=Armor Plates.= From experiments of the effects of shot and shell on armor plates in England, the following results have been obtained: Where it is required to perforate the plate, the projectile should be of hard material, such as steel, or chilled iron, and the form best suited for this purpose is the pointed ogeeval. The resistance of wrought-iron plates to perforation by steel projectiles varies as the squares of their thickness. Hitting a plate at an angle diminishes the effect as regards the power of perforation in the proportion of the sine of the angle of incidence to unity. The resistance of wrought-iron plates to perforation by steel shot is practically not much, if at all, increased by backing simply of wood, within the usual limits of thickness; it is, however, much increased by a rigid backing either of iron combined with wood, or of granite, iron, brick, etc. Till quite recently armor plates have been made of wrought iron only, as numerous experiments in England had served to show that notwithstanding the enormous resistance of steel to penetration it was unfit for armor plating,--the damage from the impact of shot not being localized as in wrought iron. The Italians were led, however, by the experiments with the 100-ton gun on targets of both metals at Spezzia, 1876, to adopt steel for their new ships, the “Duilio” and “Dandolo.” Since that time an armor compounded of steel and wrought iron has been introduced in England which bids fair to supersede all others. It is made by casting a heavy facing of steel upon wrought-iron plates. A section of this compound armor exhibits a gradual change of structure from the hard steel face to the soft iron backing. Its resistance to penetration is equal to steel, while in toughness and endurance under the blows of shot it resembles wrought iron. To glance at some of the heaviest armor plating afloat, the English “Inflexible” carries a maximum thickness of 24 inches of iron, the Italian frigates mentioned above 21.5 of steel, the French “Admiral Duperré” 21.6 of iron, the Russian “Peter the Great” 14 inches of iron. In regard to the power of some of the most noted of modern guns, the 12-inch calibres used now by all leading nations will penetrate, at 1000 yards, 16 to 18 inches of iron. The 38-ton English gun of this calibre has penetrated (at shorter range) 22 inches of iron and 6 inches of teak backing. The 80-ton Woolwich gun will penetrate 23 inches of iron at 1000 yards. The largest Krupp, 72 tons, will penetrate 26 inches, and the 100-ton Armstrong 30 inches at the same distance. None of the guns mentioned would penetrate at a single shot the steel armor of the Italian ships, but any of them would destroy it in a number of rounds. =Armory.= A manufactory, or place of deposit for arms. See ARSENAL. =Armory, National.= The U. S. government establishment for the manufacture of small-arms at Springfield, Mass.