Abstract: Ether theory (according to the myth) requires that as the Earth moves through space, the measured velocity of light parallel and perpendicular to its motion will vary. Two American physicists, A. A. Michelson and E. W. Morley devised a test of ‘ether drift’. To their and everyone's surprise, it didn't exist. In desperation, two new explorers, G. F. FitzGerald and H. A. Lorentz, separately advanced the weird ad hoc hypothesis that as Michelson's apparatus traversed the ether, it somehow shrank lengthwise by just the right amount to hide the effect. Various physicists devised further experiments to see the shrinkage. All failed. This chapter argues that Kelvin's insight into ether theory was outstanding, far superior to that of any of his famed predecessors, Poisson, Cauchy, MacCullagh, etc., and that most of the criticisms of him by 20th century writers were merely silly.

Keywords: ether theory, A. A. Michelson, E. W. Morley, G. F. FitzGerald, H. A. Lorentz, ether drift, Lord Kelvin, Stokes, William Thomson,