Poor, frustrated, and angered by the "fashion-mongers and mode-purveyors" of art, Richard Wagner published The Art-Work of the Future in 1849. It marked a turning point in his life: an appraisal of the revolutionary passions of mid-century Europe, his farewell to symphonic music, and his vision of the music to come. Beethoven's Ninth Symphony was unsurpassable, he wrote. Henceforth "The Folk must of necessity be the Artist of the Future," and...