| 3 | 6x9 | 3 | 6x7 |
125 | 18 | 12 | 4 | 6x10| 4 | 6x13| 2 |1-1/2 | 2 |2-3/8| 1 |2-1/8 | 4 | 6x9 | 4 | 6x7 |
150 | 21 | 13 | 4 | 8x10| 4 | 8x14| 3 |1-5/16| 3 |2-1/2| 2 |1-5/8 | 4 | 8x8 | 4 | 8x7 |
175 | 24 | 14 | 4 |10x12| 4 |10x15| 3 |1-5/8 | 3 |2-3/4| 2 |1-11/16| 4 |10x10| 4 | 10x8 |
200 | 27 | 15 | 4 |12x12| 4 |12x16| 3 |1-1/2 | 3 |3-1/8| 2 |1-13/16| 4 |12x10| 4 | 10x8 |

This table is partly given in Trautwine's Engineer's Pocket Book, and
partly made up from directions therein given.

TABLE OF DIMENSIONS FOR SMALL SINGLE TRACK PRATT TRUSSES.

At centre At end Centre End
Clear Chords Centre End of truss, of truss, Counter, Counter,
Span, each, Post, Posts, Diam. of Diam. of Diameter, Diameter,
Ft. Ins. Ins. Ins. Rods. Rods. Ins. Ins.

30 9 x 11 4 x 9 7 x 9 1 1-5/8 1-3/8 1
40 10 x 12 4 x 10 8 x 10 1-1/8 1-7/8 1-5/8 1
50 10 x 14 5 x 10 9 x 10 1-1/4 2-1/8 1-3/4 1
60 12 x 15 5 x 12 9 x 12 1-3/8 2-3/8 2 1
70 12 x 17 6 x 12 11 x 12 1-1/2 2-1/2 2-1/8 1

This bridge possesses an advantage over the Howe Truss, for the panel
diagonals can be tightened up by screws, so that every part of the
truss can be forced to perform its work. In Howe's bridge the
adjustments must be made by wedging the braces and counters.

Below are given the dimensions of a Howe bridge on the Vermont Central
R.R., at South Royalton, (single track, deck.)

No. of Upper Lower
Span. Rise. Panels. Chord. Chord. Braces. Counters.
150 20 12 4--6-1/2 x 13 4--6-1/2 x 13 2--8 x 9 1--8 x 9

Rods. Transverse Bracing.
Braces. Rods.
3--1-1/4" 6 x 8 7/8

The bridge over the White River, on the Passumpsic R.R., is a Howe
Truss, strengthened by an arch. The verticals are of wood, and the
diagonals foot on steps formed by enlarging the ends of the verticals.
The counters are in two lengths, and are adjusted by wedges at the
points where they intersect the braces. The bridge is in two spans,
and has a double track, and consequently three trusses. There are two
timber arches to each truss, and the truss is supported on them by
connecting them to the verticals by short cross pieces notched into
the posts, and resting on the upper su