DOUGLAS FIE, WHITE FIXE AND EED PINE. 



15 



The diagram shows the form of test specimen and of the holders H, which are preferably 

 of cast-iron. 



These experiments are still in progress. The following table gives certain results 

 already deduced : 



Table of Results of Direct Tension Experiments. 



It is of interest to note that throughout the whole of the exjjeriments for determining 

 the transverse and the direct tensile strength, the increments of the deflections, and also the 

 increments of the extensions or compressions, are very approximateh' directly jiroportional 

 to the loads producing such increments nearly up to the point of fracture. There would 

 therefore seem to be some reason for the hypothesis that the elastic theory may be held to 

 apply in the case of timber nearh-up to the point of fracture. The formulœ giving the skin- 

 stress and coetiicient of elasticity are based upon this theory, but the theory is 3'et far from 

 being correct, and the true theory remains to be found. In order to do this it will be neces- 

 sary to investigate a large number of influences, as, for example, the relation the bearing 

 strength of the timber and the ratio of the radius of the block to the length of the limber. 

 Again, knots in small timbers have naturally a great influence on the strength, whether 

 transverse, compressive or tensile. 



Shearing Strength. 



In the experiments to determine the shearing strength of timbers considerable ditSculty 

 was found in preparing suitable test-pieces which would not at the same time be liable to a 

 large bending action. Blocks were prepared as shown by sketches 1, 2 and 3, Init unless the 

 sides were sufliciently strongly clamped, as in fig. 1, the specimens almost invariably opened 



