Hess brought to his research a rare talent for precision work combined with a boldness in the formulation of sweeping hypotheses in which, as one colleague put it, ``he took the whole globe as his province.'' His careful attention to detail was evident in his work on peridotite, the subject of his doctoral dissertation, and on other multramafic rocks -- believed to be the principal components of the earth's mantle. The boldness and brilliant intuition for which he became even better known were manifested in his introduction of new concepts on the origin of ocean basins and island arcs (long, curved chains of islands), on mountain building, and on the cause of continental drift. Described by one of his scientific colleagues as ``a fierce fighter for science,'' he was also known for his relaxed and quietly humorous guidance in committee work which, along with his good judgment in public affairs, made him a leader among the scientists who helped guide the development of the national space program.
After taking his Ph.D. degree at Princeton in 1932, Hess spent a year as an instructor at Rutgers and another as a research associate in the Geophysical Laboratory of the Carnegie Institution of Washington before joining the Princeton faculty as instructor in 1934. In 1950 he followed his principal teacher and close friend, Arthur Buddington, as chairman of the department and in 1964 succeeded him as Blair Professor.
During the thirties Hess participated in submarine gravity studies of the West Indies island arc, and, in order to facilitate operations on Navy submarines, he acquired a commission as lieutenant, junior grade, thus initiating a long association with the United States Naval Reserve, where he ultimately rose to the rank of rear admiral. Called to active duty in 1941, he discharged important wartime duties and, at the same time, kept alive his scientific curiosity. Early in the war, he developed a successful system for estimating the daily positions of German submarines in the North Atlantic, and in order to obtain a first-hand test of the effectiveness of his detection program, he served, at his own request, on a hazardous mission aboard the submarine decoy vessel U.S.S. Big Horn. Later he took part in four major landings in the Pacific as commander of the attack transport U.S.S. Cape Johnson. Utilizing the transport's sounding gear, he was able to take thousands of miles of depth soundings that led to his discovery of the flat-topped sea mounts -- submerged ancient islands -- that he later named ``guyots'' in honor of the Swiss geographer Arnold Guyot, founder of the Princeton geology department and first Blair Professor. One of the guyots found by others after Hess's initial discoveries was named ``Hess Guyot'' in his honor.
On his return to Princeton from war service, Hess organized, secured funding for, and directed the Princeton Caribbean Research Project. Supported by the University, the National Science Foundation, the Office of Naval Research, several oil companies, and the governments of Puerto Rico, Venezuela, and Colombia, this continuing program explored every aspect of Caribbean geology and provided a valuable training ground for graduate students from many parts of the world, producing thirty-four Ph.D. dissertations.
In 1960 Hess made his single most important contribution, which is regarded as ``part of the major advance in geologic science of this century.'' In a widely circulated report to the Office of Naval Research, he advanced the theory, now generally accepted, that the earth's crust moved laterally from long, volcanically active oceanic ridges. ``Sea-floor spreading,'' as the process was later named, helped establish the concept of continental drift as scientifically respectable and triggered a ``revolution in the earth sciences.'' This report was formally published in his History of Ocean Basins (1962), which for a time was the single most referenced work in solid-earth geophysics.
Hess also made significant contributions to the affairs of his department, the University, and the national scientific community. During his sixteen years as chairman, the Department of Geology enjoyed substantial growth, later recognized by the change of its name to Department of Geological and Geophysical Sciences. During this same period Hess's faculty colleagues elected him to the Advisory Committee on Appointments and Advancements in eleven successive years and also the faculty advisory committee on the election of a new president in 1957, when Robert F. Goheen was chosen to succeed Harold W. Dodds. Following his election to the National Academy of Sciences in 1952, Hess was called on frequently to head national scientific committees, serving as chairman of the Academy's Committee for Disposal of Radioactive Wastes, the National Research Council's Earth Sciences Division, and the Academy's Space Science Board, which was established to advise the National Aeronautics and Space Administration on scientific aspects of the development of the national space program. At the time of his death, he was one of ten members of a scientific panel appointed to analyze rock samples brought back from the moon by the Apollo 11 crew.
Hess's achievements were widely recognized by fellow scientists. He was elected to the American Philosophical Society and the American Academy of Arts and Sciences, in addition to the National Academy of Sciences, and to foreign membership in the geological societies of London, South Africa, and Venezuela. He also served as president of the Mineralogical Society of America, as well as of the Geological Society of America, which gave him its highest award, the Penrose Medal, in 1966. That same year he was elected to foreign membership in the Academia Nazionale dei Lincei of Rome, the world's oldest academy of science, and became the first earth scientist from the Western hemisphere to receive its $32,000 Feltrinelli Prize. Three years later, just a few months before his death, Yale conferred on him an honorary degree of Doctor of Science.
His death, of a heart attack, occurred on August 25, 1969, in Woods Hole, Massachusetts, while he was presiding at a Space Science Board conference he had organized to reformulate the scientific objectives of lunar exploration. He was buried in the Arlington National Cemetery and was posthumously awarded the National Aeronautics and Space Administration's Distinguished Public Service Award.
In a faculty memorial minute, his Princeton colleagues observed: ``Harry Hess had a deep, almost a religious, reverence for the awesome order of the universe. He possessed that combination of a driving urge to discover truth and a profound humility before the vast truths yet unknown which is the mark of the truly creative scholar.''
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