1887.] NEW YORK ACADEMY OF SCIENCES. 151 



establishing numerous piers in swift currents and on treacherous 

 foundations, brought about, first, the long-span timber bridge, 

 and subsequently, the modern structures in wrought iron, which 

 have become so common in our times. The history of the arch 

 in bridge construction extends from a period further back than 

 the beginning of the Christian era to the present day; but the 

 days when great engineers like Perronet, Nimmo, Telford, Een- 

 nie, and others, could acquire fame by building chaste and 

 beautiful arch bridges of stone masonry seem, unfortunately, to 

 have passed. 



One of the largest and most picturesque structures of this 

 kind in the world, unsurpassed in many respects by the most 

 famous arches of history, constitutes a part of the Potomac 

 Aqueduct, near the city of Washington, This magnificent 

 structure, called the Cabin John Bridge, erected by General 

 M. C. Meigs, of the U. S. Army, will probably remain the 

 most conspicuous memorial in this country of a system which, 

 for highways and railways, is gradually being replaced by iron. 



Cast-iron arch bridges were first introduced a little over one 

 hundred years ago in England, and for a time met with marked 

 public favor. The facility with which cast iron lends itself to 

 the introduction of minor decorations in forms and mouldings 

 enabled bridge architects to present a great variety of pleasing 

 designs, and numerous bridges were constructed about the be- 

 ginning of this century which attracted much attention. It has 

 been claimed that Thomas Paine, whose name has been 

 preserved in history only through his atheistical writings and 

 doctrines, was the inventor of the cast-iron arch bridge. This 

 claim is, however, not well founded, inasmuch as this kind of 

 bridge was already in use in England before Paine sailed from 

 America with the object of carrying his plans abroad, where he 

 thought they might be favorably considered. 



The cast-iron bridge had, however, but a brief historical 

 record. The want of sufiBcient elasticity, the imperfection of 

 castings, and the liability to rupture under certain strains or 

 blows, have caused cast-iron to be thrown out of the catalogue of 

 available materials for the principal elements of bridges of any 

 considerable importance. 



