Like most center-of-mass demonstrations, the key to understanding stable equilibrium is that the center of mass of the system must lie directly below the point of support.
The nicely-finished horse and rider demonstration at the
left was sent to me a number of years ago by a Japanese reader of The
Physics Teacher, who had read my note (reference below) on balancers.
It appears to be a direct copy of a western demonstration from the latter
years of the nineteenth century.
This more rudimentary blancer is in the collection of historical physics teaching apparatus at Case Western Reserve University in Cleveland, Ohio
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