It seems clear that the great free diver Natalia Molchanova is dead. She was diving last Saturday off the coast of Spain, giving lessons to a rich Russian, when she made a dive of her own and didn’t return. She was almost surely the greatest diver in the history of her sport, which, as mentioned in The New Yorker in 2009, is sometimes described as the world’s second most dangerous activity, after jumping off skyscrapers with parachutes.