Circular velocity at a given radius is:

Lovett realized that while Rongi was now dropping more slowly, the poor devil's circular velocity was increasing.

Beeckman is mentioned to be one of the first persons describing inertia correctly, however he also assumes that a constant circular velocity is conserved.

In discussing the relation of the moving power of the intelligence, the resistance of the sphere, and the circular velocity, he said "this ratio ought not to be called a ratio of force to resistance except by analogy, because an intelligence moves by will alone ... and the heavens do not resist it."