It is almost needless to remark that this seemingly abrupt transition is but one incident in the startling progress made during the century in all the arts of peace as of war. Like the others, it is due to an intellectual activity, greater probably than that of our predecessors, and directed since the peace of 1815 less upon external political interests than upon scientific investigation, and upon the application of the results to the improvement of processes of every kind. The changes in conception and in development of the instruments of naval warfare result from the increased power of dealing with refractory material which has been acquired by scientific and practical men in the laboratory and the workshop. Thus viewed, though so rapid in realization as to amount to a revolution, not only is the change seen to be the outcome of a long, though silent preparation, but it is brought also into its due relation to the general movement of the age, and found to share its special characteristics. Our ancestors of the eighteenth century had their own problems, noble and absorbing, but chiefly political in character. While new worlds were being gathered into the embrace of European civilization, the leading powers struggling among themselves for pre-eminence in the work, and while the harvest was ripening for the French Revolution, science crept forward, but slowly and silently, the pre-occupation of the few, not the interest of the many. The object of the present article is to describe the type of war vessel prevalent universally among civilized nations when the nineteenth century opened, and to trace historically the sequence of ideas and of facts which have resulted in the type whose general acceptance is seen now in the practice of the chief naval states. SAILING SHIPS AND BROADSIDE BATTERIES When the nineteenth century began, the ships that contended for the control of the sea were, and for two centuries had been, sailing ships with broadside batteries: the guns, that is, were distributed along both sides from the bow to the stern on one, two, three, or four decks. From the largest down, all were of this type until the very smallest class was reached. In the latter, which could scarcely be considered fighting ships, the gun power was at times concentrated into a single piece, which swept from side to side round the horizon, thus anticipating partially the modern turreted ironclad with its concentrated revolving battery.