166 MILITARY SCIENCES. 



parallel to each other at 4 feet distant. It is 10 feet wide at the bottom, 

 and is employed in advancing upon the capitals of the work. The double 

 sap being completed, ordinary laborers throw out the intervening mass of 4 

 feet thickness of earth. 9. The direct double sap, or double sap with tam- 

 hour traverses {fig. 10), consists of two single traverse saps, the parapets 

 of which are turned outwards, and which run parallel to each other, 12 

 feet apart. At fixed points, A, the one sap turns at right angles to the 

 right, the other to the left, and then to the left and right twice, until they 

 again come together, and so on ; thus arise the 24 feet traverses, B, which 

 cover the passage, C. The masses of earth, G, are thrown out afterwards. 

 These saps go out from the third parallel upon the salients of the covered- 

 way. 



If the ground is unfavorable for the sap, various means must be applied. 

 Thus, a, on rocky ground, where there is only one foot of earth {pi. 48, 

 fig. 11), from two to three rows of gabions are set up, one foot from the 

 trace, and filled with the earth which is at hand. If necessary, the parapet 

 is heightened by the fascines, yy, and the banquette made of sand-bags, z, 

 or several rows of gabions, x {fig. 12), are placed one on the other, and the 

 banquette, z, made of fascines, h. Upon naked rock {fig. 13) the materials 

 for filling must all be brought. Several rows of gabions, x, are set up and 

 filled with sand-bags, y, with which also the parapet is completed, and a 

 banquette, z, made. If, on such ground, a sap is to be carried forward 

 under fire of the enemy's small arms {fig. 14), then the blind, A, is set up 

 before the commencement of the work, and only under its cover is the 

 parapet, B, to be constructed of gabions, a:, and fascines, and of the earth 

 brought from the rear. c. On marshy ground {fig. 15), if at a distance from 

 the place, a dyke, ab, is constructed of water-fascines laid crossing each 

 other, and the required earth taken from the ditches, qq. The parapet, x, 

 is 6 feet high, of fascines with earth, and the banquette, z, of fascines or 

 sand-bags. If the work is under fire {fig. 16), a dyke, ab, is made, like a 

 ,sap, behind a rolling gabion, and as soon as it is completed the parapet is 

 constructed of three rows of gabions, x, and an upper row, y, but the ban- 

 quette is made of sand-bags, z. If the soil is only swampy in parts, the 

 communications may be preserved over these by means of wooden trestles, 

 m {fig. 17 ^ front view, fig. 17 ^ side view), which are pressed down into 

 the soft earth, bridged over, and covered by the blind A. d. Upon over- 

 flowed ground, the construction is as in fig. 15 ; but when water is found 

 at the depth of two feet, the parapet is built of earth, x {fig. 18), taken from 

 the ditches, qq, run in front and rear. When this work is done under fire 

 {fig. 19), the blind, A, is set up in front, and the parapet, x, is made, either 

 of gabions or fascines entirely, or earth is thrown up in aid from a ditch 

 run in the rear. 



2. Works of the Third Parallel. The third parallel, gg {fig. 3), being 

 completed, approaches are pushed forward by the direct double sap, y, and, 

 on arriving within about one hundred feet of the places-of-arms of the 

 covered- way, curved trenches, oo, are carried to the right and left, from the 

 corners m m, until they reach the prolongation of the faces of the covered- 

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