MOTION. 



463 



i. 251. 



Fig. 251 shows the consecutive positions of 

 the leg during two siiccesssive steps. To 

 render them more distinct they are divided 

 into two groups. The \8Jigures of the 

 Jirst group show all the positions through 

 which the leg passes while the toe rests 

 upon the ground. The 10 of the second 

 show the successive positions during the 

 time the body is carried forward by the 

 swinging leg. The positions from 1 to 4 

 show that division of time of the Jirst 

 when both legs are on the ground ; 

 the figures 5 to 14 ijine the portion of 

 time of the first step when one leg rests 

 on the ground while the other swings; 

 from 15 to 18, that division of the second 

 step where both legs rest on the ground ; 

 No. 19 to 28 show the portion of time 

 when one leg swingx while the other rests 

 on the ground. 



step must have been = 2.64 feet. In this 



2000 



case also the length of the leg was 34 inches, 

 which gives 19.961 inches for the length of the 

 synchronous pendulum, and for the time of 

 each half oscillation 0".357; hence the time of 

 taking each step was longer than the time in 

 which the leg was susceptible of swinging 

 without muscular effort, as a pendulum, by 

 about 0".093. 



The step is considered as commencing at the 

 instant when the hindmost leg is raised from 

 the ground. Let us then suppose the whole 

 sole of the foot of the right leg, which is in 

 advance of the left, to be in contact with the 

 ground, upon which it acts as a fulcrum; the 

 hip, knee, and ankle-joints to be in a state of 

 partial flexion, and the line from the head of 



the femur to the ankle-joint to be vertical, as 

 in fig. 251, No. 4. In this position, the right leg 

 supports the whole weight of the trunk, and the 

 left, being extended obliquely backwards, does 

 not contribute to the support of the burthen. 

 The flexed position of the right leg lowers the 

 centre of gravity, and the effective portion of 

 the force of extension, acting only in a vertical 

 direction, produces no horizontal motion. At 

 this moment, the left leg having previously 

 communicated a slight horizontal impulse to the 

 centre of gravity, and the trunk being inclined 

 forwards, the head of the femur of the right 

 leg is propelled from No. 4 towards No. 18. 

 The leg, instead of being vertical, is now di- 

 rected obliquely forwards and upwards. In 

 order that the head of the femur with its load 

 may be sustained at the same height above the 



