312 TIMBER 



spruce, oak, and birch timber, 4 inches square. Between 

 1893 and 1895 the' moduli of breaking and elasticity had 

 increased while deflection had diminished the wood had 

 become stiffer it had during this period been stored in 

 dry lofts of the building. In 1901 further tests made on 

 similar timber which during those eight years had been 

 seasoning, and which was further dried for ten or twelve 

 days at 100 Fahr., showed that the modulus of breaking 

 under compression, bending, and shearing stresses had all 

 increased, as well as that of elasticity, and that that of 

 deflection, which had diminished from 1893 to 1895, was 

 on the increase, but not in any particular relation to the 

 lapse of time. 1 



Doubtless one reason why dry timber shows higher 

 tests than wet timber is that the timber shrinks in drying 

 and its volume is diminished, in the case of pines and 

 spruces by about 10 per cent, and some timbers considerably 

 more, but the numbers of fibres in the wood resisting 

 strain remain the same ; its cross section, too, is smaller, 

 although the result is generally calculated upon the original 

 section ; this, however, would only account for a very small 

 portion of the increase. The remarks as to the gradually 

 increasing strength of wood as it dries point to the con- 

 clusion that beams and joists in buildings are capable of 

 bearing safely a heavier load some years after erection than 

 when originally put up. 



Timber columns are fairly uniform in tests up to, say, 

 15 diameters long, and up to this point give way by direct 

 crushing ; in longer columns the larger proportion fail by 

 lateral flexure or " buckling " sideways, and generally, as 

 was the case in Lanza's tests, fail at knots. In the West 

 Australian tests, with columns of a ratio of 18 to 1, 60 

 per cent, failed by side flexure. 



1 Min. of Proc. Inst. O.E., Vol. CLVIL, p. 452. 



