We may therefore accept now the words of a French tactician, Morogues, who wrote a century and a quarter ago: "Naval tactics are based upon conditions the chief causes of which, namely the arms, may change; which in turn causes necessarily a change in the construction of ships, in the manner of handling them, and so finally in the disposition and handling of fleets." His further statement, that "it is not a science founded upon principles absolutely invariable," is more open to criticism. It would be more correct to say that the application of its principles varies as the weapons change. The application of the principles doubtless varies also in strategy from time to time, but the variation is far less; and hence the recognition of the underlying principle is easier. This statement is of sufficient importance to our subject to receive some illustrations from historical events. The battle of the Nile, in 1798, was not only an overwhelming victory for the English over the French fleet, but had also the decisive effect of destroying the communications between France and Napoleon's army in Egypt. In the battle itself the English admiral, Nelson, gave a most brilliant example of grand tactics, if that be, as has been defined, "the art of making good combinations preliminary to battles as well as during their progress." The particular tactical combination depended upon a condition now passed away, which was the inability of the lee ships of a fleet at anchor to come to the help of the weather ones before the latter were destroyed; but the principles which underlay the combination, namely, to choose that part of the enemy's order which can least easily be helped, and to attack it with superior forces, has not passed away. The action of Admiral Jervis at Cape St. Vincent, when with fifteen ships he won a victory over twenty-seven, was dictated by the same principle, though in this case the enemy was not at anchor, but under way. Yet men's minds are so constituted that they seem more impressed by the transiency of the conditions than by the undying principle which coped with them. In the strategic effect of Nelson's victory upon the course of the war, on the contrary, the principle involved is not only more easily recognized, but it is at once seen to be applicable to our own day. The issue of the enterprise in Egypt depended upon keeping open the communications with France. The victory of the Nile destroyed the naval force, by which alone the communications could be assured, and determined the final failure; and it is at once seen, not only that the blow was struck in accordance with the principle of striking at the enemy's line of communication, but also that the same principle is valid now, and would be equally so in the days of the galley as of the sailing-ship or steamer.