93. To start the gallery through the scarp wall, a miner is “attached” to the wall by protecting him from fire along the ditch, from sorties, and from loaded shells, etc., rolling down upon him from the parapet by suitable traverses and splinter-proof.
This operation is of course very dangerous, and is generally impossible unless the fire of the defence along the ditch is previously silenced. To expedite the work of the miner a gun is sometimes brought down through the gallery, and the face of the wall is shattered by its fire before the miner is “attached.”
CHAPTER IV.
BLASTING AND DEMOLITIONS.
BLASTING.
94. Blasts are small mines used generally for breaking up rocks, or masonry in demolitions.
95. Holes for placing the charges are drilled usually with drill-bars or churn-drills, known also as jumpers.
These are steel bars sharpened to a chisel edge. The drill-bar is usually held by one man and struck with a hammer by another; it is turned slightly after each blow in order to make a round hole.
For small holes the driller holds the drill in one hand and strikes with the other.
The churn-drill is a longer bar, generally sharpened at both ends and enlarged in the middle. It is used for drilling vertical holes by raising and dropping it in the holes, turning it slightly after each blow.