Humboldt and his companion sailed from the Road of New Barcelona on the 24th November at nine in the evening, and next day at noon reached the island of Tortuga, remarkable for its lowness and want of vegetation. On the 26th there was a dead calm, and about nine in the morning a fine halo formed round the sun, while the temperature of the air fell three degrees. The circle of this meteor, which was one degree in breadth, displayed the most beautiful colours of the rainbow, while its interior and the whole vault of the sky was azure without the least haze. The sea was covered with a bluish scum, which under the microscope appeared to be formed of filaments, that seemed to be fragments of fuci. On the 27th they passed near the island of Orchila, composed of gneiss and covered with plants, and toward sunset discovered the summits of the Roca de Afuera, over which the clouds were accumulated. Indications of stormy weather increased, the waves rose, and waterspouts threatened. On the night of the 2d December a curious optical phenomenon presented itself. The full moon was very high. On its side, forty-five minutes before its passage over the meridian, a great arc suddenly appeared, having the prismatic colours, but of a gloomy aspect. It seemed higher than the moon, had a breadth of nearly two degrees, and remained stationary for several minutes; after which it gradually descended, and sank below the horizon.