TIMBER: ITS STRENGTH, AND HOW TO TEST IT. if 
of the timber, and similarly, apparently no effect upon these 
properties, or no marked effect, was produced by the modern 
system of rapid artificial seasoning of wood, as usually carried 
out by currents of hot air. Whether or not the durability 
may be affected is another matter, and that it was impossible 
to determine in an investigation of this nature. 
Of the mechanical tests made upon specimens of timber, 
there are practically four of importance—tensile tests, compressive 
tests, cross-bending tests, and shearing tests. I will now deal 
briefly with each of these in order. 
TENSION EXPERIMENTS. 
Tension experiments are difficult to carry out, owing to the 
fact that, unless the specimens are prepared with very great 
care, it is almost impossible to ensure a pure tensile fracture. 
Most wood has little power to resist shear stress along the 
grain, or, in other words, the lateral adhesion of the longitudinal 
FIG. 3. 
fibres to one another is very slight, hence shear very easily 
takes place along this line of weakness, and, therefore, unless 
the longitudinal fibres run perfectly truly through the specimen, 
which it is very difficult to ensure, a shear fracture very often 
occurs long before the real tensile strength of the material has 
been developed. 
For the purpose of this lecture, I made a series of experiments 
on four different kinds of home-grown timber, viz., ash, beech, 
birch, and oak, and on hickory and mahogany, and the results 
that I have obtained are represented in the attached Tables. 
One set of specimens was flat (see Fig. 3), carved so that in 
the centre the cross section was rectangular, 1} inches wide and 
4 inch thick; the ends were left very much larger in section, and 
