Fizeau–Foucault apparatus unit. At the time, Foucault was working at the Paris Observatory under Urbain le Verrier. It was le Verrier's belief, based on extensive celestial mechanics calculations, that the consensus value for the speed of light was perhaps 4% too high. Technical limitations prevented Foucault from separating mirrors R and M by more than about 20 meters. Despite this limited path length, Foucault was able to measure the displacement of the slit image (less than 1 mm) with considerable accuracy. In addition, unlike the case with Fizeau's experiment (which required gauging the rotation rate of an adjustable-speed toothed wheel), he could
Foucault pendulum vector diagrams On one side of the pendulum swing the surface velocity vectors are angled upwards and to the side but on the other side the vectors are angled downwards and to the opposite side. Since these vectors are not all in the same plane as the pendulum swing and are not balanced in the same direction there is a change in relationship between the surface and the plane of the pendulum swing. The surface velocity vectors underneath the swing of the pendulum can be separated into three components ("x", "y", and "z") for the 3-dimensional system in order to evaluate the