Lucien J. B. LaCoste (1908-1995) was a pioneer in exploration geophysics in the field of gravimetry.
Memorial 1995 
Lucien LaCoste, an important pioneer in geophysics, died on 8 March 1995 in Austin, Texas, at the age of 87. LaCoste was a genius whose innovations have dominated gravimetry and the gravity method of exploration since his firm, LaCoste and Romberg, Inc. (L&R), produced its first instrument just prior to US entry into World War II. The innovations which subsequently poured out of L&R have practically defined this aspect of the discipline by continually increasing the accuracy of measurement and extending the conditions under which these measurements are possible. Remarkable though these achievements are, they are no more so than the man himself.
The first LaCoste and Romberg instruments had an effect in gravimetry analogous to mass extinctions in paleontology; i.e., the 20 or so gravity meters considered state-of-the-art in 1940 were all made obsolete within a few years by the first L&R instrument. Nearly all subsequent designs, whether by LaCoste and Romberg or others, have utilized the principle of the “zero-length spring” which LaCoste discovered in 1933 while a student at the University of Texas.
What an instrument that first one was! Its mechanical sensitivity permitted read- ings to a few parts in 10^-8 g with a simple optical system; it was stable enough to allow reproducible measurement of gravity differences of better than 1 part in 10^7 despite the mechanical and thermal disturbances inherent in field work; and it was robust enough to survive a serious truck accident with minimal damage. LaCoste, in collaboration with Arnold Romberg and then alone (after his partner’s death), adapted this instrument to a wide variety of applications, steadily reduced its size, and generated innovation after innovation which continually expanded the frontiers of gravity exploration.
The first, in 1946, was the underwater meter in which the sensor was mounted on an elevator whose motion counter- acted the wave-induced motion of the sea floor. After stalwart service, these instruments were replaced by an improved model. The sensors, however, were still in excellent shape and were reincarnated as long-period vertical seismometers for the International Deployment of Accelerometers program. The submarine gravity meter (1955) incorporated a heavily air-damped sensor, a gimbal suspension, and long-period inertia bar pendulums for correcting for the swinging of the gimbals. Arriving in rapid succession were the earth-tide meter (1956); an improved version of the submarine meter for use on surface ships in moderate seas (1958); and the model G gravity meter (1960). The latter, a land meter with a reading accuracy of 10^-8 g, weighs only 8.5 kg (including battery and carrying case). It has been the most used meter for land work ever since its development and was the workhorse of the International Gravity Standardization Net of 1971.
A new marine instrument (the S-meter) produced in 1965 featured a sensor with greatly increased air damping, stiffened to withstand horizontal forces, and operated on a gyrostabilized platform. An accuracy of about 10^-6 was soon demonstrated. This became the instrument most used for marine and, later, airborne surveys. Well over 100 were built with significant improvements along the way. Many of these, with upgrades to take advantage of modem computer technology, are still state-of-the-art dynamic gravity meters. The first borehole gravity meter, completed in 1966, was essentially a G-meter built to operate at 100°C and to be leveled and read inside a cylindrical sonde. Its accuracy, 1.6 x 10^-8, was truly remark- able in view of the downhole temperature variations and lack of space for thermal insulation.
The D-meter, similar to the G-meter but with increased accuracy bought at the expense of decreased range, ap- peared in the mid-1970s. It was followed, in 1978, by the “slimhole” borehole instrument in which the gravity sensor was reduced to 67% of the size of the G-meter. Both of these instruments were capable of measuring to a few parts times 10^-9g. LaCoste’s last major achievement (1983) was the straight line marine gravity sensor which used fluid damping and obviated the necessity for precise machining and minute adjustment of the air dampers in the S meter, while conferring several other important advantages.
Lucien was inventive beyond all normal measure; each problem was a challenge and he derived great pleasure from coming up with a good solution. The literature was a springboard for him, rather than a definition of what could be done, and he had the gift of stripping a complex situation down to its fundamentals. He 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, and tested, problems were identified. The devices were rebuilt and retested and so on, often for years, before a new instrument was allowed out of the lab. This development work was efficiently dovetailed with production; he 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, he inspired and held together a loyal group of highly skilled employees, financed his development work out of current earnings, made a profit, and enjoyed himself tremendously. He more than once turned down offers of government funding, 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 would say.
Lucien was an avid tennis player. He lettered three times at the University of Texas and played a good game into his late 70s. Everyone who spent time with him was impressed with his modesty, unassuming friendliness, intellectual and scientific honesty, and complete integrity. He loved to receive informed criticism of his instruments from people who had used them in the field, this frequently resulted in a “fix” and the critic would forevermore be credited. Lucien had genuine admiration for the skills and accomplishments of his com- petitors. For many years his principal competition came from the Worden gravity meter. “People expect Sam Worden and me to be enemies, but we’re not. We’re good friends. I like him a lot,” he would say, and then tell you why he so admired his rival.
His attitude concerning the straight line meter is quite revealing of his character. He spent several years on its development. This involved perfecting a new mechanical suspension and overcoming the problems inherent in the use of fluid damping, thus eliminating cross-coupling corrections and the effects of vibration, and increasing resistance to degradation as a result of rough handling. As a result, he might have been expected to push customers into buying the new instrument. Instead, he actively discouraged sales because he felt the accuracy given by the new design was not substantially better than that of older models which had been well maintained. In this case, his modesty may have been misplaced. Many regret that so few straight line meters were built.
Lucien was awarded SEG’s Kauffman Medal in 1967 and named an Honorary Member in 1986. He was featured in the December 1984 issue of TLE, and the reader is referred to that article for more information about this remarkable man whose career is unlikely to be repeated. 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 and very competitive sci- entific field for 50 years through sheer creative genius, while maintaining complete independence and the highest standards of integrity? It is the stuff of which dreams are made.
Biography Citation for the 1986 SEG Honorary Membership 
Contributed by T. R. LaFehr
"Breakthroughs are always exciting because one day you think there is no good solution and the next day there is no problem."
-Lucien LaCoste, August 22, 1985
Dr. Lucien J. B. LaCoste knows about breakthroughs: he is responsible for a large number of them during the last fifty-five years, and his record of accomplishments in the field of gravity instrumentation is truly incredible. In showing its respect for one of its truly outstanding members and to one of the most gifted and productive persons in the broader scientific community, the SEG stated:
"The Honors and Awards and Executive Committees unanimously elect Dr. Lucien J. B. LaCoste to Honorary Membership for his outstanding contributions to the geophysical profession, especially his several inventions in the field of gravity instrumentation. He conceived the idea of the zero-length spring, now the basis for nearly all conventional gravity measurements, and solved the many problems associated with making the new instrument practical. That achievement alone gives Dr. LaCoste ample recognition in the long and distinguished field of gravity measurement which began in Galileo's time. However, Dr. LaCoste holds a singular place in modern gravimetry for providing many more breakthroughs in the measurement of gravity in very difficult environments for more than 50 years. His underwater, air/sea, and borehole gravity meters have enjoyed unparalleled success."
I can think of no one more deserving of this recognition than Dr. LaCoste: thinker, teacher, inventor, entrepreneur, and friend to so many. His inventiveness started very early in his professional life and is still very much a part of his work.
As a student at the University of Texas, Dr. LaCoste was assigned by his professor, Arnold Romberg, the task of designing a long-period seismograph. While waiting for a tennis opponent who did not show up, Dr. LaCoste conceived the idea of a zero-length spring suspension to obtain significant mechanical magnification. He and Dr. Romberg formed a company and built a gravity meter based on this principle.
Dr. LaCoste was honored by SEG in 1967 for his remarkable achievement in building shipborne gravity meters. While this was a very significant breakthrough for marine exploration, it represents only a small part of his amazing career. After inventing the zero-length spring, he developed an ingenious servo-elevator system for compensating underwater gravity meters subjected to wave action and soft bottom conditions. He established the crosscoupling corrections amid controversy (now recognized as a standard correction in dynamic gravity measurements.) During the last two decades, Dr. LaCoste has been as inventive as ever. He developed a crosscorrelation method for dynamic gravity. He built the borehole gravity meter, capable of reading the earth's gravity field to one part in 109. He solved numerous problems related to temperature, confinement, remoteness, and instrument drift. He recently invented the straight-line meter which holds promise for solving difficult motional problems.
Dr. LaCoste's inquiring mind, inventiveness, and strong inclination toward practical solutions led to business successes unparalleled in the history of gravity instrumentation. LaCoste and Romberg, Inc. has produced far more underwater, shipborne, and borehole gravity meters than all other manufacturers combined.
Future generations of geophysicists will join us in marveling that one person can accomplish so much, but they will not be able to share with Lucien's contemporaries our unique stroke of fortune in knowing this man. One could point out the injustice of limiting a description of his main achievements to the few inadequate sentences written here, but even several pages of discussion of these alone would leave unsaid something very important: Lucien's intellectual and scientific honesty, his unassuming friendliness, his refreshing ability to reduce difficult material to its central and intrinsic meaning, and his dogged determination to get to the bottom of a problem combine to make him a remarkable legend in his own time.
Biography 1967 
Lucien LaCoste received his B. S. degree in electrical engineering in 1931 and his M. A. and Ph. D. degrees in 1933 (Physics) from the University of Texas. From 1933 to 1935 he was a Research Fellow at the California Institute of Technology ; and from 1935 to 1939 he was an Instructor, and later an Assistant Professor of Physics, at the University of Texas.
Since 1939, Dr. LaCoste has been a partner in the firm of LaCoste and Romberg. For five months in 1942 he was a staff member at the Radiation Laboratory at MIT. From 1942 to 1945 he was the Director of War Research at the University of Texas.
LaCost is a member of SEG, AGU, the Institute of Radio Engineers, Sigma Pi Sigma, Tau Beta Pi, Phi Beta Kappa, and Sigma Xi.
Chapin, D. (1999). ”The fertile mind of Lucien J. B. LaCoste (1908–1995).” The Leading Edge, 18(10), 1212–1213.doi: 10.1190/1.1438188
Chris, H. (1995). ”Memorials.” The Leading Edge, 14(9), 1002–1003. doi: 10.1190/tle14091002.1
Clark, R. (1984). ”Lucien LaCoste.” The Leading Edge, 3(12), 24–29.doi: 10.1190/1.1439039
Lucien LaCoste, UT Austin Physics Department Web page 
- Chris, H. (1995). ”Memorials.” The Leading Edge, 14(9), 1002–1003.
- 1986 Honorary Membership Award, Awards Citations of the SEG, Page 78
- Geophysics, 1967, vol XXXII n. 1.
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