nds for the more expensive ones now in
use. The methods of tests consisted in applying a load along the
diagonal of a box, an action similar to that which occurs when a
box is dropped on one of its corners. The load was measured at
each one-fourth inch in deflection, and notes were made of the
primary and subsequent failures.

For details of tests and results, see:

Cir. 47, U.S.F.S.: Strength of packing boxes of various woods.
Cir. 214, U.S.F.S.: Tests of packing boxes of various forms.

_Vehicle and Implement Woods_

Tests were made by the U.S. Forest Service to obtain a better
knowledge of the mechanical properties of the woods at present
used in the manufacture of vehicles and implements and of those
which might be substituted for them. Tests were made upon the
following materials: hickory buggy spokes (see Fig. 5); hickory
and red oak buggy shafts; wagon tongues; Douglas fir and
southern pine cultivator poles.

Details of the tests and results may be found in:

Cir. 142, U.S.F.S.: Tests on vehicle and implement woods.

_Cross-arms_

In tests by the U.S. Forest Service on cross-arms a special
apparatus was devised in which the load was distributed along
the arm as in actual practice. The load was applied by rods
passing through the pinholes in the arms. Nuts on these rods
pulled down on the wooden bearing-blocks shaped to fit the upper
side of the arm. The lower ends of these rods were attached to a
system of equalizing levers, so arranged that the load at each
pinhole would be the same. In all the tests the load was applied
vertically by means of the static machine.

See Cir. 204, U.S.F.S.: Strength tests of cross-arms.

_Other Tests_

Many other kinds of tests are made as occasion demands. One kind
consists of barrels and liquid containers, match-boxes, and
explosive containers. These articles are subjected to shocks
such as they would receive in transit and in handling, and also
to hydraulic pressure.

One of the most important tests from a practical standpoint is
that of built-up structures such as compounded beams composed of
small pieces bolted together, mortised joints, wooden trusses,
etc. Tests of this kind can best be worked out according to the
specific requirements in each case.

APPENDIX

SAMPLE WORKING PLAN OF THE U.S. FOREST SERVICE

MECHANICAL PROPERTIES OF WOODS GROWN IN THE UNITED STATES

Working Plan No. 124

PURPOSE OF WORK

It is the general purpose