by Joseph Horowitz Knopf; 492 pages; $30

Dictators might have envied the cult of personality that centered on Arturo Toscanini in America. For a half-century he reigned supreme in the popular estimation as the world's greatest conductor, and when he died in 1957 at the age of 89, the New York Times spoke for the nation: "Both as an operatic and symphonic conductor, he achieved a stature no other conductor before him had attained."

Or did he? Although revisionists set to work soon after the maestro's death, Understanding Toscanini is the most detailed examination yet of the man, his work and his audience. "To study how Americans perceived...