Page:Popular Science Monthly Volume 69.djvu/252

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HE hydrographic or drainage basin of the Mississippi River (Fig. 1) is equivalent in area to one third of the United States. Thirty-two states and territories contribute water to the volume of the river; eight of these divisions send water to no other system. The discharge of rivers is not in any proportionate way related to the size of their drainage basins. The potent factors which determine the volume of discharge are the precipitation of rain over the basin and the character of the soil. The upper Ganges has a basin less than one seventh that of the Mississippi. It equals the latter river, however, in the volume of its discharge. The Hoang Ho, with a basin area fifty per cent, only of that of the Mississippi, discharges more than twice as much water into the sea. If the discharge of the Mississippi proportionally to the size of its basin equaled that of the Po, the volume of the discharge of the former would be multiplied by six. The Danube more nearly equals the Mississippi in the ratio of discharge to size of

 Missouri type has the maximum rainfall in April, May and June; Tennessee, in February and March; Lake, a late spring maximum in June, and an early fall maximum in September.