34 The Realm of Nature CHAP. 



through the valleys. Now by neglect the terraces have been 

 broken down, and the soil is all swept into the valleys. 

 The mountain-sides, being bare and rocky, allow the occa- 

 sional heavy showers to dash down in impetuous torrents 

 to flood temporary streams, which, when the rain passes, 

 give place to channels of dry stones. The land becomes 

 baked in the fierce rays of the sun by day, and chilled by 

 intense radiation through the clear dry air at night, the 

 range of temperature having increased as the rainfall 

 diminished. 



435- Man and the Degradation of Energy. Men are 

 continually at work altering the distribution of matter and 

 energy on the Earth. Gold is sought for in all lands, and 

 accumulated in enormous quantities in London, Paris, 

 Berlin, and other towns. Diamonds are more numerous in 

 Amsterdam than in Africa, India, or Brazil ; and so with 

 other mineral commodities. The salts of the soil on which 

 its fertility depends are being removed by every crop of wheat, 

 to be ultimately cast as useless sewage into the sea. Land 

 deprived of its salts ceases to yield crops ; the natural process 

 of restoration by weathering (310) is too slow, and manures, 

 which every year are becoming scarcer, must be sought far 

 and near to replace them. No animal but man is so im- 

 provident. All others restore the mineral constituents to the 

 land from which they gathered their food, and so insure a con- 

 tinuous supply. The potential energy laboriously stored in 

 growing trees is destroyed by reckless timber-cutting, and 

 the use of wood as fuel. The accumulated savings of energy 

 stored up in coal are being expended in every industrial 

 occupation, and coal is rapidly becoming scarcer. Every 

 consumption of energy, except that of the regular income of 

 solar radiation ( 119), is impoverishing the Earth, and 

 accelerating the natural process of the degradation of 

 Energy ( 75). The great steamer, driving its giant bulk 

 across the ocean at 20 miles an hour, consumes as much 

 potential energy in every revolution of the propeller as 

 served in former days for the stately clipper, rising and 

 dipping over the crests of the sea under the impulse of the 

 sun -driven winds, to make the whole journey. Tidal 



