When the object cannot be seen from the mortar, owing to the interposition of some obstacle, as a parapet or a hill, two persons in sight of each other, one of whom can see the mortar, and the other the object, must by successive changes of position, place themselves in the vertical plane of fire, and at the points thus determined, stakes must be driven, one of which will serve as the object.
15. How may precision of fire be secured at night with mortars?
The direction is preserved by nailing or screwing two boards to the platform outside of the cheeks; the elevation is marked on the quoin, or the quoin may be nailed in the proper position.
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PART III.
CHARGES.
1. What is the charge of a piece of artillery?
The powder with which it is loaded.
2. What is the ordinary service charge of powder for heavy guns?
One-fourth the weight of the shot.
3. What is it for firing double shot?