  Interferometric tests of a f/1.2 2.5-m diameter liquid mirror show RMS
surface deviations about wave/20 and Strehl ratios of order 0.6, showing that
it is diffraction limited. The mirror is certainly better than implied by the
data because of aberrations introduced by the auxiliary testing optics. We have
made detailed studies of the scattered light of the mirror. We have studied the
behavior of the mirror under external perturbations. With this article we have
reached an important milestone since we now have a good understanding of liquid
mirrors.
