TEE EVOLUTION OF NATIONS 179 



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 de- 

 pended on as long as rain continues to fall. Here, however, it is neces- 

 sary to recall the significance of climatic position, size and surface con- 

 figuration, 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 desir- 

 able 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 develop- 

 ment. Both small areas and monotonous uniformity of surface be- 

 come 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 de- 

 gree of surface diversity is not simply more desirable through its rela- 

 tion to variety of initiative, but, because of its relation to water power, 

 may be regarded as second in importance only to the conditions per- 

 mitting 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 nega- 

 tive. 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 



