(See Fig.

12.) This longitudinal shear is maximum at the neutral plane and decreases toward the upper and lower surfaces.
[Illustration: FIG.

12 .-- Horizontal shear in a beam.] Shearing across the grain is so closely related to compression at right angles to the grain and to hardness that there is little to be gained by making separate tests upon it.

Knowledge of shear parallel to the grain is important, since wood frequently fails in that way.

The value of shearing stress parallel to the grain is found by dividing the maximum load in pounds (P) by the area of the cross section in inches (A).
{ P } { Shear = -- - } { A } Oblique shearing stresses are developed in a bar when it is subjected to direct tension or compression.