  During the last twenty-five years evidence has been mounting that a
black-hole surface area has a {\it discrete} spectrum. Moreover, it is widely
believed that area eigenvalues are {\it uniformally} spaced. There is, however,
no general agreement on the {\it spacing} of the levels. In this letter we use
Bohr's correspondence principle to provide this missing link. We conclude that
the area spacing of a black-hole is $4\hbar \ln 3$. This is the unique spacing
consistent both with the area-entropy {\it thermodynamic} relation for black
holes, with Boltzmann-Einstein formula in {\it statistical physics} and with
{\it Bohr's correspondence principle}.
