2T8 Improvement in the Construction of Bridges, Sfc. 



1st. An immense additional strength may be obtained, with 

 much less quantity of plank in the string-pieces, in proportion to 

 the strength, stiffness, and durability thereby gained ; especially, 

 as double the number of tree-nails pass through all the string- 

 pieces which are in the middle of each truss, or between the two 

 series of truss-braces, and thereby secure the splices of the plank 

 composing the string-pieces, in a much more effectual manner, 

 against their tension strain, which is great, and therefore requires 

 the best possible security to counteract it. This manner is 

 effectual, even without the aid of iron, to a greater degree than is 

 practicable in any other manner known in practical mechanics. 



2. The great evil, so much complained of in the first mode, by 

 all bridge builders, viz. of keeping the trusses straight, or from 

 warping, twisting, or leaning sidewise, is by this improvement 

 entirely done away ; it being more easy to keep the trusses in 

 their true position, and have them remain so, than in any other 

 mode ; because, first, the trusses are of greater thickness, and 

 therefore less liable to admit of any curve, twisting, or deviation 

 from their true position. And secondly, because the trusses run 

 horizontally, they are less liable, even with the same thickness, 

 to get out of their straight and vertical position, than would be 

 the case with the arched bridge, which, by rising higher at the 

 crown of its arches, gives much greater leverage to its own grav- 

 ity, and to the winds, for a deviation from its true position, to 

 that of a curved or twisted one, which might impair its strength 

 or safety. 



It may be stated, as it is believed by the patentee, that with 

 this last improvement, his mode of construction, for all important 

 purposes, is such as to avoid all possible objections of every kind, 

 for whatever purpose it may be used ; but more especially for 

 bridges of very wide spans, as also for railroads and aqueducts, 

 which indispensably require great strength, and a level road-way, 

 which other bridges would not admit of, to an equal degree, how- 

 ever much might be expended in their construction. 



The patentee is aware, that some engineers have by some 

 means obtained the opinion, that this improvement, though good, 

 and very strong for a proper extent of span, as well as more 

 economical than other modes, is not as well suited to very wide 

 spans, as possibly some other mode might be ! There could not, 

 most certainly, be formed an opinion more erroneous. With 



