PIONEER AND PONTOON SERVICE. 171 



a, the posts, h, the cross-pieces, g, and the string-pieces, c, the lining of the 

 boards, e, and the pieces, d. Upon the string-pieces, c, and the roof-beams, 

 q, the fascines, hh, a bed of loam, /, and finally a bed of common earth, K. 

 The roof is braced by the strutts, w, which are mortised into the sleepers, n, 

 and the whole structure is protected by the embankment, m, against the 

 hostile shot. If the bottom is moist, a foundation is requisite according to 

 fig. 49. The gates are all barricaded ; bomb-proof barracks are built ; and 

 all the parapets of the covered- way made accessible by means of sally-ladders, 

 A (fig. 50), supported upon posts, x. The next step is the arrangement of 

 cut-offs in the attacked bastions, ravelins, and places-of-arms. If the bas- 

 tions are hollow, it is best to close the gorges by a straight line, but for full 

 bastions the proper cut-offs are shown in pi. 49, figs. 28, 29, 30, and 31; 

 in the demi-lune a redoubt, A, is placed (fig. 32), with flanks, pq, and in the 

 faces the coupures, vwx. The branches of the covered-way are strength- 

 ened by the double palisades, w (fig. 33), between the traverses, P and V. 

 Fig, 34 gives the ground plan of a wooden tambour in the salient place-of- 

 arms ; fig. 35, its section. The interior space, p, of the tambour is so nar- 

 row, that shells falling upon the roof-screen, w, roll over the counterscarp 

 into the ditch. 



G. PIONEER AND PONTOON SERVICE. 



1. Mines. 



Thus far we have treated only of attack and defence above ground ; but 

 there is a subterranean warfare also, carried on by means of mines, and 

 this is the duty of the corps of sappers and miners or pioneers, and its rules 

 form a separate department of engineering. If gunpowder be inclosed in 

 mason-work, earth, or rock, and then fired, the explosion drives away all 

 the parts which can yield. Such an arrangement, so prepared as to be fired 

 at any instant, is called a mine ; the inclosure containing tne powder is the 

 chamber, but the chamber itself when filled is the oven (fourneau). Mines 

 are employed to blow up the walls of the fortification, the works of the 

 besiegers, and in case of necessity part of their troops. In the practice of 

 mining, a shaft is first sunk, and from its bottom a gallery, the mine-gallery, 

 carried out to the spot where the fourneau of the mine is to be placed. To 

 sink a shaft, a curb {pi. 51, fig. 5), abed, whose cross-pieces lap eighteen 

 inches over each other, is first sunk ; the excavation continues until the 

 second curb, ab (fig. 6), is laid, and then boards, a (fig. 4), are thrust down 

 between the curbs and the earth. Between the boards, a, and the second 

 curb come wedges, and the two curbs are connected by strips, b. The 

 excavation is now continued to the third curb, cased, and so on till the 

 shaft is deep enough. The curbs are placed four or five feet from each 

 other, the two last, however, being always the height of the intended gallery 

 apart. The side of the shaft, when this is to lead out, is not cased, but the 



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