<a href="https://en.wikipedia.org/wiki/torsion_balance" class="extiw" title="w:torsion balance">torsion balance</a> used by <a href="https://en.wikipedia.org/wiki/Paul_R._Heyl" class="extiw" title="w:Paul R. Heyl">Paul R. Heyl</a> in his measurements of the <a href="https://en.wikipedia.org/wiki/gravitational_constant" class="extiw" title="w:gravitational constant">gravitational constant</a> <i>G</i> at the US National Bureau of Standards (now NIST) between 1930 and 1942.  It consists of a horizontal beam with small weights at either ends, suspended by a delicate quartz fiber.  The two large cylindrical weights attract the small weights on the ends of the arms, exerting a torque on the beam that twists the fiber.  The angular deflection of the beam is proportional to the gravitational force between the large and small weights.
National Institute of Standards and Technology
National Institute of Standards and Technology (NIST)