more. the same height, those within cannot be destroyed Sect II. OF THE SECOND AND THIRD SYSTEMS till such time as those before them are taken : of M. VAUBAN. guns might be placed in the covert-way and outworks to obstruct the enemy's approach; and, M. Vauban's Second and Third Systems were when they come near the place, they might be chiefly designed, as we have stated, to protect the transported into the inner works; and, as the besieged from the ricochet fire of his own invenbody of the place would be much lower, the ex- tion, and to improve the near defence. To acpense would be considerably diminished. . It complish these and some minor purposes, he should not, however, be forgotten that, when composed the body of the plan of works which works are low, they are easily enfiladed by the resemble small bastions, and are called towerricochet batteries, though this might be partly bustions. His second method is thus exemplified. prevented by making the parapets near the He begins his construction inwards, and fortifies saliant angles, for the space of eight toises on outwards, which is found a very convenient plan each side, five or six feet higher than the rest of for improving a place. the works, Let A B, Plate III, fig. 2, be the interior side 2. The covert-way should be lower than the of an hexagon of 120 toises, some authors will level ground, otherwise the body of the place have it 130, and say that they are so at Landau, must be raised very high, especially where there draw AC, BD, from the centre through the exare several outworks: this is to be understood tremities of the sides; set off six toises from A only when the works exceed each other in height, to b, and from B to c; through the points b and otherwise it need not be below the level. (, draw lines at right angles to AB, from the 3. The bases of all inward slopes of earth point b set off six toises to f outwards, and four should be at least equal to the height, if not from b to d inwards; and from the points f,d, draw perpendiculars fr, d n, to the capital AC; 4. The bases of all outward slopes of earth, then, if r E is made equal to r f, the point E will two-thirds of their heights. be the saliant angle of the tower bastion; and E 5. The slopes of all walls or revetments should f d n half that tower. be one-fifth of their height; or one-sixth might, If in the capitals there be taken from the saliperhaps, be sufficient; the height of a wall is ant angles of the tower-bastions, the distances estimated from the bottom of the ditch, and not EC, FD, each of forty toises, the points C and from the beginning of its foundation. D will be the saliant angles of the counterguards 6. The slopes of all parapets and traverses before the towers; from the points C and D are one-sixth of their breadth; that is, three feet draw the lines of defence Cc, Db, to the points towards the field, or the inside, where the ban- where the flanks of the towers cut the curquettes should be three feet higher than the out- tain; and which set off fifty-six toises for the side. faces of the counterguards; the flanks are found 7. When the revetment of a rampart goes as in the first method, and likewise the tenailles. quite up to the top, four feet of the upper part The ditch before the saliant angles of the towers is a vertical wall of three feet thick, with a square is six toises, and its counterscarp drawn to the stone at the top of it projecting six inches; and extremities of the flanks of the counterguards ; a circular one below, or where the slope begins, the right line which joins the ends of these flanks of eight or ten inches djameter ; they go quité will determine the inside of the tenailles. round the rampart, and the circular projection The ditch before the counterguards is twelve is called the cordon. Where the straight part toises at the saliant angles, and the counterscarp of the wall ends, and the slope begins, the wall is drawn to the opposite shoulders in the same is always made five feet thick; and the counter manner as in the first method. forts or buttresses reach no higher than that place. The capital of the ravelin is forty-five toises ; 8. When the rampart is partly walled and its faces, when produced, terminate on those of partly turfed, then one-fifth of the height which the counterguards, within ten toises of the shoulis turfed must be added to five feet, to get the ders; ten toises are cut off from the faces by thickness of the wall above. And, having the the flanks which are parallel to the capital as thickness of any wall above, by adding one-fifth usual. of its height from the bottom of the ditch, the The ditch before the ravelin is ten toises, the sum will be the thickness wall at the covert-way five, the semi-gorges of the places bottom; but, if a sixth part is only taken for the of arms twelve, the faces seventeen, and the slope, then a sixth part must be added. glacis twenty: For instance, suppose a rampart of thirty feet The following is the construction of M. Vauhigh from the bottom of the ditch, and that ten ban's third method, according to his plan of of these are to be turfed, then the fifth part of ten, New-Brisach. This method is applied to an ocwhich is two, added to five, gives seven for the tagon, whose exterior side, A B fig. 3, is 180 toises; wall above ; and as this wall is twenty feet high, the perpendicular CD thirty; the faces AK, the fifth of which is added four, and four to the BL, of the counterguards sixty; the flanks LN, thickness seven above, gives eleven for the thick- KM, are found by setting off twenty-two toises, ness near the foundation. Plate III. fig. 1, as chords to the arcs described from the opposite represents, in military perspective, the profiles shoulders as centres; from the extremities of the of the body of a place, the ravelin and covert- Aanks a line is drawn, which will be parallel to way: which gives a clear idea of what is meant the exterior side A B, meeting the capitals AE, by a profile, and from which those of all other BF, of the counterguards at G and H; this works may be easily conceived. line terminates the inside of the tenaille, as likewise the saliant angles G, H, of the tower- likewise disposed the covert-ways and dry ditches bastions. in such a manner that the besieger, not being able If EF be drawn parallel to GH, and at nine to dig the ground deeper than about one foot withtoises distant from it, the intersections E, F, with out finding water, may be obliged to convey to the capitals of the counterguards, will be the the spot the requisite materials for his lodgments centres of the towers; from which set off seven and the passage of the ditches in question. But toises from E to o for the semi-gorges, and draw this disposition, as well as the combined use that the tanks bc through the extremities of these Coeborn makes of wet and dry ditches, and which semi-gorges perpendicular to the line E F; these forms an essential part of his systems, evidently flanks are four toises inwards from a to c, and requires that the fortifications should be erected five outwards from a to b; the faces b G are in aquatic ground, as he supposes them to be. drawn from the point b to the point G, and the We shall therefore only advert to their principal lines joining the inside of the flanks at the end of and more general features. four toises will complete the towers. In his first system, Coehorn supposes the The ditch is six toises before the saliant angle polygon to be a regular hexagon, and that the of the towers, and its counterscarp meets the line surface of the water is but four feet lower than GH, within ten toises of the extremities M, N, of the ground. the flanks of the counterguards. Let therefore the interior side, AB plate IV. If from the point n, where the line E F inter- fig. 1, of an hexagon be 150 toises, take A C, BD, sects the perpendicular CD produced, you set each equal to thirty-nine, and the capitals A E, off five toises to the point r, and the lines of de- B F, each of eighty; and AG, BH, of forty; fence are drawn from the extremities of the semi- from the points E, F, draw the lines of defence gorges a of the towers through this point r: through the points D, C; and through the points then the flanks of the counterguards produced G, H, lines parallel to ED, FC; in which take will determine the little tlanks p, q, of the inside GI, HK, each equal to forty toises, for the rampart, and the extremities of these little flanks, length of the higher faces of the bastions. being joined, will give the curtain between them. To determine the lower faces EM, FN, draw The great ditch before the counterguards is 10 perpendicular to IG, equal to four toises ; fifteen toises, and its counterscarp parallel to the or parallel to IG, likewise equal to four; then faces; the capital of the ravelin is tifty-five toises, r M perpendicular to EM will determine the and that of the redoubt within it twenty-three; lower face E M. the faces of the ravelin are drawn to the faces of In order to determine the tower 3, see fig. 2, the counterguards within fifteen toises from the in r M, take rS of five toises; draw Sm parallel shoulders, and those of the redoubt parallel to to E M, and equal to fourteen; in (r produced these: twelve toises are cut off from the faces of take likewise r n equal to four, and in E M, MV, the ravelin, and six from those of the redoubt, by to eight; then if the points n, m, are joined by a the flanks which are parallel to the capital; the right line, and m, V, by an arc of sixty degrees ditch before the ravelin is twelve toises, and that you will have the outline of the tower. before the redoubt six; the covert-way and glacis The lines I (), and Or, express two walls, the are the same as in the second method. It must first has two embrasures, and the second three ; be observed, that the parapets of the counter- by which the author intended to defend the dry guards, on both sides of the saliant angles, are ditch, and the approach to the tower. raised four feet higher, for the space of twenty If from the points C, D, fig. 1, there be set off feet, above the rest, to prevent the enfilades of on the lines of defence fourteen toises to the the ricochet batteries. points Y, W, and upon each of the bases YI, WK, be described 'an equilateral triangle, the Sect. III.—OF THE Systems of M. Mingo, angles opposite to these bases, will be the centres BARON OF COEhorn. of the higher flanks Y I, W K. This officer, a contemporary with Vauban, was And if R be the intersection of the two lines a lieutenant general in the Dutch service, and of defence, R M bisected at S, and RC at Q; director general of all the fortified places belong- by drawing SQ, v SQ R will be half the tenaille; ing to the united provinces and along the Scheldt. and drawing from the point C. a line parallel He was the inventor of three systems of fortifica- to 1 Y, so as to meet the tower upon which the tion, in which he chiefly attended to the means mear flank is described in the same manner as of Aanking and covering the works as effectually the former. as possible, whilst those parts of the fortifications The parapets o, the three flanks, and those of which are advantageously situated for the be- the parts m V, V M, of the towers, are twentysieger's batteries, would not afford sufficient four feet thick ; the other parts M r,rnm, but He also liad for his object to sixteen ; and all the other parapets in general are facilitate an active and obstinate defence to the twenty feet. garrison; for which purpose he contrived such There is a wet ditch before the mean Alank dispositions as would, in his opinion, enable the of six toises broad, and another = behind besieged troops to oppose the besieged, within the towers of the same breadth, over which are the fortifications, with forces superior to his, and made two draw-bridges, parallel to the higher upon a larger front; besides securing the retreat faces. of these troops, and exposing those of the be The space X between the higher and lower sieger to the fire of the casemated batteries, co faces of the bastions is a dry ditch, whose bottom vered caponiers, crenelled galleries, and coffers, is but six inches above the surface of the water in which are employed in the systems. Cochorn the wet ditch. space for them. |