. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap. XLIII.] knee, but when the leg behind it leaves the ground, it gradually becomes straightened (3, 4, 5 of Fig. 219, thick line), so that the body is kept from being lowered. The leg behind is thus hanging, so to speak, and performs a pendular movement (indicated by the arrow between 4 and 5), swinging forwards past the leg which is now supporting the body, till it reaches a posi- tion as far in front of the supporting
. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap. XLIII.] knee, but when the leg behind it leaves the ground, it gradually becomes straightened (3, 4, 5 of Fig. 219, thick line), so that the body is kept from being lowered. The leg behind is thus hanging, so to speak, and performs a pendular movement (indicated by the arrow between 4 and 5), swinging forwards past the leg which is now supporting the body, till it reaches a posi- tion as far in front of the supporting leg as it was for- merly behind it, when it toil c h e s the ground. It has Fig> Positions of the Legs now become Walking, the forward leg (had beg of 1, 2, and 3), while the leg formerly in front lias come to occupy the posterior position (4, 5, dark lines; and 1, thin line). In slow walking there is a time when both feet are on the ground, the forward foot acting as a fulcrum, on which the foot behind pushes the body. But as the pace increases, the period during which both feet touch the ground grows O O O less and less, till one foot has no sooner touched the ground than the other leaves it. This is shown spe- cially well by Marey's graphic method of registering the movements of the two feet by a tambour in each shoe, connected with a revolving cylinder. The same method shows that in running there is an appreciable period when both feet are off the ground. The forward impelling force urges the body on wards against the resistance of the air, the friction between the feet and the ground, etc. It is evident from Fig. 218 that the horizontal component of the H H—7. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original M'Gregor-Robertson, J. (Joseph), 1858-1925. Philadelphia, H. C. Lea's son &a
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