Those who are about to leap are taught by Nature, without any Reasoning of their own, to hoist up their Arms and Legs with Impetuosity; These parts obeying the Impetus, and rising, together with the rest of the Body, 'till such time as the Effort is expired. This Impetus is attended with a quick Extension of the Body, which before was bent like a Spring, in the Reins, the Joncture of the Thighs, the Knees, and the Feet; and the Body, in this Extension, describes an oblique Line, inclining forwards, and at the same time rising upwards; thus the Motion directed forwards, carries the Body in that Direction; and the Motion intended upwards, heaves up the Body on high; and these two, thus Conjoyn'd, discribe a large Arch; which is the Line, wherein a Man is observed to leap.