CLIMATE. The climate of the Andes differs widely in different parts, with latitude, altitude, and exposure. The eastern slope of the system from the northern end southward to latitude 25°, comprising the portions drained by the Ori noco and Amazon, and lying almost entirely within the tropics, has a heavy, and, in many localities, a profuse, rainfall. Farther southward in the temperate zone, in the region of prevailing westerly winds, the rainfall on this side of the range diminishes, becoming very light in Argen tina, with only eight inches or less in the driest parts. On the west side of the system, the rain fall conditions are very nearly reversed, though in the north, in Colombia, the tropical rainfall passes around the end of the range and extends down the western side for some distance, giving to the valleys of the Magdalena, Cauca, and Atrato abundant moisture, and extending south ward along the coast as far as Guayaquil, Ecua dor. Thence southward, the western coast is an arid and desert region, as far as latitude 30° S. Below this point the precipitation increases, as the westerly winds bring moisture, end the south ern coast is well watered.
From Guayaquil a cooler climate is reached either by going south or by going directly up the mountains. The base of the mountains, within the tropics, has a mean annual temperature of S0° F. or more, while in southern Argentina it is not more than 25'. Within the tropics the temperature ranges from 80° at the base of the mountains to 20° or less at their summits, a range due to altitude alone. Upon the Titicaca plateau Arctic conditions prevail, with frost every month of the year. Where the rainfall is copious, as it is on the eastern side within the tropics, the range of temperature between sum mer and winter is slight, while upon the west coast, in the same latitudes, where desert con ditions prevail, the range is very great. In gen era], as the mountains are ascended, the contrasts of temperature become greater, owing to the rare faction of the air. At great altitudes, even, the contrast between day and night is great. South of the latitude of Coquimbo, 30° S., these temperature conditions are reversed, the west slopes having the smallest annual and diurnal range.