The king's instrument maker, George Adams, did not make many models for King George III, but this is a particularly fine example. A hay cart was placed on a cobbled 'horse-way', which has a channel cut to imitate a rut. The inclination of the horse-way could be varied, as could the diameter of the wheels and the weight in the cart. The weight needed to keep the cart stationary was a measure of the efficiency of the wheels.
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