John Harrison’s longcase pendulum clock, c.1726

In the 17th and 18th century knowing your longitude was the biggest problem on earth. Navigating the seas for warfare and trade was risky. A country's future safety and wealth could depend on knowing your position at sea.

John Harrison (1693-1776) invented the portable sea clock to solve this problem. To make his sea clock, Harrison needed an accurate regulator clock, so he made his own. He invented the grasshopper escapement to improve the accuracy of timekeeping

This clock was one of workshop clock Harrison made and owned to regulate his sea clock.

Find out more in our Measuring Time gallery, or on Dr John Taylor's website.