The first description of the Sagnac effect in the framework of special relativity was done by Max von Laue in 1911, two years before Sagnac conducted his experiment. By continuing the theoretical work of Michelson (1904), von Laue confined himself to an inertial frame of reference (which he called a "valid" reference frame), and in a footnote he wrote "a system which rotates in respect to a valid system K 0 is not valid". Assuming constant light speed c , and setting the rotational velocity as ω ω , he computed the propagation time τ τ + of one ray and τ τ − − of the counter-propagating ray, and consequently obtained the time difference Δ Δ τ τ = τ τ + − − τ τ − − . He concluded that this interferometer experiment would indeed produce (when restricted to terms of first order in v / c ) the same positive result for both special relativity and the stationary aether (the latter he called "absolute theory" in reference to the 1895-theory of Lorentz). He also concluded that only complete-aether-drag models (such as the ones of Stokes or Hertz) would give a negative result.