172 MILITARY SCIENCES. 



first frame, c (fig. 9), (chassis) is placed in the earth. The excavation is 

 now carried horizontally, placing new chassis, ef, every two or three feet, 

 and casing with boards as in the shaft, but only on three sides. For earth 

 of very loose consistence the chassis abc {fig. 7) is employed, which is put 

 together in the gallery in the manner shown at a c {fig. 8). If the excava- 

 tion is carried from the surface of the earth to the depth designed for the 

 bottom of the gallery, this is called working the gallery above ground {pi. 51, 

 figs. 1, 2, 3). Then strong beams, a {fig. 1), are laid across the space, and 

 sunk in the ground, so that they extend on each side three feet beyond the 

 side of the gallery, the breadth of which is determined by the beams, h, laid 

 upon these. These squares being dug out four feet deep, a new propping 

 is formed by means of the pieces c and d {figs. 1, 2), which are mortised 

 into the short pieces e {fig. 2), at five feet distance from each other, boards 

 having first been driven in behind b and e. The strips, h, keep the pieces 

 at the same distance. Fig. 3 shows the cross-section of the gallery. The exca- 

 vation being completed, the frame for a wooden gallery is set up, or a gallery 

 is built of mason-work. At the extremity of a mine gallery, a h {fig. 1 1), the 

 chamber, A, is hollowed in the side wall, hd, so that it stands six inches from 

 the top wall ; if the gallery has a fall, hd must be levelled. The size of the 

 chamber is governed by that of the box, gfcd {fig. 12), which it is to con- 

 tain, and which is filled through the vacant space a hfg. The box gfc d is 

 partly sunk in the floor h i. The saucisson, a tube one inch in diameter made 

 of canvas filled with powder {a, fig. 10), lies in the wooden fuse-case, hcde, 

 secured by the slings, g, and passes at e {fig, 12) into the powder-box, where 

 it is fast nailed. The powder-box being filled, is tamped in the following man- 

 ner. The vacant space, A {fig. 14), above the box, B, is filled with pieces of 

 wood ; in front of this powder-box 2-inch plank, h, are laid over one another 

 to the roof, c c, cased with the boards, a, braced by the pieces, d, and then 

 the vacant space filled with stone. The part of the tamping, cccc {fig. 27), 

 being completed, the gallery along C c is tamped with stone or sand-bags, 

 strengthened every six feet by pieces of wood, e. When the mine is to be 

 fired, the end of the saucisson is nailed upon a board, cut open, and set off 

 by a piece of lighted tinder. For this purpose the box-trap {fig. 15) is used. 

 Upon its slide, A, lies the tinder, b, which, when the slide is drawn out, falls 

 and kindles the powder at c. If a number of fourneaux are to be fired at 

 the same time, for instance ten fourneaux, A {fig. 16), the saucissons are 

 laid as shown in that figure. If saucissons are led from the fourneaux only 

 to the main gallery {fig. 17), at each entrance by a small gallery, a block, A 

 {figs. 17 and 18), with a ring, x, and at the turn of the gallery, the block 

 B {figs. 17 and 19), with the roller y, are fixed, and then a cord, soaked in 

 iinseed oil, led through the rings and over the roller ; by means of this cord 

 the slides of all the box-traps in^^. 16 can be drawn at once. The charge 

 of a mine is regulated according to the effect desired from it. When a 

 mine, a {pi. 51, fig. 20), is fired in firm ground, it first lifts the earth above 

 it in a gentle hill {fig. 33) ; this hill being raised so far that its boundary 

 extends to the margin of the crater of explosion, hhhh {fig. 20), flame and 

 smoke break out, and then follows the explosion ; a part of the earth is 

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