94 THE WOODPECKERS 



elusion that this form was better adapted to hfe 

 on a tree-trunk than the square or the forked 

 tail would be, reasoning by a different process 

 called induction. An induction examines many, 

 and, if possible, all the facts before drawing any 

 conclusion ; a deduction examines the facts after 

 the conclusion is reached. There is no hard-and- 

 fast line between the two kinds of reasoning, but 

 we may say that a deduction is reasoning out a 

 guess and an induction is guessing out a rea- 

 son. Deductions are easier and quicker ; induc- 

 tions are surer, and in preparing them we often 

 make other discoveries. 



The rounded tail is no doubt the best ; but 

 we have yet to decide whether the sharper curve 

 is more advantageous than the lesser curve, as 

 we thought probable from our observations. 

 And there is still another deduction from our 

 experiment which we did not make. If in the 

 rounded tail the middle pairs of feathers do most 

 of the work, and if use increases the size and 

 efficiency of a part, which is almost an axiom in 

 science, we should expect to find the middle tail 

 feathers not only strongest in all woodpeckers 

 but also strono-est in increasins: ratio in the 

 species that use them most. To determine this 

 we must study the use of the tail and the struc- 

 ture and shape of the individual tail feathers. 



