  Through the simultaneous measurement of the transverse size as a function of
longitudinal position, and the longitudinal distribution of luminosity, we are
able to measure the $\beta_y^\ast$ (vertical envelope function at the collision
point), vertical emittance, and bunch length of colliding beams at the Cornell
Electron-positron Storage Ring (CESR). This measurement is possible due to the
significant ``hourglass'' effect at CESR and the excellent tracking resolution
of the CLEO detector.
