In Part One of this dissertation, I analyze various accounts of two etherdrift experiments, the Trouton-Noble experiment and an earlier experiment by Trouton. Both aimed at detecting etherdrift with the help of a condenser in a torsion balance. I argue that the difficulties ether-theorists Lorentz and Larmor had in accounting for the negative results of these experiments stem from the fact that they did not take into account that, if we charge a moving condenser, we not only change its energy, (...) but also its momentum and its mass. I establish two additional results. The Trouton experiment can be seen as a physical realization of a thought experiment used by Einstein to argue for the inertia of energy. Closely following Rohrlich, I develop an alternative to Laue's canonical relativistic account of the Trouton-Noble experiment to show that the turning couple Trouton and Noble were looking for is a purely kinematical effect in special relativity. I call this effect the Laue effect. ;In Part Two, I use these results to illustrate some general claims about the post-1905 version of Lorentz's ether theory. I use to illustrate that Lorentz needs to assume more than the contraction of rods and the retardation of clocks to make his ether theory empirically equivalent to special relativity. I use to illustrate that what makes the addition of such assumptions unsatisfactory is not that it would make the theory ad hoc, in the sense that it would compromise its testability, but that it makes Lorentz invariance a symmetry of the dynamics in a classical Newtonian space-time, whereas, in fact, it is a symmetry of the relativistic Minkowski space-time. To provide the necessary context for my claims, I give a detailed account of the conceptual development of Lorentz's theory from 1895 to 1916. In particular, I analyze the relation between the so-called theorem of corresponding states and what I call the generalized contraction hypothesis. I show that the various versions of Lorentz's theory have been widely misunderstood in the literature. (shrink)