  Detailed measurements of the longitudinal thermopower of two-dimensional
electrons in the first excited Landau level are reported. Clear signatures of
numerous fractional quantized Hall states, including those at $\nu = 5/2$ and
7/3, are observed in the magnetic field and temperature dependence of the
thermopower. An abrupt collapse of the thermopower is observed below about $T=
40$ mK at those filling factors where re-entrant insulating electronic states
have been observed in conventional resistive transport studies. The thermopower
observed at $\nu = 5/2$ is discussed in the context of recent theories which
incorporate non-abelian quasiparticle exchange statistics.
