In science, John Strutt (1842-1919) (IQ:185|#52), aka Lord Rayleigh, was a English physicist noted for his 1870 discussions with Maxwell on the so-called truth of the second law of thermodynamics; his 1871 "scatter theory" solution to the blue sky problem, about which he gave the definitive explanation of in 1899; his 1892 discussions with Willard Gibbs on statistical mechanics; his 1894 isolation, with William Ramsay, of the element argon (work for which he would win the 1904 Nobel Prize in physics); and his 1900 formulation of spectral energy flux density of black body radiation, which led to the ultraviolet catastrophe problem, and hence to the "energy element" solution by Max Planck, which launched the science of quantum mechanics. Strutt is considered by some to be the “last of the great Victorian polymaths”. [4]

Ultraviolet catastrophe
Strutt notably obtained the spectral energy flux density J of black body radiation in 1900: [1]

$J(\nu,T) = \frac{2 \pi kT\nu^2}{c^2}$

where ν is frequency of the radiation, c the speed of light, k the Boltzmann constant, and T the temperature of the black body.

This formula worked well for small frequencies, but did not fit experimental data at high frequencies; this issue that came to be called the ultraviolet catastrophe; only to be reconciled by German physicist Max Planck in 1901, who incorporated Boltzmann’s views on the partition of energy in his version of the second law, thus launching the quantum revolution. [2]
 Photograph of Strutt and William Thomson at Strutt's family home, Terling Place, Witham, Essex, UK, in 1900. [5]

Why is the sky blue?
See main: blue sky problem
Strutt is also famous for being the first to explain the blue color of the sky in 1871, an explanation now referred to as Rayleigh scattering; a problem previous worked on by other great geniuses of antiquity, such as: Aristotle, Da Vinci, Newton, Goethe, and Clausius. [4]

Gibbs
In 1892, American engineer Willard Gibbs wrote Strutt with characteristic modesty on his now-famous book on statistical mechanics: [3]

“Just now I am trying to get ready for publication something on thermodynamics from the a priori point of view, or rather on 'Statistical Mechanics' . . . I do not know that I shall have anything particularly new in substance, but shall be contented if I can so choose my standpoint (as seems to me possible) as to get a simpler view of the subject.”

Supposedly, by the term a priori Gibbs meant related to or derived by reasoning from self-evident propositions. In any event, ten years later this work resulted in a classic book, Elementary Principles in Statistical Mechanics (1902), which has since been called the "bible of statistical physics", which put statistical mechanics on a new and more general basis.

Cavandish professorship
Strutt, of note, was second Cavendish Professor of physics, following James Maxwell, from 1871 to 1879, after which he was followed by J.J. Thomson (1884-1919), who in turn was followed by Ernest Rutherford (1919-1937), who was in turn followed by William Bragg (1938-1953), who in 1919, at the age of 25, became the youngest-to-date winner of a Nobel Prize (in physics, for his X-ray crystallography work) and who was the director of the Cavendish Laboratory, Cambridge, when the epochal discovery of the structure of DNA was made by James Watson and Francis Crick in February 1953. [6]

References
1. Rayleigh, Lord. (1900). "article", Philosophical Magazine, 49: 539.
2. Müller, Ingo. (2007). A History of Thermodynamics: the Doctrine of Energy and Entropy (ch. 7: Radiation Thermodynamics, pgs. 197-232, esp. 230). New York: Springer.
3. Josiah Willard Gibbs (1829-1903) – AIP.org.
4. Lilienfeld, Pedro. (2004). "A Blue Sky History." Optics and Photonics News, 15(6): 32-39.
5. John Strutt and William Thomson (1900) – SciencePhoto.com.
6. Cavendish Professor of Physics – Wikipedia.