THE ERECT POSITION. 



263 



be equal. The moments are found by drawing the shortest line fb from 

 / to the direction of the force ac, and the line fd to the direction along 



which gravity acts. Then bf x push = fd x 



weight of body. 



If the push be greater than -r. x weight of 



body, then the body will be pushed over. 



It also follows that the longer fd is, the 

 greater must be the push in order that over- 

 turning may take place ; indeed, we may say 

 that the larger the area of underpropping the 

 more stable is the body. In the erect position 

 at attention the area of underpropping is as 1 

 in Fig. 150, and coincides with the area covered 

 by the feet, together with the area between 

 them. Under ordinary circumstances we stand 

 with the feet somewhat apart as in 2, when the 

 area of underpropping is increased. When Ave 

 wish to resist a push from the sides, we stand as in 

 3 ; and when, as in fencing or boxing, we wish to 

 resist a push from the front, Ave stand as in 4. 



Strictly speaking, the body not being a rigid 

 mass, there can be no question of stable or even 

 unstable equilibrium. In fact a living subject 

 is constantly in motion, even when trying hard to stand " motionless." 

 Vierordt 1 by a simple recording method obtained tracings of the SAvaying 

 movements of persons standing upright. Leitersdorffer 2 proved by this 



Fig. 149.— To show the effect of 

 a push acting in the direction 

 of the arrow ac in overturning 

 the body, which is viewed as a 

 rigid body resting on the feet. 



Fig. 150. — Shows the area of underpropping and the plumb of the 

 centre of gravity (</). — (1) At attention. (2) In an erect and 

 easy attitude. (3) When resisting a force applied from the 

 left. (4) When resisting a force applied from the front, as in 



boxing. 



method the influence of the area of underpropping and the difference between 

 trained and untrained subjects. 



1 "Physiol, des Menscheii," Tubingen, 1862, S. 365. 

 - "Das niilitarische Training," Stuttgart, 1894, S. 42. 



