In reading a large number of works bearing upon the subjects of this Introduction, I have remarked a curious freedom of quotation in most of the writers. I find the same sentence, or at least the same thought, repeated in several books without any reference to the author who first put it forth. Each writer seems to have studied his predecessors with such minuteness that he can quote their very words, but he does not appear to remember whence the words came. When a thought has once been perfectly expressed, it were a ridiculous vanity to seek to frame it in different words, and so far it is undoubtedly wise to make use of the best of what has preceded us; nevertheless, it is well to acknowledge our debt. Yet thoughts, and even phrases, impress themselves on the memory till one unconsciously comes to appropriate them as his own; and this, I doubt not, is the cause of much of the plagiarism I have noticed. It is extremely probable that I have been guilty of the same sin. I have crowded my pages with marks of quotation, sometimes with foot references, sometimes without (for the student of the subject will know where to look for them), but it is quite likely that I have often unconsciously used another’s phrase or metaphor without rendering thanks. So I now append a list of the principal European books I have used, and beg once and for all to record my indebtedness to their writers. The original Arabic authorities will dispense with my acknowledgments, and the catalogue of them would not assist the English reader who wishes to proceed further in the study of the subject, for whom this list may prove useful. BURCKHARDT, J. L. _Notes on the Bedouins and Wahábys._ 2 vols. 1831. DEUTSCH, EMANUEL. _Literary Remains._ 1874. DOZY, R. _Essai sur l´Histoire de l´Islamisme_, trad. par V. Chauvin. 1879. FRESNEL, F. _Lettres sur l´Histoire des Arabes avant l´Islamisme._ 1836-38. HUGHES, REV. T. P. _Notes on Muhammadanism._ 2d ed. 1877. KREMER, A. VON. _Geschichte der herrschenden Ideen des Isláms._ 1868. —— _Culturgeschichte des Orients unter den Chalifen._ 2 vols. 1876, 1877. LANE, E. W. _The Modern Egyptians._ 5th ed. 1 vol. 1860. —— _The Thousand and One Nights_ (notes). 2d ed. 3 vols. 1859, 1860. —— _Selections from the Kur-án._ 1st ed. 1843. —— _Arabic-English Lexicon_, Preface, &c. 1863. LYALL, C. J. _Translations from the Hamâseh and the Aghânî; The Mo´allaqah of Zuheyr._ (Journal As. Soc. of Bengal, 1878.) MUIR, SIR W. _The Life of Mahomet._ 4 vols. New edition.[25] 1867. NÖLDEKE, TH. _Geschichte des Qorâns._ 1860. —— _Beiträge zur Kenntniss der Poesie der alten Araber._ 1864. PALGRAVE, W. GIFFORD. _Central and Eastern Arabia._ 6th ed. 1871. PERCEVAL, A.-P. CAUSSIN DE. _Essai sur l´Histoire des Arabes avant l´Islamisme._ 3 vols. 1847, 1848.