Jebel Tuwaiq, the salient physical feature of central Arabia, was found to extend for some 60 m. S. of Wadi Dawasir much farther S. than was previously suspected giving this crescent-shaped plateau a length from Zilfi (lat. 25 N.) of over 500 m. It has an average breadth of 20 m. and a mean elevation of nearly 3,000 ft. above sea-level and 600 ft. above the great plain on the west. The positions of the southern Nejd oases, most of which are sit- uated on or around the Tuwaiq plateau, have been ascertained ; and much further light has been thrown on the limits and peculiar char- acter of the Nefudh and Dahana sand-belts on the N. and N.E. respectively, the former proving to be comparatively hard gravelly plain covered at intervals with parallel sand-belts of varying width and the latter a continuous area of deep sand forced by wind pres- sure into high sand billows or dunes.
Exploration. The journeys of recent travellers have been mostly confined to the central and northern parts of Arabia; but a little new ground has also been broken in the W. and S.W. Some of these explorers, notably Philby, Shakespear and Bell, made route traverses by prismatic compass, checked at intervals by determinations of lat. and long, which greatly enhanced the value of their work (see Map).
Central Arabia. Foremost among the explorers since 1910 is H. St. J. B. Philby. In 1917, when on a mission to the emir of Nejd, he crossed the peninsula from sea to sea, a feat previously accom- plished by only one other European Capt. Sadlier, in 1819 his line being from 'Oqair ('Ojair) on the Persian Gulf to Jidda, by way of Hofuf, Riyadh and Taif. He attributes the exceptional fer- tility of the Hofuf group of oases to the reappearance at the surface there of the rainfall of a very large area. Beyond Riyadh, Philby was the first European to follow, for most of the way, thegreat central pilgrim route to Mecca. He passed Ghat Ghat, a centre of the Waha- bist revival (see AKHWAN MOVEMENT). After 80 m. of limestone desert alternating with belts of Dahana, his route lay across the high- lands of Nejd, a granitic tract 150 m. in breadth, where he found altitudes up to 3,100 ft.; this tract forms part of the great divide between the N.E. and S.E. slopes of Arabia in which, in about lat. 23i N. and long. 43i E., lie the head-waters of W. Sahaba. For no less than 200 m. between the small settlement of Qusuriya, long. 44 30' E., and Khurma, lat. 22 N., long. 42 E. a village of mud huts on the confines of the Hejaz and a point of conflict between the King of the Hejaz and the emir of Nejd he found no settled habitation, but encountered vast herds of gazelles. After crossing the Rakba plain he reached Taif and, following down the gorge of W. Fatima, reached Jidda.
In a subsequent journey, May-June 1918, Philby explored southern Nejd, going 300 m. southward from Riyadh to Dam and back. His route outward lay through the previously unvisited oases of lowland Aflaj and W. Dawasir and he returned along the crest of Tuwaiq by way of highland Aflaj and El Fara. He determined astro- nomically the positions of a number of places, including Riyadh (lat. 24 37' N., long. 46 41' E.), Abu Jifan (lat. 24 29' N.), Hair (lat. 24 21' N.), Sulaiyil (lat. 20 25' N., long. 45 29' E.) and Dam (long. 44 40' E.), and ascertained various heights by aneroid read- ings. As a result of the journey, the hydrography of the Tuwaiq plateau, the backbone of central Arabia, is now as well known as any part before the World War. Philby's estimate of the popula- tion of Riyadh is 1215,000, and its most conspicuous buildings are the palace of the emir and the great Wahabi mosque. The oases of Nejd were found to comprise, usually, a nucleus town with scat- tered hamlets, and not more lhan a few square miles of cultivated land around in each case; and populations never exceeding 10,000. In Aflaj and Kharj he made a notable discovery of ruin fields of considerable area, scattered with stone circles varying from 1045 paces in diameter about heaps of rubble, in the middle of which usually stand large blocks of stone resembling the bases of pillars. Situated on hillsides some distance from cultivation, they suggest burial mounds of an early era, and open up an interesting field for investigation. In both districts, the peculiar system of irrigation from natural reservoirs or deep well pits by means of subterranean channels, or karez, was unexpectedly found to prevail. At Umm el Jebel, just S. of Laila, is a lake f m. by j m., possibly the largest sheet of permanent water in Arabia, and also a number of reservoirs of unusual size, one measuring 500 by 600 yards. In the Makran depression, S. of Badia (lat. 22 N.), are other perennial pools of water surrounded by woods of well-grown trees. The oasis of Dam (his main objective) locally known as " the wadi," Philby found to consist of some 20 separate settlements with a total population of 9,000, mostly of negro origin or of the Dawasir tribe. Dam itself has a population of about 3,000 and owes its importance to its situ- ation near the line of trade between Yemen, Aden, Nejran (seven days distant), and central Arabia.
The negative results of Philby's journeys were almost as valuable as the positive : he found that the Nejd oases are not tropical para- dises; that there is no chain of oases linking Nejd with either Asir or Yemen; and that there is no region of fertility between southern Nejd and Oman, or any settled spot between it and either Oman or Hadhramaut.
Northern Arabia. In 1910, Lt.-Col. G. E. Leachman set out from Kerbela for Hail (J. Shammar) and Riyadh, but, after pass- ing Leina, he had to return to Samawa. Again, in 1912, he left Damascus intending to cross Arabia from N. to S. He got as far as Riyadh by way of Hazil, Leina, and Boreida, but the emir of Nejd refusing him safe conduct, he was obliged to turn eastward and emerged by the usual road through El Hasa to 'Oqair. As a result of these journeys he drew attention to W. Khar, an important affluent of the Euphrates, and discovered its possibilities as a line of communication between Syria and Iraq via the oasis of Jauf, noting that water is obtainable at regular intervals along it. He was first among Europeans to visit the remarkable wells of Leina, of which there are several hundreds, spread over an area of 56 sq. m. ; and he is the only European who has made any record of a journey from J. Shammar to Suq esh Shuyukh. His travels were equally important politically, for he laid the foundations of a good understanding between Britain and the emir of Nejd; he was treacherously shot, Aug. 1920, in Mesopotamia.
In 1913-4, Miss Gertrude Lowthian Bell travelled alone, except for native guides, from Damascus to the neighbourhood of Teima. Thence she passed eastwards over new ground along the southern margin of the Nefudh to J. Shammar and visited Hail; then northwards by Loqa to Nejef and Bagdad. The latter part of the route was especially valuable, as it added considerably to knowledge of a region hitherto traversed only by Wallin in 1848. Miss Bell is the only woman traveller in Arabia, with the exception of Lady Anne Blunt, and one of the few women who can lay just claim to the title " explorer," for she surveyed her route by pris- matic compass from' start to finish.
Capt. Shakespear, British political agent at Kuwait, who became political officer in Nejd in 1914, travelled much in northern and central Arabia. He made compass traverses of his journeys and left voluminous notes which proved of great value. In 1913-4 he crossed the peninsula from Kuwait to Suez by way of Riyadh, Boreida, Haiyaniya and Jauf el 'Amr, following an entirely new course beyond the last-named place. He was killed in action Jan. 24 1915 in a conflict between the forces of Ibn Sa'ud and Ibn Rashid whilst on special duty with the former; his death was a grievous loss to the Indian Political Service, to which he belonged, and to geography.
In 1909, Douglas Carruthers went, primarily, in search of the little known oryx beatrix, a rare antelope inhabiting the interior 01 Arabia, which hitherto had not been hunted by any European, and he obtained a complete series of skins and horns. His route, from Jiza (Ziza) in the Belqa, lay through an' unmapped region, Guar- mani, in 1864, being his only forerunner, except at Teima. He sur- veyed his route southwards to Teima, thence northwards along the Nefudh towards Jauf el 'Amr, and back to Jiza.
Alois Musil, in 19089 and again in 1910, explored extensive tracts between lat. 27 and 36" N. and long. 37 and 44 E., embrac- ing the Hamad, W. Sirhan, Hajara and Wadiyan. He is reported to have made plane-table surveys of parts of these regions which should furnish valuable data towards the mapping of northern Ara- bia ; he added greatly to knowledge of its ethnography, natural his- tory and archaeology. He is the only European who may be said to have penetrated the Hamad to any great extent.
In 1912, a journey from Kuwait through Zilfi, Boreida, and Riyadh to Hofuf and the coast again was made by Barclay Raunkiaer on behalf of the Danish Geographical Society; he made a prismatic compass survey of his route which to a small extent covered new ground. Raunkiaer died in Copenhagen, July 1915.
Capt. Aylmer and Capt. S. S. Butler, in 1907, opened up com- paratively new ground between Bagdad and Jauf.
The Hejaz. The Arabian section of the Hejaz railway was so ill- known before the World War that even the stations could not be enumerated correctly. Determination, in 1917, of the lat. and long, of Ma'an and the observation of the long, of a few stations to the S. enabled valuable adjustments to be made in the trace of the line. A belt of the Hejaz slope, some 300 m. in length between Wejh and Rabugh and a smaller tract immediately S. of Akaba were pretty thoroughly explored as a result of war operations, and a Turkish staff map of the country within a 3O-m. radius of Medina which fell into British hands added further useful data, so that a great part of the Hejaz can now be mapped with fair accuracy. Much was learnt about the Billi tribe who people the rolling country between Wejh and the railway. They were found to be pure nomads without a single settlement in their district except one small garden at El Kurr; while the Juheina and Harb to the S. of them are less nomadic.
Asir and Yemen. Towards the end of 1918, in the course of Idrisi's final campaign against the Turks, British officers could mix somewhat freely with his people on the coast and were able to meet tribesmen from the least known parts of the interior, and so an amount of knowledge, topographical, social and political, was gained. In particular, the composition and distribution of the chief tribes of Asir and Yemen was learnt. The position of Ibha (formerly Menadhir), the headquarters of the Turks, was at long last ascer- tained, though no European got there even when they surrendered. Sabia, Idrisi's capital, about 23 m. N.N.E. of Jeizan, was visited by an Indian medical officer who, for the first time, was able to. describe
