Chap. LXXXI.—Of Equilibrium.
Any figure bearing an additional weight out of the central line, must throw as much natural or accidental weight on the opposite side as is sufficient to form a counterpoise round that line, which passes from the pit of the neck, through the whole mass of weight, to that part of the foot which rests upon the ground. We observe, that when a man lifts a weight with one arm, he naturally throws out the opposite arm; and if that be not enough to form an equipoise, he will add as much of his own weight, by bending his body, as will enable him to resist such accidental load. We see also, that a man ready to fall sideways and backwards at the same time, always throws out the arm on the opposite side.
Chap. LXXXII.—Of Motion.
Whether a man moves with velocity or slowness, the parts above the leg which sustains the weight, will always be lower than the others on the opposite side.
Chap. LXXXIII.—The Level of the Shoulders.
The shoulders or sides of a man, or any other animal, will preserve less of their level, in proportion to the slowness of their motion; and, vice versâ, those parts will lose less of their level when the motion is quicker. This is proved by the ninth proposition, treating of local motions, where it is
