The second-order or transverse Doppler effect (TDE) demonstrates that both the periods and wavelengths of radiation increase (after the non-relativistic first-order effect has been eliminated) when a light source is accelerated relative to the observer. It is pointed out that the fact that an observer traveling with the light source does not detect any change in either quantity, in accord with the relativity principle (RP), implies not only that there has been a corresponding increase in the periods of all naturally occurring processes in his rest frame but also a uniform
expansion in the dimensions of all objects co-moving with him. These results constitute a key verification of Einsteinean time dilation, but it has not been recognized that they also stand in contradiction to another fundamental prediction of the special theory of relativity (SR), the Fitzgerald-Lorentz contraction effect (FLC). A survey of past claims for the validity of the FLC shows that they are either based on Gedanken experiments or on a specious interpretation of lifetime measurements for accelerated metastable particles. The manner in which the FLC is derived from the Lorentz transformation (LT) is then discussed and it is noted that it is based on a generalization of the original interpretation of its space-time variables in terms of elapsed times and distances traveled by a given object, and therefore requires separate experimental verification than observations of the constancy of the speed of light. Experimentation with the Global Positioning System (GPS) is shown to be consistent with the TDE results and thus verifies the conclusion that isotropic length expansion accompanies time dilation, not the type of anisotropic length contraction (FLC) indicated by the LT.