Adolf Bernhard Marx (1795-1866), the music critic and composer, spent much of his career as professor of music in Berlin and was a friend and mentor of Mendelssohn. His publications included an influential textbook on composition and a biography of Beethoven. The preface to this two-volume study, published in 1863, ranks Gluck (1714-87) wtih Handel, Mozart and Beethoven at the pinnacle of musical achievement. Marx describes Gluck's radical innovations...