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Figure 1: The torsion balance experiment of Henry Cavendish who in 1797 was the first to experimentally measure the gravitational constant G. (Courtesy of the Journal of Measurement and Technology.)
Figure 2: The apparatus used by the research group at the University of Washington, Seattle, to measure G to record high precision. The device, about two feet across, measures the attractiveness between a hanging plate (hidden inside the cylinder) and several spheres which rotate about the cylinder.
Figure 3: The orbiting Lageos satellite monitors its position relative to the Earth using reflected laser light. From the measured gravitational force between satellite and our planet, and independently measuring G, one can calculate the mass of the Earth.
Reported by: Jens Gundlach at the APS meeting in Long Beach, California