John Harrison

Born on 24 March 1693 in Yorkshire, England, John Harrison was a master clockmaker who solved one of the biggest scientific problems of his era: how to determine one’s longitude. The lack of a reliable longitude measure had led to many shipwrecks, and the problem was deemed serious enough for Parliament to offer up to £20 000 for a simple, practical solution. Some thinkers turned to astronomy, compiling tables that charted the position of the Moon relative to various stars; the distances between Moon and reference stars could be converted to longitude. The method eventually became effective, but it was time-consuming, involved numerous calculations, and required a clear view of the sky. The other option was to create a timepiece that sailors could use to compare local time with the known time at a reference location, such as Greenwich. Harrison set out to build such a clock, which would have to hold up to the unpredictable motion, temperature swings, and humidity fluctuations on board a ship. He created his first marine clock in 1735. Later known as H1, the clock performed relatively well on a voyage to Portugal. Harrison went on to refine his marine clock with models H2 and H3. It would take him 24 years after his first model to create his masterpiece: a sea watch called H4 (pictured below). It performed brilliantly on two transatlantic voyages, and despite some bureaucratic pushback, he eventually received a monetary award from Parliament. Captain James Cook used a copy of H4 on two of his voyages. Today you can see Harrison’s timepieces at the Royal Observatory Greenwich . Dava Sobel’s 1995 book Longitude chronicles Harrison and his battles with the proponents of the lunar distance method. (H4 photo credit: Colonel Warden, CC BY-SA 3.0 )

Date in History: 24 March 1693