FORTIFICATION. 149 



whether they are to be provided with artillery. Inclosed works are either 

 those whose polygon sides are straight sides, redoubts, or flanked works, 

 whose polygon sides are therefore broken field-forts. Redoubts may be 

 triangular, square, or polygonal, but with the number of sides increases 

 also the number of dead-angles (which cannot be defended), and therefore 

 redoubts with more than four sides are unserviceable. The side of a 

 redoubt which is to be defended only by infantry, must not inclose more 

 than 96 feet, and then a garrison of 360 to 390 men is required. If defended 

 by artillery, from 12 to 18 feet are reckoned along the crest for every 

 piece. In estimating the interior space of a redoubt, nine square feet are 

 reckoned for each man, and for each gun 360 square feet, Redoubts are 

 never constructed with sides of less than 42 feet. 



Field forts may be regular or irregular. The regular are : star forts, and 

 forts with half or with whole bastions. Star forts are redoubts having 

 their side once broken, so that they have only salient and re-entering 

 angles and no flanks ; they have usually from 8 to 12 points. A star fort, 

 if it have not more than twelve sides, is laid out by drawing a polygon of 

 the given number of sides, in such a manner that these sides, b b (Jig. 36), 

 are of the length which is to be given to the faces of the work. Then 

 upon each polygon side construct an equilateral triangle, b ab, and the line 

 of fire is completed. If, however, the position of the ground determines the 

 salient angles of the star fort, then in the centre of the sides of the polygon 

 uniting the vertices of the salient angles, perpendiculars are erected, which 

 are made } the length of their sides, and upon the points thus obtained the 

 faces are drawn. 



Forts with half bastions are laid out as follows : If a triangle is to be 

 defended with half bastions (pi. 47, Jig. 11), draw a triangle, ///, whose 

 sides have collectively f the length of the total line of fire (on which the 

 defenders stand), prolong the sides, ff J, of this triangle towards a, so that 

 fa = iff' Lay off from /to e, a distance equal to ^ ff, and erect, at e, a 

 perpendicular, which intersects the line af at d, and completes the half 

 bastion, a d being the face, de the flank, and ea the curtain. If a square is 

 to be half bastioned (Jig. 12), erect in the middle, c, of the polygon side, a a, 

 the perpendicular, cb = \ aa, draw the lines bcx, lay off, upon these lines 

 *of defence, the parts a d = ^ a a, and let fall from d the perpendiculars, de, 

 upon the corresponding lines of defence ; g h, are the lines of direction of 

 the defenders' fire. The polygon side of a square with half bastion may be 

 240 to 600 feet, and the polygon is the stronger the more sides it has. 



Forts with whole bastions belong rather to permanent fortifications. To 

 construct them, erect in the centre, c, of the polygon side, a a (Jig. 13), a 

 perpendicular, c b, which for the square must be i, for the pentagon }, and 

 for the hexagon, &c., }, of the length of the polygon side. Then draw 

 from a, through the points b, the lines abx, make ad = ^ a a, and let fall 

 from d, the perpendiculars de, upon the corresponding lines of defence, 

 when ee are the curtains, de the flanks, and da the faces of the work. 

 The curtain, which in the front. A, is straight, may be broken outwards 

 as in the front, C, once, or twice as in the front, B, where//— ^ ee. By 



ICONOORAPHIC ENCYCLOPEDIA. — VOL. III. 40 625 



\ 



