SLICHTER, LOUIS BYRNE

(b. Madison, Wisconsin, 19 May 1896; d. Los Angeles, California, 25 March 1978)

geophysics.

Slichter was the second of four sons of Mary Louise Byrne Slichter, a teacher, and Charles Sumner Slichter, a professor of mathematics and dean of the graduate school at the University of Wisconsin. Although Slichter’s father is best remembered as the teacher of Max Mason and Warren Weaver, he was also an accomplished student of analytical mechanics and had a strong interest in the application of mathematics to the study of the physical properties of the earth. In 1899 the elder Slichter developed a theory that treated the motion of groundwater through porous rock as a special case of the steady flow of a perfect fluid. Later he built a successful consulting business upon his development of an electrical technique for measuring the direction and velocity of the flow of groundwater. His taste for mathematical analysis, his dual concern with the abstract and the practical, and his ability to move with equal facility in the academic and business worlds are all mirrored in the career of his son.

Louis Slichter received his education at the University of Wisconsin, Madison, where he took a B.A. in mechanical engineering in 1917 and a Ph.D. in physics in 1922. His studies were interrupted by a brief stint as a student test engineer with the General Electric Company (1917) and wartime service in the study of methods of submarine detection (1917–1919). After completing his Ph.D., Slichter worked for the Submarine Signal Company of Boston. In 1924 Slichter entered into a business partnership with Max Mason, who had taught him mathematical physics at Wisconsin and had supervised his wartime antisubmarine work. Their firm, Mason, Slichter, and Gauld, specialized in providing scientific advice to firms engaged in prospecting for ores.

In 1930 Slichter returned to academic life as a research associate at the California Institute of Technology. The following year he was appointed to the faculty of the Massachusetts Institute of Technology, where he organized a program in geo-physics within the Geology Department. In 1940 Slichter resumed research on the problem of submarine detection, first for the National Academy of Sciences and later for the National Defense Research Committee. He directed the program that developed the magnetic airborne detector and later contributed both to the development of techniques for using rockets in antisubmarine warfare and to the design of torpedoes. In recognition of his contributions, Slichter was awarded a Presidential Certificate of Merit in 1947. After the war Slichter taught briefly at the University of Wisconsin (1945–1947) and then joined the faculty at the University of California, Los Angeles, where he directed the growth of the Institute of Geophysics and Planetary Physics until his retirement in 1963.

Slichter began his career when geophysical methods were first coming into widespread use in prospecting. During the 1920’s demand for oil and minerals could no longer be satisfied by the exploitation of deposits lying close to the surface. At the same time, physicists had begun to develop a variety of electromagnetic and seismographic instruments that promised to be of great value in underground exploration. The conjunction of a strong industrial demand and a new set of techniques produced an era of explosive growth in geophysics.

Slichter was among the many consultants who prospered from these circumstances in the 1920’s. What set him apart, however, was his command of applied mathematics and his strong interest in the theoretical foundations of geophysical prospecting. Although he published little during the 1920’s, very soon after joining the faculty at MIT he wrote a series of influential papers on the solution of inverse boundary value problems associated with the interpretation of seismological, electrical, and electromagnetic data on the earth’s crust. Such problems were central to the geophysics of prospecting, where it is necessary to interpret the observed surface readings of a space field in terms of concealed geological structures—for example, in the interpretation of travel-time curves due to a seismic pulse or the interpretation of a direct-current flow from a point electrode at the surface of a half-space of varying conductivity.

Slichter never abandoned his interest in geophysical prospecting, and during the 1940’s he extended his work by taking up problems relating to the earth’s deeper structure and processes. His 1941 paper on the cooling of the earth was notable both for its analysis of the role of radioactivity as a source of internal heat and for its emphasis on the contribution of even small amounts of convection to heat-transfer processes. Slichter’s analysis of gravimetric and seismographic evidence following the massive earthquake in Chile of 22 May 1960 constituted some of the first convincing evidence for the existence of a solid inner core, which had long been hypothesized by earth scientists.

Although Slichter was best known for his contributions to geophysical theory, he was also accomplished in the craftsmanship of experiment. In 1933 he used thirty miles of telephone circuits as lead wires in an effort to investigate the electrical conductivity of the upper crust. He succeeded in obtaining the conductivity profile to a depth of eight kilometers, a dramatic advance on what was then believed possible. During the 1930’s he was also a pioneer in the use of explosive charges and portable seismographs to study the structure of the earth’s crust. Later, while at UCLA, he took a strong interest in the collection of gravimetric and seismological data at the South Pole. In connection with this work, he invented a suspension system to minimize the effects of tilting of the ice platform on gravimetric measurements.

Slichter was married in 1926 to Martha Mary Buell, they had two daughters. He was awarded honorary degrees by the University of Wisconsin (1967) and UCLA (1969) and was the recipient of the Jackling Award of the American Institute of Mining and Metallurgical Engineers (1960) and the William Bowie Medal of the American Geophysical Union (1966). In 1944 Slichter was elected to the National Academy of Sciences. Slichter Hall at UCLA and Slichter Foreland in Antarctica are named for him.

BIBLIOGRAPHY

I. Original Works. Slichter’s major articles include “The Theory of the Interpretation of Seismic Travel-time Curves in Horizontal Structures,” in Physics3 (1932), 273–295: “The Interpretation of the Resistivity Prospecting Method for Horizontal Structures,” ibid., 4 (1933), 307–322; “An Inverse Boundary Value Problem in Electrodynamics,” ibid., 411–418; “Cooling of the Earth,” in Bulletin of the Geological Society of America, 52 (1941), 561–600: and “The Fundamental Free Mode of the Earth’s Inner Core,” in Proceedings of the National Academy of Sciences, 47 (1961), 186–190.

II. Secondary Literature. On Slichter’s family, see Mark H, Ingraham, Charles Sumner Slichter; The Golden Vector (Madison, Wis., 1972). A colorful biographical sketch and complete bibliography of Slichter’s writings to 1974 are in Robert Rakes Shrock, Geology at M. I. T. 1865-1965: A History of the First Hundred Years of Geology at Massachusetts Institute of Technology, I, The Faculty and Supporting Staff (Cambridge. Mass., 1977), 665–678. Slichter’s work during World War II is described in John Burchard, QED: MIT in World War II (New York, 1948, 47–51, 267–268. On his years at UCLA, see Clarence E. Palmer, “Louis Byrne Slichter; Builder of the Institute of Geophysics and Planetary Physics,” in Journal of Geophysical Research, 68 (1963), 2867–2870. Slichter’s contribution to the study of the earth’s core is discussed in Stephen G. Brush, “Discovery of the Earth’s Core,” in American Journal of Physics, 48 (1980), 705–724. There is one obituary notice: L. Knopoff. R. E. Holzer, and C. F. Kennel, “Memorial to Louis Byrne Slichter, 1896–1978,” in Geological Society of America. Memorials, 10 (1980).

John W. Servos