456 



SCIENCE. 



[Vol. IV., No. 93. 



chemistry must be raised to a higher plane 

 among the biological sciences. 



THE NAVIGATION OF THE NILE. 



The Nile, which during thousands of years 

 has attracted much attention from the intel- 

 ligent portion of mankind, yet remains in 

 many respects the most interesting of the great 

 rivers of the globe. Its sources, which for so 

 long a time were a mystery, have within the 

 last quarter of a century been rediscovered ; 

 but that rediscovery has only rendered it more 

 interesting, and more worthy of study. 



The great fluctuations in its flow, and the 

 remarkable, almost mathematical, regularity, 

 year after year, of these fluctuations, can now 

 be practically studied, and their causes clearly 

 understood. 



Having its great first reservoir under the 

 equator, we now know that it derives its waters 

 from the region between a few degrees south 

 of that line, and latitude about 13° north. It 

 receives its last affluent, the Atbara, south of 

 latitude 13° north, and yet continues its flow, 

 notwithstanding evaporation, receiving nothing, 

 and giving life to the lands it traverses, until 

 it pours the waters of south central Africa 

 into the Mediterranean Sea, in latitude 32° 

 north, carrying in those waters, each year, 

 masses of the debris of the mountains of the 

 interior to continually fertilize and extend its 

 delta. 



Early in June of each year the flow is the 

 least. The current near Cairo has then a 

 rapidity of only a little more than one mile per 

 hour, and the amount of water passing is only 

 from four hundred to five hundred cubic yards 

 per second. Before the end of June the annual 

 rise commences ; and by the end of September 

 the rapidity of the current reaches nearly, if 

 not quite, three and a half miles per hour, the 

 quantity of water passing a given point be- 

 coming from nine thousand to ten thousand 

 cubic yards per second. 



Late in October, or early in November, it 

 commences a somewhat rapid decline, which 

 continues until January, when the decline be- 

 comes more gradual and regular ; this gradual 

 decline continuing until about the end of May, 

 when the minimum flow is again reached, 

 to give place the following month to the new 

 annual rise. 



The great regularity of the fluctuations is 

 due to the peculiar sources of supply, and the 

 admirable system of reservoirs and checks 

 which nature has there provided. 



The Egyptian Nile is formed by the junction, 

 at Khartum, of the Blue Nile and White Nile. 



The Blue Nile (Bahr-el-Azrack) , taking its 

 rise in the centre of Abyssinia, and fed by 

 the rains which yearly fall in the mountains 

 of that country during the months of April, 

 May, June, July, and August, furnishes the 

 great masses of water which cause the rapid 

 summer rise, and also furnishes the rich silt, 

 which, torn from the mountains of Abyssinia, 

 spreads over the cultivatable lands of Egypt, 

 and yearly renews the fertility of those lands. 



The White Nile (Bahr-el-Abiad) , flowing 

 from the great reservoir under the equator, 

 guarded in that and the subordinate reservoirs. 

 Lake Ibrahim and Lake Albert, and guarded 

 also by the great system of dams called ' the 

 cataracts,' furnishes the steady flow of clear 

 water which continues throughout the year. 



No human engineer has ever devised, on any 

 thing like so grand a scale, so admirable a 

 system for the collection, preservation, and 

 distribution of irrigating waters, as has there 

 been formed by nature for the supply of Eg} T pt. 



Lake Victoria, with a surface of some fort}' 

 thousand square miles, collects and stores, for 

 the use of the Sudan and Egypt, the rain- 

 water falling on a basin of more than a 

 hundred and sixty thousand square miles of 

 surface. The average yearly rise of the lake 

 may be fairly taken, according to observations 

 made on the spot, as two feet, which gives for 

 distribution through its only outlet, the Victoria 

 Nile (the Somerset of Speke), the enormous 

 volume of more than sixty-eight thousand mil- 

 lion cubic yards of water per annum, or more 

 than two thousand cubic yards per second. 



It will be seen that this storage is so well 

 devised, that, in order to give one inch of rise 

 to the Victoria Nile, more than twenty -eight 

 hundred millions of cubic } T ards must be stored 

 in this great reservoir. 



Then come the two secondary reservoirs, — 

 first Lake Ibrahim (discovered by Col. Long 

 in 1874), in latitude north 1^°, which must be 

 filled before the flow can continue on towards 

 Egypt ; and then Lake Albert, which must be 

 filled over its surface of perhaps three thou- 

 sand square miles before the direct distribution 

 of waters through the White Nile can fairly 

 commence. But this is not all that nature has 

 there done to regularize the great distribution. 

 Between Lakes Ibrahim and Albert, there is a 

 great system of natural dams in the cataracts 

 which are found between Foweira and Lake 

 Albert. Then coming north, down the White 

 Nile, we find, first at Duffli, and soon again 

 at Beddin, successions of rapids, the results 



