Defence during third period, 107 Defence, garrison for, 99 Defence, journal of, 110 Defence, opening artillery fire by, 104 Defence, preliminary considerations, 98 Defence, preparations for, 101 Defence, provisions and supplies, 101 Demi-parallels, 86 Demolitions, deliberate, 180 Demolitions, hasty, 181 Descending galleries, 147 Detachment or brigade of sappers, 28 Detonation, 162 Dispositions for an assault, 5 Distribution of fuzes in charge, 161 Distance of line of investment, 70 Ditch, passage of, 37 Double sap, 32 Double sap, breaking out, from a parallel, 33 Double sap, changing direction of, 33 Double sap, execution of, 32 Drainage, 16, 24, 55, 59 Drawings, working, 151 Drill-bars and drills, 178 Dynamite, etc., 132-5 Dynamite, freezing of, 165 Dynamite, tamping, 179 E Earth auger, 138 Electric batteries, wires, and lights, 165-6 Elevated and sunken batteries, 44 Elevated magazine, 62 Embrasures, 53 Enfilading batteries, 82 Execution of double sap, 32 Execution of single sap, 28 Experimental mines, 125, 131, 133 Explosion, theory of, 120 Explosive, charge for blasts, 179 Explosive, charge for mines, 122-5 Explosive, choice of, 132-5 Explosive, expenditure of energy, 120