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 skilful 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. It is doubly necessary thus to study critically the history and experience of naval warfare in the days of sailing-ships, because while these will be found to afford lessons of present application and value, steam navies have as yet made no history which can be quoted as decisive in its teaching. Of the one we have much experimental knowledge; of the other, practically none. Hence theories about the naval warfare of the future are almost wholly presumptive; and although the attempt has been made to give them a more solid basis by dwelling upon the resemblance between fleets of steamships and fleets of galleys moved by oars, which have a long and well-known history, it will be well not to be carried away by this analogy until it has been thoroughly tested. The resemblance is indeed far from superficial. The feature which the steamer and the galley have in common is the ability to move in any direction independent of the wind. Such a power makes a radical distinction between those classes of vessels and the sailing-ship; for the latter can follow only a limited number of courses when the wind blows, and must remain motionless when it fails. But while it is wise to observe things that are alike, it is also wise to look for things that differ; for when the imagination is carried away by the detection of points of resemblance,--one of the most pleasing of mental pursuits,--it is apt to be impatient of any divergence in its new-found parallels, and so may overlook or refuse to recognize such. Thus the galley and the steamship have in common, though unequally developed, the important characteristic mentioned, but in at least two points they differ; and in an appeal to the history of the galley for lessons as to fighting steamships, the differences as well as the likeness must be kept steadily in view, or false deductions may be made. The motive power of the galley when in use necessarily and rapidly declined, because human strength could not