The book is a course of three lectures given by a well-known American theorist and experimenter P.. Dicke . The first lecture is devoted to the experience of Etvesh (an experiment to test the equivalence of gravitational and gravitational masses), repeated by the author with greater accuracy. The second lecture is devoted to the experiment on the detection and measurement of the flatness of the Sun and its influence on the movement of the perihelion of the planets of the solar system. The third lecture examines the problems of relativistic cosmology in connection with the evolution of the universe from an initial hot state.