The gravity meters Lucien B. LaCoste invented revolutionized geodesy and gave scientists the ability to precisely measure variations in Earth's gravity from land, water, and space.
by Chris Harrison, LCT Inc., Santa Barbara, Calif.
Can you imagine this happening today . . . brilliant young faculty member abandons a secure academic career to form a company with his senior professor, then dominates a major competitive field of geophysics for 50 years through sheer creative genius, while maintaining complete independence and the highest standards of integrity? It is the stuff that dreams are made of.
Lucien LaCoste managed to accomplish all of these feats. He was born in 1908. When he reached college age, he chose to attend the University of Texas at Austin. He was attracted by the quality of the tennis program there, which was arguably the best in the country in the late 1920s. He lettered in tennis three times, developed an interest in physics, and obtained his doctorate in 1933. He then went to the California Institute of Technology to study quantum mechanics, a move calculated to bring him back to Texas as a member of the faculty. Quantum mechanics was a new field with few qualified instructors.
And so it was and might have remained had not his professor, Arnold Romberg, given each of his students a different technical problem to solve in the fall of 1932. LaCoste's was to design a long-period vertical seismometer. While waiting for a no-show tennis partner LaCoste realized that if he could make a spring that exerted a force proportional to its length rather than to its extension beyond an initial unstressed length, he could build a suspension that was its own triangle of forces and would be in equilibrium wherever the mass was positioned. Furthermore, he realized that he could make a spring with this suspension by winding it so that it was prestressed, and that a finite force had to be exerted before the spring began to stretch. Using these principles, he and Romberg built a seismometer superior to any instrument then available.
Although the majority of long-period vertical seismometers built during the next 50 years employed the LaCoste suspension, neither LaCoste nor Romberg attempted to build them commercially. However, the founders of the American Seismograph Company had read two papers LaCoste had written about the suspension and thought it could be used to make a gravity meter. Wishing to diversify, one of them visited the university to discuss the matter with professors LaCoste and Romberg, who enthusiastically accepted the challenge. They built and demonstrated a gravity meter, but controversy developed within the partnership, and it was dissolved. The seed had been sown, however, and in 1939 LaCoste and Romberg took leaves of absence from the university, founded the LaCoste and Romberg Company, and began building gravity meters in Romberg's basement. They expected to saturate the market within a few years and then to return to academia.
The early years were difficult. Two patent problems threatened to sink the company before it had sold a single instrument. LaCoste had failed to patent the LaCoste suspension, so this invention was in the public domain. Then their patent attorney, who had earlier given them the all-clear, informed them that their instrument had to be redesigned. One of the instrument's features infringed on another patent. An alternative had to be invented and tested quickly. Customers were waiting and the fate of the company was at stake. Then World War II intervened, and both LaCoste and Romberg were involved in military research, while Arnold's son, Frederick Romberg, ran the company. They returned after the war, and then after Romberg's death, LaCoste alone embarked on a 40-year period of extraordinary creativity and inventiveness that revolutionized and dominated gravimetry and provided the instrumentation for most of the exploration and scientific work done in that field.
LaCoste and Romberg's first land meters weighed nearly 40 kg and required a two-man crew. They were replaced in 1942 by a smaller model that could easily be handled by one person. These land meters performed so well and were so robust that within a few years all the gravity meters that were considered state-of-the-art in 1940 were obsolete. The underwater meter came in 1946. After performing stalwart service, these instruments were replaced by an improved model.
In 1954, LaCoste developed a gravity meter that could be used on submarines. By 1960, he had designed the G gravity meter, a highly accurate land meter with worldwide range. Unlike its heavy predecessors, the new meter weighed only 8.5 kg—carrying case and battery included. It is still used widely used for precise gravity surveys on land. LaCoste produced a new marine gravity meter, the S meter, in 1965. It soon became the instrument most used in exploration work for marine and airborne gravity surveys. Well over 100 were built with significant improvements along the way. Many S meters have been upgraded to take advantage of modern computer technology and are still considered to be state-of-the-art.
LaCoste also designed the first gravity meter that could be used in exploratory holes drilled deep in the Earth. It was completed in 1966 and was essentially a G meter built to operate at 100°C. Its accuracy was truly remarkable considering the temperature variations it had to withstand as it traveled to different depths within the Earth and the space it lacked for thermal insulation. The D meter, similar to the G meter but with increased accuracy bought at the expense of decreased range, appeared in the mid-1970s. It was followed by the "slimhole" borehole gravity meter in 1978. The slimhole meter's gravity sensor was 67% smaller than the G meter's. LaCoste's last major achievement was the straight-line marine gravity sensor, developed in 1983, which used fluid damping to provide measurements.
LaCoste was inventive beyond all normal measure; each problem was a challenge, and he derived great pleasure from finding a good solution. Scientific literature served as a springboard for him, rather than a limiting definition of what could be done, and he had a gift for stripping a complex situation down to its fundamentals. LaCoste was a good analyst and often had a mathematical derivation tucked away in a filing cabinet, but he was also a master of the empirical and could make things work even when the situation was too complex for exact analysis. Most of all, he was patient; new devices were built, tested, problems identified, rebuilt, tested, . . . and so on, often for years before a new instrument was allowed out of the lab. This development work was efficiently dovetailed with production. LaCoste never allowed his company to get so large that he did not know what every employee was doing, and he never cut back on development even when faced with a formidable backlog of orders.
While disclaiming managerial ability and business acumen, LaCoste inspired and held together a loyal group of highly skilled employees, financed his development work out of his earnings, made a profit, and enjoyed himself tremendously. He turned down offers of government funding more than once, preferring to have complete control over what he did and to accept the risk of failure. "I'll build it and, if they like it, they'll buy it," he said. Lucien LaCoste was truly a remarkable man whose career is unlikely to be matched. He died in 1995, but his scientific legacy lives on.
For more information about Lucien LaCoste, see the December 1984 issue of The Leading Edge.
Source: Eos, December 12, 1995, p. 516.
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