Henry Cavendish

The Honourable Henry Cavendish (1731–1810), grandson of the 2nd Duke of Devonshire, was described by Biot as 'the richest of all the learned and the most learned of all the rich'. Pathologically shy and reclusive, avoiding all eye contact and communicating with his servants solely through written notes left on tables, he conducted experiments of sublime precision in his Clapham laboratory.

In 1766, Cavendish discovered hydrogen (*inflammable air*) by reacting zinc with acid, and later showed that burning hydrogen in oxygen produces water, proving water is a chemical compound rather than an element. In 1798, using John Michell's torsion balance to measure the infinitesimal gravitational attraction between lead balls, he 'weighed the Earth', measuring its density as 5.448 times water (within 1% of modern values) and calculating Newton's gravitational constant $G$.