75 12 2--8 x 10 1--8 x 10 2--6 x 6 2 x 9
100 15 3--8 x 10 2--8 x 10 3--6 x 6 or
150 20 4--8 x l2 3--8 x 10 4--6 x 8 3 x 6
200 25 4--8 x 16 3--8 x 10 4--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. Panels 8
Chords Ins. 2--1 x 1/2
Posts Ins. 1--2/3 x 5/6
Braces Ins. 2--1/2 x 1/2
Lattice Ins. 1/4 x 1/2
Width Ins. 13

There are several other forms of Bridge, the most notable among which
are the Whipple, McCallum's, Post's, Towne's, Haupt's, and Burr's. But
enough has been said to give the student an idea of the general
arrangement of the different parts of a Truss, and to enable him to
determine the strains to which the various members are subjected.
Nothing will be said in regard to Wooden Arches, as our space is too
limited.