We saw above that in order to represent the amble the marchers had to move the legs of the same side simultaneously. We have also just seen that in order to represent the trot the marcher at the back had to anticipate by a half-step. Suppose, now, that this same marcher anticipates the man in front by a quarter-step only, or by a half-pressure period, and thus will be found realized the order of succession of the limbs in the gait or pace called the walk. The feet meet the ground one after the other, since they are each in advance by half the duration of a pressure. The strokes are four in number during the period of a step of this pace; in the amble and in the trot they do not exceed two, for then the limbs strike the ground in lateral diagonal pairs.
Fig. 128.—Notation of the Pace of Stepping in the Horse (after Professor Marey).
L, Right lateral pressure; D, right diagonal pressure; L′, left lateral pressure; D′, left diagonal pressure.
If we examine the notation of the pace of walking ([Fig. 128]), we see that the right fore-foot commences its pressure when the right hind-foot is in the middle of its own, and that the hinder left begins in the middle of that of the right fore-foot, and that it is itself at the midst of its pressure when the left fore-foot touches the ground, etc. In a word, the foot-fallings occur in the following order and at regular intervals—the fore right foot is here considered as acting first: right fore, left hind, left fore, right hind, and so on in succession.
As to the nature of the bipeds which succeed one another, it is easy to understand them by means of the notation. In reading this from left to right, we see that the associations of pressure are first made by the two right feet, then by a right foot and a left one, then by two left feet, and, finally, by a left and right. It is, accordingly, a succession this time of lateral and diagonal pressures.
Fig. 129.—The Step: Right Lateral Pressure.