure of the ravelin and the re-entering place of arms, from the inner escarp of which it is separated by a passage. The counterscarp of the bastion is carried continuously along the inner edge of the mask, whilst in front of it is a ditch which separates it from a demi-caponniere forming its counterscarp and covered-way, and a glacis sloping down the ravelin of the ditch. The mask, the lunette redoubt in the ravelin, and the redoubt in the re-entering place of arms form a combined series of works of great efficiency for defence, which completely cover all but the salient portion of the face of the bastion. The flank of the bastion, as before observed, forms an angle of 80 J with the line of defence, and the advantage taken of this in the citadel of Ghent in forming a most powerful in- trenchment in the bastion, with a curtain as long as that of the main front, has also been pointed out. General Haxo, one of the ablest engineers of modern times, did not publish his scheme of defence, nor did he re produce it as a whole in the works he constructed, doubt-