Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/446

 432 FOKTIFICATION between them, without impeding the movements of the army. These objects were attained ; and the loss of the first line would not have been injurious, save in reputation, because the retreat was secure upon the second and stronger line, and the guns of the first were all of inferior calibre mounted on common truck carriages, and consequently, im movable and useless to the enemy.&quot; 1 The two lines covered an extent of fifty miles, on which were erected one hundred and fifty forts, mounting in all about six hun dred pieces of artillery. Before this formidable position, defended by a double line of works, and by an army massed and ready to move upon any point by interior communications, the French remained five months, wasting their numbers and resources ; until at length, finding it utterly impracticable to force any part of even the first line, they were obliged to retire from Portugal closely followed and harassed by the army which they had previously driven out of Spain. Yet perfect as were the lines of Torres Vedras, and though one of the ablest of the French generals and a veteran French army were foiled before them, it is not meant to infer that the system of separate field-works is a model to be followed on all occasions ; for, though the old method of covering a con siderable front by a continued line of regular bastions and curtains has been generally condemned bymodern engineers, there may be situations where the application of continued lines may be judiciously made. There is no fixed rule ; the nature of the ground and of the position to be defended must determine the proper description of works. But as in defence artillery should be combined with mus ketry, it is necessary that in the arrangement of lines provi sion should be made for the use of cannon ; and as they should be preserved for action at the right moment, they should, when practicable, be mounted on carriages of such a height as will enable them to give their fire over a full parapet, the gun and carriage disappearing below the parapet after the fire is given, so that the loading may be effected in security. In particular cases, such as in flanks where the lateral range of the guns is restricted, and where the guns are not exposed, or are exposed to indirect fire only, openings in the parapet called &quot;Embra sures &quot; may be made use of, but they have many serious disadvantages : they weaken the parapets ; they offer dis tinct marks to the enemy ; they are easily blown down by shells ; they are destroyed by the fire of their own guns ; they are difficult to construct, and still more difficult to maintain. The interior opening, called the &quot; Throat &quot; of the embrasure is made wide enough to admit the muzzle of the gun, about 20 inches ; the width of the outer opening called the &quot; Mouth &quot; is determined by the lateral range of the gun, which should not exceed 20. The slope of the bottom of the embrasure, called the &quot; Sole,&quot; is determined by the object upon which the fire of the gun is to be directed. When required for indirect fire only, the sole is made countersloping ; by this arrangement the exposure of the gun detachment is considerably lessened, and, in order to dimin ish still farther this exposure, the sides of the embrasures are made with a winding slope, steep at the throat, from 6 to 1 or less, and flattening out at the mouth to 1 to 1. As a rule, embrasures should not be made till they are re quired, so that the parapet may be made solid in the first instance (see fig. 31). The portion of parapet below the embrasure is called Genouillere (from genou, the knee), and should be 2 feet 5 inches high ; the portion between two embrasures is called a Merlon, from the Italian merlone, a battlement; the bottom of the embrasure is called its Sole; and, as has been suggested in respect to the superior slope of the parapet, it may be hori- 1 History of the War in the Peninsula, vol. iii. zontal for the first two feet from the neck, and then slope downwards as much as may be necessary for the depression NTERIOR ELEVATION SECTION THROUGH A. B. FIG. 31.- Embrasures. required in firing. The direction of the embrasure depends on the direction of the line of fire : it may be either per pendicular to the crest or oblique. In the latter case, should the obliquity be very great, or exceeding 70, the crest of the parapet must be made re-entering, so as to strengthen it near the neck, and to enable the gun-carriage to be brought up square to the parapet. The sides of the embrasure are called Cheeks, and should be revetted with sods, fascines, gabions (cylindrical baskets made of wicker, and filled with earth after they are in position), sand bags, planks, or hurdles. In fig. 32, on the left, at B, a Fio. 32. Embrasures and Barbettes. direct embrasure is seen cut straight through the parapet ; and on the right at A, an oblique one, both being intended to enfilade the ditches opposite them ; and it will be ob served that, from the obliquity of the right-hand embrasure, the interior of the work becomes so much exposed, that a traverse, T, behind the embrasure, becomes necessary. Barbettes are also shown in this figure one at the salient at D for four guns, and another at C, perpendicular to the face, for two. The terrepleine of the Barbette should be 3i feet below the crest of the parapet ; its length from front to rear from 18 feet to 20 feet; and its breadth, for a single gun, from 15 feet to 18 feet, according as it may be necessary to fire more or less obliquely; a breadth of 15 feet should be added for each additional gun. To add to the lateral sweep or range of the gun, without diminishing the banquette, or, in other words, the musketry fire, the barbette may be made wider in the rear than in front. In proportion to its magnitude should be the number of &quot; Ramps&quot; or slopes of approach ; as, for example, at C only one, at D three. The ramps should be from 8 to 9 feet wide, and their slopes should have bases equal to 4 times