From our perspective one hundred years after the fact, the null result of the Michelson-Morley ether-drift experiment clearly marked the beginning of the end for the Newtonian notions of absolute space and time. At the time, however, it took 20 years of work by H. A. Lorentz, Henri Poincaré and others for most physicists to come to the same conclusion. In 1887, fundamental physics appeared to be essentially complete. Newtonian mechanics and Maxwell's electrodynamics were in hand, and a grand unification of physics seemed within reach. It was expected that a purely mechanistic basis for the ether interpretation of Maxwell's equations could be constructed and would provide a final unity of physics. This was a concise and powerful world view that was not easily discarded, but the null result of Michelson-Morley challenged its very heart.