built these chariots deceived their own employers with them, which could have gained them fame and fortune provided nobody tried using the chariots for real navigation. Other mechanical designs for the south-pointing chariot are also possible, including ones that employ a device that is used today, the gyrocompass. However, there is no indication that the ancient Chinese knew of these. Non-mechanical possibilities Some south-pointing chariots may not have been purely mechanical devices. Someone riding inside the chariot may have used some non-mechanical method of determining the compass directions, and turned the doll on top of the chariot accordingly. There are several methods that could have been used, for example: By using a magnetic compass. The Chinese were using this for navigation by the 11th century, when south-pointing chariots were still being made and used. By using astronomical observations of the Sun and/or stars, e.g. the Pole Star. Chinese astronomical knowledge was extensive. By using local knowledge. The person in the chariot may have known the area or had a map or description of it. By observing the polarization of light from the sky. Vikings used birefringent crystals of Iceland spar to navigate across the Atlantic Ocean by this method at about the same time. Iceland spar is found in China, as well as in Iceland and some other places. Insects such as bees can respond to sky polarization and use it to find their way home. Whether the Chinese used it is hypothetical, but it is certainly possible. By observing light that had been refracted by the Earth's atmosphere. This is one of the techniques that were used by Polynesian navigators to steer ships among Pacific islands. When the surface of the Earth, ocean or ground, is colder than the air above it, a dense layer of air is formed near the surface, which refracts light downward. The result is that light can go around the curvature of the Earth, allowing things to be seen at much greater distances than simple geometry would predict. The images are very distorted, but they can be recognized by skilled navigators. Certain other Polynesian techniques can also be used on land and may have been employed by the Chinese. Unlike mechanisms that rely on the rotation of road wheels, most of these methods can be used at sea. This may account for the mention (see "Earliest sources" above) that a marine version of the