New gravity meter improves measurements

Abstract

One of the best‐known anecdotes in the history of science recounts how the observation of an apple falling from a tree led Isaac Newton to discover the law of gravitation. For good reason, Newton's discovery did not trigger the development of “free‐fall” gravity meters and grand expeditions to the far corners of the Earth to measure gravity. Directly measuring the acceleration of a body in free fall near the surface of the Earth may be conceptually simple, but it is technologically difficult. It wasn't until more than 2 centuries later that time and length measurement techniques reached levels that motivated researchers to build free‐fall absolute gravimeters. These efforts were limited to the construction of one‐of‐a‐kind “laboratory” instruments, minus one notable exception: the construction of six identical absolute gravimeters by the Joint Institute for Laboratory Astrophysics (JILA) [ Niebauer, 1987a]. Geodetic organizations worldwide used the JILA instruments to measure gravity at more than one hundred stations achieving repeatability or precision of a few microgals (1 μGal equals l×10 −8 ms −2 ).