"M. Nordmann has presented Einstein’s principle in words which lift the average reader over many of the difficulties he must encounter in trying to take it in. Remembering Goethe’s maxim that he who would accomplish anything must limit himself, he has not aimed at covering the full field to which Einstein’s teaching is directed. But he succeeds in making many abstruse things intelligible to the layman." - Summary by from the Preface by Viscount Haldane

Giving significant credit to Henri Poincaré and others whose work provided some of the basis from which Einstein developed his Special and General Theories of Relativity, Nordmann provides easily grasped examples to explain complex phenomena outside the grasp of the non-physicist. Finally, he compares and contrasts the Relativist vs. Newtonian interpretation of the world.