Hantaro Nagaoka

Physicist. The only son of Nagaoka Jisaburo (1839-1891), a samurai of Omura Domain in Hizen Province (Nagasaki Prefecture). The "han" in his name was named after his grandfather, Nakao Hanbei. In 1874 (Meiji 7), he moved to Tokyo with his family. After attending the Tokyo English School and the National Osaka English School, he entered the Faculty of Science at the University of Tokyo in 1882, graduating in 1887 and moving on to graduate school. In 1890, he became an assistant professor at the Faculty of Science at the Imperial University. In 1892, he married Misako, the third daughter of Mitsukuri Rinsho. In 1893, he obtained a doctorate in science for his research into magnetostriction, and in the same year went to study in Germany, where he learned from Helmholtz, Planck, and Kundt, and listened to lectures by Boltzmann. In 1896, he returned to Japan and became a professor at the Imperial University (until 1926). In 1917 (Taisho 6), he was appointed head of the Physics Department at the RIKEN Institute, in 1931 (Showa 6) he became the first president of Osaka Imperial University (until 1934), in 1934 he became a member of the House of Peers, in 1937 he was awarded the 1st Order of Culture, in 1939 he became president of the Imperial Academy (until 1948), and in 1944 he became counselor to the Institute of Technology.

In 1903, he presented a Saturn-type atomic nucleus model, which became the forerunner of Rutherford's nuclear model. He was active in many fields, including spectroscopy, atomic structure research, steel, and geophysics, and raised the standard of Japanese physics to an international level. In 1924, he announced the "success" of the mercury reduction to gold experiment, which caused a stir. In a notebook dated December 14, 1939, he wrote to the Nobel Committee, "Drafting a letter recommending Yukawa." In 1943, Yukawa Hideki was awarded the Order of Culture on his recommendation. Honda Kotaro was his first student, and physicist Sagane Ryokichi (1905-1969) was Nagaoka's fifth son. He was from the same hometown as philosopher Tomonaga Sanjuro, and was a distant relative.

[Satoshi Ihara]

"The Life of Hantaro Nagaoka" by Masanori Itakura, Tosaku Kimura, and Eri Yagi (1973, Asahi Shimbun)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

物理学者。肥前国（長崎県）大村藩士長岡治三郎(じさぶろう)（1839―1891）のひとり息子。半太郎の半は祖父中尾半兵衛にちなむ。1874年（明治7）一家で上京。東京英語学校、官立大阪英語学校を経て、1882年東京大学理学部入学、1887年卒業、大学院に進む。1890年帝国大学理科大学助教授。1892年箕作麟祥(みつくりりんしょう)の三女操子(みさこ)と結婚。1893年磁気ひずみ現象の研究で理学博士、同年ドイツに留学、ヘルムホルツ、プランク、クントらに学び、ボルツマンの講義を聞く。1896年帰国し帝国大学教授（～1926）。1917年（大正6）理化学研究所物理部長兼任、1931年（昭和6）大阪帝大初代総長（～1934）、1934年貴族院議員、1937年第1回文化勲章受章、1939年帝国学士院院長（～1948）、1944年技術院参与。

　1903年土星型原子核模型を発表、ラザフォードの有核模型の先駆となる。分光学や原子構造の研究、鉄鋼、地球物理学など多分野で活躍し、日本の物理学の水準を国際的な高さに引き上げた。1924年水銀還金実験の「成功」を発表、話題をよんだ。1939年12月14日付けノートにノーベル委員会あてで「湯川を推薦する手紙を起草す」とあるという。1943年の湯川秀樹(ひでき)の文化勲章は彼の推薦による。最初の門下に本多光太郎がおり、物理学者嵯峨根遼吉(さがねりょうきち)（1905―1969）は長岡の五男。哲学者朝永三十郎(ともながさんじゅうろう)とは同郷で、遠縁にあたる。

［井原　聰］

『板倉聖宣・木村東作・八木江里著『長岡半太郎伝』（1973・朝日新聞社）』

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