The reader will comprehend that in the application of these leading ideas there is considerable variety in detail. The two turrets may be looked upon at present as the least variable factor; and in disposing armor all practice agrees that the turrets and engines receive the greatest protection. But how to distribute the total available weight of armor gives rise to varieties of practice which find their reflection in similar variety in the sizes and numbers of the rapid-fire guns, to whose penetrative force there is a corresponding thickness of armor. For example, two battle-ships now building for the United States navy have four thirteen-inch guns in turrets, and in broadside fourteen five-inch, twenty six-pounder, and six one-pounder rapid-fire guns; between the two classes they have four eight-inch guns, also mounted in smaller turrets, superimposed on the main turrets. A ship since designed will have the same thirteen-inch gun fire, but in place of the eight-inch and five-inch will have fourteen six-inch rapid-fire guns. An expert officer, discussing these, says: “In the former the weight of fire per minute is two thousand and fifty pounds on the broadside and five hundred ahead or astern, while with the latter plan it is only one thousand seven hundred and fifty on the broadside and five hundred ahead and astern. But the main objection to the second plan is that the volume of effective fire is enormously diminished by the omission of eight-inch guns. The larger area covered with their armor is fairly safe from the six-inch gun at fighting ranges, whereas the eight-inch projectile at any range, and at even a considerable angle of incidence, will penetrate it.” In the judgment of the present writer the weight of this argument depends upon what is behind the armor the eight-inch only will penetrate. If battery and men, it is strong, if not decisive; if motive power only, not. HISTORY’S TEACHING AND THE FUTURE The object of this paper has been not to present an accumulation of details, but to elucidate the principles upon which the details rest. The latter, when correct, are but the application of principles to practice. Subject to the imperfections attendant on all human work, the writer is persuaded that the greatest errors in practice—and especially the lack of homogeneousness which characterizes the present battle-ships—arise chiefly from the failure to refer back to principles. Until war has given us the abundant experience which led our predecessors to the broadside seventy-four as the rule, with occasional exceptions, we must depend upon reasoning alone for the solution of our problems; and the reasoner keeps within the limits of safety only by constant reference to fundamental facts.