The beginner has a tendency to exaggerate the proximity of sounds. He thinks he is close to the enemy when he is still at a distance, and he takes steps to catch the enemy by exploding a camouflet, whose only effect is to retard his own work. USEFUL INFORMATION ON MINES. _Defensive system._--Two arrangements can be adopted: Fan-shaped arrangement (Fig. A) or arrangement of independent parallel galleries (Fig. B). The second arrangement is preferable. _Interval between galleries._--Arrangement 2 being adopted, calculate the interval between two neighboring galleries in such manner as to prevent the enemy working underground. At the head of each gallery two elbows of 6 meters, with boring chambers, are made. A 6-meter boring is made from each chamber. At the bottom of the boring a camouflet is placed, effective for radius of 6 meters (not more heavily charged or the gallery will be demolished). The camouflet of the neighboring gallery forms a tangent to the first. The interval between the two galleries can not, therefore, be greater than 36 meters. In practice we would take 30 meters. _Start, depth, and progress of work._--Start from first line. Start at 4 meters, with a slope of 20 per cent to 30 per cent down to a depth of 10 meters. Then horizontal. Length to gallery and return without ventilation can cover 30 meters. [Illustration: Fig. A. Fig. B.] _Barrage trench for miners._--If the enemy passes in spite of everything, the explosion should at least have been foreseen. The enemy's attack must be limited or stopped, and this is always possible after the explosion of the charge, which may explode well in advance of our lines and act only as a strong means of launching his attack. The barrage trench is established at from 40 to 50 meters in rear of the salient T (Fig. B). In front of the parapet T, wire entanglement R, and two machine-gun positions M^1 and M^2 are placed. When the enemy's explosion is near, only a few men are left to occupy the salient. The German explosion does not bury anyone, and when the attack is launched it breaks down at the entanglement R. _Camouflet._--The sector commander is warned when the defense is about to explode a camouflet. About 10 meters on each side of the gallery are evacuated as a precaution. The only danger is in having several sandbags fall on the sides of the gallery entrance. Warn the working party charged with the relief, in order that they may not block the passage of men in the first line. Do not fire or make any changes in that part of the trench, in order that the enemy may not locate the position. Do not fire rockets before a given time. The camouflet sometimes shakes the ground and dust is visible. Nine times out of ten the camouflet is used at night.