A study of the military history of the past, such as this, is enjoined by great military leaders as essential to correct ideas and to the skillful conduct of war in the future. Napoleon names among the campaigns to be studied by the aspiring soldier, those of Alexander, Hannibal, and Cæsar, to whom gunpowder was unknown; and there is a substantial agreement among professional writers that, while many of the conditions of war vary from age to age with the progress of weapons, there are certain teachings in the school of history which remain constant, and being, therefore, of universal application, can be elevated to the rank of general principles. For the same reason the study of the sea history of the past will be found instructive, by its illustration of the general principles of maritime war, notwithstanding the great changes that have been brought about in naval weapons by the scientific advances of the past half-century, and by the introduction of steam as the motive power. [The pages omitted point out lessons to be drawn from galley and sailing-ship warfare.—EDITOR.] Before hostile armies or fleets are brought into con_tact_ (a word which perhaps better than any other indicates the dividing line between tactics and strategy), there are a number of questions to be decided, covering the whole plan of operations throughout the theater of war. Among these are the proper function of the navy in the war; its true objective; the point or points upon which it should be concentrated; the establishment of depots of coal and supplies; the maintenance of communications between these depots and the home base; the military value of commerce-destroying as a decisive or a secondary operation of war; the system upon which commerce-destroying can be most efficiently conducted, whether by scattered cruisers or by holding in force some vital center through which commercial shipping must pass. All these are strategic questions, and upon all these history has a great deal to say. There has been of late a valuable discussion in English naval circles as to the comparative merits of the policies of two great English admirals, Lord Howe and Lord St. Vincent, in the disposition of the English navy when at war with France. The question is purely strategic, and is not of mere historical interest; it is of vital importance now, and the principles upon which its decision rests are the same now as then. St. Vincent’s policy saved England from invasion, and in the hands of Nelson and his brother admirals led straight up to Trafalgar.