EARTHWORKS IN FIELD FORTIFICATION.—As the most readily constructed, earth works naturally recommend themselves to the engineer, who, in the field, is called upon to defend the position of an army against sudden attack., Their utility has been shown in their employment from the earliest times; and modern experience tends to prove that earth-parapets are of all fortifications among the most difficult to overcome. An army maneuvering before a superior force, can scarcely hope to avoid battle being thrust upon it, unless, strengthened by ficldworks, it be rendered more nearly equal to the adversary. Napoleon, Marlborough, Eugene, Wellington, have given their names as witnesses to the indispensability of such works. The Russian parapets at Borodino made the French victory so sanguinary a triumph that it was useless to the victors. A few redoubts at Pultowa saved Peter the great from total defeat by his formidable Swedish rival. The world-famed lines of Torres Vedras enabled Wellington with 50,000 troops, half of whom were untried Portuguese, to withstand for five months, and ultimately to drive back, the hitherto victorious army of 70,000 French, under such commanders as Massena, Ney, and Junot. The earthworks surrounding Sevastopol partook greatly of the nature of fieldworks for the protection of a large army, and history will not for get to recount the resistance they offered for almost a year to the best troops of the civilized world.
For a line, wh3ther of earth or masonry, to be efficient, it must combine artillery fire with that of musketry. The guns will generally be so placed as to command some spe cific line of approach, such as a ravine, a line of abattis, or some portion of the glacis. They should themselves be as little exposed as possible, not should the gunners be uncovered more than is absolutely requisite. To effect this, the gun is generally made to fire through an embrasure (q.v.) in the parapet, instead of over the latter. The embra sure is a cutting through the solid parapet, 20'in. wide at its inner extremity, and out wards half as much as the width 'Of the parapet. • In cases where it is necessary, for proper command, that the line of fire should not be lower than the top of the parapet, the embrasure is made through an additional parapet—raised, as in the previous case of the bonnet, above the original one: The bottom of the embrasure is called the sole, and slopes downward sufficiently to allow of a certain depression being given to the gun.
The remainder of a parapet below the sole is the genouillere (from genou, a knee), and in field F. should be 3 ft. high;, the portion between two embrasures is the merlin (Ital. merlon, battlement); and an embrasure need not cut the parapet perpendicularly, an angle being admissible, when an oblique fire is necessary. When, however, the obliquity would exceed 70°, it is usual, in order that the thickness of the parapet should not be too*much •diminished, to form a projecting angle in it, through' which the embrasure is cut. The, sides of the embrasures are cheeks, and require'revdting.
A barbette, is a platform raised behind a parapet, higher than the general interior, with a view to guns being fired from it over the parapet.
There are certain fixed rules in all F., such as':—F. The length of lines must never exceed musketry range, or the flanking-works would become ineffective for their object. 2. The angles of defense should be about right angles. 3. Salient angles should be as obtuse as possible. 4. Ditches should have the best possible flanking. 5. The relief of the flanking,works must be determined by the length of the lines of defense. 6. The value of almost every detached work depends on the support it can give to or receive from an army or other work or works. 7. The reduction of every fortified work is merely a question of time; and a work fairly surrounded is sure to fall, unless relieved from without.
Fieldworks, which, it must be borne in mind, are intended merely to support or strengthen an army, may either have a complete circuit of parapets, or may be open at the gorge in the rear. The latter are, of course, the simplest; but they are only avail able in positions which the enemy cannot turn, or where protected by the sweeping fire of other works behind. Of this class the redan, a mere salient angle, is the simplest and the representative form. Of the closed forts, there are redoubts, usually square; star-forts, now considered objectionable; bastioned forts,.which flank their own ditches almost perfectly, while scarcely susceptible of being flanked themselves.