it quickly loses, 1st, velocity, because it presents a larger area to the resisting air; 2d, penetration, because it has to force a larger hole through the armor; and 3d, accuracy, because the spinning of the rifle-shot constantly shifts from side to side any inaccuracy of weight it may have on either side of its centre, so that it has no time to deviate in either direction.  Practically, however, iron-clad warfare must be at close quarters, because it is almost impossible to aim any gun situated on a movable ship’s deck so that it will hit a rapidly moving object at a distance.  It is believed by some authorities that elongated shot can be sufficiently well balanced to be projected accurately from smooth-bores; still, it is stated by Whitworth and others that a spinning motion is necessary to keep an elongated shot on end while passing through armor.  On the whole, so far as penetrating armor is concerned, the theory and practice favor the spherical shot.  But a more destructive effect than mere penetration has been alluded to,—­the bursting of a shell within the backing of an iron-clad vessel.  This can be accomplished only by an elongated missile with a solid head for making the hole and a hollow rear for holding the bursting charge.  The rifle-shot used in America, and the Armstrong and some other European shot, are covered with soft metal, which in muzzle-loaders is expanded by the explosion so as to fill the grooves of the gun, and in breech-loaders is planed by the lands of the gun to fit the rifling,—­all of which is wasteful of power.  Whitworth employs a solid iron or steel projectile dressed by machinery beforehand to fit the rifling.  But as the bore of his gun is hexagonal, the greater part of the power employed to spin the shot tends directly to burst the gun.  Captain Scott, R.N., employs a solid projectile dressed to fit by machinery; but the surfaces of the lands upon which the shot presses are radial to the bore, so that the rotation of the shot tends, not to split the gun, but simply to rotate it in the opposite direction.

Mounting Heavy Ordnance, so that it may be rapidly manoeuvred on shipboard and protected from the enemy’s shot, has been the subject of so much ingenious experiment and invention, that in a brief paper it can only be alluded to in connection with the following subject:—­

THE STRUCTURE OF WAR-VESSELS.

Size.  To attain high speed and carry heavy armor and armament, war-vessels must be of large dimensions.  By doubling all the lineal dimensions of a vessel of given form, her capacity is increased eight fold, that is to say, she can carry eight times as much weight of engines, boilers, armor, and guns.  Meanwhile her resistance is only quadrupled; so that to propel each ton of her weight requires but half the power necessary to propel each ton of the weight of a vessel of half the dimensions.  High speed is probably