On the glacis, within 15 or 16 feet of its crest; but if the foot of the revetment cannot be seen from thence, the guns must be placed in the covered way, within 15 feet of the counterscarp.
39]
4. In what manner should the fire of siege guns be conducted in order to form a breach?
1st. Make a horizontal section the length of the desired breach along the scarp, at one-third its height from the bottom of the ditch, and to a depth equal to the thickness of the wall.
2d. Make vertical cuts through the wall, not farther than ten yards apart, and not exceeding one to each piece of ordnance, beginning at the horizontal section and ascending gradually to the top of the wall.
3d. Fire at the most prominent parts of the masonry left standing; beginning always at the bottom and gradually approaching the top.
4th. Fire into the broken mass with howitzers until the breach is practicable.
5. How long would it take to make a breach of 20 yards in length?
Breaches of more than 20 yards in length have been opened by way of experiment, and rendered practicable in less than ten hours, by about two hundred and thirty 24-pdr. balls and forty shells in one case, and by three hundred 18-pdr. balls and forty shells in another.
6. How many discharges can an iron gun sustain?