‘Ruhmkorff’s’ induction coil

A few years ago, I heard a radio programme in which a set of panellists tried to identify a city from a few seconds of street sound. It was an enthralling puzzle, where clues might be gleaned from the cries of street traders, the songs of birds, snatches of music, and the odd bark or bray.

But it made me wonder: if you could listen to the soundscape of a lab of the past, could you date it? There are sounds in our labs that are, to all intents and purposes, gone forever. Among them is the rattle of the Sprengel mercury drop pump, the hiss and whirr of the air-driven mechanical stirrer and the hum or sing of the induction coil, a device that ushered in modern physics.

The story of the coil began silently, in 1820, with the mysterious twitch of a compass needle when Hans Christian Ørsted passed an electric current through a nearby wire. The needle flipped round when the current was reversed. Unbeknown to Ørsted, the Italian scientist Gian Domenico Romagnosi had observed this almost 20 years earlier but had been ignored.