SCHMIDT, CARL AUGUST VON

(b. Diefenbach, Württemberg, Germany, 1 January 1840; d. Stuttgart, Germany, 21 March 1929)

geophysics, astrophysics.

Schmidt, the son of a schoolteacher, studied Protestant theology at the seminary in Tübingen from 1858 to 1862. In 1863 he obtained a doctorate in philosophy from the University of Tübingen, where during the same year he studied mathematics and natural science. From 1864 to 1866 he studied chemistry in Paris and then in Stuttgart at the polytechnic school until 1868. At this time he also took the examination to qualify for teaching mathematics and science in secondary school.

From 1868 to 1871 Schmidt was a student-teacher and from 1872 to 1904, professor at the Realgymnasium in Stuttgart, where he taught chemistry, physics, and mathematics. In addition, in 1896 he was appointed a full member of the Württembert office of statistics and director of the central weather bureau in Stuttgart, which he headed until 1912. From 1902 to 1912 he served on the board of directors of the earthquake research center in Strasbourg and from 1906 to 1912, on the board of the weather station on Lake Constance. The latter institution, founded by H. Hergesell, employed kites in its meteorological research.

One of Schmidt’s notable works (most of which dealt with geophysics and astrophysics) was his “Wellenbewegung und Erdbeben” (1888), in which he demonstrated that seismic waves do not spread rectilinearly from the focus of an earthquake but in curved paths. This phenomenon partly arises from Snell’s law of refraction, and partly because the quotient of density to modulus of elasticity is not constant over the entire surface of the earth. Schmidt also established the law, named for him, concerning the turning point in the apparent propagation velocity of seismic waves: and he introduced the time-distance curve into seismology. In order to measure the vertical movement of the earth he devised the bifilar or trifilar gravimeter.

In 1886, in Württemberg, Schmidt made the first seismic measurements, and in 1892 he and K. Mack established an earthquake observatory in Hohenheim. As early as 1894 he pointed out the separation of seismic waves into longitudinal and transverse components, thus anticipating the subsequent findings of Wiechert. In 1896 Schmidt became director of the entire earthquake bureau in Württemberg, a position he held until 1912. During this period the geomagnetic survey of Württemberg, which Schmidt had promoted, was completed by K. G. F. Haussmann; Schmidt wrote the preface to the publication of the results of the survey. He also reported on the results in a separate work, as well as on the geomagnetic measurement of the Riesen Gebirge (1906)–a region in which current research indicates the presence of an impact crater of a large meteorite.

In other works Schmidt treated terrestrial magnetism and the shape of the earth (1895), the displacement of the terrestrial poles (1896), continental tides (1897), and plumb-line deflection (1898). He contributed to meteorology through works on the application of thermodynamics and the kinetic theory of gases to the study of the atmosphere (1889), on the fostering of aerological observations at the kite station on Lake Constance, and on the discussion of problems of climatology. Further-more, he introduced the concept of barometric tendency into weather forecasting and investigated the mechanism of thunderstorms (1895).

Schmidt directed his astronomical research to questions of refraction in the solar atmosphere and chromosphere (beginning in 1891), and also to general problems of solar physics (rotation of the sun, sources of solar energy, the spectrum of the chromosphere, and solar flares). He also investigated phenomena on the planet Mars (1893) and commented on the stability of the rings of Saturn (1894).

Schmidt’s importance lay in the breadth of his interests and in his knowledge of the interrelated aspects of geophysics and astrophysics.

BIBLIOGRAPHY

A list of Schmidt’s works is in Poggendorff, III (1898), 1200; IV (1904), 1335–1336; and in Beiträge zur Geophysik, 22 (1929), 235–238.

On Schmidt and his work, see K. Kleinschmidt, ibid., 22 (1929), 233–235; in Meteorologische Zeitschrift, 64 (1929), 265–267; and in Unterrichtsblätter für Mathematik und Naturwissenschaften, 35 (1929), 129.

Diedrich Wattenberg