Plate 9.—Vertical fougass.
When broken up a cubic foot of stone weighs about 100 pounds.
A vertical type of fougass is also shown. A charge of 25 pounds of powder should scatter a cubic yard of stones over an area about 200 by 100 yards.
Small Land Mines
Land mines are placed in the line of the advance of the enemy and exploded either by electricity or fuse from the defense. They are made by digging holes from 2 to 3 yards deep, either by excavation or by boring. In the former case the charge is placed in a recess which extends into the solid earth at the side of the hole, which is then refilled and tamped. In the latter case the charge is placed in the bottom of the hole, which is then refilled and solidly tamped. In common earth the powder charge for a 2-yard hole is 25 pounds. That for a 3-yard hole is 80 pounds. The diameter of the crater formed will be about twice the depth of the charge.
The mines may be arranged in one or more rows. The intervals between mines should be such that the craters will nearly but not quite join. The position of the mines should be concealed as much as possible and further sophisticated by disturbing the ground slightly at points where there are no mines and so situated as to suggest a systematic arrangement.
