  However, in 1918 it was still possible for Weyl to defend his theory  in the following way. In response to Einstein’s criticism Weyl noted  that atoms, clocks and meter sticks are complex objects whose real  behavior in arbitrary gravitational and electromagnetic fields can  only be inferred from a dynamical theory of matter. Since no detailed and reliable dynamical models were available at that time, Weyl could argue that there is no reason to assume that, for example, clock  rates are correctly modelled by the length of a timelike vector. Weyl (1919a, 67) said: 