THE BLUE NILE. 47 



Khartum, where it is joined by the other Nile, called the Bahr-el-Azraq, or " Blue 

 River." The contrast is certainly striking between the two currents, the former 

 being charged with organic remains, turbid, and muddy, while the latter, flowing 

 from a rocky region, is generally much more limpid. But a greater contrast is 

 presented by the variations in their respective volumes according to the seasons. 

 The western branch, which is by far the longest, the distance from Khartum to its 

 still undetermined source being even greater than from that place to the Mediter- 

 ranean, has also the most uniform discharge. Regulated by the great equatorial 

 lakes, and again by the swampy depressions about Lake No, its contents present 

 comparatively less discrepancies from season to season. But the impetuous Bahr- 

 el-Azraq partakes rather of the nature of a torrent. As soon as the tropical 

 downpours begin to fall on the Abyssinian plateaux, the effect is felt in its rocky 

 channel. Then its discharge exceeds that of its rival, and it was on this ground 

 that Bruce and many subsequent explorers claimed the first rank for the Abyssinian 

 branch. But since the discoveries of Speke, Grant and Baker, it can be regarded 

 only as an important tributary of the Bahr-el-Abiad. Its mean volume is less 

 considerable, nor is it navigable at low water. 



The Blue Nile. 



On the other hand, if it is the White Nile that maintains the perennial stream, 

 to the Blue Nile is due its fertilising properties. Without the first there would be 

 no Egypt ; but for the second the soil of this region would lack its inexhaustible 

 fertility. Not only do the Abyssinians send down their quickening waters to the 

 Nile delta, but they also supply it with the sedimentary matter by which the land 

 is incessantly renewed, and the never-failing return of bountiful harvests insured. 

 In the Ethiopian highlands is solved the mystery of the Egyptian stream, yearly 

 overflowing its banks without apparent cause, and then retiring to its bed after 

 accomplishing its beneficent work. It is to be regretted that the discharge of both 

 rivers has not been accurately determined, the Nilometer at Khartum serving to 

 estimate that of the Blue Nile alone.* 



At the confluence we at once enter regions known to the ancients. The Bahr- 

 el-Azraq is the Astapus of Ptolemy, whose source was possibly known to the 

 Romans. At least they make it rise in a lake, the Coloe Palus, although placing 

 this lake some twelve degrees south of its actual position. Lake Tana (Tsana) is 

 regarded as the reservoir giving rise to the Abai, which is usually taken as the 

 upper course of the Blue Nile. But if length of course alone be taken into con- 

 sideration, this honour should rather be awarded to the Beshto, which has its origin 

 some 150 miles farther east. The Tana emissary, however, has the advantage of 

 being much more constant in its dischargé, thanks to the controlling action of the 



* Approximate estimate of the discharge of the two Kiles at Khartum per second : — 



Bahr-el-Ahiad. I Bahr-el-Azraq. 



High water . . 175,000 cubic feet. High water . . 213,000 cubic feet. 



Low water . . 10,000 ,, ,, Low water 5,500 ,, ,, 



