The Tyndall effect was discovered by John Tyndall, an Irish physicist, in 1869.
- When a beam of light passes through a colloid, the particles scatter the light, making the beam visible from the side
- Colloidal particles (1–1000 nm) are large enough to scatter light; true solution particles are too small
- The effect explains why: the sky appears blue, milk appears white, and fog lights show as visible beams
- Used to distinguish colloids from true solutions a true solution does not show the Tyndall effect
The path of light made visible through a colloid is called the Tyndall cone.