90 DIRECTION OF THE TRACK. 



of going all the same way. But quadrupeds, such 

 as sheep, rabbits, and hares, form tracks ; and so 

 do some insects ants for instance. The tracks of 

 ants are nearly straight lines ; and those of quad- 

 rupeds are much straighter than human foot- 

 paths, if there is nothing to confine them to a 

 particular direction. So that the formation of the 

 path is not a matter of reasoning and judgment 

 at all, but purely mechanical. When an animal 

 however small or large, walks, it must always so 

 move as that its centre of gravity is supported, 

 otherwise it would fall. Now, that is obtained 

 partly by the motions of the legs, and partly by 

 those of the upper portions of the body. The 

 more legs there are, the centre of gravity has the 

 more props, and so there is less need for counter- 

 balancing motions in the body above. Ants have 

 six legs, quadrupeds four, and man only two ; so 

 that man needs more exertion of his body to ba- 

 lance himself than the quadruped, and the quad- 

 ruped more than the ant. The man, too, is upright, 

 and even the quadruped is higher in proportion to 

 its breadth than the ant. Thus the centre of gravity 

 swings by the longest lever in the man in propor- 

 tion to his whole weight, and by the shortest in 

 the insect ; and thus the man is more affected by 

 the position of the surface on which he walks than 

 the quadruped; and the quadruped is more affected 

 in that way than the insect. Where the ground 

 is perfectly level, the man's path is nearly straight; 

 but if the ground rises to the one hand, the path 

 always takes a twist to the other, because the 

 foot which is on the high ground throws the 

 centre of gravity the other way, and the other 

 foot is advanced toward the low side, in order 



