In this video, I demonstrate the Tyndall effect, named after the 19th century Irish physicist John Tyndall. The Tyndall effect is a phenomenon where light scatters through a heterogeneous mixture (like a colloid or suspension), but not a homogeneous mixture (usually called a solution). This happens because the larger particles in a colloid or suspension scatter and reflect light, causing the beam to be thick enough to be visible. This doesn't happen in a solution because the particles are too small and finely distributed, so the beam of light passes through the solution without being visible.