Jean-Bertrand-Léon Foucault

Foucault (1819-1868), (alternatively referred to as Jean or Léon) was a colleague of Armand Fizeau, and utilised Fizeau's work and apparatus to further refine calculations of the speed of light to within 1% of modern estimations. Foucault had also shown, just prior to the work of Fizeau, that light travels slower through water than air, in contradiction of the corpuscular theory of light popular at the time.