STRENGTH AND TESTING OP TIMBER 317 



Curly-grained timber, as a rule, gives much higher results 

 than straight-grained timber in shearing tests parallel 

 to the grain. 



When the load is applied to a portion of the tested 

 specimen, as is usual in practice, the strength in cross 

 compression is, on the average, 12 per cent, higher than 

 when the load is applied over the whole surface. 



In the Western Australian timber tests it was found that 

 the strength of beams cut on the " quarter," that is, radial 

 to the circumference, was 12 per cent, less than that of 

 those cut in the ordinary manner. 



As a general rule, the weight and density of seasoned 

 timber is the measure of its strength, the heaviest timbers, 

 even those of the same species, being the strongest in com- 

 pression and bending tests ; but density is no criterion of 

 tensile strength, and some comparatively light timbers have 

 great tensile stress, as, for instance, ash and hickory. 



The weight of timber is very uncertain and very puzzling, 

 and doubtless the great variation in the weights of timber, 

 as given by different people, is mainly due to the greater or 

 lesser amount of moisture in the timber ; and to estimate 

 weights by small pieces is very uncertain, each piece of a 

 log or tree being of a different weight to an adjoining 

 piece, yet one often finds the weight of timber given to two 

 places of decimals. 



The weights per cubic foot given in this book are for 

 well-seasoned wood. 



The number of rings per inch have no bearing on the 

 weight as a rule, nor do they influence strength. Although 

 a piece of pine or fir timber with, sa}^ sixteen rings to the 

 inch might weigh more than one with, say, only six rings, 

 yet, in quite a number of cases, one finds the reverse, and 

 in the author's experience one with thirty-four rings to the 

 inch weighed less per cubic foot than one with twenty, 



