“What moral to draw, then, of the nonexistence of an innermost planet and the universal triumph of general relativity? At least this: Science is unique among human ways of knowing because it is self-correcting. Every claim is provisional, which is to say each is incomplete in some small or, occasionally, truly consequential way. But in the midst of the fray, it is impossible to be sure what any gap between knowledge and nature might mean. We know now that Vulcan could never have existed; Einstein has shown us so. But no route to such certainty existed for Le Verrier, nor for any of his successors over the next half century. They lacked not facts, but a framework, some alternate way of seeing through which Vulcan's absence could be understood.”