The resistance which spherical projectiles met from the air, their deviation in flight, owing to the frequent lack of coincidence of the centres of gravity and form, their excessive “windage,” and their light weight relatively to calibre, led to the adoption of the rifled gun and the cylindrical projectile. The principle of the former—making the shot act as a screw-bolt and the bore as a screw-thread—is very old, there being at Woolwich a barrel of this type bearing date of 1547. The objects aimed at in rifling are to give a pointed cylindrical shot rotation on its axis that it may keep steady during flight, and secondly, to obtain increased weight in the projectile from its elongated form. As to the latter consideration, it may be noted that the old 32-pounder smooth-bore was of 6-inch calibre, while the United States 6-inch rifle of to-day throws a shot of 100 lbs. weight. France, during the Crimean War, brought out the first heavy rifled gun. In 1860–61, Armstrong rifles were introduced in the British navy. The labors of Krupp met such success that at Paris, in 1867, he exhibited a rifle weighing 50 tons with a projectile of 1080 pounds. The Parrott rifle was brought out about 1856 in the United States, and was so developed that in 1862 it was the most powerful gun, for its weight and size, in existence. The adoption of rifling was the first great step on the road which engineering had laid toward the growth in power of modern ordnance. Having thus secured a projectile of great weight and moderate calibre which would bore through the air a true path to the distant mark, there remained to seek but four chief elements in the magnificent advance made within a generation by the naval artillery of our day. These factors were: 1st. Increased strength in the material of the gun. 2d. A method of construction which would not only permit enormous pressures in the powder-chamber, but would make possible the continuous acceleration of the projectile during its passage through the bore. 3d. An explosive which would satisfy the objects of the method of construction; and, 4th. A system of loading which would enable guns of great length to be charged with ease. The mounting of ordnance of any weight, its control, and its rapid and facile handling were but minor matters of engineering. In a paper such as this, of limited length and addressed to laymen, it is possible to give but a glance at the progress in the various elements of gun-construction which have been noted. Of material, little need be said. The rifle of Crimean days was a cast-iron piece; Parrott ordnance was of cast and wrought iron; and the first Armstrong gun was built of wrought iron and steel. Cast and compound materials, however, have vanished with the past. Steel—hardened and toughened to the last degree by every refinement of manufacture—forms the “reeking tube” for the “iron shard” of the century’s close.