The magician shows an antique ckock to the audience and places it into a bag or top hat. Now the magician picks up a beautiful wooden box and opens the doors to show it completely empty.
This is now done with the second, seperate box. Once both boxes have been shown empty, the magician removes the clock from the bag/ top hat and places it into one of the boxes.
The front door is opened one more time to show the clock inside box. Then the door is closed and magicaly, the clock travels back and forth from one box to the next!
For a wonderful climax, both boxes are opened to show that the clock has mysteriously vanished and reappeared in the bag/ top hat!