John William Strutt, 3rd Baron Rayleigh, English physicist and academic, Nobel Prize laureate (born 1842)

John William Strutt, 3rd Baron Rayleigh, was a British physicist and hereditary peer who received the Nobel Prize in Physics in 1904 "for his investigations of the densities of the most important gases and for his discovery of argon in connection with these studies". He served as President of the Royal Society from 1905 to 1908 and as Chancellor of the University of Cambridge from 1908 to 1919.

The Nobel Prize in Physics is an annual award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions to mankind in the field of physics. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901, the others being the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and Nobel Prize in Physiology or Medicine. Physics is traditionally the first award presented in the Nobel Prize ceremony.

June 30 is the 181st day of the year in the Gregorian calendar; 184 days remain until the end of the year.