 This much of the argument makes no appeal to relativistic physics, and the possibility of such Newtonian black holes was noted in the late 18th Century by Michell (1784) and Laplace (1796, part ii, p. 305). These Newtonian objects, however, do not precipitate the same sense of crisis as do relativistic black holes. Although light emitted at the surface of the collapsed body cannot escape, a rocket with powerful enough motors firing could still push itself free. It just needs to keep firing its rocket engines so that the thrust is equal to or slightly greater than the gravitational force. Since in Newtonian physics there is no upper bound on possible velocities, moreover, one could escape simply by being fired off at an initial velocity greater than that of light. 