Mechanical harmonic oscillator, American, c 1850.
© Science Museum / Science & Society Picture Library
Made by the American firm Waterbury, this example of a duplex escapment mechanism stores energy as motion of the wheel and strain in the spring. Small amounts of energy pas between the two as the wheel speeds and slows, and the spring coils and uncoils. In electronic watches and clocks, a capacitor and inductor do the same job.