Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/463

 FORTIFICATION 447 assailants along the covered-way checked. As Speckle planned in 1589, or long before the invention of ricochet fire by Vauban had rendered traverses an essential element in fortification, his object was not the same as that of Connontaigne, but simply to ensure a more perfect flank- iii&quot; defence of the branches of the covered-way than that afforded by the places of arms of his systems. The ditches are, as shown in fig. 3 of Plate III., on different levels the main ditch being about 23 feet deep, and the ditch of the redoubt of the ravelin only 7 feet, so that from this latter ditch there is a fall of 16 feet to the main ditch, rendering it impossible to attack the ravelin by its gorge without the aid of ladders. An examination of the several figures which represent Vauban s and Cormontaigne s systems, as also the outworks of fig. 3, Plate IV., will at once render evident the vital defect of the ordinary ar rangements of outworks that they expose through the openings of their ditches the escarp of the body of the place, or of the work on which their faces or branches are directed, to be breached. In the System of Connontaigne, as well as in the Modern System next to be con sidered, the increased projection of the ravelins, by throwing the intervening bastion into a deeply re-entering position, secures it from attack by ap proaches until the salients of the ravelins have been, taken ; but this great advantage is diminished by the power of breaching the bastion from the glacis through the opening afforded by the ravelin ditch. For the purpose of covering the communication to the re-entering place of arms, a demi-caponniere, or work composed of a parapet and glacis, was thrown across the ditch of the ravelin, as shown in the figure of the modern system (Plate IV., fig. 2), This work afforded cover also to troops assembling pre paratory to a sortie upon the enemy when making the passage of the ditch, but, from the depth of the ravelin ditch, it was insufficient to mask the revet ment of the bastion behind it. It will presently be shown how this object was afterwards effected; and it may be said that without any material change in system, Cormontaigne s variations from. Vauban s trace are unquestionable improvements 4. TJie Modern System. The Modern System, which is shown in Plate IV., fig. 2, varies little from Cormontaigne s. Its perpendicular is one-sixth of the exterior side, and the faces of the bastions are one-third. The flanks are at right angles to the lines of defence, whereas in Vauban s System they form an angle of about 82, which is not so good, because, in the Modern System, the guns placed in the flanks can fire straight along the ditch without being moved or turned on their platforms. The ravelin is formed by setting off points 34 yards from the shoulder along the face of each bastion ; a line joining these points is the base of an equilateral triangle, the vertex of which, opposite the centre of the curtain, forms the salient angle of the ravelin. The re doubt of the ravelin is formed by drawing its faces parallel to those of the ravelin from the shoulder of the parapet of the bastion; and it has flanks with a ditch about 20 yards in breadth. The cavalier in the bastion is drawn parallel to the faces of the bastion, at the distance of 48 yards from them. The ditch of the faces is 10 yards in width, but there is no ditch to the flanks. In bas tions strengthened by a cavalier retrenchment, a coupure is formed perpendicularly across the faces of the bastion ; the ditch of the coupure is 30 feet wide, and the counterscarp is traced from a point 36 yards from the shoulder of the bastion to meet the counterscarp of the ditch of the cavalier. This system originated in the school of military engineering instituted at Mezieres in 1750, and was for some time called the system of the school of Mezieres. It has, however, been much im proved since ; and the system which is now recognized as the &quot; Modern System&quot; is that of General Noizet Referring, however, to fig. 2 of Plate IV., it will be seen that coup- ures have been introduced in the faces of the ravelin; and as the ditch of the ravelin in this system is less by 7 or 8 feet than the main ditch, there is a sufficient fall be- Scale of Metres = FiO. 63. Half-Front of the Modern System. tween the two to check the enemy in his passage to the latter, whilst the demi-caponnierc is raised so much