METEOROLOGY 9 The map at the end of the bulletin based on information from the Physical Department of the Egyptian Ministry of Public Works, shows the general distribution of rain in the Sudan. The quantity increases towards the S. and S.E. and is greatest on the high mountains of Abyssinia. It may be seen from the table that the rainfall of the Red Sea Coast as represented by Port Sudan differs from that of other parts of the Sudan. In the coastai district the rain falls during the Winter months from November to January and there is hardly any in the Summer.

The vaiue of the rainfall depends not only on the total quantity but also on its distribution. For the growth of crops in the Central Sudan, 10° to 15° N. Latitude, the ideal is probably to begin with showers in June, increasing to heavy rain in July continuing with falis at intervals to support continuous growth of vegetation unti! the end of September. If the rains begin late or cease early, the crops do not mature properly and the grazing is affected in a similar way.

Heavy showers late in the season are very favourable for feeding the subsoil water and maintaining supplies to wells and sprirgs until late in the succeeding season. A large total rainfall made up of numerous light showers which evaporate directly from the surface of the ground may be of little assistance to the supply of ground water.

THE NILE FLoops.

The flow of the Nile represents the result of the rainfall over a considerable part of the basin. The annual flood arises principally from the Eastern tributaries, the Blue Nile and the Atbara, which bring the water quickly into the main stream. The height of the Nile is recorded at numerous places along its course and probably the flow of no other river, from its source to its mouth is so carefully watched and measured. At Aswan the channel is bound by hard granitic rock and is little subject to change. The records of the gauge there extend back to 1869 and form a most important series. A study of the heights attained by the series of floods during this time shows that the period from 1869 to 1899 includes a number of high ones and very few low ones while the following period of thirty years includes some very low floods and almost no high ones. The highest floods of the whole period are those of 1874 and 1878 and these were approached in several years before 1899. The highest f'ood since 1899 occurred in 1916 and the level was 93.20 m. During the previous 30 years, 1869—1898, this figure was exceeded in seventeen seasons ; in 1878 by nearly a whole metre and on seven others by more than half a metre. There has been nothing approaching these floods since 1899, and it can be said that none, among the present generation of officials, has seen a really high flood. Records of the Nile gauge at Roda, Cairo, extend from 641 to 1451 and from 1737 with one break to the present time. ‘‘If these maxima are plotted, no regular periodicity appears but it is seen that high or low years tend to occur in groups” (1). We can conclude that the flow of the Nile throughout (1) Nile Control, Cairo, 1921. p. 36.