First observations of the spontaneous discharge of an electrometer

28 June 1785

The torsion balance electrometer Coulomb used to make his observations (Image: Wikimedia commons)

In 1785, the French physicist Charles Augustin de Coulomb made three reports on electricity and magnetism to France’s Royal Academy of Sciences. His third paper described an experiment with a torsion balance, which showed that the device would spontaneously discharge due to the action of the air rather than defective insulation.

In 1850, Italian physicist Cano Matteucci and later British physicist William Crookes in 1879 showed that the rate of spontaneous discharge decreased at lower atmospheric pressures. The search for an explanation for the nature of this spontaneous discharge paved the way for the discovery of cosmic rays – high-energy particles from outer space.  

Read more: Extract from Mémoires sur l'électricité et le magnétisme (1785-89) by Charles Augustin de Coulomb.

Cosmic rays

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