There's an art/science experiment piece on display at the Exploratium (unfortunately I can't remember what it's called) that has a similar construction. The gear at one end is turned at a steady pace by an electric motor, and each successive gear attenuates the motion until you get to the last gear, which is set into solid concrete (iirc). If it were free to move, it would take a fantastic span (billions or trillions of years?) to make a full rotation.

Edit: Thanks to bockris for pointing out the name. Turns out the last gear rotates once each 13.7 billion years.