The cross ties should be 18" to 24" apart, from centre to centre, and
be 3-1/2" x 6".

Large, heavy bridges require no fastening to connect them with their
seats, but light bridges should be fastened, as the spring on the
sudden removal of a load, (as when the last car of a train has
passed,) may move it from its proper position.


=Splices.= As the upper and lower chords have to be made in several
lengths, securely fastened to each other, and, in order to weaken the
built beam as little as possible, it is necessary to adopt some form
of splicing whereby the greatest amount of tensional strength may be
retained in the chord with the least amount of cutting, and yet have a
secure joint. Such a splice is shown in Pl. II, Fig. 4, and below is a
table from Vose's Hand-book, giving reliable dimensions.

Span. A C B B C D
Feet. Feet. Inches. Feet.
50 1.00 1-1/2 1.50
100 1.25 2 2.00
150 1.75 2-1/2 2.25
200 2.00 3 2.75

This manner of splicing requires the back of the splice block to be
let into the chord stick, against which it lies, about 3/4 of an inch.
To show how the various Engineers differ, as to their estimates of the
sizes of the several parts of bridges, I subjoin two Tables--one by
Prof. G.L. Vose, a well known Engineer, and one by Jno. C. Trautwine,
an Engineer of note also--and I would premise that a bridge built