In 1903 the minimum discharge of the White Nile at its head was 380 cubic metres per second in April and the maximum discharge was 1470 cubic metres per second in December. Table 24 gives the behaviour of the river. The minimum discharge of the White Nile at Khartoum may be taken as 300 cubic metres per second. The preceding paragraph will explain how difficult it will be to know its maximum discharge until a gauge and discharge table are established for the Blue Nile 100 kilometres above Khartoum well above back water, and a gauge and discharge table in the Main Nile north of Omdurman. The difference between these two discharges will be the true discharge of the White Nile which, with its slope of ¹⁄₁₀₀₀₀₀ in flood, is not a river but a flood reservoir. The discharges taken at Duem on the White Nile and at Khartoum on the Blue Nile in 1902 and 1903 are interesting, but of little value for anything except the very date on which they were taken. They were all in backwaters. 19. =The Blue Nile.=--Compared to any river we have yet described, the Blue Nile is a true mountain stream. Draining the southern and more rainy half of Abyssinia, it is the principal source of the Nile in flood. Whatever waters it receives, it carries to the Nile and it is the true parent of the land of Egypt, for the deposit from its muddy waters is that Nile mud which has made Egypt. The Atbara carries waters which are probably more muddy than those of the Blue Nile, but compared to the Blue Nile the Atbara is a small river, and its quota is insignificant by the side of that of the larger stream. The principal tributary of the Blue Nile, the Abai, rises at a height of about 2,700 metres above sea level and after a course of 110 kilometres falls into Lake Tsana. Lake Tsana lies at a level of about 1,760 metres above sea level, and has an area of about 3,000 square kilometres and catchment basin of about 14,000 square kilometres irrespective of the lake area. On the 31st of January 1903, after a very poor rainfall, Mr. C. Dupuis found the discharge 42 cubic metres per second. Calculating from his cross section, it seems that the maximum discharge may be 200 cubic metres per second. As at Lake Victoria, possibly not more than ¹⁄₁₂th the rainfall finds its way into the lake; and, once there, the greater part is evaporated. Little seems to leave the lake, which would consequently make a very poor reservoir. The land rises from the lake in gently undulating downs as a rule. Wherever observed by Mr. Dupuis, the lake was shallow. There are many islands and some of them considerable ones. The rivers feeding the lake are the following:--the Abai discharging 9 cubic metres per second in January 1903, the Reb 2 cubic metres, the Gumara 2, the Magetch 0·3, the Arno Garno 0·3, the Gelda 0·5, the Unfraz 1·2, and many smaller streams say 1·7, or 17 cubic metres per second in all. This of course was in the dry season. Mr. Dupuis considers the evaporation as 4 millimetres per day.