Simulated appearance of<unk>  for vertically polarized light. Size and intensity exaggerated for clarity. Orientation varies with that of polarization of light source.<unk> , more commonly known as<unk> es is an image produced by the eye, an entoptic phenomenon, first described by Austrian physicist Wilhelm Karl von<unk>  in 1844.<unk>  saw it when he looked through various minerals that polarized light. Many people are able to perceive polarization of light.<unk> es may be seen as a yellowish horizontal bar or bow-tie shape (with "fuzzy" ends, hence the name "brush") visible in the center of the visual field against the blue sky viewed while facing away from the sun, or on any bright background. It typically occupies roughly 3–5 degrees of vision, about twice or three times the width of one's thumb held at arm's length. The direction of light polarization is perpendicular to the yellow bar (i.e., vertical if the bar is horizontal). Fainter bluish or purplish areas may be visible between the yellow brushes (see illustration).<unk>  may also be seen by looking at a white area on many LCD flat panel computer screens (due to the polarization effect of the display), in which case it is often diagonal.
Haidinger's brush
Tao brush
Air ioniser
Cuticura soap
Alger brush
Leech collector
Antimonial cup
Winpepi