  By monitoring $10^6$ quasars one could search for lensing by stars and
Massive Compact Halo Objects (Machos) out to redshifts $z\sim 4$. If Machos
have a present cosmological density $\Omega_{L,0}=1\%$, then the expected event
rate is $\Gamma\sim 200\,\yr^{-1}$. The expected event rate for known stars in
galaxies is $\Gamma\sim 20\,\yr^{-1}$ assuming that their present cosmological
density is $\Omega_{L,0}=0.3\%$. Typical event times are $t_e\sim 3\,\yr$ for
Machos and $t_e\sim 10\,\yr$ for stars. By comparing the optical depths to
quasars at different redshifts, one could measure the star-formation and
Macho-formation history of the universe. By comparing the time scales of events
found parallel and perpendicular to the Sun's motion relative to the microwave
background, one could measure or constrain the characteristic scale of large
scale motions. The lensing events themselves would help probe the structure of
quasars on scales of 50--1500 AU. The monitoring program could be carried out
with a single dedicated 1 m telescope with a 4 deg${}^2$ camera. Quasar lensing
events can be unambiguously distinguished from quasar variability because in
the former case the broad lines are unaffected while in the latter they respond
to the variation in the continuum on times scales $\sim 1\,\yr$.
