ondition more commonly met with in practice, as,
for example, where a post rests on a horizontal sill, or a rail
rests on a cross-tie. The former condition, however, gives the
true resistance of the grain to simple crushing.

[Illustration: FIG. 2.--Compression across the grain.]

The first effect of compression across the grain is to compact
the fibres, the load gradually but irregularly increasing as the
density of the material is increased. If the specimen lies on a
flat surface and the load is applied to only a portion of the
upper area, the bearing plate indents the wood, crushing the
upper fibres without affecting the lower part. (See Fig. 3.) As
the load increases the projecting ends sometimes split
horizontally. (See Fig. 4.) The irregularities in the load are
due to the fact that the fibres collapse a few at a time,
beginning with those with the thinnest walls. The projection of
the ends increases the strength of the material directly beneath
the compressing weight by introducing a beam action which helps
support the load. This influence is exerted for a short distance
only.

[Illustration: FIG. 3.--Side view of failures in compression
across the grain, showing crushing of blocks under bearing
plate. Specimen at right shows splitting at ends.]

[Illustration: FIG. 4.--End view of failures in compression
across the grain, showing splitting of the ends of the test
specimens.]

When wood is used for columns, props, posts, and spokes, the
weight of the load tends to shorten the material endwise. This
is ~endwise compression~, or compression parallel to the grain.
In the case of long columns, that is, pieces in which the length
is very great compared with their diameter, the failure is by
sidewise bending or flexure, instead of by crushing or
splitting. (See Fig. 5.) A familiar instance of this action is
afforded by a flexible walking-stick. If downward pressure is
exerted with the hand on the upper end of the stick placed
vertically on the floor, it will be noted that a definite amount
of force must be applied in each instance before decided flexure
takes place. After this point is reached a very slight increase
of pressure very largely increases the deflection, thus
obtaining so great a leverage about the middle section as to
cause rupture.

[Illustration: FIG. 5.--Testing a buggy spoke in endwise
compression, illustrating the failure by sidewise bending of a
long column fixed only at the lower end. _Ph