The torsion balance is a device used to measure extremely small forces. Its invention is credited to Charles Augustin Coulomb (1736-1806), but John Michell (1724?-1793) and Henry Cavendish (1731-1810) also deserve acknowledgement for their work with the device.

Michell, born in Nottinghamshire, England, was a church rector who dabbled in science. He invented a torsion balance in 1790, intending to use it to measure gravitational attraction. Using that value in Isaac Newton's (1642-1727) gravitational formula would enable him to calculate the density of the earth. Michell died before he could accomplish this, but he did make two great accomplishments in the field of astronomy which made him famous. He was the first person to make a realistic estimate as to the distance of the stars, and he discovered the existence of physical double stars.

Born in Nice, France, the independently wealthy Cavendish was part of an aristocratic...