I took lots of photographs and had planned to write a treatise on how it worked, but I quickly got bored with that idea and wrote a scientific fairy tale instead.

As I was working I noticed that the way I designed the differential gearing actually created a spare drive that sat directly below the emperor's feet, or where they would be if he were to sit in the chariot.

In practical terms the South Pointing Chariot was a simple direction finder. It could have been made to point in any direction - north, south, east or west.

The dog and the rabbit are telling us not to chase unattainable material goals.

The original item looked like a little hand cart with the figure of a man mounted on a platform between the wheels. The man's outstretched arm always pointed south.

He was so tenacious he defied the distraction of women by refusing to have them in his presence, just as later in life he denied his blindness by calling for more and more candles.

The dog, the rabbit and the hoop all feature in the painting, and take the place of the orrery.