334 NOETH-EAST AFEICA. 



were experienced both by Cailliaud in the Siwah oasis, and by Rohlfs in that of 

 Dakhel farther west. In the Arabian desert the sudden rains on one occasion 

 swept away the village of Desara, near Atfieh which was afterwards rebuilt on a 

 site farther removed from the bed of the wady. 



On the other hand, there has been at times a total absence of rain. Not a drop 

 fell for the space of six years in the district between Kosseir and Keneh ; all 

 vestiges of herbage disappeared from the valleys, and of trees the acacia alone 

 resisted the effects of this protracted drought. Nevertheless the cisterns, which 

 were fed by rain water along the old highway between Coptos and Berenice, are 

 sufficient proof that this district does not lie within the absolutely rainless zone. In 

 certain places natural cisterns or basins are met, formed by the subsidence of the 

 numraulitic rocks, and here the water is collected on an impermeable bed of 

 siliceous formations. These so-called mgheta, which difPer greatly from the surface 

 springs, usually known by the name of el-ain, nearly always contain excellent 

 water, the existence of which the surrounding tribes endeavour carefully to 

 conceal from Europeans. 



But however slight is the winter rainfall, it nevertheless suffices, even without 

 the aid of irrigation, to impart to the vegetation an appearance of freshness and 

 vitality, which again disappears during the summer months. In this respect the 

 Egyptian winter season presents the most striking contrast to that of temperate 

 Europe. In the delta, however, the rainfall represents a part only of the actual 

 discharge. Here the night dews are tolerably abundant, especially during the 

 prevalence of the marine breezes, when they are heavy enough to regularly 

 moisten the roofs and balconies of the houses in Alexandria. But the amount of 

 dew diminishes in direct proportion to the distance from the Mediterranean, and 

 in the Nubian desert, there is a slight discharge only in the vicinity of the river. 

 In the heart of the Egyptian solitudes, where the bare rocks and white sands cause 

 the heat of the sun to radiate into space during the night, it often happens that the 

 dew freezes towards the morning. At its rise the sun, which will in a short time 

 raise the temperature of the ground to over 100° F., begins by melting the 

 slight layer of hoar-frost covering the desert. Even on the arable lands the plants 

 are occasionally frozen, and Mr. Maspero picked up an icicle on the route between 

 Edf u and Esneh. The extremes of heat and cold, although less considerable than 

 in Nubia, are nevertheless very great in Upper Egypt. They increase gradually, 

 proceeding from the north southwards, ranging in this direction between the 

 isothermal lines of 20° and 25°. 



Climatic Changes during the Historic Period. 



Egypt is one of those regions whose climate must have undergone the greatest 

 changes within the historic period. To judge from the bas-reliefs decorating the 

 walls of the Saqq^arah necropolis, probably the oldest in the world, the habits of 

 the people at that time were not those of a nation everywhere hemmed in by the 

 wilderness. They had no knowledge of the camel, a domestic animal without 



