L. K N O PO FF, R. E. H O LZER , C. F. KEN NEL Institu te o f Geophysics and Planetary Physics, University o f California at L os Angeles,

Los Angeles, California 90024

O n M arch 25, 1978, w ith the death of Louis Slichter, the w orld lost a forem ost geophysicist who was also an ou t­standing leader, scholar, and teacher.

Louis was born in M adison, W isconsin, on M ay 19, 1896, son of Charles Sum ner Slichter, P rofessor o f M athem atics and D ean of the G raduate School at the University of W isconsin, and M ary Louise (Byrne) Slich­ter, also a teacher. He received both undergraduate and graduate training at W isconsin, where he was aw arded the Ph .D . in physics in 1922. W ork on subm arine de­tection problem s during W orld W ar I led him to the application of electrical and o ther physical m ethods in the geophysical prospecting for ores as a pa rtn e r in the firm of M ason, Slichter and Gauld.

Slichter entered the academ ic field first as a research associate a t C alifornia Institu te o f T echnology (1930-1931) and then as a m em ber of the faculty a t M assachusetts Institu te of Technology (1931-1945). D uring his career in exp lora­tion geophysics, S lichter was instrum ental in developing m ethods o f electrom agnetic pros­pecting fo r ores. As a consequence o f this w ork he began to consider the inverse boundary value problem and published his first w ork in geophysical inverse problem s in 1933 with reference to seismology, electrical resistivity, and electrom agnetic induction. W ith regard to the inverse problem for traveltim e seismology, he showed that it was impossible to obtain the velocity cross section uniquely in a low-velocity zone.

Early in his career a t M .I.T , he arranged to interconnect th irty miles of public-utility electricity circuits o f the state o f M assachusetts in a massive electrom agnetic induction experim ent to investigate the electrical conductivy o f the E arth at depth. He succeeded in ob tain ing the conductivity profile to a depth of eight kilom etres, a result which led to later extensions by others. It has been debated w hether the successful result o r the prelim inary arrangem ents were the m ore rem arkable.

Slichter developed three-com ponent short-period seism ographs for explosion seismol­ogy studies in New England and W isconsin and was am ong the first to consider refraction seismology as a practical tool fo r exploring the structure of the E arth ’s crust and upper mantle.

He recognized th a t the problem of the tem perature d istribution in the E arth was fundam ental to any discussion of the developm ent of the E arth or the form ation o f its surface features. His 1941 paper on the therm al history o f the E arth , which took in to account radioactivity as a source of internal heat, was a landm ark in the developm ent o f our present concepts of the E arth ’s in ternal processes. He showed tha t even a m inute am ount o f convection was im portan t for heat-transfer processes in the interior of the Earth.

D uring W orld W ar II, Louis S lichter was once again concerned w ith subm arine detection problems. He left M .I.T. in 1945 to take a professorship at the University o f W isconsin, bu t after only two years in his native state he was induced to come to the

Memorial to Louis Byrne Slichter1896-1978

2 THE GEOLOGICA L SOCIETY OF AMERICA

University of California, Los Angeles, as director of the newly formed Institute of Geophys­ics. The demands on his energies to build the Institute did not prevent him from continuing his research on problems of fundamental importance. At UCLA he added research into the gravity field of the Earth to the panoply of his other interests. He mounted expeditions to measure variations of gravity over topographic features of the sea floor by pendulum observations in submarines. He was recognized as a world leader in the analysis of the solid-earth tides. From observations made during a total eclipse in 1961, he was able to place an upper bound on the cross section for shielding of gravitational Fields by matter. He was credited with having made the first observations of the spheroidal free oscillations of the Earth, during its excitation by the great Chilean earthquake of 1960. These observations formed a basic data set for the modern version of the inverse eigenvalue problem.

Slichter was interested in prospecting problems even in his later years. He wrote a major paper concerned with the relative economic merits of conducting searches for ore bodies by drilling in a pattern based on a mathematical grid, as well as with the aid of information from surface geophysical explorations.

Because he was more widely renowned for his genius at defining new fields, for his theoretical skills, and for his devotion to the rigors of data gathering, his skills as an instrumentalist were not as well known. He was the inventor of a number of important geophysical devices. The Slichter seismographs were operated at several seismological observatories for a number of years. Slichter invented a suspension system to minimize the minute but significant effects of tilt of the ice platform at the South Pole on gravimetric measurements. At the time of his death he was developing a tilt-meter to measure the horizontal component of the Earth’s deformation in the tidal and seismic frequency bands, for installation in the ice at the South Pole.

In the more than fifteen years following his retirement he remained active in a research program which, among other things, included the carrying out of gravimetric and seismolog­ical measurements at the South Pole. This work led to the first direct observation of the fortnightly solid-earth tide. A search for the “Slichter mode” of oscillation of the inner core was left unfinished at the time of his death. Despite a long battle against ill health in his later years, he maintained a cheerful manner. His almost daily appearances at his laboratory, to the very end of his life, were punctuated by enthusiastic and stimulating discussions with his colleagues; we continued to learn from this great teacher to the end of his career.

It is difficult to say whether Louis’s brilliant scientific achievements or his personal influence over those associated with him were of greater significance. His students included several leading geophysicists both in the United States and abroad. He organized the famous conference at Rancho Santa Fe in 1950 on the “Evolution of the Earth.” This meeting included leaders in seismology, geochemistry, geochronolgy, petrology, heat flow, astron­omy, and fluid mechanics; it clearly demonstrated the value of synthesizing knowledge from diverse fields in understanding the basic problems of the Earth. From the exchange of information at this conference, it appeared that fractionation of the continents might provide enough differential heating to drive convective processes in the Earth’s mantle.

Louis’s greatest achievement was in building the Institute of Geophysics and Planetary Physics at UCLA. He brought distinguished scientists from a variety of disciplines to UCLA to participate in a continuing colloquy in the interdisciplinary fields of the physical sciences of the natural environment. At the time of his retirement, eight members of the Institute were members of the National Academy of Sciences; the Institute was the foremost organization of its kind in the world. Other institutes elsewhere, spanning a variety of geophysical disciplines, were patterned in later years after the Institute at UCLA. It is the chief monu­ment to his genius with people; a multidisciplinary Institute, after all, mirrored and expressed his own breadth.

MEMORIAL TO LOUIS BYRNE SLICHTER 3

In the minds of his colleagues, Louis will remain personally identified with his continu­ing spirit of good humor, which was a real part of his creativity and leadership. His friendship, warmth, and contagious enthusiasm were integral parts of his ability to generate an extraordinary affection from his colleagues. Martha, Louis’s companion for more than fifty years, is also closely identified with him in the affection of his colleagues. She and their two daughters Mary Lou Whaling and Susan Merry survive him.

It is only natural that Louis Slichter should have been the recipient of many honors. Among these were the Presidential Certificate of Merit (1947); Rockefeller Research Fellow (1946); citation “in recognition of eminent professional services,” University of Wisconsin (1957); the Jackling Award, American Institute of Mining and Metallurgical Engineers (1960); the Thirty-eighth Annual Faculty Lecturer of the University of California, Los Angeles (1963); William Bowie Medalist, American Geophysical Union (1966); Honorary D.Sc., University of Wisconsin (1967); Honorary LL.D., UCLA (1969); Member, National Academy of Sciences and Fellow, American Academy of Arts and Sciences; Fellow, Geologi­cal Society of America, American Physical Society, and American Geophysical Union. Slichter Hall at UCLA and Slichter Foreland in Antarctica have been named for him.

SELECTED BIBLIOGRAPHY OF L. B. SLICHTER

1929 Certain aspects of magnetic surveying: American Institute of Mining and Metallurgi­cal Engineers Transactions, v. 81, p. 238-258.

1932 Observed and theoretical electromagnetic model response of conducting spheres: American Institute of Mining and Metallurgical Engineers Transactions, v. 102, p. 443-459.

----- Theory of the interpretation of seismic travel-time curves in horizontal structures:Physics, v. 3, p. 273-295.

1933 An inverse boundary value problem in electrodynamics: Physics, v. 4, p. 411-418.----- The interpretation of the resistivity prospecting method for horizontal structures:

Physics, v. 4, p. 311-322.1934 Investigation of electrical resistivity of Earth’s crust at great depth by use of power

line and telephone line facilities: Technical Engineering News, v. 25, p. 8-10.1939 (with Pekeris, C. L.) Problem of ice formation: Journal of Applied Physics, v. 10,

p. 135-137.1941 Cooling of the Earth: Geological Society of America Bulletin, v. 52, p. 561-600.1947 Geophysical prospecting for ores: Mining Congress Journal, v. 33, no. 2, p. 47-51.1950 The Rancho Santa Fe Conference Concerning the Evolution of the Earth: Proceed­

ings, National Academy of Sciences, v. 36, p. 511-514.1951 An electromagnetic interpretation problem in geophysics: Geophysics, v. 16,

p. 431-449.----- The crustal structure in the Wisconsin area deduced from large quarry blasts

(unpublished).1953 (with Price, A. T.) Exceptional cases of electromagnetic interpretation problems:

Royal Society [London] Proceedings, ser. A, v. 216, p. 434-435.1954 Seismic interpretation theory for an elastic Earth: Royal Society [London] Proceed­

ings, ser. A, v. 224, p. 43-63.1955 Geophysics applied to prospecting for ores (Fiftieth Anniversary volume): Economic

Geology, p. 885-969.

4 T il l ; GEOLOGICAL SOCIETY OF AMERICA

1959 (with Knopoff, L.) Field of an alternating magnetic dipole on the surface of a layered Earth: Geophysics, v. 24, p. 77-88.

1960 The need of a new philosophy of prospecting (1960 Jackling Lecture): Mining Engineering, v. 12, p. 570-576.

1961 (with Ness, N. F., and Harrison, J. C.) Observations of the free oscillations of the Earth: Journal of Geophysical Research, v. 66, p. 621-629.

----- The fundamental free mode of the Earth’s inner core: Proceedings, National Academyof Sciences, v. 47, p. 186-190.

1965 (withCaputo, M., and Hager, C. L.) An experiment concerning gravitational shielding: Journal of Geophysical Research, v. 70, p. 1541-1551.

1967 Spherical oscillations of the Earth: Royal Astronomical Society Geophysical Journal, v. 14, p. 171-177.

1974 (with Jackson, B. V.) The residual daily Earth tides at South Pole: Journal of Geo­physical Research, v. 79, p. 1711-1715.

1976 (with Nakanishi, K., and Knopoff, L.) Observation of Rayleigh wave dispersion at very long periods: Journal of Geophysical Research, v. 81, p. 4417-4421.(with Zürn, W., and Beaumont, C.) Gravity tides and ocean loading in southern Alaska: Journal of Geophysical Research, v. 81, p. 4923-4932.

1979 (with Zürn, W., Syrstad, E., Knopoff, L., Smythe, W. D., and Uffelman, H.) Long period gravity tides at the South Pole: Journal of Geophysical Research, v. 84, p. 6207-6212.

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