PortCities London
UK Bristol Hartlepool Liverpool London Southampton
You are here:  PortCities London home > The working Thames > Port of science and discovery
Text Only About this Site Feedback
Explore this site
About maritime London
Early port
Tudor and Stuart port
18th-century port
19th-century port
20th-century port
People and places
Port communities
Crime and punishment
Leisure, health and housing
Thames art, literature and architecture
The working Thames
London's docks and shipping
Trades, industries and institutions
Port of science and discovery
Historical events
Ceremony and catastrophe
London in war and conflict
Fun and games
Things to do
Timeline games
Matching games
Send an e-card

Greenwich and the story of time

Lines around the world
Measuring latitude and longitude
Finding longitude at sea
The first accurate chronometer
The Prime Meridian at Greenwich
Greenwich Mean Time (GMT)
Greenwich Meridian Trail
Send this story to a friend Send this story to a friend
Printer-friendly version Printer-friendly version
View this story in pictures View this story in pictures

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.
View full size imageJohn 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.
View full size imageKendall'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.
View full size imageJohn 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.
View full size imageJohn 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.
View full size imageJohn Harrison's third marine timekeeper, H3. © NMM
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.
View full size imageJohn Harrison's fourth marine timekeeper H4. © NMM
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.


Page 5 of 8. Previous page Next page


Find out more
StoriesMaritime Greenwich: A World Heritage Site
A unique historical landscape
Hot spotMaritime Greenwich
Uncover the history of this unique historical landscape
TrailMeridian Trail
Follow the Meridian Line trail through Greenwich Park.
National Maritime Museum/Royal Observatory Greenwich New Opportunities Fund  
Legal & Copyright Partner sites: Bristol Hartlepool Liverpool Southampton About this Site Feedback Text Only