Jean Bernard Léon Foucault was born on 18 September 1819, in Paris and died on 11 February 1868, also in Paris. Foucault was educated at home, then studied medicine and later went on to study physics. In 1850, he did an experiment using the Fizeau–Foucault apparatus to measure the speed of light; it came to be known as the Foucault–Fizeau experiment, and is often viewed as the final piece of information needed to show that light travels more slowly through water than through air.
In 1851, he provided an experimental demonstration of the rotation of the Earth on its axis. Foucault achieved the demonstration by showing the rotation of a long and heavy pendulum suspended from the roof of the Panthéon, Paris. The experiment caused a sensation and "Foucault pendulums" were suspended in major cities across Europe and America which attracted large crowds. In the following year he used (and named) the gyroscope and in 1855 he received the Copley Medal of the Royal Society for his 'very remarkable experimental researches'. Earlier in the same year he was made physicien (physicist) at the imperial observatory at Paris.
In 1862 Foucault was made a member of the Bureau des Longitudes and an officer of the Legion of Honour. He became a member of the Royal Society of London in 1864, and member of the mechanical section of the Institute a year later. His chief scientific papers can be found in the Comptes Rendus, 1847—1869. Near his death he became an observant Roman Catholic again.
Foucault may possibly have died from fatal multiple sclerosis and was buried in the Montmartre Cemetery.
The asteroid 5668 Foucault was named after him and his name is one of the 72 names inscribed on the Eiffel Tower.