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 first law of motion as set forth in his Principia. The body, once set in motion by a force, continues after the force is withdrawn to move forward in the same direction until another force interferes. The horse, therefore, without further spurring, continues to advance at the same speed, until something else occurs.

This, then, is what we mean by the "attack" of the spurs; nothing brutal, sudden, sharp, or unexpected, merely the supplementing of the effect of the legs, which alone were not sufficient. But the animal has life, and consequently, senses and will. It does, for a time, continue to go forward in a state of equilibrium, under the impulse of the original force. Sooner or later, however, some new sensation becomes a disturbing force. It loses its uniform motion in a straight line, and with it the state of equilibrium. Thereupon, hand and legs, spurs, if necessary, must again come into action.

In such a case, the spurs are a corrective, not by their own direct effect, but because they help to restore the state of equilibrium, and thus to inhibit the animars own will, which is the disturbing force. But though the good-will of the horse is a pleasant state, it really is very little matter what the horse thinks. The only point is submission to the will of the rider, who, by complete and continual control of the physical horse, sets quite on one side the will of the moral horse. Then and only then is the horse an utter captive, unable to disobey, unable to move