As a consequence of these investigations, the present work assumed a form for which one journey of nine months in the countries concerned scarcely seems enough justification. That the book was not completed sooner has been due to the impossibility of spending any time continuously either in research or on writing during the three years which have elapsed since I returned. The fact that this book has been the occupation only of such spare time as I have had available accounts for its many conscious deficiencies, which are unfortunately not the more excusable in a volume of the type which it purports to be. If I can feel that it will have served to stimulate the curiosity of students or have assisted them to find their way about the literature on the subject, I shall consider that as a reward calculated to enhance the pleasure which I have derived from writing and reading about this—to me—fascinating topic. It will be one of my lasting regrets that I was unable to complete with Angus Buchanan his journey across the Sahara from Nigeria to Algiers. The delays which we encountered in Air obliged me to return to resume my duties in that branch of H.M.’s Service in which I was then serving. This is not the place to mention the many things which I owe to Angus Buchanan; perhaps the greatest advantage I derived was the promise we gave one another to travel again together if an occasion should come to him and leisure from another profession to me, whereby we might be enabled to renew our companionship of the road. I am grateful to him for permission to use several of his photographs in the present volume as well as certain information which he collected when we were separately engaged on our different work. To T. A. Glover, the Cinematographer, whose services Angus Buchanan secured to accompany him, I owe many pleasant memories of days spent together and his excellent advice in taking most of the photographs which are included in this book. The French officers whom I encountered in the course of my wanderings were as charming and as friendly as perhaps, of all foreign nations, only Frenchmen know how to be. Were the relations between our respective countries always even remotely similar to those which subsisted between us, there would be no room for the suspicion and pettiness which so often mar diplomatic and political intercourse. The mutual confidence in which we lived is illustrated by two events.