For six decades, between 1854 and 1904, Amos Webber, a black freeman living in the north, recorded his daily experience in diaries. In 1985 Bancroft Prize-winning historian Nick Salvatore discovered them in a Harvard library. Salvatore has woven Webber's diaries into a landmark biography of an ordinary man pursuing a rich and independent life even as he shrewdly observed the society that freed black people from slavery also banished them to the margins of history. Photos & illus.