  We calculate the spectrum of glueball masses in non-supersymmetric Yang-Mills
theory in three and four dimensions, based on a conjectured duality between
supergravity and large N gauge theories. The glueball masses are obtained by
solving supergravity wave equations in a black hole geometry. We find that the
mass ratios are in good numerical agreement with the available lattice data. We
also compute the leading (g_{YM}^2 N)^{-1} corrections to the glueball masses,
by taking into account stringy corrections to the supergravity action and to
the black hole metric. We find that the corrections to the masses are negative
and of order (g_{YM}^2N)^{-3/2}. Thus for a fixed ultraviolet cutoff the masses
decrease as we decrease the 't Hooft coupling, in accordance with our
expectation about the continuum limit of the gauge theories.
