1887.] NEW YORK ACADEMY OF SCIENCES. 159 



pleted in 1758. The length of each span was 364 feet. It was 

 destroyed by the French in 1799. 



Another famous bridge of timber, called the Colossus of 

 Fairmount, was erected over the Schuylkill, at Philadelphia, by 

 Louis Wernwag, towards the close of the last century. It had 

 the form of a very fiat arch, having a span of 340 feet. Its 

 slender, graceful appearance was much admired. Fannie Kem- 

 ble, in her journal, compared it to a " scarf rounded by the 

 wind and flung across the river." It was destroyed by fire in 

 1838. 



Timothy Palmer, of Newburyport, Mass., built several notable 

 bridges, one of which crossed the Schuylkill at Philadelphia. 

 The construction was a combination of king-posts and bracing 

 with the arch. Another was built across the Piscataqua Kiver 

 about seven miles above Portsmouth. Both these bridges re- 

 ceived extended notices in both American and foreign journals. 



Among the architects of notable timber bridges during the 

 early part of the century appear the names of Burr, Towne, 

 Long, and Howe — Long and Howe having followed Towne, and 

 produced modifications of his truss to which their names have 

 since become attached. 



Townees truss was such a remarkable and important improve- 

 ment — the application, in fact, of a new mechanical principle in 

 bridge building — that it was immediately extensively copied, the 

 most important example being the bridge erected across the James 

 Eiver at Eichmond, built by Mr. Moncure Robinson. The total 

 length of this bridge was 3,900 feet. It was supported on 

 eighteen granite piers at distances apart varying from 130 to 150 

 feet, the total cost being about $100,000. Other bridges on the 

 same principle were built, one across the Susquehanna 2,200 feet, 

 jvith span of 220 feet; another at Nashua, N. H. ; at Newbury- 

 port, Springfield, Northampton, Philadelphia, Trenton ; one 

 near New York, another near Troy, and many others in the 

 Southern and Middle States. 



These bridges have nearly^all disappeared, wrought iron having 

 taken the place of timber, while the principle of Towne is still 

 preserved in new constructions. 



Of wrought-iron bridges it is hardly necessary to treat at this 



