ww.tc John Harrison Limited Edition @ Girard-Perregaux

As part of its ww.tc collection, which indicates the time around the world,

Girard-Perregaux introduces an exceptional limited series dedicated to John Harrison, one of the greatest British watchmakers. In October 1707, the English admiral Sir Cloudesley Shovell made an error when estimating the longitude of his squadron of warships. As a result, the squadron ran aground on the Scilly Isles off the south-west coast of England and was wrecked, causing the deaths of some 2,000 men including the admiral himself.

In 1714, the British Parliament passed the Longitude Act, offering a reward of 20,000 pounds (the equivalent of several million dollars today!) to anyone who could find a method of calculating a ship's longitude to within half a degree (approximately 30 km).

Leading scientific minds of the era studied the subject closely, as did the watchmaker John Harrison, whose approach promised the great advantage of simplicity. His idea was to use a clock to measure the time difference between the journey’s starting point and the ship's current position.

Because the Earth completes one full revolution in approximately 24 hours, each hour thus represents 15 degrees of rotation, or 15 degrees’ difference in longitude. By measuring the difference between the exact local time at the ship's position (determined using a sextant) and the exact reference time (at the point of departure, indicated by the clock) the longitude of the ship can be calculated. The challenge was therefore to create a clock that would maintain its accuracy even when pitching and rolling on the world’s roughest seas. Making this timepiece became John Harrison's eternal quest.