  We report on a pre-eclipse dip of the X-ray binary Her X-1 observed by the
Rossi X-ray Timing Explorer (RXTE) in July 1996. We present the evolution of
the spectral parameters in the 3-18 keV range with a temporal resolution of 16
s and show that the varying flux of the spectrum can be interpreted solely by a
time varying column density. We also find that the lightcurve is characterized
by symmetric substructures with recurrence time of a few minutes that can be
successfully modeled by Gaussian profiles.
