Longitude: The Hidden Evidence

The story of the Yorkshire carpenter John Harrison has been made famous by Dava Sobel’s bestselling book Longitude, but it has never been clear why, after building a sea-clock that appeared to work well, Harrison refused to compete for the Longitude prize and spent twenty-four years on further research. New documents have come to light which help to explain the puzzle. Harrison’s only sea-trial of a clock was on a trip to Lisbon in 1737. It has been assumed that the clock kept good time. But it now seems that it arrived in Lisbon with a very substantial error -- far greater than would be allowed on a test to win the prize.

This was not reported at the time. Why the clock went wrong, how Harrison addressed the problem, and why the facts were hidden are still unknown.

The Board of Longitude was established in 1714 to encourage development of a ‘practical and useful’ method for finding longitude at sea and adjudicate the award of a prize for success on a voyage to the West Indies. It met for the first time nearly a year after the Lisbon trial. Harrison’s clock (now known as H-1) was the first proposal deemed worthy of a Board meeting in twenty-three years.