English: Diagram of torsion balance used in the Cavendish experiment performed by Henry Cavendish in 1798. It measured the force of gravity between masses M and m, yielding the value of the gravitational constant G. Labels: (M) mass of stationary lead balls, (m) mass of movable lead balls, (F) gravitational force between each pair of balls, (${\displaystyle \theta }$) angle of deflection of balance from equilibrium position, (${\displaystyle \kappa }$) torsion spring coefficient, (r) distance between centers of balls when balance is deflected (L) length of balance beam between centers of small balls. See Cavendish experiment, Harvard Lecture Demonstrations, Harvard Univ.