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# What is Story of John Harrison’s Clocks?

Longitude is a measurement of how far east or west you are from Greenwich, London, England, where the prime meridian is a specially defined imaginary north-south line that runs between Greenwich’s geographic poles. Longitude is measured in degrees in the east and west of the prime meridian. But do you know what is John Harrison’s contribution to the longitude problem?

The British government promised £20,000 in 1714 to solve the longitude problem, which had resulted in thousands of deaths owing to poor ship location. John Harrison, a carpenter, spent 40 years perfecting the clock, which only lost 39.2 seconds on a 47-day journey.

## Who is John Harrison?

John Harrison was a self-taught clockmaker who worked as a carpenter. He created a series of fantastic precision longcase clocks in the mid-1720s. These clocks had a month-to-month accuracy of one second, which was significantly superior to any other clocks at that time.

After seven years of tinkering, Harrison invented the marine chronometer in 1735, a timekeeping device powered by the motion of a ship rather than gravity. It was so precise that sailors could use it as a portable time standard, comparing their local time to Greenwich Mean Time to calculate longitude or the east-west location on Earth.

Harrison aimed to create a portable clock that could keep time to within three seconds per day to solve the problem of longitude. This would make it far more accurate than even the most expensive watches at the time. (Source: Royal Museums Greenwich

## It’s Time to Leave a Legacy

Harrison proposed that, rather than relying solely on the position of the stars, you could navigate longitude by telling time. Harrison reasoned that keeping a standard time while at sea and comparing it to the time of wherever you are on the globe could be used to calculate longitude.

In pursuit of this theory, Harrison began work in 1727 on developing a clock that could “stay accurate as it got tossed and turned on the open sea.” Having already established himself as a dependable clockmaker, the inventor spent the next seven years developing the H1 clock, which was made entirely of wood.

Harrison’s H1 clock is the story of how he finally had the opportunity to try it at sea after testing it on smaller bodies of water such as rivers. Despite the crew’s difficulties early in the voyage, the clock functioned flawlessly. As a testament to his invention, Harrison saved the ship, which had veered more than 60 miles off course.

Though Harrison’s invention was initially helpful, they asked him to create a more accurate version of the device when he presented it to the British Parliament and their Board of Longitude.

Harrison spent the next 19 years perfecting his second chronometer design, determined to make a more precise invention.

In 1751, Harrison’s efforts would come full circle. He created a miniature version of his life’s work that resembled a small pocket watch. After Harrison had his son take the device with him on a trip to Jamaica, a ship captain offered to buy it on the spot. The inventor was eventually compensated for his years of work by the Board of Longitude. (Source: Royal Museums Greenwich