80 



OF WOOD IN GENERAL. 



of the beam and not represented at the butt. These different 

 " structural aggregates " differ materially in strength, the central 

 cone with its numerous knots being the weakest part, whilst the 

 strongest is the hollow cylinder formed of cones that occur as 



FIG. 41. A beam, showing structural aggregates. 1, central or pith cone ; 

 2, cylinder of rings continuous throughout ; 3 and 4, partial cylinders, 

 making "bastard faces" on the sides. (Modified from Roth.) 



rings both at butt and top (Fig. 41). Quarter-sawing secures the 

 most advantageous uniformity in the proportion of each of these 

 aggregates in every plank. 



In ordinary tangent-sawed timber it is, as pointed out by Mr. 

 Laslett, important to notice that there is an outside and an inside 

 to every board, and that it is desirable in construction to leave the 



FIG. 42. Plank well laid, with inside, or inner rings, downward. (After 

 Laslett.) 



outside exposed, as shown in Fig. 42, since otherwise (Fig. 43) the 

 inner rings of wood soon shell out. 



Seasoning. All wood when first felled contains a large 

 quantity of moisture, and this, together with the readily decom- 

 posable organic or protoplasmic matter also present, furnishes 

 (especially at temperatures between 60 arid 100 F.) the most 



