LOCOMOTION 



355 



on a registering " tambour." From fig. 252 it will be seen that 

 the curve of vertical pressure oscillates from side to side of the 

 line of weight of the body. During the transfer of the weight 

 of the body from one leg to the other the perpendicular oscilla- 

 tion has a negative value. It will also be easily seen that the 

 curve of tangential pressure (H) is negative at the moment when 

 the heel touches the ground and becomes positive at the end 

 of the " unrolling " of the foot. This " unrolling " has been 

 compared by the brothers Weber to the motion of the felloe of a 

 wheel, a somewhat rash comparison seeing that the radius, in 

 this case the lower member, changes in length. 



The rear leg is lifted during this " unrolling " and before the 

 other leg becomes vertical. The toe of the hinder foot, as it 

 leaves the ground, transmits a thrust to the trunk by which its 

 weight is thrown forward on to the front leg. If this were not the 

 case the body would fall backwards. The propulsive effort, 

 therefore, takes place during the period of " double support," 

 and produces its whole effect during the support. 



494 



In Fischer's experiments, the period of support was f-rof 



1,000 



a second which added to that of the "double support" gives : 

 494 81 575 



1,000 + 1,000 " : i,oo<r 



od Of 3 up port 



Pen od of oscillation Double 



>. __ \JUPP0Tt~ 



Analysis of phases of a double step in thousandths of a 

 second (after du Bois-Reymond). 



Fig. 253 is a diagramatic representation of the periods of 

 activity of the two legs, by R. du Bois-Reymond, expressed in 

 thousandths of a second. As explained above, the angle 

 corresponding to the " unrolling " of the foot averages 53, 

 and increases with the length of the pace (vide fig. 251). The 

 translation of the hip and the impulse given to the trunk must in- 

 crease in the same proportion, and as, by the separation of the 

 legs, the trunk and the general centre of gravity, is lowered, long 

 paces must cause a more pronounced vertical oscillation than 



