A reclusive scientist weighed the entire planet using lead balls and a twisted wire

Henry Cavendish built a torsion balance in 1797, with small lead spheres hung from a thin wire attracting larger fixed spheres through gravity alone. By measuring how far the wire twisted, he calculated the gravitational constant precisely enough to work out Earth's density and, from that, its total mass. Cavendish himself just called it 'weighing the world.'

— Henry Cavendish, Cavendish experiment — Philosophical Transactions of the Royal Society, 1798