Drawing of a whirling arm and gun mount, by Benjamin Robins Detail drawings of the drum and weight for the whirling arm, a machine for conducting experiments in aerodynamics and drag ['resistance of the air']. With a mount apparatus, possibly for rifle experiments. The whirling arm's drum was spun rapidly by a falling weight which in turn revolved an arm (of 4 feet in length) attached to the conical head of the device. Bodies for testing were attached to this and achieved speeds of several feet per second for brief periods. 1740s