The usual method of directing the trenches or zig-zags, is by observing during the day some near object in a line with the salient parts of the work, and which may serve as a direction in the night; or if the night be not very dark, the angles of the works maybe seen above the horizon; but as both these methods are subject to uncertainty, the following is proposed, to answer every case: having laid down the plan of attack, the exact positions of the flanked angles of the works of the front attacked, and particularly of those most extended to the right and left, mark on the plan the point of commencement for the first portions of zig-zag; the point where it crosses the capital; and the point to which it extends on the other side of the capital: this last point will be the commencement of the second branch; then mark off the point where this branch crosses the capital and its extent on the other side; and this will give the commencement of the third branch; and so on for the others. Thus provided with a plan ready marked off, it will be very easy, even in the darkest night, to lay down the points where the zig-zags are to cross the capital, and the points to which they are to be produced beyond them. The first parallel is generally run about 600 yards from the place, and of such extent as to embrace the prolongations of the faces of all the works which fire upon the trenches; and each end has a return of about 30 or 40 yards. The second parallel is constructed upon the same principles, and of the same extent as the first; at the distance of about 300 yards from the salient angles of the covert way. This parallel is usually formed of gabions, each workman carrying a gabion, a fascine, a shovel, and a pick ax. After this the trenches are usually carried on by sap.—See that word. The half parallels are about 140 or 150 yards from the covert way, and extend on each side sufficient to embrace the prolongation of the branches of the covert way. The third parallel must not be nearer than the foot of the glacis, or it will mask the ricochet batteries. It is generally made rather wider than the other parallels. Cavaliers of the trenches must not be nearer than 28 yards from the covert way, or they will be liable to be annoyed by hand grenades. See likewise the words _Approaches_, _Sap_, and _Battery_. _TROU DE LOUP_—A cone reversed. Diameter of the base 4 feet 6 inches; depth 6 feet; picket 6 feet long, and from 4 to 5 inches square; contain ¾ of a cubic fathom of earth, and are usually placed 2 in 3 fathoms. _TUBES_—of tin plates are the best for service. Tubes must pass through a gauge of ²/₁₀ of an inch diameter. The composition is mealed powder, mixt up stiff with spirits of wine. They are made up in bundles of 100 each. _Length of Tin Tubes._