THE OPTICAL VARIABILITY OF PKS-2155-304

The BL Lacertae object, PKS 2155-304, has been photometrically monitored for the past decade (1979-1990). Optical variations have been observed on time scales ranging from several minutes to several years. The variations detected with time scales on the order of minutes are among the fastest optical variations detected for a BL Lacertae object. These rapid variations have provided constraints on the mass of the supermassive black hole, assumed to be present at the center of the object, of 5.5 +/- 0.4 x 10(8)M. less-than-or-equal-to M less-than-or-equal-to 8.1 +/- 1.0 x 10(9) M..