[Footnote 1: The use of motor cars for reconnaissances in the Libyan Desert, initiated by the British Army during the Great War, has been considerably developed in the last few years by Prince Kemal el Din Hussein (son of the late Sultan of Egypt), who has made several long exploratory journeys with a fleet of cars of the caterpillar type, specially constructed so as to be capable of carrying considerable loads over sandy tracts which were impassable to the Army patrols. The expeditions organized and led by His Royal Highness have resulted in important additions to geographical knowledge concerning the Libyan Desert, especially the southern and western regions, which have hitherto been practically inaccessible. I had the pleasure of accompanying the Prince on three of his journeys, and am much indebted to him for thus affording me the opportunity of making many observations which would otherwise have been impossible to me. I have further to thank him for kind permission to illustrate this paper by reproductions from a selection of the excellent photographs taken by him during our travels.] [Footnote 2: Kindly communicated by Mr. A. R. Boyce, Director of Sudan Surveys.] [Footnote 3: Printed by the French Army Staff, 1926.] [Footnote 4: By way of comparison, it may be remarked that the area (at the sea-level contour) of the Qattara depression is about four times that of the Dead Sea and Jordan Valley depression; but the latter (reckoning to the lowest point of the bed of the Dead Sea) is about six times the deeper of the two.] [Footnote 5: A similar ambiguity of meaning very commonly attaches to Arabic geographical terms. Thus _beled_ may mean either a village or an entire country; _gebel_, either a mountain or a desert; _gezira_, either an island or a part of the Nile bank which is alternately covered and uncovered by the rise and fall of the river; _bir_, which properly signifies a well, is often used to denote a spring or a water-cistern; _wadi_, though its proper meaning is a valley, is also sometimes employed for a closed-in depression, as in the case of the Wadi Natrun.] [Footnote 6: ‘Nouveaux Mémoires des Missions de la Compagnie de Jesus dans le Levant,’ Tome ii. (Paris, 1717), p. 74. This little book contains a map of Egypt, prepared by Father Sicard at Cairo in 1715, on which the “Mer sans eau” is shown with “bateaux petrifiez” depicted alongside it.] [Footnote 7: See “Particulars concerning the Valley of the Natron Lakes, and that of the Old Bed of the River” (with map) by Andreossi, General of Artillery, in ‘Memoirs Relative to Egypt, Written in That Country during the Campaigns of General Bonaparte in the Years 1798 and 1799, by the Learned and Scientific Men who Accompanied the French Expedition’ (London, 1800), p. 270.] [Footnote 8: See Rohlfs’ ‘Drei Monate in der libyschen Wüste’ (Cassel, 1875), p. 337; and Jordan’s ‘Physische Geographie und Meteorologie der libyschen Wüste’ (Cassel, 1876), p. 214.]