The Tyndall effect, also known as Tyndall scattering, is light scattering by particles in a colloid or else particles in a very fine suspension. It is named after the 19th-century physicist John Tyndall. It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth power of the frequency, so blue light is scattered much more strongly than red light. An example in everyday life is the blue colour sometimes seen in the smoke emitted by motorcycles, in particular two-stroke machines where the burnt engine oil provides the particles.