The Bruce-Oosterwijck sea clock played an important role in the long quest for a practical way of determining longitude at sea, helping solve a problem that made sea voyages incredibly hazardous.

Made in 1662, the clock was part of the first attempt to establish longitude at sea with a purpose-made mechanical timepiece. Latitude (the north-south position of a point on the Earth's surface) could be worked out by observing the height of the sun or stars above the horizon. Longitude (the east-west position) was harder to ascertain.

The ‘longitude problem’ is a famous example of a scientific endeavour with a truly global effect. However, the early Scottish contribution is less well-known.

Who were Bruce and Oosterwijck?

Alexander Bruce, Earl of Kincardine commissioned the mechanism for this clock from the Dutch maker Severyn Oosterwijck in 1662. Bruce lived in the Netherlands as part of the Stuart court in exile. He was also one of the founder members of the Royal Society.

Oosterwijck (c.1637- c.1694) was a leading clockmaker and craftsman of the Dutch golden age. He played a key part in the birth of the pendulum clock. He became the first Master of the Hague Clockmaker’s guild, having been one of the petitioners for its incorporation.

How was longitude worked out?

As the Earth rotates, different places on the globe experience different times. Sunrise comes first to Moscow, then Edinburgh, then New York. On a smaller scale, sunrise (and noon, and sunset) comes just over four minutes earlier in Edinburgh than in Glasgow to its west. If you have a clock which was set to the exact sun time in one place and it keeps accurate time as you carry it somewhere else, you can work out how far east or west you have travelled. The difference between the local time from the sun where you are, and the time at your reference location gives the longitude.

To use this method to work out longitude at sea required a clock that would keep accurate time on board a ship. It had to work in humid conditions on a pitching and tossing sea. In the 17th century, this was easier said than done.

Knowing your latitude and longitude at sea is not enough for good navigation. It is also vital to know where the ports and dangerous rocks are, which requires accurate maps.  British expertise in mapping led to the worldwide adoption of Greenwich Meridian (the North-South line through the Royal Observatory, Greenwich, London) as the universal zero for longitude in 1884. Longitude was calculated by working out the time difference between your location and Greenwich Mean Time.

The first sea clock

The first practical pendulum clock was invented in 1656 by the Dutch mathematician and astronomer Christiaan Huygens (1629–95). He then turned his attention to the creation of an accurate sea clock for determining longitude.

Huygens collaborated with Bruce on the project and the Scot introduced a number of new features to the Dutchman's designs. Bruce had four sea clocks made, two of them by Severyn Oosterwijck.

The clock on trial

By the end of 1662, Bruce’s initial sea-trials were proving promising. More formal sea-trials were carried out, with reports suggesting that the clocks had performed exceptionally well.

However, these reports eventually proved to be inaccurate. Captain Robert Holmes had been entrusted with the trials of the clocks (though his attention was clearly more devoted to plundering Dutch merchant shipping). He reported implausible success beyond even the best hopes for the clocks. Samuel Pepys was asked to investigate, and he found that the glowing reports were entirely fictitious. Despite the optimism of the 1660s and extensive discussions over patents and profits, the new marine timekeepers turned out not to be the solution that had been hoped for.

It was another century before the English clockmaker John Harrison would famously solve the longitude problem.

In 1714, a prize was offered to anyone who could find a way of calculating longitude at sea. The fame of this award continues to the present day; the Longitude Prize acknowledges the work of those who find practical solutions to pressing challenges like antibiotic resistance, dementia, and other global issues.

How the clock became part of the national collection

After its sea trials in the 1660s, Bruce's clock was converted into a domestic clock. It disappeared from the historical record. There is no knowledge of its whereabouts between c.1670 and 1972.

Interest in the clock was forgotten, and it was accepted as a later 17th-century domestic clock. However, it was still of considerable importance due to its date, maker, and quality of craftsmanship. It owes its survival to serving as a working clock over the centuries and has only recently been recognised for its role in the quest for longitude. 

Fine art auctioneer Dreweatts 1759 provided practical assistance with our purchase of this timepiece. It was acquired with support from the National Heritage Memorial Fund and the Art Fund.

The Bruce-Oosterwijck sea clock (museum reference T.2018.215) is on display in the Earth in Space gallery at the National Museum of Scotland.