Most popular science accounts and even text-books on the Special theory of Relativity start by describing the Michelson-Morley experiment,which leaves the impression that it played a decisive role in the development of relativity by Einstein.Some books like Kleppner/Kolenkow mention that it probably was of no great significance but fail to mention exactly what experiments,if any led Einstein to relativity.

One book does that.

According to any standard physics textbook,it was the "ultraviolet catastrophe" which led Max Planck to hypothesize about quanta.The problem was that the observed spectrum of a blackbody didn't match that predicted by theory--the Rayleigh-Jeans formula.One fine evening,he discovered the power of the energy quantization and the Quantum era began.This story was repeated recently in my physics class,and no doubt happens throughout the world.

That,alas,is fiction.The fact,as always is far stranger.Planck,was in fact,a reluctant revolutionary.