58 THE ENGINES OF THE HUMAN BODY 



— which is 10 inches long — under the lid to the extent 

 of i inch, then the advantage we gain in power is as 

 i to 10 ; we thereby increase our strength tenfold. If we 

 push the chisel under the lid for half its length, then our 

 advantage stands as 10 to 5 ; our strength is only doubled. 

 If we push it still further for two-thirds of its length, then 

 our gain in strength is only as 10 to 6'6 ; our power is 

 increased by only one-third. Now this has an important 

 bearing on the problem we are going to investigate, for 

 the weight of our body falls on the foot, so that only 

 about one-third of the lever — that part of it which is 



Fig. 13. — Showing a chisel used as a lever of the second order. 



formed by the heel — projects behind the point on which 

 the weight of the body rests. The strength of the 

 muscles which act on the heel will only be increased 

 by about one-third. 



We have already seen that a double engine, made up 

 of the gastrocnemius and sokus, is the power which is 

 applied to the heel when we walk, and that the pad of 

 the foot, lying across the sole in line with the ball of the 

 great toe, serves as a fulcrum or rest. The weight of the 

 body falls on the foot between the fulcrum in front and 

 the power behind, as in a lever of the second order. We 

 have explained why the power of the muscles of the calf 

 is increased the more the weight of the body is shifted 

 towards the toes, but it is also evident that the speed and 

 the extent to which the body is lifted are diminished. If, 

 however, the weight be shifted more towards the heel, the 



