60 



ELEMENTARY WOODWORKING 



Fig. 74. Showing Weather 

 Checks and " Shake " 



Looking at the length of the log we see that the 



lines in a board, which we call the grain, are really 



the edges of the annual rings. 



It often happens in the forest 

 that the wind sways the trees 

 to such an extent that the an- 

 nual rings separate and slide one 

 within the other ; this produces 

 a defect in the wood called a 

 slialie (see s, Fig. 74). 



There are other characteris- 

 tics of wood known as tvarping 

 and shrvikage. 

 After a tree has been cut down the cut end at first 



looks like Fig. 72. If it is allowed to lie for some 



time exposed to the weather, its 



appearance changes to Fig. 74. 



This is due to the evaporation 



of the sap, and as there is more 



sap toward the outside, the shrink- 

 age is greatest there and becomes 



less toward the center where the 



heartwood is comparatively dry. 



This is an important fact to 



know, because if we had cut the log, while it was 



still green, into planks, as shown in Fig. 75, the 



Fig. 75 



