Polytechnic Association Proceedings. §21 



vent greater changes of form, or in other words to neutralize the 

 momentum arising from loads and wind. 



The method employed was sufficient for the spans at that time 

 in use, and in connection with the stiff railing, fulfilled entirely the 

 conditions necessary for a good bridge for common traffic. For the 

 time in which Fiuley lived, his bridges were astonishing structures in 

 reference to the insufficient knowledge of the art of frame bridge 

 building, and spans of three hundred and six feet at the commence- 

 ment of the nineteenth century, appear bolder than twelve hundred 

 hundred feet in our days. 



We can learn by studying Finley's plan, how the neglect of his 

 well-founded directions caused many disasters to suspension bridges. 



It is astonishing how few understood him. Instead of keeping 

 the stiffening continuous beams, and instead of proportioning the 

 same according to the spans and loads of the bridges, it was 

 believed to be an unnecessary weight and increase of cost of bridges; 

 and instead of adapting great deflections of cables or chains, it was 

 believed to be a better arrangement by taking flat arcs, and deflec- 

 tions equal one-fifteenth of the spans, whereby the cost of bridges 

 became nearly double as great as before. 



Till the year 1801, according to Finlej'^'s patent, eight bridges 

 had been built in the United States, and there have been added 

 forty others between th6 years 1801 and 1808. The largest of all 

 was the Schuylkill chain bridge, of three hundred and six feet span. 



It is not uninteresting to know the names of some of the first 

 buildings of this kind. 



The Potomac bridge, near Washington, had one hundred and 

 thirty feet span, its floor being fifteen feet wide; the Cumberland 

 bridge in Maryland, had the same span; the Brandywine bridge, 

 near Wilmington, was built with one hundred and forty-five feet 

 span, and a thirty-feet wide floor, and two other bridges were built 

 of one hundred and twenty feet span each, at Brownsville, Fayette 

 county, in the State of Pennsjdvania. A bridge across the Merri- 

 mac, three miles from Newburyport, in the State of Massachusetts, 

 carried out by an engineer of the name John Templeman, of the 

 District of Columbia, is more particularly described, and is one of 

 the most interesting buildings in the history of bridges. The span 

 of this bridge was two hundred and forty-four feet; the abutments 

 forty-seven feet long and thirty-seven feet high, were made of good 

 masonry. The two roadways of fifteen feet width each, were strong 

 enough to allow for the passage of horses and carriages, whatever 



