It is packed in the chamber with great care, and under the immediate supervision of the responsible officer. The packages containing the fuses are distributed uniformly throughout the mass, and the wires uncoiled and led back into the gallery, the free ends of the two wires of each fuse having been previously twisted together for safety against electric currents and for identification. These wires, which must be long enough to reach through the tamping, are all collected together and led back through it in a wooden or other conduit, which protects them from injury while tamping the mine. When electric lights are used, great care must be taken to remove the light and all its conducting wires before the wires of the fuses are uncoiled and laid along the gallery. =72. Tamping.=--Mines are tamped with sods and earth, wood and earth, sand-bags, etc., etc. When sods are used the branch is filled for about 3 feet with sods carefully laid and packed with the joints filled with earth. About 3 feet of earth is solidly packed against this, then alternate layers of sods and earth until the desired length of tamping is obtained. To tamp with wood and earth or sand-bags, a wooden shield is first placed across the branch and firmly braced; behind this, earth is solidly packed or sand-bags carefully laid until the required length of tamping is obtained. Sometimes a second shield is put up behind the earth tamping, and firmly braced in position. The strength of the tamping is also increased by pieces of timber crossing each other diagonally, with their ends resting against the sides of the branch. Sand-bags make the best tamping, as they offer high resistance and are easily placed and removed. The tamping should have a length equal to at least 1½ times the line of least resistance of a common mine corresponding to the charge, and if not of the best quality, to twice this line. =73. Firing Mines.=--If electric fuses are used the main conductors or lead wires coiled upon a reel are taken in and the ends properly joined to the fuse wires; they are then led through the galleries, attached to the battery, and fired at the designated instant. Under no circumstances should the main lead wires be connected to the battery or dynamo until everything is ready for firing. If a Bickford fuse is used its length is regulated to the desired time of firing from its known rate of burning. The miner lights the end and retires; the explosion takes place approximately at the calculated time. With the “Lightning Gomez” or similar fuses a length reaching to the firing-point may be used. It is lighted at the desired time, and burns with such rapidity that for lengths not exceeding 300 or 400 feet the time of burning is inappreciable.