Under the present circumstances, and governed by the intentions of the legislature, as manifested by their annual appropriations of money for the purposes of defence, it has been concluded to combine--1st, land batteries, furnished with heavy cannon and mortars, and established on all the points around the place favorable for preventing vessels from lying before it; 2d, movable artillery which may be carried, as an occasion may require, to points unprovided with fixed batteries; 3d, floating batteries; and 4th, gun-boats, which may oppose an enemy at its entrance and co-operate with the batteries for his expulsion. On this subject professional men were consulted as far as we had opportunity. General Wilkinson, and the late General Gates, gave their opinions in writing, in favor of the system, as will be seen by their letters now communicated. The higher officers of the navy gave the same opinions in separate conferences, as their presence at the seat of government offered occasions of consulting them, and no difference of judgment appeared on the subjects. Those of Commodore Barron and Captain Tingey, now here, are recently furnished in writing, and transmitted herewith to the legislature. The efficacy of gun-boats for the defence of harbors, and of other smooth and enclosed waters, may be estimated in part from that of galleys, formerly much used, but less powerful, more costly in their construction and maintenance, and requiring more men. But the gun-boat itself is believed to be in use with every modern maritime nation for the purpose of defence. In the Mediterranean, on which are several small powers, whose system like ours is peace and defence, few harbors are without this article of protection. Our own experience there of the effect of gun-boats for harbor service, is recent. Algiers is particularly known to have owed to a great provision of these vessels the safety of its city, since the epoch of their construction. Before that it had been repeatedly insulted and injured. The effect of gun-boats at present in the neighborhood of Gibraltar, is well known, and how much they were used both in the attack and defence of that place during a former war. The extensive resort to them by the two greatest naval powers in the world, on an enterprise of invasion not long since in prospect, shows their confidence in their efficacy for the purposes for which they are suited. By the northern powers of Europe, whose seas are particularly adapted to them, they are still more used. The remarkable action between the Russian flotilla of gun-boats and galleys, and a Turkish fleet of ships-of-the-line and frigates, in the Liman sea, 1788, will be readily recollected. The latter, commanded by their most celebrated admiral, were completely defeated, and several of their ships-of-the-line destroyed.