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Greenwich and the story of time

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The first accurate chronometer

The government's challenge

John Harrison. From an engraving by Tassaert, published in 1768, after a painting by King. Under the superintendance of the Society for the Diffusion of Useful Knowledge.

John Harrison. © NMM

The British government received hundreds of applications for their challenge to invent an accurate device for measuring longitude at sea. Many were good ideas, so small cash grants were offered so that inventors, scientists and mathematicians could develop them into useful solutions.

John Harrison

A carpenter and clockmaker living in Lincolnshire called John Harrison made one of these applications.

Kendall's third attempt at a marine timekeeper, K3. © NMM

Harrison had already made domestic clocks that ran very well indeed. On hearing of the Longitude prize he decided to dedicate himself to developing a clock that would keep accurate time on board a ship at sea.

Unlike the complicated ‘Lunar Distance’ method, scientists knew, in theory at least, that longitude could be found by using a portable timekeeping device.

Watches were invented 200 years before Harrison, but they were all too inaccurate to be of much use to a navigator. A well-made watch of the early 18th century might keep time to two or three minutes a day at best. What was needed to win the Longitude prize was an accuracy of two or three seconds a day!

The first chronometers

John Harrison's first marine timekeeper, H1. © NMM

His first attempt, now known as ‘H1’, was tested on a voyage to Portugal, not the West Indies as the government had promised. Despite this, the voyage was a success and the clock ran well. It proved for the first time that the mechanical portable timekeeper could be used by navigators.

With funding from the Board of Longitude, the government body set up to oversee the longitude prize,

John Harrison's second marine timekeeper, H2. © NMM

Harrison developed a further two machines, but neither ran much better than the first.

Harrison was still determined, and in 1750 made a breakthrough that would lead to one of the greatest inventions of all time. This was the first accurate portable timekeeper, what we now call a precision watch.

Harrison turned the way scientists thought about timekeeping on its head.

John Harrison's third marine timekeeper, H3.

Instead of adapting a slow beating pendulum clock for use at sea, as Huygens had done, he made a new type of watch that, due to its fast beating mechanism, would keep good time on board a moving ship.

The Prize

After dedicating his entire working life to the longitude problem, Harrison expected prompt and full payment for his invention. Unfortunately, the government was not so easily convinced, despite successful trials of the watch on journeys to both Jamaica and Barbados.

John Harrison's fourth marine timekeeper H4.

Eventually, after much argument, discussion and debate his prize money was paid in one form or another, but never the £20,000 lump-sum he had dreamed of.

Four of Harrison’s experimental timekeepers can be seen today at the Royal Observatory.

Chapter Index

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Glossary

Longitude

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