  Much interest has been generated recently by the ongoing MACHO, EROS and OGLE
projects to identify gravitationally lensed stars from the Large Magellanic
Cloud and Galactic bulge, and the positive identification of several events
(Alcock et al, (1993), Aubourg et al, (1993) and Udalski et al, (1993)). The
rate at which such events are found should provide considerable information
about the distribution of the low mass compact objects, brown dwarfs etc.
responsible for the lensing, and their relative importance as a component of
the cosmological `dark matter'. We show measurement of the polarisation of
starlight during these events can yield considerably more information about the
lensing objects than was previously considered possible. Furthermore, the
consideration of extended sources is shown to have a significant effect on the
interpretation of the profiles and statistics of the events.
