  Quasi-coherent oscillations have been detected in the extreme ultraviolet
flux of the dwarf nova SS Cygni during observations with the Extreme
Ultraviolet Explorer satellite of the rise and plateau phases of an anomalous
outburst in 1993 August and a normal outburst in 1994 June/July. On both
occasions, the oscillation turned on during the rise to outburst and persisted
throughout the observation. During the 1993 outburst, the period of the
oscillation fell from 9.3 s to 7.5 s over an interval of 4.4 days; during the
1994 outburst, the period fell from 8.9 s to 7.19 s (the shortest period ever
observed in SS Cyg, or any other dwarf nova) within less than a day, and then
rose to 8.0 s over an interval of 8.0 days. For both outbursts, the period $P$
of the oscillation was observed to correlate with the 75--120 \AA \ count rate
$I_{\rm EUV}$ according to $P\propto I_{\rm EUV}^{-0.094}$. A magnetospheric
model is considered to reproduce this variation. It is found that an effective
high-order multipole field is required, and that the field strength at the
surface of the white dwarf is 0.1--1 MG. Such a field strength is at the lower
extreme of those measured or inferred for bona fide magnetic cataclysmic
variables.
