29. How is the content of a barrel found?
Multiply half the sum of the areas of the two interior circles, taken at the head and bung, by the interior length; or, to the area of the head, add twice the area at the bung, multiply that sum by the length, and take one-third of the product for the content.
156]
30. What is meant by the term, enfilade?
Sweeping the whole extent of a work, line of troops, deck of a ship, &c., with shot or shells.
31. What does defilade mean?
The art of disposing guns, troops, or works in such a manner, that they shall be protected from a plunging-fire from adjoining heights.
32. What are the dimensions required for an earthen parapet to resist the fire of field or siege guns?
6 feet for 6-pdrs.; 14 feet for 12-pdrs.; 18 feet for 24 or 18-pdrs.; four feet of oak or brick will resist cannon shot.
33. What thickness of ice will admit the passage of infantry, cavalry, and artillery?