The chariot is a two-wheeled vehicle upon which is a pointing figure connected to the wheels by means of differential gearing. Through careful selection of wheel size, track and gear ratios, the figure atop the chariot will always point in the same direction, hence acting as a non-magnetic compass vehicle.
The south pointing chariot was invented in China over 2000 years ago. I'm not sure that it was ever more than a curiosity. Still, it's a very curious and remarkable curiosity, and I can't imagine how anyone ever thought it was a possible project.
I don't think I could understand how it worked without having built one, but the video may be more comprehensible to other people.
Any other nominees for "how did that ever occur to them?" inventions?
Link found at Less Wrong.
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