He died in Paris on 15 October 1934 at the age of 74. His brother, Lucien Poincaré (1862–1920), a physicist, became inspector-general of public instruction in 1902. He is the author of "La Physique moderne" (1906) and "L'Électricité" (1907). Jules Henri Poincaré (1854–1912), an even more distinguished physicist and mathematician, was his first cousin.