Pole Depression

“Two hoops of thin iron are placed upon an axis which passes through their poles. The two ends of each hoop cross each other at right angles, and are fastened together, and to the axis at the bottom. At the upper end they slide up and down on the axis, which is turned rapidly by wheel-work as represented. These hoops, before the motion begins, have an oval form, but when turned rapidly, the centrifugal force causes them to expand, or swell at the equator, while they are depressed at the poles, the two polar regions becoming no more distant than a and b.” —Comstock, 1850

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