Years later, however, Orville recalled that what really aroused the Wrights' interest in aviation was "the reading of a book on ornithology." Both Wilbur and Orville would mention this book in their diaries more than once, but never by name, and its identity remains a mystery. Some scholars feel it was not a "book" at all, but rather a pamphlet of translated excerpts of L'Empire de l'Air by Louis-Pierre Mouillard, a panegyric on bird flight that appeared in the Smithsonian Annual Report in 1892. Wilbur would later call the book "one of the most remarkable pieces of aeronautical literature ever published." The truth is, however, L 'Empire was never completely translated into English … and Wilbur could not read French.