  Five observations of the hard X-ray spectrum of Her X-1 from \xte show that
the $\sim 41$ keV energy of the cyclotron scattering line is constant within
statistics of a few percent per observtion. Comparison with other observations
over many years indicates strongly that the centroid energy of this absorption
line has increased some time between 1991 and 1993 by 23%, from 34 keV to 41
keV. Moreover, the cutoff energy of the spectral continuum increased at the
same time from 16 keV to 20 keV, which is, within the statistical error of 5%,
in direct proportion to the centroid. This may be a sign thatboth these
characteristics of the spectrum are controlled in the same way by the magnetic
field strength in the region of scattering.
