Page:Popular Science Monthly Volume 5.djvu/341

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in the same race, between those subject to a moist heat and those subject to a dry heat, for the purpose of suggesting its probable connection with the fact that the lighter-skinned races are habitually the dominant races. We see it to have been so in Egypt. It was so with the races spreading south from central Asia. There is evidence that it was so in Central America and Peru. And if, heat being the same, darkness of skin accompanies humidity of the air, while relative lightness of skin accompanies dryness of the air, then, in this habitual predominance of the lighter-complexioned varieties of men, we find further evidence that constitutional activity, and in so far social development, is favored by a climate conducing to rapid evaporation.

I do not mean that the energy thus resulting determines, of itself, higher social development: this is neither implied deductively nor shown inductively. But greater constitutional activity, making easy the conquest of less active races and the usurpation of their richer and more varied habitats, also makes possible a utilization of such habitats that was not possible to the aborigines.



AN important advance in our knowledge of hydraulics has been recently effected through the observations of M. Révy, a member of the Institute of Civil Engineers of Vienna, on the great rivers of Paraná and Uruguay in South America. The results of his observations have just been published in England, in a book entitled "The Paraná, the Uruguay, and the La Plata Estuaries," an excellent account of which appears in the April number of the Edinburgh Review from which the following statement is derived. Before giving the details and results of M. Révy's observations, it is advisable to furnish a brief description of the character and appearance of the streams observed.

The La Plata is simply an estuary or arm of the sea into which empty the Uruguay and the Paraná. It trends in a northwesterly direction, is 70 miles wide at its mouth, and 150 long to the mouth of the Uruguay. Higher up still it loses itself in the Paraná Guayaza and the Paraná de las Palmas, embouchures of the Paraná proper, which branches 72 miles above to form a delta. The Uruguay and the Paraná are the main arteries of the vast basin formed by the Andes on the west, the mountain-chain which runs parallel with the Atlantic Ocean on the east, and on the north by the great range of Cordilleras which stretch directly across the South American Continent at the fifteenth parallel of south latitude. Their water-shed is the southern slope of these Cordilleras, while that of the Amazon