experiment (c. 1805), extended in the 20th century to show it is a particle at the same time Observation of the Arago spot by François Arago in 1819 validated a new wave theory of light by Augustin-Jean Fresnel disproving skeptics like Siméon Denis Poisson. Hans Christian Ørsted discovers the connection of electricity and magnetism by experiments involving a compass and electric circuits (1820) Michael Faraday discovers magnetic induction in an experiment with a closed ring of soft iron, with two windings of wire (1831) James Prescott Joule demonstrates the mechanical equivalent of heat, an important step in the development of thermodynamics (1834) Christian Doppler arranges to have trumpets played from a passing train. The ground-observed pitch was higher than that played when the train was approaching then lower than that played as the train passed and moved away, demonstrating the Doppler effect (1845) Léon Foucault's namesake Foucault pendulum is first exhibited. It demonstrates the Coriolis effect and the rotation of the Earth (1851) Edwin Hall discovers a voltage across a conductor with a transverse applied magnetic field, the Hall effect (1879) Michelson–Morley experiment exposes weaknesses of the prevailing variant of the theory of luminiferous aether (1887) Heinrich Hertz demonstrates free space electromagnetic waves, predicted by Maxwell's equations, with a simple dipole antenna and spark gap oscillator (1887) Guglielmo Marconi demonstrates that radio signals can travel between two points separated by an obstacle. Marconi's servant is behind a hill 3 kilometers away and fires his rifle upon receiving the signals (1895). J. J. Thomson's cathode ray tube experiments (discovers the electron and its negative charge) (1897) Loránd Eötvös publishes the result of the second series of experiments, clearly demonstrating that inertial and gravitational mass are one and the same. (1909) Robert Millikan's oil-drop experiment, which suggests that electric charge occurs as quanta (whole units), (1909) Heike Kamerlingh Onnes demonstrates superconductivity (1911) Ernest Rutherford's gold foil experiment demonstrated that the positive charge and mass of an atom is concentrated in a small, central atomic nucleus, disproving the then-popular plum pudding model of the atom (1911) Arthur Eddington leads an expedition to the island of Principe to observe a total solar eclipse (gravitational lensing) - see Eddington experiment. This allows for an observation of the bending of starlight under gravity, a prediction of Albert Einstein's theory of relativity. It was confirmed (although it was later shown that the margin of error was as