Authors
H. St. John Philby, Rub' Al Khali: An Account of Exploration in the Great South Desert of Arabia under the Auspices and Patronage of His Majesty 'Abdul 'Aziz ibn Sa'ud, King of the Hejaz and Nejd and Its Dependencies, The Geographical Journal, Vol. 81, No. 1 (Jan., 1933), pp. 1-21
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H. St. J. B. Philby (1933) studied this question.