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 4J by 5^ inches, 

 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- 

 braces are differently secured, and may cross each other or not, 

 as shown in the section. By crossing, greater strength is ob- 

 tained. 



JVo. 4. A section of a bridge, %oiili the floor, side railing, 8fC. on the top of the 

 trusse!. The floor may easily he made to turn ofl^ the water, and with side hoard- 

 ing, would be effectually secured from the weather. A scale is annexed. 



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. 5. 



17th. Tree-nails 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 with 

 a small lathe, attached to some water or other machinery. They 

 should be unseasoned, to be easily made, but must afterwards be 

 well seasoned before driven into the work ; they will season 



