204 



It has been found that the- " density" is no criterion as to the " Tenacity" or Tensile strength 

 of the material, and hence, therefore, affords no guide as to the relative strength of beams, which largely 

 involves the tensile strength of the timbers. Thus. Karri, which when seasoned is lighter and less dense 

 than any of the above-mentioned timbers, is very much stronger in tension and as a "beam" than all 

 others, excepting Yate and Salmon Gum. 



Red Gum also, which is comparatively light when seasoned, is very strong in tensiqh, although 

 not so high when used in beams, due to its lower compressive strength, (pp. 14.-15.) 



Hardness. 



The hardness of a body is its power of resisting the insertion of another body 

 into its mass. Woods which offer considerable resistance to being worked by 

 instruments are termed hardwoods, and those which may be easily worked are termed 

 softwoods. Eucalyptus timbers pass under the name of hardwoods, but reference to 

 any work which deals with their physical properties shows that the variation amongst 

 them, in this respect, is very great indeed. 



Schlich (Fisher), v, 34, states that the factors on which the hardness of a wood 

 depends are — its anatomical structure, the coherence of its fibres, the amount of resin 

 it contains, its degree of moisture, and the kind of instrument used. The chapter is 

 interesting, but Eucalyptus timbers are not used as illustrations. 



The determination of degrees of hardness is one for the engineer, and I content 

 myself with quoting the observations and results of Stone, Julius, and Warren, who 

 are distinguished members of the engineering profession, and they have given special 

 attention to the subject. 



The hardness of timber is unfortunately just as much dependent upon our impressions as are taste 

 and smell, but its commercial importance is much greater, hence many attempts have been made to 

 express a scale of hardness in words. 



Xordlinger expressed it in figures corresponding with the weight of sawdust removed by a given 

 number of strokes of a saw; another observer employed a rasp; a third turned balls of the wood to be 

 tested, and measured the distance they rebounded when dropped from a given height; another (Hough, 

 I believe) dropped a pointed weight upon the wood and measured the depth of indentation. The 

 ne -tin. d-' jp nil u-ele- (mi;hi r Xonllinger's saw (to say nothing of his biceps) is needed to produce the 



• : i ' ■ i '-nl i .in. I the -■■' i alw ays l" 1 equally keen; and the like with bhe rasp, Lgain, the burned 



ball could never be reproduced exactly, even in the i-amc wood, and in most woods a ball would soon 

 become distorted by warping, By Hough's method the bottom of the depression made by the impact 

 of the point would rise up in some woods from their elasticity, while in others it would remain deeply 

 impressed. My own method, though inure complicated, presupposes nothing that cannot be reproduced 

 by others. Imt unfortunately it requires a machine of considerable complexi y, which, as I have had no 

 leisure so far to make exhaustive researches in this direction, is merely described in bhe Appendix. After 

 all, it is not hardness alone that is measured, but more accurately the resistance to impact, spoken of by 

 Hough, or. in other words, the amount of force which wood will absorb when struck. We are, therefore, 

 thrown hack upon vague terms such as " hard " Very hard." " moderately hard," &c, &c, coupled with 



the iiaiie- of a few well-known woods for comparison, so that they are pot quite empty words. Gamble's 



se.de of hardness, expressed in this fashion, is good hut cannot lie used by English readers, as his 

 standard wood- are ,,n Indian. I have, therefore, used Nordlinger's scale, in which the type species are 

 chiefly familiar European woods and as it embraces a longer and rather more convenient series. I cannot 



