Speed of light refraction

The speed of light was determined more accurately using an earthbound experiment involving a toothed wheel and mirrors. Foucault's best figure was off by just 0.7 percent. He also found that light traveling through water traveled only three-fourths as fast as through air.
 Jean-Bernard-Léon Foucault France 1849 Speed of light refraction

The speed of light was determined more accurately using an earthbound experiment involving a toothed wheel and mirrors. Foucault's best figure was off by just 0.7 percent. He also found that light traveling through water traveled only three-fourths as fast as through air.