surrounded by revolving electrons, in a manner like Saturn and its rings (Nagaoka
1904).
In addition to the study of atomic structure, Nagaoka undertook the spectroscopic
study of Zeeman effects for some metals. A Zeeman effect appears as the splitting of
a spectral line into several components in the presence of a magnetic field. Nagaoka
was highly impressed by the discovery of George Ellery Hale (1868–1938) in 1908
of the existence of strong magnetic fields in sunspots, which were derived using the
Zeeman effect behaviors of many Fraunhofer lines. Hale found the maximum
strength of the field ranged from 2900 to 4500 Gauss in different spots (Hale
1908a, b).
In the early twentieth century, spectroscopic observations were not yet initiated in
Japan. Impressed by the role of spectroscopy and the Zeeman effect, Nagaoka wrote
in the Astronomical Herald (Nagaoka 1909):
Recently, the application of optics, especially spectroscopy, to the study of the physical state
of celestial objects has been gaining more and more importance. Spectroscopy is the oldest
and the most useful application of optics.
In the article, Nagaoka explained the mechanism of Zeeman effects in spectroscopy
and its importance in astrophysics.
From a physical point of view, he was also interested in astrophysics, and some of
his results were presented in the Astrophysical Journal. One example is “Vacuum
Arc for Obtaining Spectra Extending from Visible Light to Soft X-Rays” (Nagaoka
and Sugiura 1923).
Geophysics was also one of Nagaoka’s research subjects. He studied geomagnetism under C. S. Knott at Tokyo Imperial University. When Knott and Tanakadate
planned to conduct geomagnetic surveys all over Japan in 1887, Nagaoka accompanied Knott to survey eastern Japan. When a great earthquake occurred in Aichi and
Gifu Prefectures (Nobi earthquake, 濃尾地震), causing severe and widespread
damage in 1891, Tanakadate and Nagaoka analyzed the variation of geomagnetism
before and after the earthquake and discovered a relationship between them. The
following year, the Meiji government established the Investigation Council for the
Prevention of Earthquake (震災予防調査会) to which Tanakadate and Nagaoka
were both appointed as members.
When Nagaoka returned from Europe in 1896, he brought a Repsold gravimeter
that was of greater precision than that used by Tanakadate in the early 1880s. He
used this gravimeter to measure the gravity at Kyoto, Kanazawa, Tokyo, and
Mizusawa in collaboration with his student Shinjo Shinzo. Nagaoka also made
comparative measurements of the gravitational force at Potsdam and Tokyo, from
which the study of the large-scale distribution of gravity in Europe and Japan became
possible. Subsequently the work of Nagaoka was taken over by Shinjo (next
section).
After retirement from Tokyo University in 1925, Nagaoka was appointed head
scientist of Riken (理研, Institute of Physical and Chemical Research) and then
served as the first president of Osaka Imperial University, from 1931 to 1934. In
1925, he was awarded an honorary doctorate together with W. W. Campbell,
28
2 Astronomy from Meiji to Taisho Period 1868–1926
1904).
In addition to the study of atomic structure, Nagaoka undertook the spectroscopic
study of Zeeman effects for some metals. A Zeeman effect appears as the splitting of
a spectral line into several components in the presence of a magnetic field. Nagaoka
was highly impressed by the discovery of George Ellery Hale (1868–1938) in 1908
of the existence of strong magnetic fields in sunspots, which were derived using the
Zeeman effect behaviors of many Fraunhofer lines. Hale found the maximum
strength of the field ranged from 2900 to 4500 Gauss in different spots (Hale
1908a, b).
In the early twentieth century, spectroscopic observations were not yet initiated in
Japan. Impressed by the role of spectroscopy and the Zeeman effect, Nagaoka wrote
in the Astronomical Herald (Nagaoka 1909):
Recently, the application of optics, especially spectroscopy, to the study of the physical state
of celestial objects has been gaining more and more importance. Spectroscopy is the oldest
and the most useful application of optics.
In the article, Nagaoka explained the mechanism of Zeeman effects in spectroscopy
and its importance in astrophysics.
From a physical point of view, he was also interested in astrophysics, and some of
his results were presented in the Astrophysical Journal. One example is “Vacuum
Arc for Obtaining Spectra Extending from Visible Light to Soft X-Rays” (Nagaoka
and Sugiura 1923).
Geophysics was also one of Nagaoka’s research subjects. He studied geomagnetism under C. S. Knott at Tokyo Imperial University. When Knott and Tanakadate
planned to conduct geomagnetic surveys all over Japan in 1887, Nagaoka accompanied Knott to survey eastern Japan. When a great earthquake occurred in Aichi and
Gifu Prefectures (Nobi earthquake, 濃尾地震), causing severe and widespread
damage in 1891, Tanakadate and Nagaoka analyzed the variation of geomagnetism
before and after the earthquake and discovered a relationship between them. The
following year, the Meiji government established the Investigation Council for the
Prevention of Earthquake (震災予防調査会) to which Tanakadate and Nagaoka
were both appointed as members.
When Nagaoka returned from Europe in 1896, he brought a Repsold gravimeter
that was of greater precision than that used by Tanakadate in the early 1880s. He
used this gravimeter to measure the gravity at Kyoto, Kanazawa, Tokyo, and
Mizusawa in collaboration with his student Shinjo Shinzo. Nagaoka also made
comparative measurements of the gravitational force at Potsdam and Tokyo, from
which the study of the large-scale distribution of gravity in Europe and Japan became
possible. Subsequently the work of Nagaoka was taken over by Shinjo (next
section).
After retirement from Tokyo University in 1925, Nagaoka was appointed head
scientist of Riken (理研, Institute of Physical and Chemical Research) and then
served as the first president of Osaka Imperial University, from 1931 to 1934. In
1925, he was awarded an honorary doctorate together with W. W. Campbell,
28
2 Astronomy from Meiji to Taisho Period 1868–1926