Improvement in the Construction of Bridges, §c. 295 
tween the bottom beams, to keep the bottom part of the bridge 
secure against any motion or vibration sideways, by wind, travel, 
or transportation. 
15th. Side-braces (see No. 1) are pieces about 43 by 54 Sirlce 
connected with the side-truss, the top-beam, and the principal 
rafters, for the purpose of preventing the side-trusses from leaning, 
or inclining up or down stream. In the section No. 4, the side- 
ces are differently secured, and may cross each other or not, 
8s shown in the section. By crossing, greater strength is o 
tained. ; 
- The floor may easily be made oboe n off the water, a — with s 
ing, would be effectually secired from th eee: A scale 
ROAD WAY. 
No. 4. A section of a prides: with the floor, side railing, §-c. on the ‘ep ‘i ae 
trusse: 
pices: 
16th. Side-walks are sometimes made for foot travel, and may 
be in the inside or on the outside. They are parted off by a 
railing 3 or 4 feet high, and if on the outside, may be made very 
ornamental, as seen in No. 6. 
17th. Tree-iets of two inches diameter, made of white oak 
or other hard wood, are used for securing the truss-braces and 
string-pieces together, as seen in Nos. 2 and 3. They should be 
exactly fitted to the augers used, so as when seasoned to drive 
tight, and make solid work. Tree-nails may be made different 
Ways, but the best and most economical is, to saw them out 
Square from plank, with a circular saw, and then turn them ets 
a small lathe, attached to some water or other machinery. They 
should be andiennsel to be easily madé, but must afterwards be 
Well seasoned before driven into the work; they will season 
