66 



ANIMAL MECHANICS 



load when it supported only one half of the weight, 

 are now perpendicular under the pressure, and 

 are capable of sustaining the whole. If roads 

 were made perfectly level, and had no holes in 

 them, the wheels of carts might be made without 



dishing ; but if a 

 cart is calculated for 

 a country road, let 

 the wheelwright con- 

 sider what equiva- 

 lent he has to give for 

 that very pretty re- 

 sult proceeding from 

 the obliquity of the 

 spokes, or dishing of 

 the wheel. 

 When we return to consider the human thi^h- 



o 



bone, we see that the same principle holds; that 

 is to say, .that whilst a man stands on both his 

 legs, the necks of the thighbones are oblique 

 to the line of gravitation of the body ; but when 

 one foot is raised, the whole body then being 

 balanced on one foot, a change takes place in the 

 position of the thighbone, and the obliquity of 

 that bone is diminished ; or, in other words, now 

 that it has the whole weight to sustain, it is per- 

 pendicular under it, and has therefore acquired 

 greater strength. See Fig. 18. 



FIG. 18. 



