A Watch That Could Finally Leave the Wall

A pendulum clock is honest, but only if it stands still. Put one in a pocket and the swing falls apart. In 1675, Christiaan Huygens solved the problem for portable timepieces by fitting a small coiled spring, a hairspring, to a watch's balance wheel. Announced in the Journal des Sçavans that February, it meant a watch could keep steady time in a coat pocket or on horseback, in any position at all.

Huygens wasn't working alone in the idea. The English scientist Robert Hooke claimed he had thought of a spring-regulated balance earlier, and his surviving notes suggest he may have. Huygens, though, was first to publish a working design, and the two men's rival claims were never fully resolved. Historians still argue about who deserves the credit.

What survived the dispute is the mechanism itself. Two small pins, sliding along the coiled spring, let a watchmaker fine-tune its rate: shorten the spring's effective length and the watch runs faster. The dial marked A and R, for slow and fast, on later watches traces back to a similar regulator refined a few decades afterward.

That balance wheel and hairspring, regulated by two tiny pins, is still the beating heart of a mechanical watch. Three and a half centuries on, most fine watches still adjust their rate essentially the way Huygens's did.