Lord Rayleigh

John William Strutt, 3rd Baron Rayleigh, known as Lord Rayleigh, was born on 12 November 1842 at Langford Grove, Essex, England, and died on 30 June 1919 at Witham, Essex. He graduated from Trinity College, Cambridge, in 1865, succeeded James Clerk Maxwell as Cavendish Professor of Experimental Physics at Cambridge in 1879, and from 1884 continued his research privately at his family estate at Terling, Essex, while also serving as professor of natural philosophy at the Royal Institution from 1887 to 1905. In the early 1890s he noticed that nitrogen gas extracted from air was consistently about half a percent denser than nitrogen prepared chemically from nitrogen compounds, a small but reproducible discrepancy he could not explain; working with the chemist William Ramsay, the two identified the cause as a previously unknown, chemically unreactive gas present in air, which they named argon, from the Greek for inactive, and published jointly in 1894. He was awarded the 1904 Nobel Prize in Physics for his investigations of the densities of the most important gases and his discovery of argon, awarded the same year Ramsay's Nobel Prize in Chemistry recognized the same discovery from the chemistry side. He is also known for explaining why the sky is blue, an effect now called Rayleigh scattering, and for the Rayleigh criterion describing the resolving power of optical instruments.