The Congreve Clock was invented in the year 1808 by Sir William Congreve. To regulate the time, the Clock uses a ball rolling along zig-zag manner. The ball takes from 15 seconds to one minute to complete the zig-zag track. The first version of the Clock was gifted to the Prince of Wales by Congreve in the year 1808. Congreve hired Gravel and Tolkien for making the first working version. The second model is kept at the Collection of Buckingham Palace. The Congreve Clock is also referred as Oscillating Path Rolling Ball Clock. The Time taken for the ball to travel depends on the cleanliness of the track.