Third, at the pace the horse advances the two feet, on the same side, at the same time, and when they reach the ground again there is but one impact; then the two feet on the other side are advanced and strike in the same way. Thus, the rhythm of the action strikes the ear as that of the movement of an animal with two feet instead of four. In this there can be no mechanical mistake, for in the revolution of the four-legged pacing horse we count one, two, and in the revolution of the two-legged man we count one, two. The conclusion, therefore, seems to be inevitable that the two legs on the same side of the pacing horse act in perfect unison in performing the functions of one leg. At the trot the horse advances the two diagonal feet at the same time, and when they reach the ground again there is but one impact; then the two other diagonal feet are advanced and strike in the same way. Thus, the rhythm of the action strikes the ear as that of the movement of an animal with two feet instead of four. In this there can be no mechanical mistake, for in the revolution of the four-legged trotting horse we count one, two, and in the revolution of the two-legged man we count one, two. The conclusion, therefore, seems to be inevitable that the two diagonal legs of the trotting horse act in perfect unison in performing the function of one leg. In the mechanism of the gait then that is midway between the walk and the gallop there is no difference in results, nor distinction in the economy of motion, except that the pacer uses the lateral legs as one, and the trotter the diagonal legs as one. In use, there is a vertical distinction, if that term should be allowed, between the gait of the pacer and the trotter. The action of the pacer is lower and more gliding which fits him for the saddle, while the action of the trotter is higher and more bounding which makes him more desirable as a harness horse. In the processes of inter-breeding to the fastest, this distinction, if it be a distinction, seems to be coming less real, or at least less observable. While the essential oneness of the pace and the trot is indicated above from the mechanism and unity of the two gaits, there is a great mountain of evidence to be developed when we reach the consideration of breeding subjects, in which we will meet multitudes of fast trotters getting fast pacers, and fast pacers getting fast trotters; fast pacers changed over to fast trotters and fast trotters changed over to fast pacers, and the final evidence that speed at the one gait means speed at the other. Having briefly explained what a pacer is, it is now in order to take up the question of whence he came.