Iron and wooden truss-bridges should be thrown down by breaking the main braces near the piers, or the chords near the centre, by charges placed in a joint if possible. High explosives are particularly valuable for this purpose. In wooden bridges they may be placed in auger-holes bored for them, and in iron bridges inside the hollow members, between eye-bars, or in other similar places. =107. Tunnels, Canal-locks=, and similar constructions must be attacked with large charges, so placed as to temporarily or permanently disable the work, as may be considered necessary. The location of each charge should be determined and its amount computed from these considerations before the destruction is attempted. A temporary obstruction is frequently all that is necessary or desirable for these works, and the damage done to them should be carefully regulated with a view to their subsequent repair and use. =108. Railroads.=--Railroads are temporarily disabled by tearing up the track, making hot fires of piles of ties, placing the rails upon them so that they will heat and bend by their own weight; or, better still, twisting the rails while hot by suitably-shaped steel hooks and wooden levers of the kind devised by General Haupt (Pl. XII, Fig. 33). Rails so twisted cannot be again used until re-rolled. =109. Rolling-stock.=--Railroad cars may be disabled by breaking one or more wheels with sledges, or may be destroyed by burning. Locomotives may be disabled temporarily by carrying away the smaller parts of the mechanism, or permanently by breaking the engine-cylinders with sledges; bursting the boilers or burning out their fire-boxes by drawing out nearly all their water, fastening down the safety-valves, and building a hot fire in the furnaces; or by making a hot fire under them so as to heat and thus bend or warp the reciprocating parts of the machinery. =110.= In all hasty demolitions with explosives the charges should be well in excess of those computed by the ordinary rules: first, because the explosives will not be so placed as to act to the greatest advantage; and, second, because the demolition should be _immediate_ and _complete_. INDEX. A PAGE Additional operations--intrenched camps, 91 Advance from first parallel, 84 Advanced positions, 104 Advantage lies with attack, 176 Ammunition, 44, 57, 101 Angle template, 137, 148 Approaches, 16 Approaches, execution of, 20-3 Approaches, tracing, 18 Approaches, over-ground, 31