THE WOODPECKER'S TOOLS: HIS TAIL 91 



and it can be nothing else unless we combine 

 those patterns. It may be square across the 

 end, it may have the middle feathers longest, 

 or it may have the outer feathers longest. To 

 one of these patterns every form of birds' tails 

 may be referred ; you can invent no other shape. 

 Let us assume that you know nothing what- 

 ever of a woodpecker's tail except that it has 

 ten feathers, is used as a prop, and is held at 

 an angle of thirty or forty degrees with the tree- 

 trunk. Now, take three strips of paper of the 

 same width and length, and of any size not in- 

 conveniently small. Fold them all down the 

 centre. Cut one square across ; cut one with a 

 rounded end and the third with a forked end, 

 making them of any shape you please so long 

 as the three papers are of the same length. To 

 give our models 

 a fair test they 

 must be of the 

 same width and 

 length. Next, pin 

 a sheet of paper 

 of any size you 

 please into the 

 form of a cylinder and stand it on end to re- 

 present a tree-trunk. Then fit the patterns to 

 the tree-trunk and see which is the form that 

 would give the most support. 



Patterns of tails. 



