The Recession of the Nebulae

Hubble’s finding in 1929 that nebulae recede with a velocity proportional to their distance might appear to be a simple generalization from measurements of specific nebulae to a generalization about all nebulae. However, his analysis did not respect any hierarchy of generalizations. Since Hubble lacked distance measurements for nearly half of the nebulae in his data set, he needed a complicated set of intersecting inductive inferences to recover his result.