10 



TECHNICAL PROPERTIES OF WOOD. 



wood (oak, ash, sweet- chestnut, ehu, rubiuia, Sec), and in 

 coniferous wood. 



In coniferous wood from localities suitable for its best growth, 

 the summer-wood is throughout so dense and hard that it difiers 

 greatly from the spring-wood, which fact secures for it special 

 qualities, and it has then well-defined annual rings. The more 

 or less gradual passage of spring-wood into summer-wood is 

 sometimes interrupted by the presence of a thin zone of the 



Fig. 3. 



]•!<;. 4. 



latter appearing in the middle of the annual zone, which again 

 passes into the usual form of spring-wood and interrupts the 

 regularity of the summer-wood. These are termed douWe rings, 

 and may be ascribed to the action of frost, insect-attacks, 

 drought, &c., causing temporary changes in the tension of the 

 bast and wood in the cambium-zone. Such double or fictitious 

 rings rarely occur in temperate regions, and must be carefully 

 distinguished from the true annual rings. 



(b) ]J'i(Jth ofthr Auutial Hitnis. 



The absolute width of the annual rings naturally varies 

 considerably under different circumstances : the longer the 



