In the Fall of 1900, Frederick T. Trouton started work on an ingenious experiment in his laboratory at Trinity College in Dublin. The purpose of the experiment was to detect the earth’s presumed motion through the ether, the 19th century medium thought to carry light waves and electric and magnetic fields. The experiment was unusual in that, unlike most of these so-called ether drift experiments, it was not an experiment in optics. Trouton tried to detect ether drift by charging and discharging a capacitor in a torsion pendulum at its resonance frequency, which he hoped would set the system oscillating. The basic idea behind the experiment came from George Francis FitzGerald (see Fig. 1), whose assistant Trouton was at the time. Consider Fig. 2 below. A battery is used to charge a capacitor. If the power is switched on, an electromagnetic field is produced largely confined to the volume between the plates of the capacitor. If the system is at rest in the ether, the charges will only produce an electric field; if the system is moving, the charges will also produce a magnetic field. As Trouton wrote in his paper on the experiment: