Underscoring in the movies is to music what a lone gemstone is to a piece of jewelry: a bit of loose treasure bereft of a setting. No composer in the history of cinema has produced more gemstones of the first water than John Williams. But will selections from his Harry Potter soundtracks sound throwaway alongside finished enchantments by Mozart (the overture to The Magic Flute), Paul Dukas (the symphonic poem The Sorcerer’s Apprentice), and Ravel (the one-act opera The Spellbound Child)? Maybe not; all will depend on how the fragments are fused. But make no mistake: Williams has wizardry up his sleeve, in spades. Stéphane Denève conducts. —M.G.