(b. Tokyo, Japan, 15 January 1881; d. Chiba prefecture, Japan, 19 January 1947)
Ishiwara was the son of Ryo Ishiwara, a minister of a Japanese Christian church, and of Chise Ishiwara. He was graduated from the department of theoretical physics of the College of Science of the Imperial University of Tokyo in July 1906 and continued his studies at the graduate school of the college. He became a teacher at the Army School of Artillery and Engineers in April 1908 and in April 1911 was appointed assistant professor at the college of Science, Tohoku Imperial University. From April 1912 to May 1914 he studied in Munich, Berlin, and Zurich and was greatly influenced by Sommerfeld and Einstein. In May 1914 he became full professor at the Tohoku Imperial University, and in May 1919 he was awarded an Imperial Academy prize for his study on the theory of relativity and the quantum theory.
In August 1921 a love affair forced Ishiwara to resign his post at the university, and, ending his scientific career, he subsequently devoted himself to writing. He edited four volumes of a complete edition of Einstein’s works in Japanese translation (1922-1924) and wrote many popular books and articles introducing and explaining the latest developments in physics. Shortly before the outbreak of World War II he wrote many essays criticizing the government’s control over the study of science.
Ishiwara’s fields of study included the electron theory of metal, the special and general theories of relativity, and the quantum theory. Between 1909 and 1911 he wrote numerous papers dealing with the theory of relativity: on propagation of light within moving objects, cavity radiation, dynamics of electrons, and the energy-momentum tensor of the electromagnetic field. He concentrated particularly on the principle of least action; and in 1913, using this principle, he drew the energy-momentum tensor, which was also done by Minkowski. Ishiwara tried to revise the concept of a constant velocity of light within the theory of relativity, arguing that a variable time scale, such that the product cdt remained constant, would produce equivalent results. From this point of view, between 1913 and 1915 he investigated the interrelationship among the theories of gravity as set up by Gunnar Nordstrom, Abraham, and Einstein and proved that each of their theories can be derived from Ishiwara’s theory.
Ishiwara later tried to develop the five-dimensional theory unifying the gravitational and electromagnetic fields. As suggested by Sommerfeld’s paper (1911) proposing the quantization of the aperiodic process in terms of the action integral, Ishiwara presented, in 1915, an interpretation of the quantum by relating it to the elementary cell in the phase space. That is, he assumed that the motion of a material system is such that we may divide its phase space into elementary cells of equal probability, whose extension is
He utilized this assumption in discussing the spectra of hydrogen and helium and also the spectra of characteristic X rays.
Ishiwara’s papers were published in Proceedings of the Tokyo Mathematico-Physical Society and Science Reports of Tohoku Imperial University. His major works are “Über das prinzip der kleinsten Wirkung in der Elektrodynamik bewegter ponderabler Körper, in Annalen der Physik, 6th ser., 42 (1913), 986-1000; “Zur relativistischen Theorie der Gravitation,” in Science Reports of Tohoku Imperial University, 4 (1915), 111-160; “Universelle Bedeutung des Wirkungsquantums.” in proceedings of the Mathematico- physical Society, 8 (1915), 106-116;and Sōtaisei Genri (“Principle of Relativity”; Tokyo, 1921).
Obituaries are in Kagaku, 22 (1947), 93-99.