destructive to solid plates. So that there is as yet no common
ground of comparison. The cost of laminated armor is less than half that
of solid plates. Thin plates, breaking joints, and bolted to or through
the backing, form a continuous girder and add vastly to the strength of
a vessel, while solid blocks add no such strength, but are a source of
strain and weakness. In the experiments mentioned, there was no wooden
backing behind the armor. It is hardly possible,--in fact, it is nowhere
urged,--that elastic wooden backing prevents injury to the _armor_ in
any considerable degree. Indeed, the English experiments of 1861 prove
that a rigid backing of masonry--in other words, more armor--increases
the endurance of the plates struck. Elastic backing, however, deadens
the blow upon the structure behind it, and catches the iron splinters;
it is, therefore, indispensable in ships.

_Vertical and Inclined Armor_. In England, in 1860, a target composed of
4-1/2-inch plates backed with wood and set at 38 deg. from the horizon was
injured about one-half as much by round 68-pounder shot as vertical
plates of the same thickness would have been. In 1861, a 3-1/4 plate at
45 deg. was more injured by elongated 100-pounder shot than a 4-1/2 vertical
plate, both plates having the same backing and the weights of iron being
equal for the same vertical height. When set at practicable angles,
inclined armor does not glance flat-fronted projectiles. Its greater
cost, and especially the waste of room it occasions in a ship, are
practically considered in England to be fatal objections. The result of
Mr. Stevens's experiments is, substantially, that a given thickness of
iron, measured on the line of fire, offers about equal resistance to
shot, whether it is vertical or inclined. Flat-fronted or punch shot
will be glanced by armor set at about 12 deg. from the horizon. A hard
surface on the armor increases this effect; and to this end, experiments
with Franklinite are in progress. The inconvenience of inclined armor,
especially in sea-going vessels, although its weight is better situated
than that of vertical armor, is likely to limit its use generally.

_Fastening Armor_. A series of thin plates not only strengthen the whole
vessel, but fasten each other. All methods of giving continuity to thick
plates, such as tonguing and grooving, besides being very costly,
have proved too weak to stand shot, and are generally abandoned. The
_fastenings_