CHAPTER XXX
THE PASSAGE BACKWARD
THE passage backward follows from the piaffer, and therefore presupposes a horse educated to the perfect state of assemblage and equilibrium.
A horse at the slow piaffer—which is, of course, the only form of the piaffer considered by the scientific equitation— balances itself on the same spot, all four legs flexing at the knees and hocks, but without gaining ground. The center of gravity is, therefore, midway of the body, and exactly under the seat of the rider. Under these conditions, the horse is like a large ball which rests upon a smooth and level surface, with which it is in contact, only at one end of a diameter. Evidently, the slightest force applied at the other end of this diameter will send the ball rolling in the direction of the force. So, in the piaffer, a force applied alternately on the two sides of the center of gravity makes the horse receive its weight alternately on its two diagonal bipeds. As the center of gravity shifts to the right, the left diagonal biped is raised, and vice versa.
If, then, under these conditions, the rider leans forward, the horse must move forward, under the operation of the same law. But if, when the horse is lifting his legs in diagonal alternately upon the same spot, the rider's weight is inclined backward, the
