must therefore be stronger, as each plate depends solely on
its own; and the resistance of plates must be decreased, either by more
or larger bolt-holes. The working of the thick plates of the European
vessels Warrior and La Gloire, in a sea-way, is an acknowledged defect.
There are various practicable plans of fastening bolts to the backs of
plates, and of holding plates between angle-irons, to avoid boring
them through. It is believed that plates will ultimately be welded.
Boiler-joints have been welded rapidly and uniformly by means of light
furnaces moving along the joint, blowing a jet of flame upon it, and
closely followed by hammers to close it up. The surfaces do not oxidize
when enveloped in flame, and the weld is likely to be as strong as the
solid plate. Large plates prove stronger than small plates of equally
good material. English 4-1/2-inch armor-plates are generally 3-1/2 feet
wide and to 24 feet long. American 4-1/2-inch plates are from 2 to 3
feet wide and rarely exceed 12 feet in length. Armor composed of light
bars, like that of the Galena, is very defective, as each bar, deriving
little strength from adjacent, offers only the resistance of its own
small section. The cheapness of such armor, however, and the facility
with which it can be attached, may compensate for the greater amount
required, when weight is not objectionable. The 14-inch and 10-inch
targets, constructed, without backing, on this principle, and tested in
England in 1859 and 1860, were little damaged by 68-and 100-pounders.

The necessary thickness of armor is simply a question of powder, and
will be further referred to under the heads of Ordnance and Naval
Architecture.

ORDNANCE AND PROJECTILES.

_Condition of Greatest Effect_. It is a well-settled rule, that the
penetration projectiles is proportionate directly to their weight
and diameter, and to the square of their velocity. For example, the
10-1/2-inch Armstrong 150-pound shot, thrown by 50 pounds of powder at
1,770 feet per second, has nearly twice the destructive effect upon
striking, and four times as much upon passing its whole diameter through
armor, as the 15-inch 425-pound shot driven by the same powder at 800
feet. The American theory is, that very heavy shot, at necessarily low
velocities, with a given strain on the gun, will do more damage, by
racking and straining the whole structure than lighter and faster shot
which merely penetrate. This is not yet sufficiently