1328

THEORY AND PRACTICE OF ENGINEERING.

Rook II.

holds up the collar, in the middle of itslength, to the king-post; a brace parallel tothe principal rafters unites the several portionsof the framing together : three purlins oneach side support the commonrafters, forming a roof that couldbe lifted off in one entire piece.

Fig. 2125.

ROOF AT ST. GENEVIEVE, PARIS .

At the Opera des Arts , at Paris , over the proscenium, it was necessary to have a lofty andspacious room for the purpose of mounting the scenes and other useful purposes; this isadmirably contrived, and the principal timbers of the roof are so framed as to resist anyeffects they might be subject to when heavy weights were suspended from them.

.TIETT

Fig. 2126.

ARTS, PARIS .

Roofs framed with pieces of timber which act as struts as well as braces are both simpleand strong in their arrangement.