PLACING THE HORSE 



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 im- 

 mobile. 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 momen- 

 tum, 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 



177 



