In order to form some idea of the time in which a field work may be completed, compute the number of cubic feet of earth to be excavated, thus; multiply half the sum of the breadth of the ditch at top and at bottom, by the depth, for the number of square feet in the profile; and this multiplied by the distance between the workmen in feet, will give the number of cubic feet each man has to dig: or being multiplied by the length of the ditch, gives the cubic contents of the ditch. Now, one man is supposed to be able to move 216 cubic feet of earth in a day, during the summer; but this is not always the case. If a field work be completed in 24 hours, it will be as much as the most diligent workmen are capable of. This time is generally allowed for the formation of a weak profile; 48 hours for that of a stronger, with a revetement of fascines; and 72 for the strongest. The different slopes for the works must depend upon the nature of the soil, and the materials of which the work is composed. The interior slope of the parapet, though it be fascined, should be ⅙ of its height; exterior about ⅔ its height. The slope of the banquette equal to its height. The slope of the scarpe or counterscarpe of the ditch, should be from half its height to its full height, according to the soil. The superior slope of the parapet must entirely depend upon the situation of the work, and that of the surrounding country. The interior slope of the parapet is generally lined with fascines, to keep up the earth; but it is not absolutely necessary to fascine the exterior slope, if the soil be pretty stiff. The embrazures are generally made 20 inches wide on the inside, and 9 feet on the outside; they must always be lined with something to retain the earth; turf is generally preferred, as fascines are so apt to take fire. The manner of making the materials for field works, may be seen under the heads _Fascines_, _Gabions_, _Hurdles_, &c. and the manner of estimating the quantity of materials for works of this kind, may be seen under the word _Battery_. _Fortification—Permanent._ A _parapet_, to resist cannon, should never be less than 18 feet thick in earth, and 8 or 9 in masonry. A wall need only be two feet thick in masonry, to resist musquetry. The parapet should always be 4½ feet above the banquette, and 7½ or 8 feet above the rampart, or terre plein. The _Rampart_ should always be sufficiently wide to allow for the platform, and for two carriages passing each other; about 9 fathoms at top. A parapet of earth, though it takes more room, is always preferable to one of masonry, when it can be raised; though the only objection to the masonry is the number of splinters it produces. Entire _Revetements_ of masonry are not advantageous for the same reason. The masonry of revetements should not be so high as to be seen or battered from a distance: earth parapets are battered in vain, as the earth forms a natural slope.