the most useful joints in general use,
and these, together with the descriptions, will enable a good idea to be
formed of their respective merits and methods of application.

The lapped joint (fig. 1) is used for temporary structures in
lengthening timbers and is secured with iron straps and bolts; a very
common use of the lap joint is seen in scaffolding secured with cords
and wedges.

The fished joint (fig. 2) is used for lengthening beams and is
constructed by butting the ends of two pieces of timber together with an
iron plate on top and bottom, and bolting through the timber; these iron
connecting-plates are usually about 3 ft. long and 1/4 in. and 1/2 in. in
thickness. This joint provides a good and cheap method of accomplishing
its purpose.

The scarf joint (figs. 3, 4 and 5) is used for lengthening beams, and is
made by cutting and notching the ends of timbers and lapping and fitting
and bolting through. This method cuts into the timber, but is very
strong and neat; in addition for extra strong work an iron fish-plate is
used as in the fished joint.

[Illustration: FIG. 6.--Notching.]

[Illustration: FIG. 7.--Cogging.]

The ends of floor joints and rafters are usually _notched_ (fig. 6) over
plates to obtain a good bearing and bring them to the required levels.
Where one timber crosses another as in purlins, rafters, wood floor
girders, plates, &c, both timbers are notched so as to fit over each
other; this _cogging_ (fig. 7) serves instead of fastenings. The timbers
are held together with a spike. In this way they are not weakened, and
the joint is a very good one for keeping them in position.

[Illustration: FIG. 8.--Dovetail.]

[Illustration: FIG. 9.--Housing.]

[Illustration: FIG. 10.--Halving.]

Dovetailing (fig. 8) is used for connecting angles of timber together,
such as lantern curbs or linings, and is the strongest form. When an end
of timber is let entirely into another timber it is said to be _housed_
(fig. 9). Where timbers cross one another and require to be flush on one
or both faces, sinkings are cut in each so as to fit over each other
(_halving_); these can either be square (fig. 10), bevelled (fig. 11) or
dovetailed sinkings (fig. 12). The end of one piece of timber cut so as
to leave a third of the thickness forms a _tenon_, and the piece of
timber which is to be joined to it has a mortice or slot cut through it
to receive the tenon; the two are then wedged or pinned with wood pins