Lucien LaCoste

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Lucien LaCoste 1908-1995 was a prominent physicist, metrologist. He was coinventor of the modern gravimeter, invented the zero-length spring, and vehicle-mounted gravimeters. He was also co-founder of a prominent company selling gravimetric instruments.

LaCoste discovered the zero-length spring in 1932 while performing an assignment in Arnold Romberg's undergraduate physics course. A zero-length spring is a spring supported in such a way that its exerted force is proportional to its length, rather than the distance it is compressed. That is, over at least part of its travel, it does not conform to Hooke's Law of spring compression.

The zero-length spring is extremely important to seismometers and gravimeters because it permits the design of vertical pendulums with (theoretically) infinite periods. In practice, periods of a thousand seconds are possible, a hundred-fold increase from other forms of pendulum.

Over a short period starting in 1932, the design of these instruments was revolutionized, obsoleting all previous designs.

During this period, LaCoste and his physics teacher Arnold Romberg invented the first modern seismographs and gravimeters, using steel and quartz (respectively) zero-length springs.

While a graduate student, LaCoste decided to go into business together with Romberg, selling advanced gravimeters to oil-exploration companies.

LaCoste's most famous invention is the ship, and aircraft-mounted gravimeter. These revolutionized exploration for minerals by allowing wide-ranging geological surveys. The chief problem that Lacoste defeated was to distinguish the accelerations of the vehicles from the accelerations due to gravity, and measure the minute changes in gravity. Since the accelerations from the vehicle typically are hundreds to thousands of times more forceful than the measured changes, this invention was considered impossible until LaCoste demonstrated it.

These inventions give no flavor for LaCoste's fun-loving, often puckish character. These anecdotes were related by one of his many friends, C.R. Dawson.

As a young man, Dr. LaCoste once caused a near-riot in an Austin speakeasy (a Prohibition-era illegal bar) by looking up from a book and ordering a glass of milk.
Dr. LaCoste was a fine tennis player. One summer, while he was studying at his family home near Fort Sam Houston in San Antonio, he received a phone call from some friends saying that another friend (later to become one of San Antonio's top surgeons) had just been given a rude and unsporting drubbing in a tennis match at the San Antonio Country Club. LaCoste interrupted his reading, ran the few miles from his house to the country club, handily defeated the offender in straight sets, and ran back home to resume his studies.