LATELY I HAVE FOUND MYSELF REACHING for William Carlos Williams' poetry, more so than for the poems of his great peers--Marianne Moore and Wallace Stevens--who were among the first to recognize his gift. The first, who were, by miracle, his classmates at the University of Pennsylvania, as were H.D. and Ezra Pound. At some point, Carlos Williams became separated in my mind from other American poets. When I asked myself what made Williams seem so different, the answer came from one of the unlikely heroes Williams breathes new life into in one of the finest non-fiction works written by an America...