John William Strutt (1842-1919) was an English physicist. He discovered the phenomenon now called Rayleigh scattering, explaining why the sky is blue, and predicted the existence of the surface waves now known as Rayleigh waves. Rayleigh's textbook, The Theory of Sound, is still referred to by acoustic engineers today. He was elected Fellow of the Royal Society in 1873. He participated in the House of Lords, but only spoke if politics attempted to become involved in science. He died in 1919 at the age of 76.