The paper offers a historical overview of Einstein's oscillating attitude towards a "phenomenological" and "dynamical" treatment of rods and clocks in relativity theory.This may sound like two obscure philosophical viewpoints, but it goes to the heart of why Einstein is credited for special relativity. Lorentz and Poincare had all the theory and equations and experiment interpretation before Einstein, so the only way to credit Einstein is to claim that there was something superior about his viewpoint.
But Einstein was not clear about what his viewpoint was, and he seemed to alternate between two viewpoints of Lorentz. Nobody cared much at the time, because the spacetime geometry viewpoint of Poincare and Minkowski is what became popular. Nevertheless, this paper explores Einstein's viewpoint in detail.
FitzGerald and Lorentz first deduced the length contraction as the logical consequence of interpreting Michelson-Morley as showing that the speed of light is constant even tho motion is relative. Then they gave an explanation in terms of the electromagnetic molecular forces. At the time, not everyone realized that solid objects are held together by electromagnetic molecular forces, so some people liked the way that Einstein skipped that part of the argument. He used rigid measuring rods, even tho the length contraction shows that there is no such thing.
Einstein's approach is often explained in positivist terms, altho Einstein's later philosophy disavowed such an approach.