as struts and ties, by having iron rods through their centre holding the two ribs together.

Fig. 24 shows a detail, or enlarged view, of the iron skewback and post at each end of the truss shown in Fig. 22.

Fig. 25 shows the method adopted for supporting the roof and gallery of the City Armory at Cleveland, O.

Open-Timber Trusses. - One of the principal characteristics of the Gothic style of architecture is that of making the structural portions of the building ornamental, and exposing the whole construction of an edifice to view; and, as the pointed arches and steep roofs were developed, the roof-truss became an important feature in the ornamentation of the interior of the Gothic churches.

These trusses were built almost entirely of wood, and generally of very heavy timbers, to give the appearance of great strength. One of the simplest forms of these trusses is shown in Fig. 26. As may be seen in the figure, the truss is really not much more than a

beam braced by brackets at the ends, though it does not, in its appearance to the eye, offer any suggestion of a beam. Fig. 27 shows another form of a small roof-truss ornamented according

The rafters are connected near the top of the truss by a short tie beam; but this would offer but little resistance to the rafters spreading at their lower ends: hence the truss must depend upon some outside force to keep it intact. This outside force is generally the resistance of the masonry walls which support the truss. These walls

are generally very heavy, and are often re-enforced on the outside by buttresses built against the wall directly opposite the rooftrusses. In most cases such a wall possesses sufficient stability to withstand the thrust of the truss, and hence the tie-beam may be dispensed with; but in a wooden building the walls offer no resistance whatever to being thrust out, unless tied at the top, and hence no truss which exerts an outward thrust on the walls

should be used in such a building. It is therefore impracticable to use a hammer-beam truss in a wooden building. In roofs where this form of truss is used, the ceiling is generally formed of matched sheathing nailed to the under side of the jack-rafters between the purlins, thus allowing them to be seen. The purlins are generally decorated; and false ribs are often placed vertically between them, so as to divide the ceiling into panels.

The rafters should be made very large to prevent them from breaking at the point A.

Fig. 29 shows a hammer-beam truss, the same in principle as that shown in Fig. 28, only a little more developed, and more highly ornamented. This figure shows the ends of the hammerbeams carved to represent different kings.