158 THE REIGN OF LAW. 



it battle. Nay, more, the one is connected with 

 the other in some mysterious manner which we 

 cannot trace or understand. A dead bird weighs 

 as much as a living one. Nothing which our 

 scales can measure is lost when the "vital force" is 

 gone. It is The Great Imponderable. Never- 

 theless, vital forces of unusual power are always 

 coupled with unusual mass and volume in the 

 matter through which they w T ork. And so it is 

 that a powerful bird must always also be compara- 

 tively a heavy bird. And then it is to be remem- 

 bered that the action of gravity is constant and 

 untiring. The vital force, on the contrary, how- 

 ever intense it may be, is intermitting and capable 

 of exhaustion. If, then, this force is to be set 

 against the force of gravity, it has much need of 

 some implement through which it may exert itself 

 with mechanical advantage as regards the particu- 

 lar purpose to be attained. Such an implement is 

 the lever — and a long wing is nothing but a long 

 lever. The mechanical principle, or law, as is 

 well known, is this, — that a very small amount 

 of motion, or motion through a very small 

 space, at the short end of a lever produces a 



