Fig. 3.—View from the summit of Gebel Elba.
The phenomenon of “glories,” or rainbow-coloured rings round the shadow of one’s head cast on to clouds below when the summit was clear, was well observed in the mornings. Three rings were specially distinct and vividly coloured on April 26, and I was able to measure the diameters with an improvised subtense apparatus; measuring to the middle of the yellow in each case, I found the diameters of the rings to be 4½°, 8¾°, and 13°, so that the diameters increase in arithmetical progression. The shadow cast by one’s head and body was most distinct when the cloud-bank was most opaque; the rings, on the other hand, were most brilliant when there was only a thin film of cloud.
The temperatures experienced on the summit were remarkable for their range. On April 25, 26, and 27, 1908, the air was still and full of wet mist, and the days were oppressively hot, while the nights were also warm and damp. On April 28, a cold north-west wind set in, which soon cleared the air; but with the clearness came such a chilling of the air that it was impossible to stand up to the instruments for observations for more than a few minutes at a time; one was glad to take shelter behind rocks from the biting blast, and though we were well within the tropics and the spring was far advanced, we sat shivering with blankets round us even in the sunniest and most sheltered spots we could find. The cold lasted till May 4, when we descended the mountain to be half roasted in the plains below.
As already remarked, Gebel Elba is well supplied with water sources. The two chief are Bir Akwamtra and Bir Kansisrob, both situated on the north side of the mountain. Between them is a small spring called Megwel Akau. On the south side of the mountain are two other wells called Bir Salalat O Sir, and Bir Sararat Serimtai. In times of rainfall there must be scores of rock pools along every drainage line.
Karam Elba is a granite hill rising to 586 metres above sea, close to the north-east foot of Gebel Elba, from which it is separated by a narrow wadi. Close north of Karam Elba are some low granite hills called Takrat Riba, while on the south side is another small granite hill called Mikeriba.
To the east of Karam Elba are some granite hills which, though of no great height, are conspicuous owing to their position on the coast-plain, and being used as landmarks by the local Arabs they bear special names. These are: Alafot, Taar Ara, Kreishim, Abai Sis, and O Wota, the last-named being the largest of them all. Some low banks north of Alafot are called Alafot Onqwab.
Qash Amir (“Scragged Hill” of the Admiralty Charts) is an isolated hill rising abruptly from a sandy plain at the head of Wadi Eikwan, about fifteen kilometres west-north-west of Gebel Elba. Qash Amir well deserves the title given to it by the Admiralty surveyors, for it is a mass of sharp granite spikes which my best guides, skilled climbers though they were, could only ascend with the greatest difficulty. Its top, marked by a beacon, is 724 metres above sea-level and has the position latitude 22° 14′ 31″, longitude 36° 12′ 20″. I had intended to occupy the summit as a main station, but the guides who were sent to erect the beacon reported that the summit was so sharp a spike that there was barely room for a beacon to be built, and that it would be impossible to set up a theodolite tripod on it, while there was not even a narrow ledge where one could sleep within several hundred metres of the summit.
Gebel el Sela is a straggling group of high rugged granite hills rising from the sandy plain to the north-east of Qash Amir. The highest of its peaks reaches to 560 metres above sea-level.
Gebel Sul Hamid is an extensive tract of low dark hills, covering some hundred square kilometres or so to the west of Qash Amir. Its highest peak is 572 metres above sea. The north part of the tract is drained by the Wadi Di-it, the eastern part by the Wadi Eikwan, while the southern drainages pass into a very shallow channel which courses westward over a sandy plain towards Wadi Di-ib, but becomes choked with sand at O Harbub before reaching that great trunk wadi.
Gebel Balatitda is a group of high hills lying between Gebel Sul Hamid and the Wadi Di-ib. Its highest point is 592 metres above sea-level. Bir Meheriqa is situated at the south-west of the mass, on the east side of Wadi Di-ib. The north flanks of Gebel Balatitda are swathed in blown sand.