(b. Aichi prefecture, Japan, 24 March 1870; d. Tokyo, Japan, 12 February 1954)
Honda was the son of Hyosaburo and Sato Honda, who were farmers. In July 1897 he was graduated from the department of physics at the College of Science, Tokyo Imperial University, and went on to study at the university’s graduate school. In August 1901 he became a lecturer at the college from which he had graduated. From February 1907 to February 1911 he studied at Göttingen and Berlin, and upon his return he became a professor at the College of Science, Tohoku Imperial University.
In 1916 Honda was awarded an Imperial Academy prize for his study on iron. In May 1919 the Iron and Steel Institute (in 1922 renamed the Research Institute for Iron, Steel, and Other Metals) was made part of the Tohoku Imperial University, with Honda as its director. In 1931 he was awarded the Emperor’s Prize for his invention of a method of producing K.S. magnetic steel. From June 1931 to May 1940 he was president of Tohoku Imperial University, and in 1940 he became an honorary professor there. From April 1949 to May 1953 he was president of Tokyo Science University.
Honda performed geophysical research, including a survey of seiches (surface oscillations) in lakes and swamps throughout Japan and an examination of spouting in thermal springs, but his fame is based on his study kof magnetic substances as well as of the metallurgy of iron and steel. He taught many researchers in these two fields. Until 1907, under the guidance of Hantaro Nagaoka, he did research in magnetostriction, measuring the changes of magnetization and magnetostriction in iron, nickel, and cobalt at temperatures ranging from that of liquid air to 1,200° C. While in Göttingen he learned the technology of metallurgy under Gustav Tammann, particularly the method of alloying, thus laying the basis for his future contribution to the study of the physical metallurgy of steel. In 1909 Honda moved to Berlin and, under Henri du Bois, studied the effect of a change in temperature on the magnetic coefficients of elements. He measured forty-three different elements at temperatures ranging from room temperature to 1,000° C. and discovered that there is a very close relationship between the magnetic coefficient and the periodic law.
Honda used the accumulated data from his extensive measurements to arrive at very significant conclusions. After his return to Japan in 1911, with the assistance of his pupils, he made many measurements of the magnetic coefficients of gaseous bodies and, from 1914, of various chemical compounds. These studies provided much valuable material for his future study of magnetism.
Immediately before the outbreak of World War I, in order to improve shipbuilding technique, there was a great demand in Japan for basic scientific studies of iron and steel. In response to this demand Honda entered into the new field of the physical metallurgy of iron and steel. Starting from existing methods, he developed the methods of thermobalance and magnetic analysis. The focal points of his study were the transformation of steel, the tempering of steel, and the characteristic features of cementite, Fe3 C. Later he also studied nonferrous alloys.
Honda discovered the A0 transformation of cementite and proved that what was then thought to be the A2 transformation of iron and steel was not a true transformation (1915). He obtained these results by studying the way in which the property of one component metal affected the character of an alloy by changing the ratio of the alloy’s components. Through this method he invented K.S. magnetic steel in 1917 and new K.S. Magnetic steel in 1934.
Parallel with these studies Honda pursued the ferromagnetic theory based on the theory of molecular magnets of J. A. Ewing (1916–1923); and after investigating the magnetization of single crystals of iron, nickel, and cobalt, he discovered anisotropic magnetism (1926–1935).
In his extremely wide-ranging researches, Honda often noted many phenomena ignored by others at the time. For instance, in 1920 he observed the magnetic transformation point of ferric oxide, Fe2O3 (Morin temperature), even before Morin discovered it. He also observed the abnormality in the magnetic susceptibility curve of a few antiferromagnetic substances.
I. Original Works. of Honda’s many papers published in Science Reports of the Tohoku Imperial University, the major ones are “Die thermomagnetischen Eigenschaften der Elemente,” 1 (1911–1912), 1–42; “On the Magnetic Transformation of Cementite,” 4 (1915), 161–167, written with H. Takagi; “On the Nature of the A2 Transformation in Iron,” ibid., pp. 169–214; “On K. S. Magnet Steel,” 9 (1920), 417–422; and “On the Magnetisation of Single Crystals of Iron,” 15 (1926), 721–753, written with S. Kaya. The results of his studies on magnetic substances are systematically presented in Magnetism and Matter (Tokyo, 1917); and Magnetic Properties of Matter (Tokyo, 1928).
II. Secondary Literature. On Honda’s life and work, see Memories of Professor Kotaro Honda (Tokyo, 1955), a book of recollections by his pupils; and Teijiro Ishikawa, The Life of Kotaro Honda (Tokyo, 1964); neither work is written in academic style, however, and both lack a bibliography.