Voigt's 1887 explanation of the Michelson-Morley result as a Doppler effect using absolute space-time is examined. It is shown that Doppler effects involve two wave velocities: (1) the phase velocity, which is used to account for the Michelson-Morley null result, and (2) the velocity of energy propagation, which, being fixed relative to absolute space, may be used to explain the results of Roemer, Bradley, Sagnac, Marinov, and the 2.7° K anisotropy.