Shot Tower

Before 1782, lead shot was cast in moulds or cut from sheet and rolled between plates — slow, and never quite round. William Watts noticed that molten lead falling freely pulls itself into a sphere, because surface tension is the only force shaping it once it leaves the sieve, and that it solidifies before it lands if the drop is long enough. His answer was a tower: pour lead through a perforated pan at the top, let it fall a hundred feet, catch it in a tank of water. No mould, no machining, no finishing, and the spheres are round because nothing else was available for them to be. It is one of the purest cases of a process where the physics does the manufacturing and the equipment merely provides room for it to happen.