  Bound states of heavy quarks are considered. Using the path integral
formalism we are able to rederive, in a gauge invariant way, the
Leutwyler-Voloshin short distance analysis as well as a long distance linear
potential. At all distances we describe the states in terms of nonperturbative
field correlators, and we include radiative corrections at short and
intermediate distances. For intermediate distance states (particularly $b\bar
{b}$ with $n=2$) our results improve, qualitatively and quantitatively,
standard analyses, thanks mostly to being able to take into account the
finiteness of the correlation time.
