From 1917 he studied stellar structure, applying discoveries in atomic physics to the understanding of radiation pressure, and using A. Einstein’s discovery of mass–energy equivalence to explain energy generation in stars. He obtained observational proof that gravity bends light, as predicted by the general theory of relativity, when he measured slight apparent changes in the positions of stars seen near the Sun during the total solar eclipse of 1919; the accuracy of his results has since been questioned, but their announcement influenced the acceptance of general relativity. In 1924 he derived the mass–luminosity relation. His work was summarized in The Internal Constitution of the Stars (1926).