RECENT INVESTIGATIONS IN REGARD TO QUALITY OF TIMBER. 285 
said that the timber between the heights of 5 and 20 metres 
shows practically equal resistance. 
Timber produced by old pines is much stronger than that of 
young trees. Thus, again taking the average of the Branden- 
burger stems grown on a good situation, we have the following 
figures :— 
Resistance to crushing in Ibs. per square 
inch at the height of— 
1 Metre. |» 9 Metres. 16 Metres. 
Trees from 61-120 years,. . 7154 a 5418 
y) over 120 Sameera ct’ 7921 | 7024 6256 
| 
It has already been pointed out that there is an intimate 
relationship between sp. gr. and the development of the autumn 
wood, and the same is true in regard to the strength of timber. 
Expressed as lbs. of pressure per square inch, an average of 10 
stems shows that :— 
When the ¥ of autumn wood is under 30, the resistance is 5792 
2? yr) ” 2? 31-35 ” ? 6469 
? 2? ”? re) 36-40 2 7 7295 
over 40 - as 7959 
» 2) 23 2? 
Timber furnished by trees growing on the better classes of soil 
is distinctly stronger than that produced by poor soil. 
The close relationship between sp. gr. and resistance to crush- 
ing is thus expressed by Prof. Schwappach :— 
“1, The quality of the locality being constant, the sp. gr. 
that corresponds to a definite degree of pressure- 
resistance will be lower in the case of old trees than 
of young. 
“2, The age being constant, the sp. gr. that corresponds to 
a definite degree of pressure-resistance will be lower in 
the case of timber from good than from poor soil. 
“The converse is also the case, so that we may say :— 
«3, The more favourable the conditions of growth, the lower 
may be the sp. gr. for any definite amount of resistance 
to pressure. 
