52 represents a plan and section of a full-sap.
When the direction of the trench is such that the men are exposed on both sides, it will be necessary to throw up an embankment both to the right and left.

This operation is called the _double sap,_ and is executed by two parties of sappers, working side by side.

In this sap it will be necessary to frequently change the direction of the trench, or to throw up traverses, in order to cover the men at a distance from the sap-roller.

Wing-traverses, on the side of the trench which is least exposed, some times serve the same purpose as a double sap.
_Mines_ .-- By _mining_, as a military term, we understand the operations resorted to for the demolition, with powder, of a military structure of any description.

The term _mine_ is applied both to the excavation charged with powder for the purpose of producing an explosion, and to the communications which lead to this excavation.
The place in which the charge of powder is lodged is called the _chamber_, the communication by which this place is reached the _gallery_, and the excavation made by the explosion is termed the _crater_.
The form of the crater caused by an explosion in ordinary soils is assumed to be a truncated cone, the diameter, _c d_, (Fig.