Pendulum clock mechanism, Salomon Coster, The Hague, 1657, Inv V09853

The back-and-forth movements of a pendulum are all of equal duration. This was known to the Hague aristocrat Christiaan Huygens, and consequently he wanted to make an accurate clock with one. In December 1656 he suddenly realised how to do it. He took an existing table clock, put it on its side and replaced the foliot (a weighted rod swinging to and fro) with a stirrup. Through that stirrup he put his pendulum. The clock turned out to work, and more accurately than ever. He applied for a patent, and subsequently granted the sole right to manufacture his timepieces to the Hague clockmaker Salomon Coster. Shortly afterwards the Rotterdam clockmaker Simon Douw patented his own pendulum clock mechanism. Huygens immediately went into action, and an embittered conflict ensued when it emerged that Douw had copied Huygens' design with only a minor modification. From then on this clockmaker was known to Huygens as 'the plagiarist'.