It is directed by the commander-in-chief that the vessels of the squadron under his command, shall heave to, on approaching Napa, and make signal for a pilot, when an officer familiar with the localities and landmarks will be sent off from the vessel in port to pilot her in, or point to her commander the position of the dangers to be avoided. Should there, however, be no vessel in port, then boats are to be sent ahead, and anchored upon the extremities of the reefs, between which the vessel intends to pass. MACAO, October 1, 1853. * * * * * NOTE.—The spar-buoys, above described, were securely moored at the time they were placed in their respective positions, by order of Commodore Perry, but may be displaced, or entirely removed by the heave of the sea, or by the natives, and should therefore not be entirely relied upon. OONTING, OR PORT MELLVILLE, ISLAND GREAT LOO-CHOO. BY LIEUTENANT S. BENT, U. S. NAVY. Oonting harbor is on the N. W. side of Loo-Choo, and distant about thirty-five miles from Napa. Sugar Loaf island, an excellent landmark, lies about twelve miles to the W. N. W’d of the entrance. The island is low and flat, with the exception of a sharp conical peak near its eastern extremity, which rises to a height of several hundred feet. Passing to the northward of Sugar Loaf island, an E. S. easterly course will bring you to the mouth of the harbor, and to the northward and westward of Kooi island. It is advisable to heave to here, or anchor in twenty or twenty-five fathoms water, until boats or buoys can be placed along the edges of the reefs bordering the channel, for without some such guides, it is difficult for a vessel of large draft to find her way in between the reefs, which contract, in places, to within a cable’s length of each other, and are at all times covered with water. The ranges and courses for the channel, are first: Hele rock in range with double-topped mountain bearing south thirty-seven degrees east. Steer this course, keeping the range on until Chimney rock bears S. ½  E.; then for Chimney rock, until Point Conde bears south forty-nine degrees east; then for Point Conde, until entering the basin of Oonting, when anchor; giving your ship room to swing clear of the reef making out to the northward of Point Conde, and you will be as snug as if lying in dock; with good holding ground, completely land-locked, and sheltered almost entirely from every wind. Good water is to be had at the village of Oonting. SAILING DIRECTIONS AND OBSERVATIONS, UPON LLOYD HARBOR, BONIN ISLANDS. FROM REPORTS OF ACTING MASTERS MADIGAN AND BENNETT, OF THE U. S. SHIPS SARATOGA AND SUSQUEHANNA. The entrance to the harbor of Port Lloyd, on the western side of Peel island, one of the Bonin group, is well defined; so that it can scarcely be mistaken.