Page:Popular Science Monthly Volume 6.djvu/65

Rh by the effect of their flexion; and this takes place at the very moment when the body was at its greatest elevation.

Galloping, a gait that children in their amusements sometimes adopt, gives the tracings shown in Fig. 8. The tracings produced by leaping are shown in Fig. 9.

 .—Step-curves and reactions. There is an encroachment of one curve over the other, and then a suspension of the body. The curve O, which corresponds with the reactions, shows the effect of the two successive impulses exerted on the body by the feet.

Among the characters belonging to the various modes of progression, the rhythm of the impact of the feet is one of the most striking. The strokes of the feet upon the ground give rise to sounds the order of whose succession is sufficient for a person, with an ear accustomed to them, to recognize the kind of pace which produces them. In order to give the figure of each of these rhythms, Prof. Marey employs the musical notation, modified so as to furnish at the same time the notion of the duration of each pressure, that of the foot to which this pressure

 .—The line R, the curve of reactions, shows that the maximum of elevations corresponds with the middle of the pressure of the feet.

belongs, and also the length of time during which the body is suspended. This notation of rhythms is constructed in a very simple manner from the tracings furnished by the apparatus. Fig. 10 represents the curve which corresponds with the act of running in man. Below this figure let us draw two horizontal lines, 1 and 2; these will form the staff on which will be written this simple music, consisting only of two notes, which M. Marey calls right-foot and left-foot. From