284 TIMBERS AND THEIR USES 



herent strength, and other mech.anical properties 

 of wood except in the outermost annual ring of 

 growth. 



" The popular belief that sap is up in the 

 spring and summer and is down in the winter 

 has not been substantiated by experiment. 

 There are" several differences in the composition 

 of sap, but so far as the amount of sap in a tree 

 is concerned there is fully as much, if not more, 

 during the winter than in summer. Winter-cut 

 wood is not drier, to begin with, than summer- 

 felled— in reality, it is likely to be wetter. 



" The iraportant consideration in regard to 

 this question is the series of circumstances 

 attending the handling of the timber after it is 

 felled. Wood dries more rapidly in summer 

 than in winter, not because there is less moisture 

 at one time than another, but because of the 

 higher temperature in summer. This greater 

 heat is often accompanied by low humidity, and 

 conditions are favourable for the rapid removal 

 of moisture from the exposed portions of the 

 wood. Wood dries by evaporation, and other 

 things being equal, this wiU proceed much faster 

 in hot weather than in cold. 



" It is a matter of common observation that 

 when wood dries it shrinks, and if shrinkage is 

 not uniform in all directions the material pulls 

 apart, causing season checks. If evaporation 



