INTRODUCTION. 



the sample carefully for any signs of discoloration, 

 especially certain rusty-looking streaks which betray 

 the presence of various kinds of " rot"; for signs of an 

 undue proportion of " knots " — i.e. the buried proximal 

 ends of branches long dead. Many woods have their 

 own special odours ; and the suspicious connoisseur will 

 bring his olfactory sense into play to ascertain if the 

 odour is characteristic, or if it is unduly overpowered by 

 certain musty or sour smells which denote the existence 

 of fungi, or insects, or chemical decompositions which 

 may cause trouble. 



Even the sense of touch is sometimes employed by 

 the expert, though probably to a far less degree by the 

 buyer of large timber, than by the more sympathetic 

 cabinet-maker or turner. 



2. BY THE ENGINEER AND BUILDER. 



Those who use timber as material for construction, 

 will naturally have a way of their own of criticising 

 our piece of wood. The engineer or builder will be 

 especially concerned as to the loads that pieces of 

 given length and diameter will sustain ; the amount 

 of change it will exhibit in volume, by swelling or 

 shrinking ; the shocks it will endure and respond to 

 elastically ; and how long it will last when exposed to 

 the vicissitudes of a variable climate or other medium. 



The methods by which he gains the information 

 desired are simple, and for the most part direct. 



He subjects pieces of known length and diameter 

 to various increasing strains. He finds that all woods 

 offer resistance to strains or pressures applied in the 

 direction of the longitudinal axis of the stem, or radially 

 or tangentially across this axis ; and he compares the 



