(b. Tilsit, Germany, 26 December 1861; d. Göttingen, Germany, 19 March 1928)
Wiechert was the only son of Johann Christian Wiechert, a merchant who died when his son was very young. His mother devoted herself to providing for Wiechert’s education and moved with him to Königsberg. Wiechert never left her until she died in 1927, although he married the daughter of a Göttingen lawyer named Ziebart in 1908.
Wiechert graduated in physics from Königsberg University in 1889 and became a lecturer in physics there in 1890. During the following seven years he carried out research on the atomic structure of electricity and matter. In 1897 he was appointed to the University of Göttingen and became the founder of one of the world’s most famous schools of geophysics. From 1897 to 1914 some of the most far-reaching results concerning the internal structure of the earth emerged from the work of Wiechert and his pupils, who included B. Gutenberg, K. Zöppritz, L. Geiger, and G. Angenheister.
When Wiechert took up his appointment at Göttingen, seismology was beginning to develop as a quantitative science. In 1892 John Milne had produced the first seismograph capable of providing global coverage of ground motions resulting from large earth earthquakes. Following a study trip to Italy in 1899 Wiechert decided that he could greatly improve the seismographs then in use, and by 1900 he had produced his famous inverted-pendulum seismograph and had worked out its theory. This instrument was radically different in design from all previous seismographs and consisted essentially of a heavy mass (up to several tons in some versions) that can oscillate about a pivot below it, the mass being held near the equilibrium position by the pressure of thin springs at the top. The records which were made on smoked paper were outstandingly clear and gave a far closer representation of the ground motion than any previous seismographs had done. Wiechert’s first seismograph recorded horizontal components of the motion, but he later designed instruments to measure vertical components as well. Wiechert seismographs are still used in some of the world’s observatories and continue to supply valuable information.
The Göttingen school of geophysics produced much important work under Wiechert’s leadership including the early tables prepared by Zöppritz that gave the travel times of earthquake waves through the interior of the earth, and Gutenberg’s calculation giving the value of 2.900 kilometers for the depth of the earth’s core. Wiechert himself had contributed to the mathematical theory underlying these calculations and, with Gustav Herglotz, he evolved the basic mathematical process whereby the velocities of seismic waves deep in the interior of the earth can be derived from the travel-time tables. Wiechert had, moreover, been one of the first to suggest the presence of a dense core in the earth and had produced the first theoretical model of the planet that allowed for it.
Wiechert played an important part in the world organization of seismology as one of a small group responsible for founding the International Association of Seismology in 1905, an organization that still flourishes. He also set up geophysical observational centers in the German colonies before World War I, a network that contributed vitally to the early development of seismology.
In addition to his work on seismology, Wiechert contributed to other branches of geophysics, particularly atmospheric electricity. Under his direction various methods were developed for measuring potential gradients and conductivity in the atmosphere.
When World War I came, Wiechert turned his attention to the transmission of sound waves through the atmosphere, applying his knowledge of earthquake theory to observations of sound waves with a view to determining features of the stratification of the atmosphere. He also began investigating the fine structure of the crust of the earth, using specially designed portable seismographs to record waves from artificial explosions. In this research he was one of the pioneers of geophsical prospecting by seismic methods.
Wiechert carried out his work with indefatigable energy and tenacity despite extreme deafness in his later years and the shadow of a serious illness, to which he succumbed at the age of sixty-six.
Wiechert’s most important publications are “Theorie der automatischen Seismographen,” in abhandlungen der K. Gesellschaft der Wissenchaften zu Göttingen, Math,-phys. Kl., n.s. 2 , no. 1 (1903), 1; “Über Erdbebenwellen I, II,” in Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Math.-phys. Kl (1907), 415–549, written with K. Zöppritz: “Our Present, 415–549, written with K. Zöppritz: “Our Present Knowledge of the Earth,” in Report of the Board of Regents of the Smithsonian Institution (1908), 431–449; and “Bestimmung des Weges der Erdbebenwellen im Erdinneren,” in Physikalische Zeitschrift, 11 (1910), 294–311, written with L. Geiger.
An account of Wiechert’s life and scientific work is in “zum Gedenken Emil Wiecherts anlässlich der 100. Wiederkehr seines Geburtstages,” in Veröffentlichungen des Institutes für Bodendynamik und Erdbebenforschung in Jena, no. 72 (1962), 5–21, which includes a full list of Wiecert’s publications.
K. E. Bullen