oersted's needle, 1828.
© Science Museum / Science & Society Picture Library
This apparatus demonstrates a discovery made in 1820 by the Danish physicist Hans Christian oersted (1777-1851). When an electrical current flowed above and below the compas needle, the needle swung acros the wire. This seemed to show that the current was producing a magnetic effect. Energy in the form of electric current changes into magnetic energy, which causes the motion of the magnetic needle. This needle is believed to have been supplied by Watkins and Hill in 1828.