The projectile used with these guns is of a cylindrical form, but pointed at the head, and the moulds in which these shots are cast are so arranged that the head of the shot is moulded in iron, while the body is surrounded with sand. The rapid cooling induced by the contact of the cold metal causes the head of the shot to solidify very quickly, so that the carbon in the iron is not separated as in ordinary casting. In consequence of this treatment, the head of the shot possesses the hardness of steel, and is therefore well adapted for penetrating iron plates or other structures. The projectiles are turned in a lathe to the exact size, and then shallow circular cavities are bored in them, and into these cavities brass studs, which are simply short cylinders of a diameter slightly larger than the cavities, are forced by pressure. The projecting studs are then turned so as accurately to fit the spiral grooves of the guns. Thus the projectile in traversing the bore of the piece is forced to make a revolution, or part of a revolution, about its axis, and the rapid rotation thus imparted has the effect of keeping the axis of the missile always parallel to its original direction. Thus vastly increased accuracy of firing is obtained. [Illustration: FIG. 95.—_Millwall Shield after being battered with Heavy Shot.—Front View._ ] [Illustration: FIG. 96.—_Rear View of the Millwall Shield._ ] Shells are also used with the Woolwich rifled guns. The shells are of the same shape as the solid shots, from which they differ in being cast hollow, and having their interior filled with gunpowder. Such shells when used against iron structures require no fuse; they explode in coming into collision with their object. In other cases, however, the shells are provided with fuses, which cause the explosion when the shot strikes. Fig. 93, page 195, represents one of the 35–ton guns, made on the plan introduced by Mr. Fraser. This piece of ordnance is 16 ft. long, 4 ft. 3 in. in diameter at the breech, and 1 ft. 9 in. at the muzzle. The bore is about 1 ft. Each gun can throw a shot or bolt 700 lbs. in weight, with a charge of 120 lbs. of powder. It is stated that the shot, if fired at a short range, would penetrate a plate of iron 14 in. thick, and that at a distance of 2,000 yards it would retain sufficient energy to go through a plate 12 in. thick. The effect of these ponderous missiles upon thick iron plates is very remarkable. Targets or shields have been constructed with plates and timber backing, girders, &c., put together in the strongest possible manner, in order to test the resisting power of the armour plating and other constructions of our ironclad ships. The above two cuts, Figs. 95 and 96, are representations of the appearance of the front and back of a very strong shield of this description, after having been struck with a few 600 lb. shots fired from the 25–ton gun. The shots with chilled heads, already