The usual road, however, between Farafra and Dakhla runs south-east from Qasr Farafra to Bir Dikker, and then follows what is known as a gassi, or path swept by the wind free from sand, through a field of biggish dunes, and enters Dakhla Oasis in its north-western corner. This road emerges from the southern side of Dakhla Oasis at the town of Mut, in the form of the Derb el Terfawi, leading to Bir Terfawi and Selima Oases.
Two other roads enter Dakhla Oasis from the north—the Derb el Tawil, or “long road,” that leaves the Nile Valley at Beni Adi, and, after crossing the limestone plateau, descends the cliff that bounds the oasis on the north by a pass known as El Agaba, in the eastern part of the oasis, and leads to Tenida; the other is a little-used road, called the Derb el Khashabi, that runs direct from the north-western corner of the oasis to some point in the Nile Valley to the south of Beni Adi, or perhaps goes direct to Assiut.
There are two roads in regular use between Dakhla and Kharga Oases—the northernmost leads to the well ’Ain Amur, high up on the northern side of a small detached limestone plateau, and the other, the Gubary road, runs along the foot of the cliff on the southern side of this plateau. The latter is waterless and rather longer than the ’Ain Amur road, but runs over the level, and is consequently the one most used, as the ’Ain Amur road necessitates a laborious climb up to the plateau, with a correspondingly difficult descent. It has, however, the advantage of having a well of rather bitter water about midway along it, and in consequence is occasionally used by small parties, especially in the hot weather. Several branch roads split off from the Gubary road, and lead to Beris and the places in the south of Kharga Oasis; but they are hardly ever used.
Dakhla Oasis is bounded on its western side by a field of dunes. The traces of several old roads are to be seen leading in this direction and, before the dunes came down to this part, were probably used by caravans proceeding to Kufara; but these are now, I believe, never followed. Traces of the disused road from Mut, via Owanat, to the Central Sudan has already been mentioned.
Several roads lead over the eastern cliff of Kharga depression; from the southern end of the oasis one goes, via the little oasis of Dungun, to Tumas, near Derr; a second goes, via the small oasis of Kurkur, to Aswan; a third leads in a north-easterly direction to Esna; while a fourth makes across the desert to Farshut. Esna can also be reached from the centre of the oasis by a road starting from Qasr Zaiyan. From Kharga village, in the north of the oasis, roads run to Sohag, Girga, Farshut, Qena, Luxor and Esna. But the main road running to Kharga is the Derb el Arbain, or “Forty days” route of the old slave traders, which leaves the Nile Valley near Assiut and enters the oasis at its northern end, runs through it from north to south, and then proceeds, via the wells of Shebb, Selima Oasis, Lagia and Bir Natrun, to Darfur.
The other great caravan road traversing the Libyan Desert from north to south is that starting from Benghazi, and proceeding, via Jedabya, Aujila and Jalo, to the Kufara group of oases—this was practically the route followed by Rohlfs’ and the Forbes-Hassanein expeditions. From Kufara it continues, via Bushara, Asara and Tikeru, into Wanjunga and on into Central Sudan.
It will be noted that most of the roads traversing the Libyan Desert run roughly from east to west. This is unfortunate, as it necessitates their crossing the sand belts which run approximately at right angles to them, the direction of these belts being due to the strongly predominant character of the northerly winds.
The winds of the Libyan Desert are a rather interesting problem. The prevailing direction from which they blow lies slightly to the west of north, which is not quite the quarter to be expected.
All along the North African coast lies the Mediterranean. The temperature of an area of water of this size and depth changes very slowly, and would not be appreciably affected by one or two days’ sunshine. In the absence of wind, the heat of the atmosphere lying over the sea is largely controlled by that of the water itself.
On the other hand, the Libyan Desert, owing to its lying nearer the equator, is subjected to a much hotter sun. Its intensely arid character prevents it from being cooled in any way by evaporation, and it is entirely unshaded by any vegetation. Under the heat of the tropical sun, the stones and sand of which it is composed very rapidly heat in the sun’s rays. The air overhanging it consequently gets greatly heated in its turn, becomes lighter and so rises, and the colder, denser air from the Mediterranean has to rush in and take its place.