Page:Popular Science Monthly Volume 62.djvu/556

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THE Nile Reservoir at Aswân will contain over 1,000 million tons of water. This statement will probably convey little meaning to most people; and in truth the quantity may be made to appear either small or large at will by a judicious selection of illustrations. Thus the absolute insignificance to Egypt of 1,000 million tons of water in a reservoir, as compared with a reasonable rainfall, will be apparent at once when it is considered that the annual rainfall on the area included within the four-mile cab radius from Charing Cross is about 100 million tons, and that the rainfall on London and its suburbs within a thirteen-mile radius would, therefore, about suffice to fill the Nile Reservoir. On the other hand, we may, by choosing other illustrations, restore the Nile Reservoir to the dignity of its just position of one of the greatest engineering works of the clay. Thus the question of the water supply of London, and its prospective population of 1114 millions, has been prominently before the public for some years; and many will remember what was termed the colossal project of our member, Sir Alexander Binnie, late Engineeer of the London County Council, for constructing reservoirs in every reasonably available valley in Wales, to store up water for London, and to supply compensation water to the Welsh rivers affected thereby. Well, the united contents of the whole of those reservoirs would be less than half that of the great Nile Reservoir. Again, the Nile Reservoir would hold more than enough water for one year's full domestic supply to every city, town and village in the United Kingdom with its 42 million inhabitants. But possibly the best way of giving an idea of the magnitude of the work, and its utility to cultivation in a thirsty land, is by considering the volume of the water issuing from the reservoir during the three or four summer months, when scarcity of supply prevails in the river and the needs of the cultivators are greatest. At that time the flow from the reservoir will be equivalent to a river double the size of the Thames in mean annual flood condition. It will be recognized at once that a good many buckets would have to be set at work to bale out a river like that, and yet the scarcity of water in the Nile itself, and in the canals, during the months of April, May and June, is such that even dipping the water out of the channels in buckets has to be con-

  1. Address given before the Royal Institution of Great Britain.