PROPERTIES OF WOOD. 



45 



the summer-wood substance, the spring-wood must yield, and the log 

 shrinks circumferentially. The radial shrinkage of the summer-wood, 

 however, is constantly interrupted by the alternate rows of spring- 

 wood, so that there would not be so much radial as circumferential 

 shrinkage. As a matter of fact, the tangential or circumferential 

 shrinkage is twice as great as the radial shrinkage. 



Putting these two factors 

 together, namely, the length- 

 wise resistance of the pith rays 

 to the radial shrinkage of the 

 mass of other fibers, and sec- 

 ond, the continuous bands of 

 summer wood, comparatively 

 free to shrink circumferentially, 

 and the inevitable happens; the 

 log splits. If the bark is left 

 on and evaporation hindered, 

 the splits will not open so wide. 



There is still another effect 

 of shrinkage. If, immediately 

 after felling, a log is sawn in 



two lengthwise, the radial splitting may be largely avoided, but the 

 flat sides will tend to become convex, as in Fig. 39. This is ex- 

 plained by the fact that circumferential shrinkage is greater than 

 radial shrinkage. 



If a log is "quartered," 1 the quarters split still less, as the inevitable 

 shrinkage takes place more easily. The quarters then tend to assume 

 the shape shown in Fig. 40, C. If a log is sawed into timber, it checks 

 from the center of the faces toward the pith, Fig. 40, D. Sometimes 

 the whole amount of shrinkage may be collected in one large split. 

 When a log is slash-sawed, Fig. 40, I, each board tends to warp so 

 that the concave side is away from the center of the tree. If one 

 plank includes the pith, Fig. 40, E and H, that board will become 

 thinner at its edges than at its center, i. e., convex on both faces. 

 Other forms assumed by wood in shrinking are shown in Fig. 40. 

 In the cases A-F the explanation is the same; the circumferential 

 shrinkage is more than the radial. In J and K the shapes are ac- 

 counted for by the fact that wood shrinks very little longitudinally. 



^ee Handwork in Wood, p. 42. 



Fig". 39. Shrinkag-e of a Halved Log". 



