MOTION. 
463 
Fig. 251. 
Pee Hee 
PAG aks. 1S 13-14 
15 1617 18 
Fig. 251 shows the tive positions 0 
the leg during two successsive steps. To 
render them more distinct they are divided 
into two groups, The 18 figures 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 first 
step, when both legs are on the ground ; 
the figures 5 to 14 give 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 swings while the other rests 
on the ground. 
ig. 90 Of. @ & 24 2 6 27 28 
5280 
~ step must have been 5 = 2.64 feet. In this 
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 
