Edvard Hugo von Zeipel proved in 1908 that if there is a collision singularity, then J ( q ( t ) ) tends to a definite limit as t → → t ∗ ∗ , where J ( q ) = ∑ ∑ i m i | q i | 2 is the moment of inertia. This implies that a necessary condition for a noncollision singularity is that the velocity of at least one particle becomes unbounded (since the positions q remain finite up to this point).