flO PROPERTIES OE WOOD. 



Emile Sardino, and 'the general results obtained by the latter 

 for props 14 c. in diameter at the small end are as follows : 



Breaking-weight 



in kilos. 



Oak 5,220 



Maritime pine .... 4,790 



Silver-fir or spruce . . . 4,750 



Larch 4,310 



Scots or Black pine . . . 3,740 



With a diameter of 18 c. the superiority of oak was further 

 accentuated, but the larch came at the bottom of the list. It 

 was presumably of bad quality. 



The windlass is about the only case in which wood is 

 required to resist torsion, and the dimensions of wooden 

 windlasses are usually sufficient. Guaiacum-wood resists sheer- 

 ing strains best, as in pullies ; beech, apple and pearwood 

 also resist sheering well, hence the use of these woods in 

 golf-clubs. Hornbeam-wood resists both crushing and sheer- 

 ing strains and is used for cogs and skittles. When subject to 

 a crushing strain, according to Laslett, its fibres, instead of 

 breaking off short, double up like threads. Tr.] 



The most important strength of wood is the resistance it 

 offers to a force acting at right angles to its grain, and is 

 termed transverse strength. As long as the change in the 

 form of the piece of wood is only temporary and it recovers 

 its original shape after the strain is withdrawn, the wood is 

 said to be perfectly elastic. If, however, a change of form 

 remains after the withdrawal of the strain, the limits of perfect 

 elasticity have been exceeded. The modulus of elasticity 

 of a piece of wood corresponds to its change of form until the 

 limits of elasticity have been reached, while the modulus of 

 rapture gives the force in kilograms, when breakage results, 

 after the limits of elasticity have been exceeded. 



Investigations regarding the strength of wood date from the 

 early part of the nineteenth century; it was chiefly Duhamel 

 dn Monrean who attempted to discover a relation between the 

 specific, weight of wood, that is so easily determined, and its 

 strength, tlui determination of which is much more difficult. 



