[Footnote 3:  See Brush, Warren D.:  A microscopic study of the mechanical failure of wood.  Vol.  II, Rev. F.S.  Investigations, Washington, D.C., 1912, p. 35.]

Tension at right angles to the grain is closely related to cleavability.  When wood fails in this manner the thin fibre walls are torn in two lengthwise while the thick-walled fibres are usually pulled apart along the primary wall.

|--------------------------------------------|
|                 TABLE III                  |
|--------------------------------------------|
|  TENSILE STRENGTH AT RIGHT ANGLES TO THE   |
| GRAIN OF SMALL CLEAR PIECES OF 25 WOODS IN |
|              GREEN CONDITION               |
|         (Forest Service Cir. 213)          |
|--------------------------------------------|
|                  |    When    |    When    |
|   COMMON NAME    | surface of | surface of |
|   OF SPECIES     | failure is | failure is |
|                  |   radial   | tangential |
|------------------+------------+------------|
|                  |  Lbs. per  |  Lbs. per  |
|                  |  sq. inch  |  sq. inch  |
|                  |            |            |
|    Hardwoods     |            |            |
|                  |            |            |
| Ash, white       |      645   |      671   |
| Basswood         |      226   |      303   |
| Beech            |      633   |      969   |
| Birch, yellow    |      446   |      526   |
| Elm, slippery    |      765   |      832   |
| Hackberry        |      661   |      786   |
| Locust, honey    |    1,133   |    1,445   |
| Maple, sugar     |      610   |      864   |
| Oak, post        |      714   |      924   |
|   red            |      639   |      874   |
|   swamp white    |      757   |      909   |
|   white          |      622   |      749   |
|   yellow         |      728   |      929   |
| Sycamore         |      540   |      781   |
| Tupelo           |      472   |      796   |
|                  |            |            |
|    Conifers      |            |            |
|                  |            |            |
| Arborvitae        |      241   |      235   |
| Cypress, bald    |      242   |      251   |
| Fir, white       |      213   |      304   |
| Hemlock          |      271   |      323   |
| Pine, longleaf   |      240   |      298   |
|   red            |      179   |      205   |
|   sugar          |      239   |      304   |
|   western yellow |      230   |      252   |
|   white          |      225   |      285   |
| Tamarack         |      236   |      274   |
|--------------------------------------------|

COMPRESSIVE OR CRUSHING STRENGTH

Compression across the grain is very closely related to hardness and transverse shear.  There are two ways in which wood is subjected to stress of this kind, namely, (1) with the load acting over the entire area of the specimen, and (2) with a load concentrated over a portion of the area. (See Fig. 2.) The latter is the condition 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.