DescriptionGravesande'sring and ball.png English: Ring and ball apparatus in a 1912 scientific instrument catalog for performing Gravesande's experiment
and Co., p. 22 Author Christiaan Huygens (1629-1695) and Willem Jacob Gravesande (1688-1742) in (1751) Christiani Hugenii Zulichemii Opera varia, 1, Lugduni