66 OF WOOD IN GENERAL 



discoloration at the top, rind-gall, worm-holes, or splits produced 

 in seasoning being indications of weakness. Bright-coloured and 

 smooth-working wood is generally better than any that is dull or 

 works with a rough surface ; and heavier wood is in all respects 

 stronger than lighter wood of the same species. 



Where lightness and stiffness are desirable, coniferous wood is 

 generally preferable ; and, where a steady load has to be supported, 

 the denser coniferous woods equal those of broad-leaved trees, 

 which are costlier and heavier. Where, however, moving or 

 jarring loads have to be sustained, the tougher hard woods should 

 be used. 



Conversion of timber. — Split wood is straighter in grain and 

 more easily seasoned than sawn timber ; and, when sawn, timber 

 will prove stronger and more durable, will season better and will 

 warp less if sawed as nearly as possible along the radii of the annual 

 rings, or, as it is termed, " quarter " or " rift " sawed. Tiiis 

 method is more expensive than tangent sawing ; but a Httle con- 

 sideration will show how it secures — ^in flooring boards, for instance 

 — a more even exposure of the grain — i.e., the hard bands of summer 

 wood — on the surface. It must be borne in mind that in a squared 

 beam with the pith in its centre, whilst we have some complete 

 annual cones of wood appearing as rings at the butt end and taper- 

 ing to a point or to smaller rings at the top, we shall also have other 

 imperfect cones represented by rings at the top but presenting 

 tangent or " bastard " faces on the sides of the beam and not repre- 

 sented 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 

 cyHnder formed of cones that occur as rings both at butt and top 

 (Eg. 40). Quarter-sawing secures the most advantageous unifor- 

 mity 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 

 outside exposed, as shown in Kg. 41, since otherwise (Fig. 42) the 

 inner rings of wood soon shell out. 



Durability of wood. — All wood when first felled contains a 

 large quantity of moisture, and this, together with the readily 

 decomposable organic or protoplasmic matter also present, furnishes 

 (especially at temperatures between 60"^ and 100° F.) the most 

 favourable conditions for the growth of those fungi which are the 

 main causes of decay. If completely submerged, or buried, or 

 when once dried and kept so, timber may last indefinitely. The 

 piles in the Swiss lake-dwellings must be many centuries old ; and 



