Summary: THE capture of particles elusive and ephemeral by Paneth and Hofeditz has proved a turning point in the century-old controversy around the question “Do free radicals exist ?” In justice to recent developments, the Faraday Society's discussion in September 1933 centred chiefly round entities falling within the definition: “Free radicals are complexes of abnormal valency, which possess additive properties, but do not carry an electrical charge and are not free ions”. The book under review is concerned with such radicals, of which “the most striking property is their short life”.