586 



SCIENCE. 



[N. S. Vol. XXII. No. 567. 



of 66 feet of water, which forms a lake of 

 more than 100 miles in length up the Nile 

 Valley, containing 38,000 million cubic feet 

 of water. 



The dam is pierced with 180 sluices, or 

 openings, through which the whole Nile 

 flood, about 360,000 cubic feet per second, 

 is discharged. A flight of four locks, each 

 260 by 30 feet, allows of free navigation 

 past the dam. The foundation-stone of 

 this great work was laid in February 1899, 

 and it was completed in less than four 

 years. At the same time a very important 

 dam of the pattern of the barrage north of 

 Cairo was built across the Nile at Assiut, 

 just below the head of the Ibrahimieh 

 Canal, not with the object of storing water, 

 but to enable a requisite supply at all times 

 to be sent down that canal. 



The chief use of the great Assuan reser- 

 voir is to enable perennial irrigation, such 

 as exists in lower Egypt, to be substituted in 

 upper Egypt for the basin system of water- 

 ing the land only through the Nile flood; 

 that is, to enable two crops to be grown 

 instead of one every year, and to enable 

 cotton and sugar-cane to take the place of 

 wheat and barley. But a great deal more 

 had to be done in order to obtain the full 

 beneficial result of the work. About 450,- 

 000 acres of basin irrigation are now being 

 adapted for perennial irrigation. Many 

 new canals have had to be dug, others to be 

 deepened. Many new masonry works have 

 had to be built. It is probable the works 

 will be finished in 1908. There will then 

 have been spent on the great dam at 

 Assuan, the minor one at Assiut, and the 

 new canals of distribution in upper Egypt 

 about six and a half millions sterling. For 

 this sum the increase of land rental will 

 be about £2,637,000, and its sale value will 

 be increased by about £26,570,000. 



DRAINAGE. 



In the great irrigation systems which I 



have been describing for a long time little 

 or no attention was paid to drainage. It 

 was taken for granted that the water would 

 be absorbed, or evaporated, and get away 

 somehow without doing any harm. This 

 may hold go,od for high-lying lands, but 

 alongside of these are low-lying lands, into 

 which the irrigation water from above will 

 percolate and produce waterlogging and 

 marsh. Along with the irrigation channel 

 should be constructed the drainage channel, 

 and Sir W. "Willcocks, than whom there is 

 no better authority on this subject, recom- 

 mends that the capacity of the drain should 

 be one third that of the canal. The two 

 should be kept carefully apart — the canal 

 following the ridges, the drain following 

 the hollows of the country, and one iu no 

 case obstructing the other. This subject of 

 drainage early occupied the attention of 

 the English engineers in Egypt. In the 

 last twenty years many hundred miles of 

 drains have been excavated, some as large 

 as 50 feet width of bed and 10 feet deep. 



IRRIGATION IN AMERICA. 



If it is to Italy that we should look for 

 highly finished irrigation works and care- 

 ful water distribution, and to India and 

 Egypt for widespreading tracts of watered 

 land, it is to America that we naturally 

 look for rapid progress and bold engineer- 

 ing. In the western states of America 

 there is a rainfall of less than 20 inches 

 per annum, the consequence of which is a 

 very rapid development of irrigation works. 

 In 1889 the irrigation of these western 

 states amounted to 3,564,416 acres. In 

 1900 it amounted to 7,539,545 acres. Now 

 it is at least 10,000,000 acres. The land in 

 these states sells from 10s. to £1 per acre 

 if unirrigated. With irrigation the 'same 

 land fetches £8 10s. per acre. The works 

 are often rude and of a temporary nature, 

 the extensive use of timber striking a for- 

 eigner from the old world. Some of the 



