1. =Introduction.=--In the introduction to his brilliant essay on the Hydrology of the Nile[1], an essay, which, though written in 1865, foreshadowed much of what we know to day, Lombardini remarked, with much truth that, no river in the world lends itself to hydrological studies on so majestic a scale as the Nile. The most interesting river of the ancient world, it is still the most interesting river of our time; and, in spite of all that ancient and modern discoveries have unfolded, its discharges are to-day more difficult to unravel and weave together than those of any other stream in either hemisphere. These discharges are still a mystery, and it will need years and years of patient observation and study, at the hands of the Sudan Irrigation Department, to enable us to state with exactitude why its floods rise and fall with such regular and stately precision, why they are never sudden and abrupt, and why its summer supplies can never be completely cut off even in their traverse of over 3000 kilometres through the burning and parched Sahara. Though the mystery of the Nile is far from being solved to-day, still an enormous step in advance has been made by the publication of Sir William Garstin’s Report on the Basin of the Upper Nile[2]. This Report not only contains the results of three years’ observations of the Egyptian Survey Department in the Sudan, of Sir William Garstin’s own observations and studies, but also a mass of information of the Nile and its tributaries collected by Capt. H. G. Lyons. R. E., through four years of uninterrupted study. Those who know the intelligence and method with which Capt. Lyons works, will rate this information at its proper value. [1] _Saggio idrolico sul Nilo_, by ELIA LOMBARDINI, Milan 1865. [2] _Report on the Basin of the Upper Nile_ by SIR WILLIAM GARSTIN. Blue Book Egypt (2) 1904. Lombardini gathered together all the information available at the time that Sir Samuel Baker announced the existence of the Albert Nyanza shortly after Speke and Grant had proclaimed to the world that the Victoria Nyanza was the true source of the Nile. From the information then available he deduced the laws and operations of the great river. About twenty years later, just before the rebellion in the Sudan closed the Nile to the civilized world, a German savant, Joseph Chavanne[3], in his book on the rivers of Africa, collected and tabulated on clear and methodical lines much of the information available in 1883. Though many of his facts are erroneous, his method is clear and his ideas just. Sir William Garstin, in his Report, has developed the information at his disposal on such practical lines as are needed to study the question of insuring an abundant supply of water to the Nile in Egypt during the times of low supply. [3] “_Afrikas Ströme und Flüsse_” by JOSEPH CHAVANNE. Wien 1883.