The Tyndall effect is a phenomenon where light is scattered by small particles in a colloid or in very fine suspensions. This scattering makes the path of the light beam visible, often seen in a beam of sunlight passing through a dusty room or in a glass of water with suspended particles. This effect is named after the scientist John Tyndall, who studied it in the 19th century. It helps distinguish between solutions and colloids; for example, a clear solution like saltwater does not exhibit the Tyndall effect, while a colloidal mixture like milk does.