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Fig.6.

Fig.9.

Fig. 1.

Fig.13.

London.Published by Thomas Tegg, 73 Cheapside August 1.1827.

D

PLATE I

M

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J. Shury, sculp

OF M. VAUBAN.

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 : guns might be placed in the covert-way and outworks to obstruct the enemy's approach; and, when they come near the place, they might be transported into the inner works; and, as the body of the place would be much lower, the expense would be considerably diminished. It should not, however, be forgotten that, when works are low, they are easily enfiladed by the ricochet batteries, though this might be partly prevented by making the parapets near the saliant angles, for the space of eight toises on each side, five or six feet higher than the rest of the works.

2. The covert-way should be lower than the level ground, otherwise the body of the place must be raised very high, especially where there are several outworks: this is to be understood only when the works exceed each other in height, otherwise it need not be below the level.

3. The bases of all inward slopes of earth should be at least equal to the height, if not

more.

4. The bases of all outward slopes of earth, two-thirds of their heights.

5. The slopes of all walls or revetments should be one-fifth of their height; or one-sixth might, perhaps, be sufficient; the height of a wall is estimated from the bottom of the ditch, and not from the beginning of its foundation.

6. The slopes of all parapets and traverses are one-sixth of their breadth; that is, three feet towards the field, or the inside, where the banquettes should be three feet higher than the outside.

7. When the revetment of a rampart goes quite up to the top, four feet of the upper part is a vertical wall of three feet thick, with a square stone at the top of it projecting six inches; and a circular one below, or where the slope begins, of eight or ten inches diameter; they go quite round the rampart, and the circular projection is called the cordon. Where the straight part of the wall ends, and the slope begins, the wall is always made five feet thick; and the counterforts or buttresses reach no higher than that place. 8. When the rampart is partly walled and partly turfed, then one-fifth of the height which is turfed must be added to five feet, to get the thickness of the wall above. And, having the thickness of any wall above, by adding one-fifth of its height from the bottom of the ditch, the sum will be the thickness of the wall at the bottom; but, if a sixth part is only taken for the slope, then a sixth part must be added.

For instance, suppose a rampart of thirty feet high from the bottom of the ditch, and that ten of these are to be turfed, then the fifth part of ten, which is two, added to five, gives seven for the wall above; and as this wall is twenty feet high, the fifth of which is added four, and four to the thickness seven above, gives eleven for the thickness near the foundation. Plate III. fig. 1, represents, in military perspective, the profiles of the body of a place, the ravelin and covertway: which gives a clear idea of what is meant by a profile, and from which those of all other works may be easily conceived.

M. Vauban's Second and Third Systems were chiefly designed, as we have stated, to protect the besieged from the ricochet fire of his own invention, and to improve the near defence. To accomplish these and some minor purposes, he composed the body of the plan of works which resemble small bastions, and are called towerbastions. His second method is thus exemplified. He begins his construction inwards, and fortifies outwards, which is found a very convenient plan for improving a place.

Let A B, Plate III. fig. 2, be the interior side of an hexagon of 120 toises, some authors will have it 130, and say that they are so at Landau, draw AC, BD, from the centre through the extremities of the sides; set off six toises from A to b, and from B to c; through the points b and c, draw lines at right angles to AB, from the point b set off six toises to foutwards, and four from b to d inwards; and from the points f,d, draw perpendiculars fr, d n, to the capital AC; then, if r E is made equal to rf, the point E will be the saliant angle of the tower bastion; and E fd n half that tower.

If in the capitals there be taken from the saliant angles of the tower-bastions, the distances EC, FD, each of forty toises, the points C and D will be the saliant angles of the counterguards before the towers; from the points C and D draw the lines of defence Cc, Db, to the points where the flanks of the towers cut the curtain; and which set off fifty-six toises for the faces of the counterguards; the flanks are found as in the first method, and likewise the tenailles.

The ditch before the saliant angles of the towers is six toises, and its counterscarp drawn to the extremities of the flanks of the counterguards; the right line which joins the ends of these flanks will determine the inside of the tenailles.

The ditch before the counterguards is twelve toises at the saliant angles, and the counterscarp is drawn to the opposite shoulders in the same manner as in the first method.

The capital of the ravelin is forty-five toises; its faces, when produced, terminate on those of the counterguards, within ten toises of the shoulders; ten toises are cut off from the faces by the flanks which are parallel to the capital as usual.

The ditch before the ravelin is ten toises, the covert-way five, the semi-gorges of the places of arms twelve, the faces seventeen, and the glacis twenty.

The following is the construction of M. Vauban's third method, according to his plan of New-Brisach. This method is applied to an octagon, whose exterior side, A B fig. 3, is 180 toises; the perpendicular CD thirty; the faces AK, BL, of the counterguards sixty; the flanks LN, K M, are found by setting off twenty-two toises, as chords to the arcs described from the opposite shoulders as centres; from the extremities of the flanks a line is drawn, which will be parallel to the exterior side A B, meeting the capitals AE, BF, of the counterguards at G and H; this line terminates the inside of the tenaille, as

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If EF be drawn parallel to GH, and at nine toises distant from it, the intersections E, F, with the capitals of the counterguards, will be the centres of the towers; from which set off seven toises from E to a for the semi-gorges, and draw the flanks bc through the extremities of these semi-gorges perpendicular to the line EF; these flanks are four toises inwards from a to c, and five outwards from a to b; the faces b G are drawn from the point b to the point G, and the lines joining the inside of the flanks at the end of four toises will complete the towers.

The ditch is six toises before the saliant angle of the towers, and its counterscarp meets the line GH, within ten toises of the extremities M, N, of the flanks of the counterguards.

If from the point n, where the line EF intersects the perpendicular CD produced, you set off five toises to the point r, and the lines of defence are drawn from the extremities of the semigorges a of the towers through this point r: then the flanks of the counterguards produced will determine the little flanks p, q, of the inside rampart, and the extremities of these little flanks, being joined, will give the curtain between them. The great ditch before the counterguards is fifteen toises, and its counterscarp parallel to the faces; the capital of the ravelin is fifty-five toises, and that of the redoubt within it twenty-three; the faces of the ravelin are drawn to the faces of the counterguards within fifteen toises from the shoulders, and those of the redoubt parallel to these twelve toises are cut off from the faces of the ravelin, and six from those of the redoubt, by the flanks which are parallel to the capital; the ditch before the ravelin is twelve toises, and that before the redoubt six; the covert-way and glacis are the same as in the second method. It must be observed, that the parapets of the counterguards, on both sides of the saliant angles, are raised four feet higher, for the space of twenty feet, above the rest, to prevent the enfilades of the ricochet batteries.

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This officer, a contemporary with Vauban, was a lieutenant general in the Dutch service, and director general of all the fortified places belonging to the united provinces and along the Scheldt. He was the inventor of three systems of fortification, in which he chiefly attended to the means of flanking and covering the works as effectually as possible, whilst those parts of the fortifications which are advantageously situated for the besieger's batteries, would not afford sufficient space for them. He also had for his object to facilitate an active and obstinate defence to the garrison; for which purpose he contrived such dispositions as would, in his opinion, enable the besieged troops to oppose the besieged, within the fortifications, with forces superior to his, and upon a larger front; besides securing the retreat of these troops, and exposing those of the besieger to the fire of the casemated batteries, covered caponiers, crenelled galleries, and coffers, which are employed in the systems. Coehorn

But

likewise disposed the covert-ways and dry ditches in such a manner that the besieger, not being able to dig the ground deeper than about one foot without finding water, may be obliged to convey to the spot the requisite materials for his lodgments and the passage of the ditches in question. this disposition, as well as the combined use that Coehorn makes of wet and dry ditches, and which forms an essential part of his systems, evidently requires that the fortifications should be erected in aquatic ground, as he supposes them to be. We shall therefore only advert to their principal and more general features.

In his first system, Coehorn supposes the polygon to be a regular hexagon, and that the surface of the water is but four feet lower than the ground.

Let therefore the interior side, AB plate IV. fig. 1, of an hexagon be 150 toises, take A C, BD, each equal to thirty-nine, and the capitals A E, BF, each of eighty; and AG, BH, of forty; from the points E, F, draw the lines of defence through the points D, C; and through the points G, H, lines parallel to ED, FC; in which take GI, HK, each equal to forty toises, for the length of the higher faces of the bastions.

To determine the lower faces EM, FN, draw IO perpendicular to IG, equal to four toises; or parallel to IG, likewise equal to four; then r M perpendicular to EM will determine the lower face E M.

In order to determine the tower 3, see fig. 2, in r M, take rS of five toises; draw Sm parallel to E M, and equal to fourteen; in Or produced take likewise rn equal to four, and in EM, M V, to eight; then if the points n, m, are joined by a right line, and m, V, by an arc of sixty degrees you will have the outline of the tower.

The lines I O, and Or, express two walls, the first has two embrasures, and the second three; by which the author intended to defend the dry ditch, and the approach to the tower.

If from the points C, D, fig. 1, there be set off on the lines of defence fourteen toises to the points Y, W, and upon each of the bases YI, W K, be described an equilateral triangle, the angles opposite to these bases, will be the centres of the higher flanks Y I, W K.

And if R be the intersection of the two lines of defence, R M bisected at S, and RC at Q; by drawing SQ, v SQR will be half the tenaille; and drawing from the point C, a line parallel to IY, so as to meet the tower upon which the mean flank is described in the same manner as the former.

The parapets o. the three flanks, and those of the parts m V, V M, of the towers, are twentyfour feet thick; the other parts Mr, rnm, but sixteen; and all the other parapets in general are twenty feet.

There is a wet ditch before the mean flank of six toises broad, and another z behind the towers of the same breadth, over which are made two draw-bridges, parallel to the higher faces.

The space X between the higher and lower faces of the bastions is a dry ditch, whose bottom is but six inches above the surface of the water in the wet ditch.

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