882 NOETH-EAST AFEICA. contrarj', the north-west winds prevail almost as far south as the entrance of the Gulf of Aden. In order to avoid this opposing current, mariners from India or from the Hadramaut coast found it convenient to land their cargoes at some port more easily accessible than the Gulf of Suez. To this cause was due the great importance acquired by the ports of Berenice and Myos Hormos, inducing the Ptolemies and the Caesars to open up highways, provided with watering stations, across the desert between the Nile and the Red Sea. In Egypt also the northern currents prevail normally during the hot season, thus tending to temper the excessive summer heats. Their prevalence is due to the higher temperature of the surrounding sandy deserts, and to the same cause must be attributed the predominance of the same winds even in winter. From the end of March to the beginning of May alone, a struggle takes place between the opposing currents. During this season Egypt is frequently exposed to the influence of the so-called " fifty days' wind," although it seldom prevails for such a length of time ; nor is it ever felt during the night. Everything becomes parched by the hot breath of the khamsin, which is charged with particles of dust, according to Pictet, in the proportion of one gramme to 35 cubic feet of air. At times this pestilential wind deserves the name of simun, or " poison," and numerous instances are recorded of caravans and travellers who, even in Lower Egypt, have lost their pack-animals, killed by the deadly blast of the khamsin. A graphic description is given by Mrs. Speedy of one of these frightful sand- storms, by which her party were nearly overwhelmed in the Arabian desert. " On the horizon coming up behind us was a dense wall of impenetrable dust and sand. It had been scarcely visible in the morning, and even at the time I am now speaking of it was only rising into view. But the keen Arabs, children of the desert, had descried the long dark line as it lay almost immovable in the early morning, and scented the possible danger. Should the wind rise it would be brought up rapidly, and might sweep over us before we could reach Tokar. " We were soon going like the wind. We on our camels, and the Arab on foot, fled before that sandstorm at the rate of between seven and eight miles an hour for over three hours, doing nearly four- and- twenty miles in that time. We had not gone half-way when I insisted on stopping, fearing that the man would be utterly exhausted ; and it was during that rest that I discovered the real state of the case. " We dismounted and sat down among the imdidating ridges of sand on the vast plain, when I turned my head and clearly perceived what we were flying from. The whole truth broke upon me, and for the moment I felt almost paralysed. The wind was rising, coming up as the day advanced, and we were yet a long way from Tokar. There was but one thing to be done. Up again and press on as before. I think we scarcely spoke again before we reached Tokar; the one absorbing thought was to get forward. " Shortly before we arrived at the town, however, the Arab slacken^ his pace and turned round. He made us turn too, and pointed out that the wind had unexpectedly changed, and swept the storm, which had at first set out in our direction, another way. The great thick wall, which might have imprisoned us
