  The specific heat of superfluid $^{3}$He, disordered by a silica aerogel, is
found to have a sharp discontinuity marking the thermodynamic transition to
superfluidity at a temperature reduced from that of bulk $^{3}$He. The
magnitude of the discontinuity is also suppressed. This disorder effect can be
understood from the Ginzburg-Landau theory which takes into account elastic
quasiparticle scattering suppressing both the transition temperature and the
amplitude of the order parameter. We infer that the limiting temperature
dependence of the specific heat is linear at low temperatures in the disordered
superfluid state, consistent with predictions of gapless excitations everywhere
on the Fermi surface.
