Light reflected by shiny transparent materials is partly or fully polarized, except when the light is perpendicular to the surface. Polarization was first discovered in 1808 by the mathematician . A polarizing filter, such as a pair of polarizing sunglasses, can be used to observe this effect by rotating the filter while looking through it at the reflection off of a distant horizontal surface. At certain rotation angles, the reflected light will be reduced or eliminated. Polarizing filters remove light polarized at 90° to the filter's polarization axis. If two polarizers are placed atop one another at 90° angles to one another, very little light can pass through both.