The Congreve, or Rolling Ball Clock, is named after its inventor Sir William Congreve and is a favourite of clock collectors. The original clock was presented to the Prince of Wales in 1808 and is part of the Royal Collection at Buckingham Palace. Congreve was a prolific inventor famous for making the first solid fuel rockets at The Royal Arsenal in Woolwich in 1805 and subsequently used during the Napoleonic wars. It has been suggested that his clock was created for military purposes and the first "ball" used to trip the escapement was a musket ball!! This certainly makes sense because the principle of the mechanism is such that the accuracy is limited to +/- 15 minutes per day.