The short piece “Time for the future,” about the Long Now clock (Physics Today, March 2012, page 28), was delightful. The clock is a unique application of classical physics—the torsion pendulum—in a scientific world that seems dominated by the physics of the very small and the very large. Charles Augustin de Coulomb and Henry Cavendish used such pendulums to establish fundamental laws of electricity and gravitation, respectively. Even today, contemporary torsion-pendulum measurements are used to refine the value of G, the universal gravitational constant.1
Perhaps less well known to readers is the fact that, like the Long Now device, clocks powered by expansion and contraction of gases have been around since the early 17th century. They were invented by Cornelis Drebbel, a multitalented Dutch builder. One of his original clocks was owned by James I of England and was well known throughout Europe. Today, commercially produced Atmos clocks use a liquid and gas mixture of ethyl chloride to power the bellows.
In a recent book, I introduced the Long Now clock by contrasting the idea of “long now” with “short now.” I argued that “short now” might be equated with that supremely annoying interval known as the New York minute—defined as “the nanosecond time interval between the moment the red light at your intersection turns green and the time when the New York driver behind you honks his horn to get you moving.”2
There are a multitude of good stories and good physics associated with pendulums. Thank you for again demonstrating their fascination and relevance.
