128 



PROPERTIES OF TIMBER 



resilience of the wood of certain types of Willow is responsible 

 for their use in the manufacture of cricket-bats, whilst the ancient 

 esteem of Yew {Taxits haccata) for bows, and the modern use of 

 Ash for aeroplane-construction, are the outcome of the elasticity 

 and toughness of these woods. The clastic limit of Ash is only 

 reached under a strain of about 5,000 lb. per square inch as com- 

 pared with 3,500 lb. for Douglas Fir. Such qualities are probably 

 not only the result of length of fibre, but also one of physical or 





Fig. G2. — Transverse sections of the secondary wood of the Sycamore [Acer 

 pseiidoplataiius) (right) and the Oak (Quercus) (left). Note the fibres 

 (/), which are mucli thicl^er-walled in the latter than in the former.' 

 fu, medullary ray ; T', vessels. 



chemical constitution of the xylcm walls. Liability to splitting 

 is often due to a large size of the constituent elements, and it is 

 the reverse condition vdiich renders the timlier of the Hornbeam 

 [Carpinus) so suitable for cog-wheels, etc. Tlie " figure " of 

 timber, to which many woods owe their \-alue in cal)inet-work, 

 is dependent on the direction of the fibres and the prominence 

 of the medullary rays when cut in certain planes. 



To render timber suitable for use, the cut log needs to undergo 

 a process of seasoning, which involves the drying out of the 



