  The four observables associated with gravitational lensing of distant quasars
by intervening galaxies: image splittings, relative amplifications, time
delays, and optical depths, provide separate measures of the strength of the
gravitational constant $G$ at cosmological distances. These allow one, in
principle, to factor out unknown lensing parameters to directly to probe the
variation of $G$ over cosmological time. We estimate constraints on $\dot{G}$
which may be derivable by this method both now and in the future. The limits
one may obtain can compete or exceed other direct limits on $\dot{G}$ today,
but unfortunately extracting this information, is not independent of the effort
to fix other cosmological parameters such as $H_0$ and $\Omega_0$ from lensing
observations.
