/j82
rhouUl be lowest, that they may be commanded by those that arenearer.
11. None of the works should, if it can4>e helped, be beyond thepoint bank reach of the cannon within the tow n.
!2. Wet ditches are preferable for small places, dry ones forlarge places.
13. Bastions with large flanks and large gorges are much es-teemed.
14. The flanked angles of bastions should not be much less thana right one, but arc better when obtuse not exceeding 120 or 130degrees.
15. The faces of bastions should in length not differ much from100 yards.
16. A curtin should not be much longer than 180 yards, nor muchshorter than 100 yards.
17. The angle of the curtin should be between the limits of 90and 100 degrees.
The art of fortification is divided into two parts; regular andirregular.
o
Regular Fortification is that built in a regular polygon, the sidesand angles of which are all equal, being commonly about a mus-ket-shot from each other. Although authors agree as to the ge-neral form iu the present manner of fortifying, yet they mostly (lif-ter in particular constructions of the parts. As it would be su-perfluous to treat of all the different methods hitherto proposed,we shall explain those only which are most esteemed by the bestjudges, and have been most generally practised.
CONSTRUCTION OF THE MEAN FORTIFICATION', ACCORDINGto M. Vauisan’s Method.
Vauban ’s method is divided into little, mean, and great; the j
little is chiefly used in the construction of citadels, the mean in thatof all sorts ot towns, and the great in particular cases only. Weshall give t lie construction of the mean, as being most useful; andrefer the reader to the follow ing table, for those dimensions whichare different in these several fortifications. Inscribe in a circle apolygon of as many sides as the fortification is designed to havefronts; let AB, fig. I. Plate LXXIV, be one of the sides of half ahexagon, which bisect by the perpendicular CD ; divide half ofit AG into nine equal parts, and one ot these into 10 others; thenthese divisions will serve as a scale to construct all the parts of fhefortification, and each of them is supposed to he a toise or fathom,,that is, six’ French iecf, or somewhat more than 5' English feet;and therefore the whole side AB is supposed lobe 180 toises. Asthe dividing of a line into so many equal parts is very troublesome,it is much easier to have a scale of equal parts by which the worksmay be constructed. If therefore, in this case, the radius is takenequal to 180 toises, and the circle described with that radius beingdivided into six equal pails, or the radius being carried six tiino*round, we will have an hexagon inscribed ; AB being bisected bythe perpendicular CD as before, set oil' 30 toises from C to D,and draw the indefinite lines ADG, BDF ; in which take the partsAE, BH, each equal to 50 toises; from the centre E describe anare through the point 11, meeting AD in G, and from the centre11 describe an arc through the point E, meeting BD ini'; orwhich is the same, make fcach of the lines EG, I IF, equal to thedistance Ell ; then the lines joining the points A,E,F,G,11,B, willbe the principal or outline of the front. If the same constructionhe performed on the other sides of the polygon, we will have theprincipal or outline of the w hole fortification. If, with a radius ot20 toises, there be described circular arcs, from the angular pointsB,A,M,T, and lines are drawn from the opposite angles, E,I1, &c.so as to touch these arcs, their parts a h, h c, A'c. together with thesearcs, will represent the outline of the ditch.
'Table of Dimensions.
1
Forts.
Mean.
Great.
80
90
too
110
1 20
130
140
150
160
170
180
190
200
260
Perpendiculars.
10
11
124
14
15
16
20
21
23
25
30
31
25
22
Faces of Bastions,.
22
25
28
30
33
35 !
40
42
45
47
50
35
55
60 ,
Capital of Ravelin,.
25
28
30
35
33
40
45
50
50
52
55
55
60
50
Tn the first vertical column are the numbers expressing thelengths of the exterior sides from 80 to 260. In the second, theperpendiculars answering to these sides. In the third, the lengthsof the faces of bastions; and in the fourth, the lengths of the ca-pitals of the ravelins. 'The forts are mostly, if not always, squ ares:for which reason, the perpendiculars are made one-eighth of theexterior sides; because if they were more, the gorges of the bas-tions would become too narrow. 1 he little fortification is chieflydesigned for citadels, which are commonly pentagons; the perpen-diculars are made one-seventh of the exterior side: the mean isused in all kinds of fortifications, from an hexagon upwards to anynumber of sides; and the great is seldom used but in an irregularfortification, where there are some sides that cannot be made lesswithout much expence ; or in a town which lies near a great river,where the side next the river is made from 200 to 260 toises: andas that side is less exposed to be attacked than any other, the per-pendicular is made shorter, which saves much expence. 'Thefaces of the bastions are all tw o-sevenths of the exterior sides, ornearly so, because the fractions are neglected. In general, in allsquares the perpendicular is one-eighth of the exterior side, and allpentagons one-seventh, and in all tnerest upward one-sixth.
Of the Construction of Orillons and retiredFlanks.
Describe the front MPQRST as before, and divide the flanknto three equal parts, of which suppose Sr to be one ; from the.jopposite flanked angle M draw a line Mr, in which take the part 1mr of five toises; take likewise lln in the line of defence MR,
| produced, equal to five toises, and join n m, upon which as aj base describe the equilateral triangle n /) m, and from the angle /),opposite to the haw as centre, is described the circular think mu.Ami if Sr he bisected by a perpendicular, ami another he erectedupon the face ST, at S ; the intersection of these two perpendicu-lars will be the centre of the are which forms the orillon. Theorillons are very useful in covering the retired flanks, which can-not he seen hut directly in the front; and as these orillons areround, they cannot be so easily destroyed as they would he if theywere of any other figure.
Construction of Ravelins or Half-moons.
Fig. 1. No. 1. Set off 55 toises, from the re-entering angle O ofthe counterscarp, on the capital OL, or on the perpendicularproduced; and from the point I, draw lines to die shoulders AB twhose parts EM, LN, terminated by the counterscarp, will l ,ethe faces, and MO, ON, the semi-gorges of the ravelin required.'This is Mr. Vauban ’s method of constructing ravelins, accordingto some authors : and qtliers will have the faces of the ravelin toterminate on those of the bastions within three toises of the should-ers ; which seems to be the best way, for these ravelins cover theHanks much better than the others. T'se ditch before the ravelinis 12 toises, its counterscarp parallel to the faces of the ravelins;and is made in a circular are, before the valiant angle ; as likewiseall ditches are in general. When the ravelins are made with flanks,as in fig. 2, the faces should terminate on those of the bastions, atleast five toises from the shoulders. The Hanks are made by set 1ting off 10 toises from the extremities of the faces, from /to h, andy from