Smithsonian and Mario Pei's important contribution to Esperanto.

If I understand well, a division of the  Smithsonian National Museum, Folkways, offers the important book by Mario Pei,  Wanted One World Language, as an audio-book.  I rarely buy material on-line, but this may be an exception.  Between the years 1950-1970, Mario Pei's positive view on Esperanto, was the first source of information, for most American Esperanto speakers.

http://www.folkways.si.edu/TrackDetails.aspx?itemid=23529
Se mi bone komprenis la plej grava muzeo de usono enretigis la plej gravan
libron pri Esperanto eble de la jaroj 1950-1970.