Page:Popular Science Monthly Volume 78.djvu/183

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indication of permanent national importance so far as the advantages derived from mechanical energy are concerned; for the reason that, with intelligent management, the power from running water may be depended on as long as rain continues to fall. Here, however, it is necessary to recall the significance of climatic position, size and surface configuration, since available water power, except in special cases, is the component result of the total quantity of water falling on the land and the proportion of it which runs off through the streams, determined largely by the configuration of the surface. Under the accepted desirable conditions of medium and reliable climatic values, the rainfall on any considerable area would be adequate and sufficiently uniform with respect to the supply in the different seasons of the year. Hence, size of the area and configuration of the surface take on added importance, in that they largely determine the possibilities of water-power development. Both small areas and monotonous uniformity of surface become less desirable, for the reason that in flat regions the fall of the rivers and the condition of their banks do not favor ready or extensive power development; and a small area, whatever its surface, means small actual quantity of water falling on it. Consequently the moderate degree of surface diversity is not simply more desirable through its relation to variety of initiative, but, because of its relation to water power, may be regarded as second in importance only to the conditions permitting agriculture.

For illustration Britain again serves the purpose best, since Britain has for two centuries stood at the forefront of the nations of the world, has developed in a restricted area a large population existing on the basis of exchanging the products of power for the necessities of life, and has, in that development, depended for power almost entirely on a limited supply of coal. Furthermore, Britain is confronted by the realization that the time is not far distant when that coal supply will begin to fail. The question is, therefore, will the small area of Britain with its medium rainfall and moderate diversity of surface offer the means of replacing the steam power now used by power from running water, and through that water power make it possible to maintain, on the existing basis, a population which in the past has increased at the rate of nearly half a million annually? Britain must do that or else be confronted by one of two conditions: either a static population, such as France has exhibited in recent decades; or a declining population due to inability any longer to support the number.

From the standpoint of the power of running water available on the land, the question for Britain probably must be answered in the negative. For example, the average yearly rainfall for Britain, as a whole, is distinctly less than 36 inches; but accepting that figure, for the sake of generosity, and estimating the surface run-off at the high value of