rface of the arches. It is a
very stiff bridge, and similar to the one at Bellows Falls, both
having their axis oblique to the channel of the stream they cross. The
timbers could hardly be procured now, except at great expense.

No.
of Upper Lower
Span Pan- Rods Chord Chord Braces Counters Uprights Arches
els
182 14 21 2--8 x16 2--8 x17, 1--21 x8 1--8 x10 21 x11 2--8 x9
1--5 x16 2--4 x17,
1--5 x17,

Diagonals 6 x 8, Rods 7/8. Floor timbers suspended both from
arches and truss, 9 x 13; stringers 10 x 14.

In the Cheshire Bridge, the braces are only 20x8, and the span is only
175 feet, the number of Panels being 14, as in the W.R. Bridge--the
other dimensions are the same. Below are given the dimensions of a
Howe Truss of 108 ft. span, weight to be borne on upper chord.

No.
of Upper Lower E. Floor
Rise Camber Pan- Chord Chord Braces Counters Rods Timbers
Ft. Ins. els Ins. Ins. Ins. Ins. Ins. Ins.

13-1/2 3 12 8--3 x12 8--3 x12 2--8 x10 1--7 x10 2--2-1/8 9 x16

As plank is used for the chords, the pieces must be bolted thoroughly
with 5/8 bolts.

A form of bridge that has been used to some extent on the Baltimore
and Ohio Railroad, by Mr. Latrobe, is the Arch Brace Truss. In this
form of Truss the braces lead directly from the abutments to the head
of each vertical; thus the load is transferred at once to the
abutments, without passing through a series of web members. The
counterbracing is effected by means of a light lattice,--and is
applied to both sides of the chords, and the intersections of the
diagonals are fastened while the bridge is strained by a load--thus
preventing recoil--so that the effect of a moving load is to lighten
the strain on the lattice--without otherwise affecting the Truss.

[Illustration: Pl. III. with Fig. 1., Fig. 2., Fig. 3., Fig. 4., Fig. 5.]

There are two models of this style of bridge, to my knowledge; one
built by Prof. G.L. Vose, on a scale of 1/2 an inch to the foot,
and representing a span of 150 feet, which supported 2,500 lbs. at
the centre, and a movable load of 150 lbs., proving itself to be
strong and rigid enough for any thing. The other, on a scale of 1
inch to the foot, and representing a span of 76 feet, was built by
the Class of '73, of