When the light is subjected on the colloidal solution it appears clear but when viewed at the right angle to the passage of light it show a mild to strong opalescence. This effect is termed as

Colloidal solutions viewed in the dark may appear reasonably clear or translucent by the transmitted light but they show a mild to strong opalescence when viewed at right angles to the passage of light, i.e., the path of the beam is illuminated by a bluish light. This effect is termed as Tyndall effect.