Spectroscopy is Applied Quantum Mechanics. Part 1: The Need for Quantum Mechanics
The article examines the failure of classical mechanics that necessitated the development of a new theory of nature. It was discovered by Josef Stefan and Ludwig Boltzmann that the total power irradiated per unit area is proportional to the fourth power of temperature where the proportionality constant is called the Stefan-Boltzmann constant. Though these relationships were verified experimentally, the question over why these relationships occur still remains.
Ball, David W., "Spectroscopy is Applied Quantum Mechanics. Part 1: The Need for Quantum Mechanics" (2007). Chemistry Faculty Publications. 136.