“Mozart! Mozart, forgive your assassin! I confess, I killed you…” The words are those of the composer Antonio Salieri, Mozart’s nemesis and eventual murderer, in Miloš Forman’s 1984 film Amadeus, whose screenplay was drawn from the play by Peter Shaffer. It’s fiction, of course. No reputable Mozart scholar believes that Salieri poisoned him; yet through the success of the multi-award-winning movie, an entire generation has grown up believing that Salieri was a mediocrity who murdered a genius out of some gigantic fit of creative jealousy

Just as ironically, Amadeus has made Salieri a far more familiar figure in our day than at any time since his death in 1825. During his lifetime Salieri was a composer performed and admired throughout the continent. If either of the two had...