No. 1. is the rib that stands in the diagont.l.
No. 2. the next succeeding one.
No. 3. the rib succeeding; No. 2.
No. 4. the middle rib of the side surcet ding No.
OA is half the springing rib : the fed t of tin •.1 are found by drawing lines from the coos of the st;.ts of the ceiling-ribs on the side All, perpendicular thereto, until they cut the top of the springing rib.
The springing ribs are here all of an equal radius, and arc portions of lesser circles of the sphere.
To Se a beam, is to join two separate picce timber, so that every superfiries of the one piece shall be respectively in the same plane with every superficies of the other ; or, in common language, that both pieces shall be in the same straight line, and flush on all sides with each Wit r.
Hence it is evident, that if the joints consist of a plane or planes at right angles to two opposite sides of the beam, but not at right angles to the plaoc of the other two opposite sides, the side of the one piece of timber with which the oblique angles are made, will form the same inclination or inclinations respectively 1% ith the plane or planes of the joint, as the opposite parallel side of the other piece will make with the corresponding or coincident plane or plant s of the said joint.
There are several methods of scarfing beams, either by the joint consisting of one plane or set cral planes, sometimes indented into each other.
Plate CX XVI. Fig. 1. sinews the method of scarfing a beam by indenting the joint at the ends, the planed, of the joint being both parallel and perpendicular to the planes of two opposite sides.
Fig. 2. is the method of scarfing a beam V. ith the coin cident parts oblique to the two sides.
Fig. 3. slims the method of scarfing a beam when the joints are both parallel and perpendicular to the tw o op posite sides, by being tabled and indented at th• ends, and keyed between the tables.
Fig. 4. represents the method of scarfing a IA am with oblique and tabled joints, and keyed between to c tables.
Fig. 5. exhibits the method of scarfing- a beam with parallel and perpendicular joints, oblique at the ends, by forming the end of each piece into a series of steps.
Fig. 6. shows the method of making a be in of two pieces of timber, wit n the length of the two parts are r o more than the length required ; for tr c whore. I f insert ing an intermediate piece on one side of it ea:h way, w ith a double series of steps.
7. shows the method of building a hum in two thicknesses, having the p. its of each I.•(If carf«I, as in Fig. 3. In this diagram, as Wei; as in tht Finn fird.t, the joints are strapped z crud-, at the sd stirr ri bolted on each side of the join(. Thestroppily is ol gat eat use in preventing the bolts from sinking id ito the N1 Fig. 8. exhibits the method t f bi.;Iding a beam in tin ee tl icknesses. as the ribs of a dome such as the Haile du Lied, at Paris.