  Using Fermat's principle, we analyze the effects of very long wavelength
gravitational waves upon the images of a gravitationally lensed quasar. We show
that the lens equation in the presence of gravity waves is equivalent to that
of a lens with different alignment between source, deflector, and observer in
the absence of gravity waves. Contrary to a recent claim, we conclude that
measurements of time delays in gravitational lenses cannot serve as a method to
detect or constrain a stochastic background of gravitational waves of
cosmological wavelengths, because the wave-induced time delay is
observationally indistinguishable from an intrinsic time delay due to the lens
geometry.
