Discover John Harrison's iconic marine timekeepers

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Essential information

Opening times: 
10.30am – 4.30pm daily
Royal Observatory, Meridian Line and Historic Royal Observatory, Time & Longitude gallery, Flamsteed House

Have you ever seen a clock that changed the world? We can show you timepieces that are not only revolutionary, but are exquisitely made.

John Harrison's marine timekeepers are arguably the most important ever made. You can see them on display in our Time galleries, at the Royal Observatory Greenwich.
  • Visit H1, H2, H3 and H4, developed and constructed over John Harrison's life time. 
  • Learn about John Harrison, the man behind the watches. 
  • Discover why the clocks are so important and how Harrison built and tested them.  

What are the Harrison clocks? 

The Harrison clocks were revolutionary in their ability to allow ships to determine their longitude at sea. This development drastically reduced the risk of ships and their crews, along with their precious cargoes, being lost at sea. The Harrison clocks were able to keep time at sea, allowing sailors and mariners to determine their longitude. It took John Harrison most of his lifetime to arrive at the design for H4, which was to be his most succesful watch. 
The clocks compensate for changes in temperature and, thanks to extensive anti-friction devices, run without any lubrication.
When Harrison unveiled H1 in 1735 it was the toast of London. Alongisde the other Harrison clocks, it is one of the great milestones in clock-making history.

Find out more about John Harrison's groundbreaking timekeepers

Visit the Royal Observatory to visit the celebrated marine timekeepers, and learn about the impact they have had. Explore the quest for longitude through displays of scientific objects, paintings and animations.