Isaac Newton believed no mechanical clock could survive a sea voyage accurately enough to find a ship's longitude. The man who proved him wrong was John Harrison, a self-taught carpenter from Yorkshire born in 1693. This episode explains why longitude is a time problem, how the 1707 Scilly disaster that drowned nearly 2,000 sailors prompted the 1714 Longitude Act and its 20,000-pound prize, and why the smallpox-and-pocket-watch origin legend is almost certainly a Victorian invention.

The conversation follows Harrison's wooden clocks, the gridiron pendulum and the self-lubricating lignum vitae grasshopper escapement, then his 1730 trip to London, the backing of Edmund Halley and George Graham, and the sea clocks H1 through H3, including the yawing problem that doomed H2 and the 17 years spent on H3 that produced the bimetallic strip and cage ...