Nature will of itself, and without any reasoning in the mind of a man going to jump, prompt him to raise his arms and shoulders by a sudden motion, together with a great part of his body, and to lift them up high, till the power of the effort subsides. This impetuous motion is accompanied by an instantaneous extension of the body which had bent itself, like a spring or bow, along the back, the joints of the thighs, knees, and feet, and is let off obliquely, that is, upwards and forwards; so that the disposition of the body tending forwards and upwards, makes it describe a great arch when it springs up, which increases the leap.