# Chaim Leib Pekeris

**Biography**

(1908-1993)

Born June 15, 1908 in Alytus, Lithuania, the son of Samuel and Chaya (Rivel) Pekeris.

Dr. Pekeris received a Bachelor of Science degree in 1929 and a Doctor of Science degree in 1934 from the Massachusetts Institute of Technology. The following two years were spent at M.I.T. and at Cambridge University as a Rockefeller Fellow. He was a member of the faculty of M.I.T. from 1937 to 1941. He then joined the Mathematical Physics Group of the Division of War Research at Columbia University, heading the group from 1945 to 1947. Following a year as a member of the Institute for Advanced Study at Princeton, he went to Israel in 1949 to head the Department of Applied Mathematics at the newly created Weizmann Institute of Science. When he relinquished that post in 1973, he was honored with the title of Distinguished Institute Professor.

Dr. Pekeris was elected to the National Academy of Sciences of the U.S.A. in 1952 and to the Israel Academy of Sciences and Humanities in 1961. He was also a foreign associate of the Royal Astronomical Society, a foreign honorary member of the American Academy of Arts and Sciences, and a foreign member of the Academia Nazionale dei Lincei.

Among his awards and honors were the Rothschild Prize in mathematics and an honorary degree from Brandeis University.

Dr. Pekeris was a pioneer in applying advanced mathematical methods to a wide range of fundamental problems related to the Earth, atmosphere and oceans. In each of the areas of research in which he has worked he showed a facility for selecting key problems for theoretical study which he then proceeded to solve with unique mathematical insight. His work furthered understanding of such diverse natural phenomena as the Earth's free vibrations, the tides of both the ocean and the atmosphere, the propagation of seismic and electromagnetic pulses and the origin of the earth's magnetic field. In molecular and atomic physics he made contributions to the solution of the Boltzmann integral equation and to spectroscopy of two-electron atoms.

The solid Earth vibrates with certain characteristic frequencies when excited by a large earthquake. The Earth continues to vibrate in free oscillation for some time much as a bell continues to ring after being struck. He calculated in detail the characteristics of the various types of free vibrations which were later shown to be in close agreement with seismograph observations made after the Chilean earthquake of 1960.

The global behavior of ocean tides was first proposed as a geophysical problem by the French mathematician, Laplace, in 1775. The solution of the world ocean problem, involving realistic shorelines and bottom topography was not possible before the advent of the high-speed digital computer. At the 1960 General Assembly of the International Union of Geodesy and Geophysics held in Helsinki, Dr. Pekeris presented the first global numerical integration of the Laplace tidal equations. The theory of tides in the atmosphere was also developed by Dr. Pekeris with Sir G. I. Taylor during his fellowship at Cambridge University.

Water-borne sound waves from explosions in shallow water were investigated by Drs. Ewing and Worzel during World War II. The waves showed marked frequency dispersion, with different frequencies traveling at different speeds. Dr. Pekeris provided a theoretical interpretation of these waves in terms of the normal-mode theory which he extended to cover the case of explosive sound. This theory would provide a basis for underwater sound transmission theory for many yearst to come.

In later years Pekeris devoted himself to explaining the origin of the Earth's magnetic field in terms of the dynamo theory. He has developed models of convective overturning in the Earth's interior which act as a self-excited dynamo to generate the magnetic field of our planet.

Over the 61 years of his scientific activity, Dr. Pekeris published 145 papers in his many fields of interest.

He Died in Rehovot, Israel, on February 24, 1993.