In the tropical countries of South America, the seasonal rains are, perhaps, more intensely copious than in any other part of the torrid zone, and the floods of its rivers are of corresponding magnitude. At the mission of San Antonio de Javita, on the Orinoco, during the wet season, the sun and stars are seldom visible, and Humboldt was told by the padre, that it sometimes rained for four or five months without intermission. The traveler collected there, in five hours, 21 lines of water in height on the first of May, and 14 lines on the 3d, in three hours; whereas at Paris there fall only 28 or 30 lines in as many weeks. Humboldt traces the transition from the one great season of drought to that of rain, which divides the year, in an interesting manner, with the atmospheric phenomena which accompany the change. About the middle of February in the valleys of Araqua, he observed clouds forming in the evening, and in the beginning of March the accumulation of vesicular vapors became visible. “Nothing,” he remarks, in beautifully graphic style, “can equal the purity of the atmosphere from December to February. The sky is then constantly without clouds, and should one appear, it is a phenomenon that occupies all the attention of the inhabitants. The breeze from the east and north-east blows with violence. As it always carries with it air of the same temperature, the vapors cannot become visible by refrigeration. Toward the end of February and the beginning of March, the blue of the sky is less intense; the hygrometer gradually indicates greater humidity; the stars are sometimes veiled by a thin stratum of vapors; their light ceases to be tranquil and planetary; and they are seen to sparkle from time to time at the height of 20° above the horizon. At this period the breeze diminishes in strength, and becomes less regular, being more frequently interrupted by dead calms. Clouds accumulate toward the south-east, appearing like distant mountains with distinct outlines. From time to time they are seen to separate from the horizon, and traverse the celestial vault with a rapidity which has no correspondence with the feebleness of the wind that prevails in the lower strata of the air. At the end of March the southern region of the atmosphere is illuminated by small electric explosions, like phosphorescent gleams, confined to a single group of vapors. From this period the breeze shifts at intervals, and for several hours, to the west and south-west, affording a sure indication of the approach of the rainy season, which, on the Orinoco, commences about the end of April. The sky begins to be overcast, its azure color disappears, and a gray tint is uniformly diffused over it. At the same time the heat of the atmosphere gradually increases, and, instead of scattered clouds, the whole vault of the heavens is overspread with condensed vapors. The howling monkeys begin to utter their plaintive cries long before sunrise. The atmospheric electricity, which, during the period of the greatest drought, from December to March, had been almost constantly in the day-time from 1·7 to 2 lines to Volta’s electrometer, becomes extremely variable after March. During whole days it appears null, and again for some hours the pith-balls of the electrometer diverge from three to four lines. The atmosphere, which in the torrid as in the temperate zone is generally in a state of positive electricity, passes alternately, in the course of eight or ten minutes, to a negative state. The rainy season is that of thunder-storms. The storm rises in the plains two hours after the sun passes through the meridian, and therefore shortly after the period of the maximum of the diurnal heat in the tropics. In the inland districts it is exceedingly rare to hear thunder at night or in the morning--nocturnal thunder-storms being peculiar to certain valleys of rivers which have a particular climate.” The substance of the explanation of the preceding phenomena, by the philosophic writer of the statement, may be briefly given: