polypi; and the danger attending them is the more to be dreaded, as they form steep rocks covered by the water, and which can only be perceived at a small distance. If a calm take place, and a ship be carried towards them by the currents, her loss is almost inevitable. Vain would be the attempt to save her by the anchor, for it would not reach the bottom, even close to those walls of coral, which rise perpendicularly from the depths of the sea. These works of the polypus, which, by continually increasing, obstruct more and more the bed of the ocean, may well be supposed, dreadful to navigators; and many shoals which now allow a vessel to pass over them, will, at no very distant period; be converted into reefs extremely dangerous to ships.
The compass experienced but little variation, while we were cruizing along this immense chain of rocks; for at their southern extremity, it was observed, to be 11° easterly, and it was diminished only two degrees, when we had reached their northern extremity.
3d. The next day we steered N.N.W.; but we saw no more breakers.
7th. At half past nine P.M. the moon being elevated about 15° above the eastern part of the horizon, we observed, in the west, a lunar rainbow. It differed in nothing from the solar rain-
