Henry Cavendish's torsion balance, 1798.
© Science Museum / Science & Society Picture Library
Model (scale 1:48). The original of this laboratory and gravity balance was made in 1798. A torsion balance is an instrument for measuring weak forces of attraction between mases, from the amount by which they twist a fine wire. The amount depends on the universal gravitational constant, and this method was used to measure its size. The French natural philosopher, Charles Augustin de Coulomb (1736-1806), devised the torsion balance in 1785. The English natural philosopher and chemist Henry Cavendish (1731- 1810) built a torsion balance to measure the gravitational force between two large mases, so that he could make the first calculation of the gravitational constant.