  WD1704+481 is a visual binary in which both components are white dwarfs. We
present spectra of the H-alpha line of both stars which show that one component
(WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf
components. Thus, WD1704+481 is the first known triple degenerate star. From
radial velocity measurements of the close binary we find an orbital period of
0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the
gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white
dwarfs predicted by the mass ratio and gravitational redshift difference
combined with theoretical cooling curves are 0.39+-0.05 solar mass and
0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first
example of a double degenerate in which the less massive white dwarf is
composed of helium and the other white dwarf is composed of carbon and oxygen.
