You open the counterscarp by saps to make yourself master of it; but, before you open it, you must mine the flanks that defend it. The best attack of the place is the face of the bastion, when by its regularity it permits regular approaches and attacks according to art. If the place be irregular, you must not observe regular approaches, but proceed according to the irregularity of it; observing to humor the ground, which permits you to attack it in such a manner at one place, as would be useless or dangerous at another; so that the engineer who directs the attack ought exactly to know the part he would attack, its proportions, its force and solidity, in the most geometrical manner. APPROACHES, in a more confined sense, signify attacks. _Counter_ APPROACHES, are such trenches as are carried on by the besieged, against those of the besiegers. APPRENTI, _Fr._ Apprentice. In France they had apprentices or soldiers among the artillery, who served for less pay than the regular artillery men, until they became perfect in their profession; when they were admitted to such vacancies as occurred in their respective branches. The system is changed. APRON, in gunnery, a square plate of lead that covers the vent of a cannon, to keep the charge dry, and the vent clean and open. APRONS--of lead for guns, according to _Deturbie_ _lbs._ _oz._ Large--1 foot long--10 in. wide-- 8 4 Small--6 inch long--4¹⁄₂ in. wide-- 1 12 Their dimensions are as follow, viz. for a 42, 32, and a 24 pounder, 15 inches by 13; for an 18, 12, and a 9 pounder, 12 inches by 10; for a 6, 5¹⁄₄, 3, and 1¹⁄₂ pounder, 10 inches by 8. They are tied fast by two strings of white marline, the length of which, for a 42 to a 12 pounder inclusive, is 18 feet, 9 feet each string; for a 9 to 1¹⁄₂ pounder, 12 feet, 6 feet for each. APPUI--_Pointe d’appui_, or point of bearing, or direction, or support, is any particular given point or body, upon which troops are formed, or by which they are marched in line or column. _Aller à l’_APPUI, _Fr._ to go to the assistance of any body, to second, to back. _Hauteur d’_APPUI, _Fr._ breast-height. AQUEDUCT, a channel to convey water from one place to another. Aqueducts, in military architecture, are generally made to bring water from a spring or river to a fortress, &c.; they are likewise used to carry canals over low ground, and over brooks or small rivers; they are built with arches like a bridge, only not so wide, and are covered above by an arch, to prevent dust or dirt from being thrown into the water--there are also subterranean aqueducts, such as pipes of wood, lead, or iron. See Muller’s _Practical Fortification_. The Romans had aqueducts which extended 100 miles. That of Louis XIV. near Maintenon, which carries the river Bute to Versailles, is 7000 toises long. ARAIGNEE, in fortification. See GALLERY.