John William Strutt, 3rd Baron Rayleigh (; 12 November 1842 – 30 June 1919) was an English
physicist who, with
William Ramsay, discovered
argon, an achievement for which he earned the
Nobel Prize for Physics in 1904. He also discovered the phenomenon now called
Rayleigh scattering, which can be used to explain 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.