on the consequences if that balance were to be for one moment destroyed. Gravitation is really an essential condition of our natural existence, like the air we breathe. Its force is precisely measured by a body's weight.
Every animal, therefore, is under the influence of two forces, the inert pull of gravity, and the active force of its own muscles. So long as the animal is recumbent, its weight is immobile, and it is in a position of inertia. To change this position under the first force, the second, the contractive force, is needed. This is developed by the muscles, by a tension sufficient to support the weight immobile upon the legs. But in order to propel the weight in any direction, the animal needs a contractive force greater than that needed to keep the weight immobile. Therefore must the muscular force be sufficient for both the weight and the velocity.
Sir Isaac Newton teaches that the motion of an animal is a series of falls, received and prevented by advancing one leg after the other. Since the force of gravity is constant, the velocity does not affect it. But the velocity does affect the momentum, which varies directly with the frequency of the falls. The greater the velocity, the more do the bases of support multiply their action; and consequently the flatter becomes the trajectory, and the more perfect the equilibrium of the forces involved.
With horses of good conformation, the center of gravity is well established. But with horses of
