Now, using the formula

we shall have, in round numbers, the following dimensions:

For the 1st panel, 25 feet long, 8 x 10
" 2d " 37 " " 8 x 10
" 3d " 49 " " 8 x 10
" 4th " 64 " " 8 x 10
" 5th " 78 " " 8 x 10

For the lattice work, a double course on each side of each truss, in long spans; and a single course, in shorter spans, of 3 x 6, or 2 x 9 plank, bolted at intersections, is sufficient.

GENERAL TABLE OF DIMENSIONS FOR ARCH
BRACE TRUSS. G.L. VOSE.

Span.Rise.Chords.Ties.Braces.Lattice.
50102—8 x 101—8 x 102—6 x 6
75122—8 x 101—8 x 102—6 x 62 x 9
100153—8 x 102—8 x 103—6 x 6or
150204—8 x l23—8 x 104—6 x 83 x 6
200254—8 x 163—8 x 104—6 x 9

The arch braces must all foot on an iron thrust block, of which a view is given in Fig. 4, Pl. III; and the centre of pressure of the braces must be directly over a bolster, to prevent crippling.

The several sticks forming a brace must be blocked together at intervals, and when they are spliced,—a butt joint should be used—and it should come in the centre of a panel. Below are given the dimensions of the Thayer Engineering School model.

Height Ins. 12
No. Panels8
Chords Ins. 2—1 x ½
Posts Ins.1—2/3 x 5/6
Braces Ins. 2—½ x ½
Lattice Ins. ¼ x ½
Width Ins.13