Where a saving of powder is of consequence, small chambers may be excavated in the haunches of the arch, and the mine carefully _tamped_ before firing it.
Bridges of wood may be destroyed by suspending casks of powder under the principal timbers, or attaching them to the supports.
Palisading, gates, doors, &c., may be destroyed in the same way, by suspending casks or bags of powder against their sides; or still more effectually, by burying the charges just beneath their base.
To demolish a tower, magazine, or house, of masonry, place charges of powder under the piers and principal walls of the building.

In wooden structures the powder should be placed under, or attached to the principal supports.

Where time is wanting to effect these arrangements, a building may be blown down by placing a large mass of powder in the interior.

The powder may be economized, in this case, by putting it in a strong case, which should be connected with the walls of the building on all sides by wooden props.
Special treatises on military mining contain full instructions for regulating the size and position of the charge for the various cases that may be met with in the practical operations of field-engineering.
As applied to the attack and defence of a fortified place, mines are divided into two general classes--_offensive_ and _defensive_ mines.

The former are employed by the besiegers to overthrow the scarps and counterscarps of the place, to demolish barriers, palisades, walls, and other temporary means of defence, and to destroy the mines of the besieged.