The Clausius-Mossotti and Lorentz-Lorenz relations

This paper focuses on a law of refraction that was discovered independently not by two researchers, not by three, but indeed by four! The law is known as the Clausius-Mossotti law, or the Lorentz-Lorenz law, and was derived either in electromagnetics or in optics, but it is essentially the same. Indeed, extremely scrupulous researchers name it the Clausius-Mossotti-Lorenz-Lorentz formula, but much is to be said about it, starting from the order of the names.