  Optical, near-infrared, and radio observations of the BL Lac object
PKS2155-304 were obtained simultaneously with a continuous UV/EUV/X-ray
monitoring campaign in 1994 May. Further optical observations were gathered
throughout most of 1994. The radio, millimeter, and near-infrared data show no
strong correlations with the higher energies. The optical light curves exhibit
flickering of 0.2-0.3 mag on timescales of 1-2 days, superimposed on longer
timescale variations. Rapid variations of ~0.01 mag/min, which, if real, are
the fastest seen to date for any BL Lac object. Small (0.2-0.3 mag) increases
in the V and R bands occur simultaneously with a flare seen at higher energies.
All optical wavebands (UBVRI) track each other well over the period of
observation with no detectable delay. For most of the period the average colors
remain relatively constant, although there is a tendency for the colors (in
particular B-V) to vary more when the source fades. In polarized light, PKS
2155-304 showed strong color dependence and the highest optical polarization (U
= 14.3%) ever observed for this source. The polarization variations trace the
flares seen in the ultraviolet flux.
