John Harrison, the Carpenter Whose Sea Watch Solved Longitude and Who Had to Fight Twenty Years to Be Paid

Finding longitude at sea is, at bottom, a clock problem: the Earth turns fifteen degrees an hour, so a navigator who knows the exact time at a reference port and compares it with local noon knows how far east or west he stands. The catch was building a clock that kept time on a pitching, rolling, freezing, sweltering ship — a thing the age’s best minds, Newton included, doubted possible. The 1714 Longitude Act, born of the Scilly disaster’s two thousand dead, offered £20,000 to anyone who could do it.

John Harrison — a Yorkshire carpenter and self-taught clockmaker who had already built wooden pendulum clocks of freakish accuracy, inventing along the way the bimetallic temperature compensation and near-frictionless escapements horology still honours — took up the problem around 1730 and gave it his life.

From sea clocks to a watch

His first three sea machines — the magnificent brass H1 (1735), H2, and the nineteen-years-in-the-making H3 — were engineering marvels on a wrong path: big machines fighting a ship’s motion. The breakthrough was a change of species. H4 (1759) is a jewelled watch, five inches across, whose fast-beating high-energy balance shrugged at motion. On its 1761-62 trial to Jamaica it lost about five seconds in 81 days — finding longitude within the prize’s strictest terms.

Then the collecting began. The Board of Longitude — dominated by astronomers backing the rival lunar-distance method, with the Astronomer Royal Nevil Maskelyne wearing more hats in the proceedings than justice liked — attributed the result to luck, demanded a second trial (passed, 1764), then paid half the prize against conditions that kept multiplying: full disclosure, surrender of all four machines, and construction of duplicate watches to prove the design repeatable. Harrison, ageing and unbending, complied at the bench and raged on paper.

”By God, Harrison, I will see you righted!”

The endgame ran through the palace. In 1772 the elderly Harrison’s son William put the case to King George III, who tested the fifth watch, H5, at his private observatory — it performed superbly — and reportedly exploded: “By God, Harrison, I will see you righted!” Under royal pressure, Parliament in 1773 granted Harrison £8,750, bringing his lifetime receipts to roughly the prize’s value — though the Board never formally awarded it to anyone. Harrison died three years later, on his eighty-third birthday.

The sea took his side. Larcum Kendall’s copy of H4, K1, sailed with Captain Cook, who called it “our trusty friend the Watch”; within two generations mass-produced chronometers hung in every serious ship, and “chronometer” navigation ruled until satellites. H1 through H4 tick today at Greenwich — H4 kept deliberately stopped, too precious to wear out — a carpenter’s answer to the ocean, in a case the size of a hand.