A. Capra's Device
In 1678, A Capra, of Italy, revived the ancient, but still favorite scheme that dates back to the 13th century. (See page 22 ante.) He illustrates his idea with the following figure and the following comment:
On the wheel A (of the facsimile engraving opposite), which must be hung well equipoised between two uprights, are appended counter-weights, eighteen in number, all precisely at the same distance from each other, and all exactly of the same weight. The counter-weights are provided with a small ring by which they are hung.
Whilst the counter-weights B are farther from the center C of the wheel, they weigh more than the counter-weights I, because these are low and nearer to the center C of the wheel, so that the counter-weights B descend and the weight I drops; and whilst the weight B is alternately descending and the weight I ascending, the wheel will revolve continually. But it must be understood that it is necessary to make the wheel perfectly true in equilibrium, so that it do not weigh more on one side than on the other on account of the counter-weights.