  The known nearby stars, moving in front of the background of distant stars
and galaxies, create 'weak gravitational lensing' variations in their
positions. These variations may be measurable with the HST, and they may allow
a direct mass determination for the nearby stars. The cross section for the HST
measurable astrometric effect is much larger than the cross section for the
photometric effect which is measurable from the ground. The mass determination
will be easier for the fainter nearby lenses which will be discovered in future
searches of faint high proper motion stars.
