OF THE ATTITUDES AND OF LOCOMOTION. 



147 



sary that the base of sustentation he situated vertically below 

 the centre of gravity. The wider, then, the base of sustenta- 

 tion is, the more secure the position : thus we stand safer 

 on two feet than one ; on the sole of the foot than on the toes 

 or heel, &c. ; for in proportion to the extent of the base of 

 sustentation, so may the centre of gravity be displaced with- 

 out risk of its falling beyond that base. The law holds good 

 in all heavy bodies ; thus, the table (a) represented in Fig. 97 



c*.' 3' ** 



Fig. 98. 



must fall, because the vertical (c), let fall from its centre 

 of gravity (e), would fall beyond the limits of its base of 

 sustentation (a), or in other words, the foot of the table. or the 

 space occupied by it; whereas the table (b) would not fall, for 

 the base of sustentation is sufficiently large to allow the 

 vertical from the centre of gravity to fall within its limits. 



On these simple principles may readily be explained the 

 safety of the position of the quadruped as he stands on four 

 limbs ; how it becomes less safe on three, still less on two ; 

 and how readily the bird secures itself on one leg in conse- 

 quence of the breadth of the foot which is the base of susten- 

 tation. Man stands readily on one limb, and with little 

 fatigue, especially if he use the other to secure his equilibrium ; 

 for the centre of gravity being in him towards the middle of 



* To show the varying centre of gravity in man. 

 L 2 



