The latitude is easy to find by observing the position of the sun at noon. Longitude is such a puzzle that captains prefer to follow the meridian up to the latitude of their point of destination before sailing westward or eastward.
In 1656 Christiaan Huygens builds the first pendulum clock, with a precision of 15 seconds per day 60 times better than the previous timekeepers. The inventor is friend with English royalists exiled in Holland. King Charles II is restored in 1660.
The Royal Society of London, created in the same year, is passionate about the Huygens pendulum and its potential application to the measurement of the longitudes. Its principle is known : the comparison of the apparent solar time with a reference of time calibrated in the port before the departure makes it possible to know the angular distance already traveled by the ship.
The application at sea is extremely difficult because of the disturbance of the clock by the agitation of the boat. In 1662 one of the founders of the Royal Society, Alexander Bruce later 2nd earl of Kincardine, designs an improvement in the stability of the Huygens clock by suspending the mechanism to a cardan ball and lowering the center of gravity of the equipment.
Bruce has two clocks made in The Hague by the clockmaker Severijn Oosterwijck who was a preferred supplier to Huygens. The idea of that duality is to reduce the measurement error by placing the clocks at both ends of the boat. One of these instruments is destroyed at sea during its delivery and in 1663 Bruce has made a replacement clock by an English clockmaker.
The captain in charge of the experiment announces excellent results which convince neither Huygens nor the Royal Society. The project is cancelled in 1665. The mechanical part of both Bruce's longitude clocks will be integrated shortly after in domestic clocks where they will remain unidentified during more than three centuries.
Both resurfaced. The English timepiece has now entered the collection of the Royal Observatory. The Dutch timepiece signed by Oosterwijck will be sold in its current housing on March 15 by Dreweatts at Donnington Priory in Berkshire, lot 108. Here is the link to the press release.