54 graves: place of forestry among sciences 



the mechanical, physical, and amatomical properties of the wood. 

 Some of these relations I may mention here. 



One of the earliest relations which foresters have established 

 with a fair certainty is that between the specific gravity of the 

 wood and its technical qualities. Some of the foresters even go 

 so far as to claim that the specific gravity of wood is an indicator 

 of all other mechanical properties and that the strength of wood 

 increases with the specific gravity, irrespective of the species and 

 genus. In other words, the heavier the wood, all other conditions 

 being equal, the greater its strength. Even oak, which formed 

 apparently an exception, has been recently shown to follow the 

 same law. If there is still some doubt that the specific gravity of 

 wood can be made a criterion of all mechanical and technical 

 properties of wood, the correlation between the specific grav- 

 ity and the resistance to compression end-wise (parallel to the 

 grain) is apparently beyond question. Thus by the specific 

 gravity the resistance to compression end-wise can be readily 

 detennined. The compression end-wise equals 1000 times the 

 specific gravity minus 70, when the moisture content of the 

 wood is 15 per cent, or (7= 1000 S — 70. 



Since in construction work the most desirable wood is the one 

 which possesses the highest strength at a given w^eight, the ratio 

 between the compression strength and the specific gravity was 

 found to express most clearly the strength of wood. This ratio, 

 however, increases with the increase in the specific gravity, a 

 fact which further substantiates the law that the specific gravity 

 of wood determines its mechanical properties. 



Another relation which has been fairly established is that be- 

 tween the resistance to compression end-wise and the bending 

 strength of timber. By the resistance compression end-wise, 

 therefore, the bending strength of timber can be determined. 



One of the other properties of wood, namely hardness, was 

 found to have a definite relation to the bending and compression 

 strength of wood and this fact tempts the conclusion that by 

 hardness alone all other mechanical properties can be deter- 

 mined. The t^st for hardness is very simple: it can be made 

 even by a small manufacturer and therefore the whole problem 



