STUBNGTU SRASONING. 19 



vided of course that every part is sound, the transverse strength 

 of the wood increases from inside outwards, and from below up- 

 wards, this increased strength being due mainly to greater uniform- 

 ity of structure and length of fibre. The results of recent re- 

 searches would show that wood felled during vegetative repose is, 

 owing doubtless to the presence of reserve matter which increases 

 the cohesiveness of the elements, stronger than wood felled during 

 vegetative activity, especially at the first burst of such activity. 

 Wood seasoned gradually is stronger than wood seasoned too 

 quickly; hence killing a tree by girdling diminishes the strength 

 of the wood. Combining the facts given in the two immediately 

 preceding sentences, we have the inference that for India the 

 rainy season, and then the cold weather, are the best time, irrespec- 

 tive of all other considerations, for the felling of timber trees. 



II. Resistance to crushing. — This resistance is required in a 

 high degree in wood for piles, posts and other uprights, wheel- 

 spokes, &c. It is always in direct proportion to transverse strength 

 and elasticity, since in nearly every case uprights that are over- 

 loaded finish up by bending and then breaking across the fibre. 

 A consideration of resistance to crushing strains is of little prac- 

 tical utility, for on account of other reasons the dimensions of pieces 

 of timber used as uprights are far in excess of the limits necessary 

 for resistance to mere crushing. 



III. Resistance to shearing. — This resistance is of importance 

 only for woods used for a few special purposes, such as sunken 

 piles, tent-pegs, chisel handles, &c. It is always greatest in the 

 direction of the fibres, for one and the same species, it will be 

 in direct proportion to the weight of the wood. For different 

 species it will depend on the cohesion of the fibres and on the ex- 

 tent to which they are anastomosed. The Terminalias, and babul, 

 khair and similar woods offer powerful resistance to shearing 

 strains. 



IV. Resistance to torsion. — This kind of strength is of even 

 still less importance than the two preceding, as it is required for 

 very few purposes (axles and axle-trees), and even then the dimen- 

 sions of the pieces of timber used are, owing to other and entirely 

 independent considerations, much in excess of what are absolutely 

 necessary for overcoming torsion alone. 



Section VII. — Loss and gain of moisture and consequent 



CONTRACTION AND EXPANSION. SEASONING, WARPING, AND 

 TENDENCY TO CEACK AND SPLIT. 



Seasoning. — Before a piece of wood can be used it must be air- 



