Breadth = 1 W d2 × constant.
Depth = √ 1 W b × constant.
The practical weight that a beam will carry with safety, permanently, should only be taken at one-fourth of the above computations.
ADHESION OF NAILS, AND SCREWS.
The percussive force required to drive the common sixpenny nail (73 to the pound) to the depth of an inch and a half into deal, with a weight of six pounds and a quarter, is four blows, or strokes, falling freely the space of one foot; and the steady pressure to produce the same effect is four hundred pounds. A sixpenny nail driven into dry elm to the depth of one inch across the grain requires a force of 327 pounds to extract it; and the same nail, driven into the same wood endways, or longitudinally, can be extracted with a force of 257 pounds.
To extract a sixpenny nail from a depth of one inch out of dry oak requires 507 pounds, and out of dry beech 667 pounds. A sixpenny nail driven two inches into dry oak would require a steady force of more than half a ton to extract it.
A common screw of one-fifth of an inch diameter has an adhesive force of about three times that of a sixpenny nail.
TRIGONOMETRY.
Plane trigonometry treats of the relations, and calculations of the sides, and angles of plane triangles.