John Lomax and his son, Alan. During the 1930s and early '40s, the Lomaxes traveled tens of thousands of miles and made thousands of recordings for the Library of Congress of obscure songs and singers. In time they won ac- claim for preserving America's endan- gered folk-music heritage. What has not been understood, says Filene, a Yale grad- uate student, is how much their personal vision, shaped the left-wing politics of the period, helped to define the very "tra- dition" they were purportedly...