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. _Photo by U. S. Forest