FORTIFICATION. 



ther curved or straight, for the flanks of 

 the bastions. If they are to be curved, 

 which are generally preferred, the points 

 t and 10 will be the centres of equal cir- 

 cles, whereof the two flanks will be equal 

 segments. 



Proceed in the same manner with the 

 other two fronts, AH and CD ; you will 

 thus complete two bastions, 3 and 4, and 

 the halves of two more, 2 and 5. Next 

 measure off' 15 toises, and draw something 

 less than quadrants, or quarters of circles, 

 from the points B and C ; the centres of 

 those quadrants being exactly opposite 

 thereto, place your scale so that you may 

 draw lines from the ends of the quadrants 

 towards the shoulders of the bastions, but 

 draw no further than suffices to touch 

 upon the perpendicular of 30 toises : thus 

 your scale would give the direction, / iv, 

 but your line would stop a little below d. 

 This being done in both directions, and 

 throughout the three faces, will give the 

 width of the ditch, and the interior lines 

 or re-entering angles of the ravelines O, 

 N, K. The body of the raveline is form- 

 ed by measuring 10 toises on the face of 

 each bastion, setting off from the shoul- 

 ders t iv towards the saliant, or projecting 

 angles, (here called flanked angles,) B 

 and C. An opening of the compasses 

 equal to u TV, (or to i v,) with the ten 

 toises included, will give the distance of 

 the saliant angle o, of the raveline N, 

 from the centre S, of the curtain u v. 

 The sides or faces of the ravelines, are 

 determined by lines, drawn from the sa- 

 liant angle to those points on the faces of 

 the bastion 3 and 4, already set off at 10 

 toises each, from their respective shoul- 

 ders t and -w. 



It should have been stated, that all an- 

 gles projecting outward from the body of 

 the place, are called saliant angles : for 

 instance, s, B, t, of bastion 3, and e, o, e, 

 of the raveline N : while such angles as 

 point inwards towards the body of the 

 place are designated re-entering angles ; 

 such as t, u, 70, on the lines of defence of 

 the centre face. When an angle re-enters 

 at such a position in the outworks, that its 

 apex or point cannot be seen, and con- 

 sequently cannot be defended from the 

 body of the place, it is called a dead an- 

 gle. Such cannot easily take place, where 

 the smallest attention is paid to the most 

 ordinary rules; but, wherever found, 

 should be exploded from the defences, 

 either by cutting off' a large part of the 

 pinch, or narrowest part, and substituting 

 a curtain, or by new modelling the de- 

 fences in that part. It may be proper to 

 observe in this place, that works intended 



VOL. V. 



for mutual defence should never exceed 

 an angle of 120 degrees, nor be less than 

 60. The medium, i. e. 90, which forms a, 

 right angle, generally considered, is indis- 

 putably the best for the above purpose. 

 Where batteries stand at such an open- 

 ing, that their direct fire, that is immedi- 

 ately to their own front, is parallel with 

 the front of the part they flank, it is call- 

 ed a razunt, or grazing fire ; but when the 

 angle is less than 90, so that the direct 

 fire would strike upon the face of the 

 work to be defended, it is termed fish- 

 ant, or plonging : both have their uses, 

 but the latter is rarely adopted, except 

 from necessity, because a direct fire, at 

 right angles, may be made to plonge, by 

 giving the cannon an inclination more pa- 

 rallel with the side of the embrasure, 

 which being angular, allows a deviation of 

 many degrees from the direct fire. 



When two lines form a very acute an- 

 gle with each other, they no longer are 

 defences ; for in case the enemy should 

 carry either of them, he would be able to 

 work its battery against the other line ; 

 and though the fire would be plonging, 

 and that too at a great disadvantage, yet, 

 as many shots would light within the em- 

 brasures, the parapet would speedily be 

 destroyed. The revetement, or masonry, 

 in thejfront of the line, so plonged, would 

 not be much hurt, as it would turn off the 

 shots. 



Before we proceed farther, it is expedi- 

 ent that the reader should examine the 

 line of the principal, following along A, 

 o, S, r, s, B, t) u, v, -w, C, b, y, z, m, D ; in 

 all which he will perceive, that every part 

 is made to flank some other. The rave- 

 lines O, N, K, will be found to give great 

 security to their several curtains, s r, u v, 

 and yz ; while at the same time they 

 wouldenfiladewhateverapproachesmight 

 be made towards the saliant angles of the 

 bastions. In examining these circum- 

 stances, all the other outworks must be 

 exempted from consideration ; our view 

 must be confined to the manner in which 

 the gates in the curtain are protected ; the 

 flanks of the bastions concealed from 

 every part but the line of their direct 

 fire ; and the spaces opposite the saliant 

 tingles subjected to a heavy cross fire. 

 The ravelines, themselves, stand at too 

 wide an angle to absolutely flank each 

 other, but they are capable of scouring 

 the glacis reciprocally, and would, as be- 

 fore remarked, subject the besieger to a 

 dangerous enfilade, or flanking fire, were 

 he to proceed without due attention to 

 their obnoxious positions. In works of 

 more Sides, where the angles of the bas- 



C c 



