"How many a man has dated a new era in his life from the reading of a book," wrote Henry David Thoreau in Walden. Today that book continues to provoke, inspire, and change lives all over the world, and each rereading is fresh and challenging. Yet as Thoreau's countless admirers know, there is more to the man than Walden. An engineer, poet, teacher, naturalist, lecturer, and political activist, he truly had multiple lives to lead, and each one speaks...