Suppose, in n-dimensional Euclidean space, a sequence of disjoint closed spheres is packed into the open unit n-cube In in such a way as to ensure that the residual set has zero volume. Then, of course, is convergent and it can be shown, for n = 2, that is divergent. Let the exponent of convergence of the packing be the supremum of those real numbers t such that is divergent and let tn denote inf, where the infimum is taken over all packings which satisfy the above conditions. In recent work Z. A. Melzak [1] has been interested in finding estimates for in two-dimensional space. He has shown that t may take the value 2 and has produced some estimates for the Apollonius packing of disks. In this note we produce what is, perhaps, the most interesting estimate for tn by showing that tn is greater than n-1. Let sn denote the exact lower bound of the Besicovitch dimensions of every residual set which is formed by a packing of spheres in In.