He found, he said, that this resistance was vastly greater than had been anticipated. It certainly was not a negligible quantity. The resistance of the air to a twenty-four pound cannon ball, fired with its battering charge of sixteen pounds of powder, was no less than twenty-four times the weight of the ball when it first issued from the piece: a force which sufficiently confuted the theory that the trajectory was a parabola, as it would have been if the shot were fired in vacuo. It was neither a parabola, nor nearly a parabola. In truth it was not a plane curve at all. For under the great force of the air’s resistance, added to that of gravity, a ball (he explained) has frequently a double curvature. Instead of travelling in one vertical plane it actually takes an incurvated line sometimes to right, sometimes to left, of the original plane of departure. And the cause of this departure he ascribed to a whirling motion acquired by the ball about an axis during its passage through the gun. The reading of the paper provoked considerable discussion among the learned Fellows, who found themselves presented with a series of the most novel and unorthodox assertions, not in the form of speculations, but as exact solutions to problems which had been hitherto unsolved; and these were presented in the clearest language and were fortified by experiments so careful and so consistent in their results as to leave small room for doubt as to the certainty of the author’s theory. Of special interest both to savants and artillerists must have been his account of “a most extraordinary and astonishing increase in the resistance of the air which occurs when the velocity comes to be that of between eleven and twelve hundred feet in one second of time”: a velocity, as he observed, which is equal to that at which sounds are propagated in air. He suggested that perhaps the air, not making its vibrations with sufficient speed to return immediately to the space left in the rear of the ball, left a vacuum behind it which augmented the resistance to its flight. His statement on the deflection of balls, too, excited much comment. And, in order to convince his friends of the reality of this phenomenon, which, though Sir Isaac Newton had himself taken note of it in the case of tennis balls, had never been thoroughly investigated, Robins arranged an ocular demonstration.