1482 WALKING. [BOOK in. 



hypothenuse, the right angle being between the right leg and the 

 ground. At a certain moment the foot of the right leg will be 

 flat on the ground and the line of gravity will pass through its 

 heel. But the centre of gravity is moving forwards: even if 

 there had been no previous steps, and so no momentum, the 

 body and with it the centre of gravity, unless prevented by 

 muscular effort, would have fallen forward; we may therefore 

 speak of the line of gravity as travelling forwards ; it passes from 

 the heel to the toe (of the right foot). If the body were simply 

 falling forwards the centre of the hip-joint would move down- 

 wards as well as forwards, describing a circle with the leg as a 

 radius. But at the moment of which we are speaking the (right) 

 leg is somewhat flexed, both at the ankle and still more at the 

 knee. And, as the line of gravity is travelling forward from the 

 heel to the toe, the active part of the performance intervenes. 

 The foot is raised from the ground from the heel forwards, until 

 it is only the ball of the great toe which is resting on the ground, 

 and the whole leg is, by muscular effort, straightened. In this 

 act the right leg acts as a lever, the ball of the great toe serving 

 as a fulcrum ; and the effect of the act is to prevent the centre of 

 gravity, or the hip-joint, from moving downwards, and to carry it 

 forwards only in more nearly a straight line. In thus carrying the 

 hips (and body) forward the leg has changed its position; from 

 being vertical and flexed with the whole sole resting on the 

 ground, it has become inclined forwards obliquely, extended 

 straight, with the toes only resting on the ground. It has as- 

 sumed the same posture as that of the left leg at the moment 

 at which we started. 



Even at that moment the left leg was behind the line of 

 gravity, and unless it moved would become more and more so as 

 the changes in the right leg went on ; hence if left to itself it 

 would swing forward much as a pendulum which had been raised 

 up would swing forward when let go. And during the changes in 

 the right leg which we have just described the left does swing 

 forward, its movement being chiefly determined like that of a 

 pendulum by gravity, though it may be assisted by direct mus- 

 cular effort, and is certainly so guided, being for instance 

 slightly flexed during the transit. It swings forward in front of 

 the line of gravity and is thus brought to the ground, the toes in 

 proper walking making contact first and the heel later, though 

 many people who wear shoes bring the heel down at least as soon 

 as the toes. It swings we say in front of the line of gravity ; but 

 that line of gravity is travelling forwards, so that in a very short 

 time the body is resting 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 position 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 



