(b. Nagasaki, Japan, 15 August 1865; d. Tokyo, Japan, 11 December 1950)
Nagaoka graduated from the department of physics of the University of Tokyo in 1887 and entered the graduate school, where he began experimental research in magnetostriction under the British physicist C. G. Knott, who was in Japan between 1883 and 1891. After receiving a doctorate, Nagaoka studied at the universities of Berlin. Munich, and Vienna from 1893 to 1896. He wasespeciallv impressed by Boltzmann’s course on the kinetic theory of gases at the University of Munich. In 1900 Nagaoka was stimulated to study atomic structure to explain radioactivity by the lecture of the Curies at the first international congress of physics in Paris, where he had been invited to deliver a paper on magnetostriction.
From 1901 to 1925 Nagaoka, a leading professor of physics at the University of Tokyo, was primarily responsible for promoting the advancement of physics in Japan. In addition to studying magnetostriction, he did work in atomic structure, geophysics, mathe- matical physics, spectroscopy, and radio waves. The present Japanese tradition of experimental and theoretical physics has been formed almost entirely by Nagaoka and his successors. These include his pupils Kotaro Honda, Jun Ishiwara, Shoji Nishikawa, and Yoshio Nishina and his protégé Hideki Yukawa. For his efforts the Japanese government awarded him the National Cultural Prize in 1937.
Nagaoka is known for his Saturnian atomic model, published in 1904. His criticism of Lord Kelvin’s Aepinus atom, proposed in the paper “Aepinus Atomized”(Philosophical Magazine, 6th ser., 3 , 257–283), was essential for the formation of his model. Rejecting the interpenetrability of two kinds of electricity, which had been supposed by Kelvin, Nagaoka arranged electrons outside the central positive charge. Thus his model consists of a number of electrons of equal mass, arranged uniformly in a ring, and a positively charged sphere of large mass at the center of the ring. This material view of electricity played the most important role in Nagaokas’ theory of the structure of matter, which was based partly on Boltzmann’s atomistic influence and partly on the reflection of unsophisticated scientific thought in Japan during the early Meiji period. He obtained the equations of motion of the ring in his model according to Maxwell’s work on the stability of the motion of Saturn’s rings, which he had read in Germany. In 1904–1905 Nagaoka dealt with band spectra, dispersion of light, and mutual action of atoms, based on the assumption of a Saturnian atom. Having renounced his model he started spectroscopic experiments to investigate the actual arrangement of electrons in the atom in 1908.
Nagaoka’s paper on the Saturnian atomic model is in Proceedings of the Tokyo Mathematico-Physieal Society, 2nd ser., 2 (1904), 92–107; and Philosophical Magazine, 6th ser., 7 (1904), 445–455.
Anniversary Volume Dedicated to Professor Nagaoka by His Friends and Pupils on the Completion of Twenty-Five Years of His Professorship (Tokyo, 1925) contains a bibliography of his works. The origin of his model is
discussed in Eri Yagi, “On Nagaoka’s Saturnian Atomic Model,”in Japanese Studies in the History of Seience (1964), no. 3, 29–47. Nagaoka’s life and work are fully discussed in connection with the development of physics in Japan in Kiyomobu Itakura, Tosaka ktmura, and Eri Yagi, A Biography of Hantaro Nagaoka (Tokyo, 1973), written in Japanese.