A Congreve clock (also known as Congreve's Rolling Ball Clock or Oscillating Path Rolling Ball Clock) is a type of clock that uses a ball rolling along a zig-zag track rather than a penulum to regulate the time. It was invented by Sir William Congreve in 1808. The ball takes between 15 seconds and one minute to run down the zig-zag track, where it trips the escapement which in turn reverses the tilt of the tray and at the same time causes the hands of the clock to move forward. Thus the angle of the plate reverses and the clock hands move forward between one and four times every minute. On versions of the clock with a dial to indicate seconds, the second hand jumps forward either 15 or 30 seconds on each oscillation depending on the length of the track.