1104 



WALKING. 



[BOOK in. 



vertically on the left leg, with the line of gravity falling at the 

 left heel. That is to say, the left leg has now assumed the posi- 

 tion which the right leg had when we began ; meanwhile, as we 

 have seen, the right leg has assumed the former position of the 

 left leg ; the step is completed, and the movements of the next 

 step merely repeat those of the one which we have described. 



It is obvious from the above that in walking there are in 

 each step periods when both feet are touching the ground, and 

 periods when one or the other foot is raised from the ground, 

 but there is no period when both feet are off the ground. This 

 is shewn in the diagram, Fig. 193, which represents two steps. 





a b c d e f g 



FIG. 193. DIAGRAM TO ILLUSTRATE THE CONTACT OF THE FEET WITH THE 

 GROUND IN WALKING. ' 



jR, the right foot. L, the left foot. In each case the curved line represents 

 the time when the foot is not in contact with the ground, and the straight line 

 when it is in contact. 



During a 5, the left leg (L) leaves the ground as indicated 

 by the curving of the line. During b e both feet are on the 

 ground. During c d the right leg (R) is above but the left 

 (L) is still on the ground. During d e both are on the 

 ground and the double step is completed, the next step begin- 

 ning again at e with the left leg leaving the ground. 



We have said that the centre of gravity is in walking pre- 

 vented from moving downwards as well as forwards, as it 

 would do in the act of falling forwards. It does not however 

 describe a straight line forwards, it, and with it the top of the 

 head, rises and falls at each step of each leg, and hence de- 

 scribes a series of consecutive curves not unlike the line of 

 flight of many birds. 



Since in standing on both feet the line of gravity falls 

 between the two feet, a lateral displacement of the centre of 

 gravity is necessary in order to balance the body on one foot. 

 Hence in walking the centre of gravity describes not only a 

 series of vertical, but also a series of horizontal curves, ina;- 



