John Harrison: How His Chronometer Saved the Lives of Sailors

The H1 was a revolution.

Google commemorated famed English horologist John Harrison on Tuesday, marking what would have been his 325th birthday with a homepage “doodle” that shows him working on his famed inventions. It may seem like a curious creation, but when he unveiled his chronometer in 1735, he helped save the lives of countless sailors with a device that could accurately measure longitude.

Born in Yorkshire, England, in 1693, Harrison was fascinated by watches from an early age. It was the Scilly naval disaster of 1707, where almost 2,000 sailors lost their lives, that set the cogs in motion for Harrison’s future fame. Parliament created the Board of Longitude in 1714 to find a way of avoiding ocean rocks. Latitude has always been relatively easy (just look up at the stars), so the board offered £20,000 (around $5,000,000 today) to anyone who could create an instrument capable of measuring longitude to 30 miles. Harrison’s H1 clock solved that exact problem.

John Harrison's H1 clock


The clock worked on the principle of time changing as ships move longitudinally. Every 15 degrees, one moves east or west and moves the clock forward or back an hour respectively, enabling one to use the sky and a clock to calculate how much they have moved. The issue was that a clock would lose time with humidity and ship movements. The board was focused on instead using the stars to measure longitude, but Harrison created a clock that could accurately keep time at sea.

The board didn’t, however, offer Harrison all of the cash upfront, instead offering £250 with the promise of a further £250 if he could devise an improved version. Harrison created a second version three years later, but a flaw led him to spend the next 19 years working on a third that he claimed even more accurate. The board, skeptical of Harrison’s claims, offered £10,000 plus further installments if he could supply the specifications to other clockmakers and prove it was possible.

Prior to his death, an incensed Harrison produced a specification for a highly accurate clock in a book so inflammatory most of his supporters abandoned him. The mechanism went untested until, 250 years later, the National Maritime Museum tested the design and declared it just five-eighths of a second off after 100 days, the most accurate mechanical free pendulum clock in history.

Harrison may have missed out on a top cash prize from the board, but his reputation has been restored as a legendary horologist.

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